Exam 2 Plant Biology
How are the gibberellins implemented in bolting and fruit development?
- Gibberellin presence can cause bolting without environmental stimulus. This can lead to early seed production. - They can also lead to the production of parthenocarpic fruits (like auxin). This seedlessness can be done by gibberellins in species such as mandarins, apples, carrots, cucumbers and eggplants.
What were the results of the phototropism experiment?
- In samples a and b of the maize tips placed on agar blocks, they determined that the same amount of auxin was generated whether the tips were in the light or in the dark. Both agar blocks accumulated 40 units of IAA. This means that light was not destroying the auxin. - Scientists split the tips of the plants in two using a really thin sheet of glass. They found that they collected the same amount of auxin in the blocks in the dark and in the light, about 40 units. This means that the experiment was not messing up the production of auxin. - Finally, they split the growing tip as well as the agar block. This means that auxin is unable to move from one side of the block to the other. - They repeated the previous steps but this time they left a space at the top of the tips. This meant that the agar block was still split but there was space for auxin transport at the top. - When the block was still split, there was equal amounts of auxin on either side. When there is space at the top for movement with the agar block split, there is more auxin accumulating on the shaded side of the maize top.
How can you force tulip bulbs to bloom?
- a lot of seeds need a cold period in order to germinate - tulip bulbs need to be left outside or in a very cold place for a period of time before they can bloom
What is ethylene and how was it discovered?
- a simple hydrocarbon - in German in the 1800s, gas lamps were used as street lamps. Leaks from these lamps were found to cause defoliation in the nearby trees. - in 1901, it was shown that ethylene was an active component of the gas lamps. The addition of ethylene to pea seedlings would cause horizontal growth to occur.
How are cytokinins involved in the regulation of roots and shoots?
- as a new undifferenitated cell, there are two options available: 1. can divide repeatedly and remain meristematic 2. elongate and eventually differentiate to become a specialized cell - which of these two options is taken is determined by the relative levels of auxins and the cytokinin.
What is the conclusion made from Darwin and Whent's findings?
- auxin is mostly made in the shoot apical meristem and young leaves with small amounts being produced in the apical meristem of the roots.
What hormones increase the rate of cell division?
- auxins - cytokinins - ethylene - gibberellins
What hormones increase the rate of cell expansion?
- auxins - ethylene - gibberellins
What hormones produce a longitudinal direction of cell expansion
- auxins - gibberellins
Why is dormancy important for temperate, herbaceous and woody perennials that are exposed to low temperatures in the winter?
- bud dormancy is initiated mid summer - dormant buds consist of embryonic shoots with apical meristems, nodes, internodes and leaf primordia - all buds are enclosed by leaf scales/bud scales. These scales prevent desiccation or drying out of the bud, they also insulate it to keep it away from the cold temperatures
How are chloroplast defined?
- by pigments they contain - the comtain both chlorophyll and carotenoid pigment
What are the three main types of plastids?
- chloroplasts - chromoplasts - leucoplasts
What are the functions of the nucleus
- controls protein synthesis - stores the nuclear genome - bound by nuclear envelope containing nuclear pores - nuclear envelope connects to endoplasmic reticulum - contains chromatin which is made of DNA and histone proteins. This forms distinct chromosomes during cell division. - contains the nucleolus which has a high concentration of RNA as well as ribosome subunit formation before they leave the nucleus through the nuclear pores
What is the commercial value of cork?
- cork harvesting is a 1.8 billion dollar a year industry - commercial cork is obtained from an oak species known as Quercus suber - the first layer of cork that is produced has no value - when the tree is 20 years old, the original periderm is removed and then a new cork cambium is able to form in the cortex - the new layer accumulates cork quickly meaning that cork can then be stripped from the tree in 10 years - the new cork cambium arises and then the cycle begins again - typically the same tree can be harvested once a decade for 150 years
What happens during periclinal cell division?
- creating girth to plants - this is parallel to the surface of the stem or root
What hormones do not produce plant cell expansion?
- cytokinins - abscisic acid
What hormones can either increase or decrease the rate of cell division?
- ethylene
What hormones produce a lateral direction of cell expansion?
- ethylene
What hormones decrease the rate of cell divison?
- ethylene - abscisic acid
What hormones decrease the rate of cell expansion?
- ethylene - abscisic acid
How does ethylene and gibberellin play a role in sex expression in cucurbits?
- high levels of gibberellins result in more male flowers being produced while high levels of ethylene results in more female flowers being produced - ethylene and gibberellin play an antagonistic role in sex expression in cucurbits
Give an example of how hormones work in practice:
- hormones modify cell expansion by changing the extensibility of the cell wall -
What is the periderm in reference to stems?
- in secondary growth, the periderm replaces the epidermis as the protective covering for the stem - it consists of: 1. cork cambium (the meristem that produces the periderm) 2. cork (the protective layer that is formed to the outside by the cork cambium 3. phelloderm (the layer produced by the cork cambium to the inside) *** The picture shows two stages of the formation of the formation of the periderm in elderberry - in the first figure you can see the three cell layers: cork, cork cambium and the phelloderm. You can also see that the periderm has started to pull away from the epidermis forming a gappy layer - in the second figure, later in secondary growth you can see that there is much more cork being developed. You can also see the epidermal cells on the top degenerating as they are being stretched by the development of the periderm.
Diagram of the vascular cambium
- initial cells: dark orange going through the middle - rows of the secondary phloem: yellow - rows of the secondary xylem: purple - the long thin cells are fusiform initials. - the short and round cells attached tp the fusiform initials are the ray initials
Describe coniferous wood.
- it has a simpler structure than angiosperm wood - they lack vessels and only have tracheids - there is relatively few parenchyma in the wood so it is dominated by long tapering tracheid cells - have a lot of resin ducts In the picture: you can see rows of long tracheid cells and sections with rays. You can also see a lot of the resin ducts.
What is the role of abscisic acid in root to shoot signaling?
- it is used to pass signals across the plant from the root to the shoot.
How does abscisic acid prevent seed germination?
- its levels increase early in seed development. This stimulates the production of seed storage proteins and therefore prevents premature germination from taking place. - the breaking of the dormancy is characterized by a decline in abscisic acid levels within the seed
What role do the gibberellins have in breaking seed dormancy?
- many seeds require a period of dormancy before germination. - commonly the dormant period is broken environmentally due to factors such as freezing or light levels. - in some species such as lettuce, tomatoes, tobacco and wild oats, gibberellin can substitute for these environmental conditions. It can therefore promote the growth of the embryo and the emergence of the seedling - Gibberellins promote growth and emergence by enhancing cell elongation. This allows the roots to penetrate the seed coat or fruit wall.
Describe the wood structure of angiosperms.
- more complex and varied among species of angiosperms. This is due to the presence of more cell types. - involves vessel elements, tracheids, fibers and parenchyma - the rays are much larger than those that we see in the conifers - the rays in angiosperms are on average 17 percent of the wood volume
Explain stomatal regulation
- normally, turgor pressure caused by a high solute concentration in the guard cells keeps the stomata open - a release of the solutes in response to the action of abscisic acid reduces the turgor pressure in the guard cells, resulting in the closure of the stomatal pore
What are the origins of abscisic acid and what roles does it play?
- originally known under two names, dormin and abscisin, they were found to be the same thing and were renamed abscisic acid. - this was originally found as a hormone which induced dormancy in buds of the ash tree and in the potato - abscisin was thought to be capable of accelerating leaf abscission. This was later found to not be the case! - it is synthesized in the chloroplasts and in other plastids of many plants. - Has a major role in prevention of seed germination, root to shoot signaling
How do plants maintain their photoperiodism and determine when to bloom?
- plants measure how long it has been dark for
Which plants have secondary growth?
- some angiosperms and gymnosperms have secondary growth a. monocots do not have secondary growth b. herbs and herbaceous plants do not have secondary growth ex. herbs and herbaceous eudicots do not have secondary growth c. all woody plants that look like shrubs or trees have secondary growth d. Most eudicots and all gymnosperms have secondary growth *** any plant that shows an obvious increase in girth as well as an obvious increase in height
What is similar between the root and stem apical meristem?
- the cork cambium is created through the pericycle
What are the gibberellins?
- there are 136 naturally occurring gibberellin hormones with very similar structures. - they are found in all plants - they are present in all parts of plants but have highest concentrations inside immature seeds - they have dramatic effects on stem and leaf elongation by stimulating cell division as well as cell elongation.
What role do gibberellins play in plant height?
- these are essential for normal cell growth - their effects can be seen really clearly with these hormones are applied to dwarf mutants - these promote dwarf mutants into growth by overcoming the dwarfism mutation
What are the cues that result in breaking of seed dormancy and initiate germination?
- these are species specific but there are some categories: 1. cold conditions - they must go through a winter to know that they are going to germinate in the spring 2. drying: some seeds need to be dried out before they germinate, this avoids them sprouting inside fruit 3. light 4. abrasion: They must be scraped up, so that it wears away the seed coat from the seed which carries a lot of growth inhibitors 5. rainfall: some seeds such as desert plats need a period of rainfall in order to grow. This is because the rainfall washes away the growth inhibitors from the outside of the seed coat.
What are day-neutral plants?
- these plants flower without respects to day length
What does reaction wood look like in angiosperms?
- they form tension wood which serves the same function as compression wood, but it pulls up the weight of the emerging branch. This can be seen as a bulge at the top of a branch.
What is photoperiodism?
- this is an external factor that effects plants - these plants only flower under certain daylight conditions - it responds to changes in proportions of light and dark within 24 hours. This allows them trespond appropriately to changes in seasons What are the thre
What is prophase?
- this is where the chromosomes shorten and thicken 1. in early prophase, the four chromosomes become visible as long threads are scattered about the nucleus 2. in prophase, these chromosomes shorten and thicken until you can see two threads (chromatids) attached to each other at the centromere 3. In late prophase, the kinetochores develop on both sides of the chromosome at the center 4. the nucleolus and nuclear membrane diappears
Explain experiments done in microgravity in order to study hydrotropism:
- this reduces the gravitropism response due to the low gravity conditions being reduced
What is the vascular cambium?
-Unlike the apical meristem initial cells, the initial cells of the vascular cambium are highly vacuolated. (large vacuoles) - There are two forms of cells that make up the vascular cambium: 1. the fusiform initials 2. the ray initials - the fusiform initials and the ray initials produce the secondary xylem and the secondary
How does auxin occur?
1. At the top there are three different cells as well as the hormone auxin. 2. auxin enters the influx system in the conducting area in a protonated form as IAAH. this is done by passive diffusion 3. It can enter the next cell using an influx carrier in its negative form, IAA-. This is done using active transport and the carrier proton AUX1. 4. Inside the cell, IAAH dissociates into an anion and a proton 5. IAA- (the anion) can then exit the cell efflux through Aux and Efflux carriers know as pin proteins
What are the six main groups of hormones in plants?
1. Auxins 2. Cytokinins 3. Ethylene 4. Abscisic acid 5. Gibberellins 6. Brassinosteroids
What are the six roles of auxin?
1. It plays a role in the differentiation of vascular tissue 2. Plays a role in induction and arrangement of leaves 3. It helps maintain apical dominance 4. It promotes lateral and adventitious roots 5. It promotes fruit development 6. Synthetic auxins are used as weed killers
What are the two forms of gibberellin related muatnts?
1. Mutants caused by a deficiency in gibberellin production Is this what is happening during the dwarfism mutation? Could this mutation just lack gibberellin so that adding the hormone allows it to continue growing? 2. Those caused by a deficiency in the gibberellin response. This causes the plant become insensitive to gibberellin
How did scientists test to see what was the cause of phototropic movements of plants?
1. Scientists snipped the growing tips of maize plants and put them in agar blocks. 2. They then measured how much auxin (IAA) accumulated in the agar blocks.
What are the two reasons why there is much less secondary phloem accumulated year after year compared to amount of secondary xylem?
1. The cambium produces less phloem then xylem 2. The soft walled cells of the phloem get crushed by the newly forming periderm
What inhibits expansion and growth by decreasing the extensibility?
1. abscisic acid 2. ethylene - this is an example of an antagonistic relationship between different hormones if you consider those that help increase cellular expansion
What are some of the functions of the cytoskeleton?
1. cell division 2. cell growth 3. differentiation 4. organelle movement
What are the steps of cytokinesis?
1. cell plate begins to form across the center of the cell across the line of cell division 2. As the cell plate matures, it grows outwards until it reaches the outer wall of the diving cell 3. once it comes in contact with the parent cell wall and a middle lamella develops in between the two layers of each daughter cell now has its own cell 4. the original cell will rupture as the daughter cells enlarge to spread out and fill the space
What are the two main structural elements of a cell?
1. cell wall 2. protoplast
What are the two main functions of the nucleus?
1. control protein synthesis 2. store the nuclear genome
What responses is phytochrome involved in?
1. dark grain seedling are said to be etiolated. They grow long, thin and pale because their plastids do not turn green until they are exposed to light. When the seedlings are given normal light, there are normal growth responses like phototropism that start to occur again. If a dark-grown seedling gets just 5 minutes of red light per day, it will start to show normal growth but if that red light ends with a flash of far red light, it will stay etiolated. 2. It is used in a shade-avoidance response in plants grown in crowded locations. When light passes through a leaf, when the light has to go through a leaf to get to another leaf, that light is depleted in both the red and blue wavelengths. These are being absorbed by the chlorophyll and the carotenoids in the first leaf and used for photosynthesis. This results in a reduction of the red to far red ratio. Plants grown in the shade where light is passed through a leaf, already gets more far red light than red light. This triggers the shade-avoidance response system. The result is a longer, taller and thinner plant which is trying to achieve apical dominance (trying to get above the shading plants).
What metrics do we use to describe the different properties of wood?
1. density 2. specific gravity
What environmental inputs regulate the endogenous circadian clock?
1. environmental input pathway 2. gating 3. temperature compensation
Growth in plants is regulated by...
1. external factors 2. hormones
What are the two types of thylakoids found in chloroplasts?
1. grana 2. stroma
What 4 elements make up the cell wall?
1. middle lamela 2. primary wall 3. secondary wall 4. plasmodesmata
What are the functions of the Golgi apparatus?
1. non cellulosic polysaccharides are secreted by the Golgi body to make cell walls 2. secrete glycoproteins 3. provides materials for plasma membranes and tonoplasm membranes to be created
What are the 4 parts of the nucleus?
1. nuclear envelope 2. nucleoplasm 3. chromatin 4. nucleolus
What are the tropisms we have learned about?
1. phototropism 2. gravitropism 3. hydrotropism 4. thigmotropism
What are the 7 parts that make up the cytoplasm?
1. plasma membrane 2. cytosol 3. organelles 4. endomembrane system 5. cytoplasm 6. ribosomes 7. oil bodies
What 4 organelles are found within the cytoplasm?
1. plastids 2. mitochondria 3. peroxisomes 4. vaculoles
Stem: What primary tissues arise from the procambium?
1. primary phloem 2. undifferentiated procambium 3. primary xylem
What are the 4 phases of mitosis?
1. prophase 2. metaphase 3. anaphase 4. telophase
Root: What are the three primary meristem tissues?
1. protoderm 2. ground meristem 3. procambium
Stem: At the beginning of growth, the apical meristem produces what three primary meristems?
1. protoderm 2. ground meristem 3. procambium
What are the three groups of photoperiodism?
1. short-day plants 2. long-day plants 3. day-neutral plants
How can hormones extend the extensibility of the cell wall?
1. stimulate a reversible cleavage of the micro fibrils (snapping them all) 2. The hydrogen bonds between he cellulose microfibrils and the hemicellulose cross bridges can be disrupted - Both of these ways allow the microfibrils to move apart and allow the cell wall to expand
What two elements make up the protoplast?
1. the nucleus 2. the cytoplasm
How are phragmosomes formed during interphase?
1. the nucleus us at one side of the cell wall and there is a large vacuole in the center 2. there are strands of cytoplasm that break up the vacuole and provides a pathway for the nucleus to migrate to the center of the cell 3. the nucleus reaches the cemter of the cell and becomes suspended by teh cytoplasmic strandes 4. the strands merge to form a phagosome through which cell division will take place 5. The phragosome fully forms and bisects the cell 6. Mitosis is completed and the cell divides along the line of the phragmosome
What are the two main roles of cytokinin?
1. the regulation of root and shoot production 2. the delay of leaf sinescence
What is the pathway of new endoplasmic membranes?
1. the rough ER has transition vesicles which pinch off of the rough ER and transport it 2. The pieces are carried to the goligi body 3. the cell wall substances are transported into the golgi body by shuttle vesicles 4. secretory vesicles from the maturing face of the golgi body pinch off from the body with these materials inside 5. the secretory vesicles migrate to the plasma membrane and fuse with it. Here it can discharge its contents and add itself to the membrane
What should be known about signal transduction pathways?
1. the signal transduction pathways are often long 2. hard to elucidate - a lot of research goes into them 3. they can be complex pathways
What features if interphase in plants are unique to plants?
1. the way that teh phragmosome is formed 2. an appearance of a preprophase band
What is cell expansion determined by?
1. turgor pressure 2. extensibility (or stretchiness) of the cell wall
How many mitochondria per cell?
100s-1000s
How many chloroplasts re found per mesophyll cell in plant leaves?
40-50
What is a golgi body made up of?
5-8 stacks (cisternae), these disks then branch into tubules.
How much space does a vacuole take up inside the cell?
90% of the cell's volume
What is the cytoskeleton?
A 2D dynamic network of protein filaments that extends through the cytosol
What is internal endogenous control of the circadian clock?
A biological clock is an internal (endogenous) timing system that continues without any external cues and controls the activities of plants
What is liginin?
A polymer that is found in the cell wall which give it its compressive strength
Describe the structure peroxisome.
A spherical organelle with a single membrane
What is an amyloplast?
A type of leucoplast that synthesizes starch
When a growing root is oriented horizontally, the amyloplasts in the central column of the rootcap: A. slide downward B. float upward C. Attach to the nuclear envelope D. Attach to the mitochondria E. Do not move
A. slide downward - helps maintain positive gravitropism in the roots
What controls the emergence of lateral roots?
Acropetal transport
Where are brassinosteroids found?
Across the plant body and they are thought to be synthesized in each organ of the plant, therefore acting locally. - This means they are not being transported across the plant and instead they are used on site.
What are cytokinins primarily involved with?
Actively dividing tissues such as seeds, fruits, leaves and root tips.
What causes the differences in gene expression in plants?
All hormones have a role in gene expression and differentiation. This is because all of the genes within a plant have the same genome. Cells are able to differentiate due to differences in gene expression. The genes can be activated or repressed by environmental factors or hormones.
Why is it crucial that the circadian clock is synchronized with the environment?
Although it can operate independent of the environment, it is important that it is synchronized with the environment because a small error each day would quickly move the plants out of step with a 24 hour day.
How do roots and shoots perceive gravity?
Amyloplasts in plants are sensitive to gravity and are called statoliths. The cells in which these statoliths occur are known as statocytes. - In the root, these cells occur in the root cap and they are highly polar. This means they are different on the top side vs. the bottom side. The nucleus is always at the top and the statoliths are towards the bottom of of the cell. - In the diagram you can see the red and white orbs which are the statoliths of different cells. If the cell if flipped on its side, the amyloplasts move through the cell and gradually become distributed on the bottom again. After a few hours, the root curves downward and the statoliths return to their original position.
What is pulvinar movement caused by?
An irreversible change in the turgor pressure and expansions and contractions on opposite sides of the pulvinus. - the turgor changes are due to fluxes in potassium and chloride ions going across the ion channels in the plasma membrane, causing water to flow in and out of the cells. These changes are controlled by phytochrome.
How can osmotic pressure be problematic for aquatic plants?
Aquatic plants with an environment of high water potential face problems. They naturally have water flooding into their cells
Why are synthetic auxins used as weed killers?
Artificially levels of auxin-like compounds can contribute to their lethal effects on weeds
What are "space cucumbers"?
Astronauts on the international space station took part in a cucumber growth experiment which made use of the low gravity in space. - cucumbers grown in microgravity showed a really strong hydrotropic response where the roots would grow sideways towards a water source. - researchers use these results to better understand the mechanisms behind hydrotropism. This is important because plant varieties that can grow better in droughts where they would be more effective at finding limited water sources
What is the only plant hormone known to be actively transported polarly or unidirectionally through the plant?
Auxin
What is bark?
Bark is all of the tissues which occur on the outside layer of the vascular cambium
How is the gravitropism response in plants mediated?
By auxin.
How might plants vary in the strength of a response?
By changing the amount of hormone that is released or by changing the sensitivity of a target cell or tissue. Or it can do both of those things in combination
How is dormancy induced?
By decreasing the day length - as the buds become dormant, they undergo a process called acclimation which includes a lot of physical and physiological changing. Acclimation results in cold hardness which is the ability of the plats to survive in the extreme cold and drying effects in winter
Select the correct answer: A. A stem growing upwards is showing positive gravitropism and positive phototropism B. A root growing downwards is showing negative gravitropism and negative phototropism C. A root growing downwards is showing positive gravitropism and negative phototropism D. A stem growing upwards is showing positive gravitropism and negative phototropism
C. A root growing downwards is showing positive gravitropism and negative phototropism
What is calcium a common example of and why?
Calcium is a common example of a secondary messenger. - calcium ion concentrations in the cytoplasm are generally low, but hormones can stimulate the transport of calcium across ion channels into the cell. These calcium ions can then bind to proteins such as protein kinases and activators. These protein kinases then modify a target proteins, eliciting a hormonal response.
What is an example of a short day plant?
Crisanthenum
What is S phase?
DNA replication occurs here
what is density?
Density is the weight per unit volume
What is dormancy?
Dormancy is a period of arrested growth which ends only ends with precise environmental cues.
What can lead to false annual rings?
Environmental factors such as abrupt changes in water availability can lead to false annual ring formation
What allows plants to respond appropriately to the changes in a day?
Environmental synchronization paired with their circadian rhythm
How long can seeds stay dormant?
For a long time - a date palm was recently successfully germinated from a 2 thousand year old seed - there are seed banks where seeds are kept in dormant conditions and protected inside a mountain in their ideal storage conditions
How is dormancy breaking species specific?
For example, in potatoes you need two months of dry storage in order to break dormancy, but the temperature does not matter. In trees, it is the photoperiodic response that breaks dormancy rather than temperatures.
Why does dormancy have a great survival value for plants?
For example, it will stop seed germination from being triggered on a mild day in the autumn, only for seedlings to die when winter hits
What is an example of learning about biochemical pathways by studying mutants?
For example: Ethylene promotes a triple response in dark grown seedlings where they show a stunted, horizonal growth as they try to look for the light. Mutants which are insensitive to ethylene are not effected and grow normally. Finding these mutants led researchers to find the ETR1 receptor system.
Where is chromatin located?
Found in the nucleus and is made up of DNA and histone proteins
Who identified the influence that Darwin described as "transmitting from the upper part of the shoot to the lower part, causing it to bend"?
Francis Whent in 1926 identified this influence as an auxin, a hormone.
In what phase does te cell double in size while the organelles, enzymes and molecules increase in number?
G1
What is interphase split into?
G1 phase, S phase and the G2 phase
When do structures required for cell division begin to assemble and the chromosome begins to condense?
G2 phase
How does gating regulate the circadian clocks of plants?
Gating means that a stimuli of equal strength encountered at a different time of the year can result in a different intensity of response. This protects the plant against responding inappropriately. An example would be responding to a mildly warm day in the middle of winter.
What is used to get barley malts to all germinate at the same time?
Gibberellins are used to make barley malts all germinate at the same time fore beer production
What is the difference between the stroma and the grana thylakoids?
Grana thylakoids are layers of disk-like thylakoids while stroma are spread throughout the chloroplast and connect teh membranes together
Stem: What primary tissues arise from the ground meristem?
Ground tissue of the cortex, pith and the pith rays
What are hardwoods?
Hardwoods are angiosperms
What does Kinetin alone lead to in regards to root and shoot expanison?
Has no effect
What did Johannes Van Overbeek discover?
He found that coconut milk was a very potent growth factor
In what amounts are hormones active?
Hormones are active in very small concentrations
What is the main way that hormones effect cell expansion?
Hormones mostly effect cell expansion by altering the extensibility
What is an example of something physical that hormones are changing in terms of physiology?
Hormones' affecting whether or not the stomata remains opened or closed
How have single celled marine plants adapted to environment of high water potential face problems. they naturally have water flooding into their cells.
How
Why is it important that plants measure darkness instead of daylight?
If you are commercially growing plants, the plants normally need to be kept in a naturally long daylight conditions to prevent flowering before they go on sale - This result showed that they did not need a very long light period and instead they just needed to flip the light on for one minute overnight rather than leave the lights on all night. This gives the same result, saving money.
Where are is the fascicular cambium in the stem?
In between the primary phloem and the primary xylem
Ethylene and climacteric fruits:
In climacteric fruits, this process of ripening is preceded by ethylene synthesis. - In climacteric fruits such as avocados, tomatoes, apples and bananas, there is a large increase in cellular respiration right before ripening occurs. - In the non climacteric fruits such as cherries, grapes and strawberries, you see a more gradual ripening. - With climacteric fruits, the addition of ethylene stimulates ripening.
What is auxin's role in the differentiation of vascular tissue?
In leaf primordia, the new leaves, auxin is synthesized at their tips. The auxin stimulates the formation of the mid vein going through the leaf. - As the leaf grows, the primary auxin sites move down, along the leaf margin to the center of the leaf. This is when they start forming lateral veins. - Auxin helps stimulate the regeneration of the vascular tissues in wounded plants
Where is heliotropism seen?
In many plants, including cotton, soybeans, lupines and sunflowers.
Give an example of a tropism:
In phototropism, the movement of a plant in response too light, movement toward the stimulus is called positive phototropism and movement away from the stimulus is known as negative phototropism. - in the diagram, the roots are showing negative phototropism (growing away from the sun) and the stem is showing positive phototropism (growing toward the sun).
How was cocnut milk as a potent growth factor tested?
In the 1950s, this was tested on tobacco planst. Tobacco planst were left to grow for a while in nutrient media made of sugar, vitamins and salts. Eventually, the growth slows and stops. When coconut milk was added after the tobacco plants stopped growing, the cells began to divide again and continue to grow.
When are phytochromes synthesized?
In the dark from precursors in the PR form
Describe the circadian rhythm of Arabidopsis.
In the model organism of Arabidopsis, there are three feedback loops that are controlled by multiple genes. The central loop: - the light of dawn activates the expression of two genes called the LHY and CCA1. This leads to increased levels of the proteins LHY and CCA1. These proteins repress the expression of the TOC1 gene. TOC1 is a positive regulator of the LHY and the CCA1 genes. Its reduction causes a reduction in the expression of those genes and proteins. By dust the CCA1 and LHY levels are at their minimum and TOC1 is at its maximum. This indirectly stimulates the expression of LHY and CCA1 genes and the cycle begins again. - The LHY and CCA1 proteins cause the expression of the CAB gene in the day time. These CAB genes encode the chlorophyll binding complexes of the light harvesting complexes in photosynthesis. - circadian clocks activate a complex series of genetic events and different proteins to be made in different amounts. This can determine the rates of physiological processes such as photosynthesis.
Where did the hydrotropic response of roots most likely originate?
In the root cap of plants. If you remove this structure, the plant no longer curves hydrotropically towards the water.
Describe the polar transport of auxin in plants.
In the shoots, the polar transport is basipetal meaning that it is being transported inward from the shoot apex. In the case where it is being produced in the tip of the shoot, it is being sent downwards. - Once this downward transport reaches the root-shoot junction, then we refer to the transport as acropetal meaning it is moving away from the center of the plant. - Similarly, if the auxin is being produced at the root tip, it is still being transported polarly. If it is being moved up towards the center of the plant the transport is basipetal.
What is the main naturally occurring auxin?
Indole-3-acetic acid (IAA)
Primary growth is a result of action at the apical meristem while secondary growth...
Is a result of action at the lateral meristems
As wood ages what happens?
It becomes nonfunctional in terms of conduction and storage - there are color changes involved with this aging process due to the lack of reserve food which tends to make it a darker color
How is ethylene promoting abscission used in the fruit industry?
It can loosen fruits such as cherries, blackberries, grapes and blueberries from their stems. This allows mechanical harvesters to come in and easily shake the fruits loose from the trees.
During osmosis, how does water flow?
It flows from high to low water potential
Why is the size of the vacuole important?
It is a relatively energetically cheap way of taking up space and creating size. It also gibes the cell tissue regidity and increases cellular pressure - allows the plant to become tall and small
What do scientists believe is the purpose of ethylene and plants trying to grow around a "dark obstacle"?
It is believed that this is an evolutionary response to a plant that wants to emerge out into the light after germination. The plant wants to overcome some physical obstacle on top of it which must be blocking the light.
What happens when PFR absorbs far red light?
It is converted into PR
What is the extensibility of a cell wall limited to?
It is limited by hemicellulose cross bridges that go between the cellulose microfibrils - this is a very strong substance
What causes bolting?
It is normally caused by environmental stimuli such as very cold weather or longer days. - Gibberellins can cause bolting to happen without the environmental stimulus
Why are the terms "hardwood" and "softwood"" misleading?
It is not always true that angiosperms have a denser wood than conifers. But there are differences in the structure of woods across these different groups
What is regulates the stomatal opening?
It is regulated by both environmental signals as well as endogenous signals such as abscisic acid
Describe ethylene and its inhibitory effect on cell expansion.
It produces a triple response in dark green pea seedlings. - pea seedling typically respond to the addition of ethylene by decreasing their longitudinal growth, increasing their radial expansion of epicotyls and roots and changing to a horizonal orientation of the epicotyl. What is happening? The pea seedling is put in the dark. When supplied with ethylene, it can grow around this "dark obstacle".
How was normal growth caused by brassinosteroids first demonstrated?
It was demonstrated in Arabidopsis - A dwarf phenotype mutant is created when the hormone brassinosteroid is lacking. These dwarf mutants have fewer and smaller cells than in what we see in the wild type. - There are giant mutants of Arabidopsis which have the gene for brassinosteroids but they are over expressed. This produces elevated levels of the hormone and increases plant size as a result.
Describe the structure of indole-3-acetic acid:
Its structure is very similar to the amino acid tryptophan. Tryptophan is a precursor to IAA production in plants
What experiment did scientists do in the 1700s involving circadian rhythms?
John Jack de Marijan showed that plant leaves move diurnally through the day - leaves move during the day to point towards the sun and at night they move down towards the center - He took a pen and attached it to a leaf by a string. The pen was part of a lever which was then attached to a revolving canvas of paper. It continues spinning throughout the day ads as the leaves move up towards the sun, the pen goes up and as the leaves move down towards the stem at night, the pen goes down. - he was able to have the leaf make its own graph showing the movement of the leaves throughout the day
Where does the emergence of lateral roots get their auxin?
Lateral root emergences use auxin transported acropetally down to the root from the shoot.
How does cytokinin play a role in the delay of leaf senesence?
Leaves tend to turn yellow as soon as they are removed from a plant due to a lack of chlorophyll. This process can be delayed by the action of cytokinins. - Cytokinins enhance leaf longevity?
Describe lettuce seed photoperiodism and germination.
Lettuce seeds need exposure to light in order to germinate. This is another photoperiodic response. A group of researchers looked at lettuce seeds and found that if you give them red light, it stimulates germination but if you expose them to just far red light, germination does not occur. - they then exposed the seeds to a series of flashing lights. When the flashes ended in red light, they germinated, when the flashes ended in far red light, they did not.
Are circadian rhythms solely based on environmental conditions?
No circadian rhythms occur even in a constant environment conditions. This means that there must be some endogenous (internal) control to these rhythms. - it is a combination of both the environment and the internal control that determines a plant's circadian rhythm.
Does the cambium produce equal amounts of phloem and xylem?
No, it produces less phloem then it produces xylem
Is stem phototropism and heliotropism the same thing?
No, stem phototropism is due to asymmetrical growth. Heliotropism is caused by a mechanism much more similar to nyctinastic movements/ sleep movements. This is where areas pulvini expand and contract due to changes in turgor pressure.
Do peroxisomes have their own DNA?
No, they import materials in order to self replicate
How is auxin involved in the formation of fruit?
Normally, if a plant is not pollinated or fertilized, the fruit will not develop. If you treat the carpals of some fruits with auxin, then parthenocarpic fruit will form without the need for fertilization. - this is where we get seedless fruits. - the developing seeds are a source of auxin
Hormones Chapter 15
Notes Below
Lecture 16 External Factors and Plant Growth
Notes Below
Secondary Growth Chapter 14
Notes Below
How do plants very in their responses to hormones?
Plants can vary in terms of how sensitive each of their tissues or cells are - this means that plants can vary in the strength of a response
How do the growth rings differ between plants found in tropical regions vs. temperate regions?
Plants that are found in temperate zones produce growth rings through the periodic activity in the vascular cambium. In contrast, in tropical zones where there aren't clear seasons in a year, the growth rings are not easily distinguishable
Wat do ribosomes consist of?
RNA and proteins which are made up of a large and small subunit
What does the nucleolus have in high conc?
RNA proteins
What are leucoplasts?
Relatively simple structures without prigments or internal membranes
If a short-day plant receives a one-minute exposure to light in the middle of the dark period rather than continuous darkness, it will: a. produce more flowers b. produce smaller flowers c. produce larger flowers d. flower at a lower temperature e. not flower
Remember that short-day plants flower when there is a certain amount of daylight or less. You also need to remember that plants are sensitive to the duration of darkness instead of the duration of the light. This means that a one minute flash of light breaks up the dark period into two chunks. For a short day plant, the minimum period of darkness is not achieved. This results in the plant not flowering so the correct answer is: e. not flower
When does cytokinesis begin?
Right after Telophase
Give an example of a plant that exhibits phenotypic plasticity:
Rorippa aquatica Two cuttings can be taken from the same plant, meaning that they both have the exact same genetic information. The first one is grown at 20 degrees Celsius and the second is grown at 30 degrees Celsius. There are profound differences in leaf morphology without any genetic change. This indicates that there is a different response to a different environment.
How was auxin transport determined?
Scientists cut out sections of a hypocotyl of a plant. - each section that was taken had a donor block that had labeled IAA in it. - One treatment group had the donor block on the top, the next treatment group got the donor block on the bottom of the excised section. - It was found that auxin was only transported downwards in the basipetal direction in the excised section with the donor block placed on top. In the excised section with the donor block placed on the bottom, it was shown that no auxin was transported upwards in the acropetal direction. - Note that there is also substantial non-polar transport of auxin through the phloem, but auxin is the only hormone that is transported polarly.
What factor in coconut milk allows plant cells to begin dividing again after they had stopped growing?
Scientists started linking the growth t the purine nucleic acids. They found the structure of the growth factors (isopentenyl adenine and zeatin) and that their structure was very similar to the purine, nucleic acid adenine. This factor is now known as a cytokinin
What experiment was done to determine how plants determine when to bloom?
Scientists studied the short-day plant cocklebur. This plant needs 16 hours a day of light or less to flower. This means that its critical value is 16. It will also flower given a single exposure to the right conditions, even if it returns right away to the long-day conditions. - when they were testing the different photoperiods in cocklebur, they accidentally turned a light on in the dark of the lab for less than a minute. This resulted in the plant not flowering so the same was not true if the light period was interrupted by a short period of darkness. The plant still flowered. - found that short-day plants actually need periods of uninterrupted darkness to flower, rather than it being uninterrupted light
What is secondary growth?
Secondary growth is an increase in thickness or girth of the plant body resulting from activity of the two lateral meristems - the vascular cambium and cork cambium
Where can ribosomes be found?
Some can be found in the cytosol, some are attached to the endoplasmic reticulum, as well as associated with mitochondria and chloroplasts
How have scientists studied gravitropism in plants?
Some studies have used mutant pea plants which are agravitropic, meaning that they do not respond to gravity - They found that the mutant plant will start moving towards a porous pot that is filled with water even if the water is above the plants roots. - further experiments showed that this response must originate in the root cap. If you take the root cap off the roots, then they do not have this response anymore. They no longer curve hydrotropically towards the water.
What is the genetic basis of florigen flowering?
Studies to determine this were conducted using mutant varieties of arabidocious. One mutant had delayed flowering.
How did the Green Revolution in the 1960s and 70's make use of gibberellin mutants?
The Green Revolution was a period of intense innovation in agricultural biotechnology which allowed people to massively increase yields of rice and wheat, but also many other crop species. - in the Green Revolution, people used dwarf gibberellin mutants which allowed for shorter stemmed varieties to be devloped
What is phenotypic plasticity?
The ability of an organism with a single genotype to produce different phenotypes. This is the ability of an organism to make a developmental response to its environment without the need for genetic change through adaptation
What happens to auxin during phototropism in plants?
The auxin moves basipetally from the tip, down towards the elongation zone.
What is a factor in the initiation of lateral roots in the pericycle?
The basipetal transport of auxin from the root's tip
What is the main component that determines cell shape?
The cellular shape is determines by the orientation of microfibrils
Describe the chemical response of plants to gravitropism.
The chutes in plants produces a higher oxygen concentration on the lower side of the shoot. This allows for cell expansion. In roots, this is reversed with a higher oxygen concentration on the lower side of the root. This inhibits the cell expansion. - This is an example of the same signal resulting in different responses in different tissues. What happens if you have two tropisms acting against eachother? Is their a heirarchy where there is a drive to do one thing over the other? What if we had a plant hanging upside down with a UV light shining up at it with no other light source. How would the plant be effected differently without a light source? Would it still try to completely grow upwards or would it not have the ability to do that?
What are softwoods?
The conifers
What is considered the communication system of the cell?
The endoplasmic reticulum because it transports materials such as lipids and proteins around the cell
What happens once gibberellins are released from grass seed embryos?
The gibberellins diffuse so that aleurone cells which are part of the endosperm and are just inside the seed coat. The gibberellin then stimulates the aleurone cells to produce hydrolytic enzymes. - The hydrolytic enzymes digest the food reserves of the starchy endosperm and sends the resulting sugars and amino acids to areas of growth.
What happens if IAA or auxin is added just above the wound of a plant?
The healing and regeneration of the vascular tissue is very fast.
What happens once abscisic acid levels are increased due to water stress or shortage?
The hormone is sent to the leaves via the xylem which triggers the closure of the stomata. This reduces water loss via transpiration.
What interaction controls leaf abscission?
The interaction between ethylene and auxin. - ethylene promotes abscission and auxin reduces the sensitivity of the abscission zone to ethylene. This is another antagonistic response between two different hormones.
What was the conclusion of the phototropism experiment?
The light drives the auxin in plants to the shaded side. This allows the plants to bend toward the light, reacting to a stimulus. - auxin moving to the shaded side produces an increased potential of cell elongation on the shaded side. This results in a growth response towards the light.
What do microtubules and microfibrils look like in contrast to eachother?
The microtubules are much thicker strands and the microfibrils run in the opposite direction and are much thinner. - this is an example of gibberellins promoting a transverse arrangement of microtubules which then sends the microfibrils in the longitudinal direction. This allows for longitudinal expansion. - Ethylene promotes lateral expansion in the it reorients the microtubules into a longitudinal direction
How do the number of growth rings vary depending on distance from the ground and why?
The oldest part of the tree is at the ground level so this is the area with the most growth rings. Once secondary growth as begun in a portion of the stem, that portion no longer increases in length
What determines the orientation of the microfibrils in a cell?
The orientation of the microtubules
What happens when leaves are removed from a plant?
The plant can no longer flower, even if it is given the right daylight stimulus. This means that leaves are likely implicated in the floral stimulus.
What does the plant do to repaired severed vascular bundles?
The plant is able to form new vascular tissues from the pith using auxin to help stimulate regeneration.
How is auxin mediated during phototropic response?
The process is mediated by a photoreceptor, a flavor protein, which absorbs light and converts the the signal into a biochemical response, phototropins I and II
What happens if the leaves and buds above a wound on a plant are removed?
The process of regeneration and formation of new vascular tissues is much slower.
How do rays differ between angiosperm wood and conifer wood?
The rays are much larger and on average, the rays in angiosperms are 17 percent of the wood volume. This is much greater than the volume of 8% that the rays take up in conifer wood. In the picture: you can see the vessels and you can see the thicker but variable sized rays in the transverse and the radial sections
What happens if you remove all of the one seeded fruits from the strawberry structure?
The receptacle begins growing together. This is because auxin is involved with the formation and the fleshing out. The fruits and seed are one of the sources of auxin
What is the role of the hormone auxin in phototropism?
The response is due to elongation of the cells on the shaded side. The cells on the shaded side become longer in order to bend toward the light.
Why is the direction of cellular expansion important to the development of the plant?
The shape of the cell is going to determine the final form of the developing organ
Root: What produces the vascular cambium?
The undifferentiated procambium and the pericycle
How is water pressure managed measured within the cell?
The water pressure is measured in terms of hydrostatic pressure, megapascals (Mpa)
What is responsible for the differences in bark between different trees?
The way the periderm is formed
What is the solution to the impermeable barrier of cork cells not allowing gas exchange?
There are lenticels in the stem and the roots which are holes that create gappy structures, allowing gas exchange
What are the brassinosteroids?
These are a group of growth promoting, steroidal hormones that have roles in cell division as well as cell elongation in roots and stems. They also have roles in vascular differentiation, flower and fruit development, stress resistance and and senescence.
What are resin ducts?
These are large, intracellular spaces which are aligned with parenchyma. These secrete resin into the duct
What are thigmonastic movements?
These are movements in response to a touch stimulus. Ex: venus fly trap - this plant has three trigger hairs inside of its modified leaves. When one of these hairs is touched, nothing happens. But when two of the hairs are stimulated, the trap snaps shut. This double touch stimulus means that it is less likely to be triggered by something like a leaf or a petal rather than a real moving insect - Once the plant snaps shut, the plant releases digestive enzymes and absorbs the liquified insect - when the two hairs get stimulated, an electrical charge is propagated through the plants by the mid rib. This activates ATP hydrolysis which starts proton transport. This initiates the opening of aquaporins leading to a surge of water from cells beneath the upper epidermis to those beneath the lower epidermis. This change in turgor pressure is what snaps the trapped shut.
What is phytochrome?
These are photoreceptors involved both flowering and germination are called phytochrome. - It has two different forms: 1. PR: absorbs red light 2. PFR: absorbs far red light
What are nastic movements?
These are plant movements that occur in response to a stimulus. Unlike the tropisms, they are independent of the position of that stimulus. This means that they are normally not moving towards something or away from something.
What are lenticels?
These are portions of the periderm that have a lot of intercellular spaces in them. Picture: shows a transverse section of a plant called Dutchman's pip showing the lenticel
What are stomata?
These are small holes in the epidermis that can be opened or closed by the action of guard cells in order to regulate gas exchange and water content.
What are second messengers?
These are substances that mediate hormonal responses
What are short-day plants?
These flower in early spring or in early fall. They must have a light period shorter than a certain critical period. Long day plants flower in the summer and they only flower if the light periods are longer than a certain critical period
Industry and climacteric fruits
These fruits are picked before they are ripe and are then sprayed with ethylene. Because ripening happens suddenly, this makes sure that the fruits ripen at the right time before they are sold
Why are second messengers important?
They add to the diversity of responses that are possible in reaction to the work of a single hormone
What are the fusiform initials in the vascular cambium?
They are long, thin cells
How do mitochondria compare in size to plastids?
They are much smaller
What type of relationship do the auxins and cytokinins have?
They are said to have an antagonistic relationship in order to balance apical meristem maintenance with growth. - this allows us to have enough cells remain meristematic to support growth and enough cells differentiating to fulfill the functions for the rest of the plant
What are the ray initials in the vascular cambium?
They are small, round and "squashy".
What are actin filaments?
They are very abundant beneath the plasma membrane where they form a network to assist in structural support, determines cell shape and allows movement of the cell surface
Where do chromoplasts come from?
They develop from chloroplasts where the chlorophyll disappears and the carotenoids are allowed to accumulate within the plastid which allows for the ripening of fruit
What causes the soft walled cells of the phloem to get crushed?
They get crushed by the newly forming periderm
How are chromoplasts similar to chloroplasts?
They have carotenoid pigments but they lack chlorophyll
Why are chloroplasts considered semi autonomous?
They have their own DNA and produce some of their own proteins but are still under the control of nuclear DNA
What dis Darwin and his son learn from their experiment with phototropism?
They learned that the tip of the plant is not the part that responds to phototropism. The part of the plant below the tip is the part that expands and enact phototropism. Darwin concluded that some influence transmitted from the upper part of the shoot (tip) to the lower part of the shoot was causing it to bend.
What happens when phytochromes are converted to PFR after being synthesized?
They move to the nucleus where they are able to have a biological response such as causing seed germination
How do chloroplasts store energy?
They store energy as starch and oil bodies
How do second messengers mediate hormonal responses?
They transfer information from the hormone receptor to the target protein. Or they can amplify the signal from the hormone
What was the impact of the Green Revolution and the development of short stemmed plant varieties?
This allowed plants to put more energy into producing grain instead of putting that same energy into wasteful heights and plant growth.
What is reaction wood?
This comes as a response to counteract gravity in order to support a leaning branch or stem. - when this happens in conifers it is known as compression wood. The reaction wood occurs underneath the branchial stem that it is supporting. This is seen as a bulging structure underneath. - this results in a cross section that is asymmetrical where the growth rings are a lot wider on the underside of the wood than they are at the top - in reaction wood, the compression wood is pushing the branch upwards.
What was one of the first experiments ever done of growth regulation?
This experiment was conducted by Charles Darwin with his son Francis and they worked on phototropism. 1. The had three of the same plants. One which was the control, and two experimental groups. 2. Their control was a plant with shoots that grow toward the light. They then had a second experimental group with a plant that had the tip of the shoot covered up so that light could never get to that part of the shoot. This is where phototropism stops and the shoot stops growing towards the light. The third group was a shoot that was covered in a spot below the tip. This plant still grew toward the light.
What is hydrotropism?
This is a growth response in cells in response to a water gradient. - roots are expected to grow towards the water, but this has been very difficult to test because the hydrotropic response is typically swamped by the gravitropic response. Roots grow down, and this response is of a greater magnitude than the hydrotropic response where roots will grow towards water.
What is a tropism?
This is a growth response involving bending or curving of a plant part toward or away from an external stimulus that determines the direction of movement.
What is unique about mutant maize?
This is a variety which lacks the ability to make abscisic acid, or it reduces the plant's sensitivity to it. This results in the seeds in the maize germinating before the plant is ready for them to do so.
What is the ETR1 receptor system?
This is found on the endoplasmic reticulum of the cell. When ethylene binds to this receptor, it leads to its inactivation and to the inactivation of the negative regulator protein CTR1.
What are circadian rhythms?
This is how plants respond within a 24 hour period - there are many plant processes that vary according to the time of the day. Some of them are listed below: 1. leaf unfurling 2. photosynthetic activity 3. seed germination 4. stomatal opening 5. flower opening 6. cell division rates 7. fragrance emission - these all vary depending on time of day
What is the structural basis for growth rings?
This is just the difference in the density of the wood that is produced through the growing season. - early wood is less dense and has wider cells and thinner cell walls than late wood
What determines the length of a day in photoperiodism?
This is not the absolute number, it is instead whether the plant blooms when the photoperiod is longer or shorter then its species or regionally specific critical value
In gravitropism, is the shoot of the plant growing downwards positive or negative gravitropism?
This is positive gravitropism because it would be growing toward the stimulus of gravity. - In contrast, the shoot growing upwards is negative gravitropism
What is heliotropism?
This is solar tracking in plants. This is seen in flowers and leaves when they move throughout the day. - the leaves and flowers keep oriented so that they face towards the sun
What is senescence in relation to leaves?
This is the death or end of a leaf's life
What is apical dominance?
This is the inhibitory effect that an apical bud has on lateral growth. - Remember that apical growth is mostly growing up, and lateral growth is mostly growing out.
What is the inner bark and what is it made up of?
This is the inner most layer of the cork cambium and the secondary phloem, right up to where the vascular cambium is. - inner bark is alive, it is a living structure
What is thigmotropism?
This is the plant's response to contact with a solid object. Does this include venous fly traps? - it is most commonly seen in plants with tendrils which are either modified stems or leaves which can coil around a solid object. - this allows plants to cling and climb - these tendrils can emerge and cling within an hour - this happens when by the cells in contact with the support shortening and the other on the opposite side elongate - this is also most likely controlled by auxin (no one has checked this yet)
What is gravitropism?
This is the plants response to gravity. If a seedling is placed on its side, the root will still grow downwards and the shoot will still grow upwards.
What is entrainment?
This is the process through which the circadian clock gets synchronized to environmental signals such as the periodic repetition of light ex: the figure shows information from a dinoflagellate which is both photosynthesizing (black line) and producing bioluminescence (red). You can see that photosynthesis peaks during the middle of the day while bioluminescence peaks during the night. - The cycle of these activities stays on a stable time clock due to the endogenous circadian clock - the second figure show hoe entrainment can alter the clock. The second graph shows bioluminescence and scientists subject the dinoflagellates to a short day and night cycle of just six hours. The response of the dinoflagellates echoes that, so there are peaks occurring and sinking which is much faster. They then put it at a normal 24 hour cycle and you can see how the peaks and valleys stretch back out again. - shows how entrainment works by recalibrating its circadian clock based on environmental signals.
What is the purpose of pruning in response to apical dominance?
This is the removal of the terminal bud by selective cutting. This allows the dormant lateral buds to develop, producing bushier plants.
What is phototropism?
This is the response where plants will grow toward the light.
What is the most known nastic movement?
This is the sleep movement (nyctinastic movements). This is where leaves orient up and down in response to night and the dark. - these movements are achieved by changes in the size of the perenchima in the pulvinus. The pulvinus has vascular tissue in the center and is surrounded by a cortex with perenchima.
What happens after auxin reaches the elongation zone in response to light?
This is where auxin accelerates the growth of the shaded side leading to the curvature toward light.
When might bolting due to gibberellin levels be useful?
This may be useful if you want to generate early seed production in a plant.
What is the temperature compensation mechanism of the circadian clock?
This mechanism allows the clock to oscillate at the same frequency over a broad range of temperatures. This is a way to buffer the plants against temperature change.
How is ethylene a promoter in the shedding of leaves or roots?
This occurs because ethylene triggers the release of enzymes which cause cell wall dissolution.
What does Kinetin and auxin together lead to in regard to root and shoot expansion?
This results in rapid cell division and the production of small, undifferentiated, meristematic cells. - different combinations of the two hormones produce very different results in terms of growth
What happens as a result of the inactivation of CTR1?
This results in the activation of the transmembrane protein EIN2. This then transmits the ethylene signal into the nucleus across the nuclear envelope. This signal turns on EIN3 transcription factors which induce the expression of ERF1 transcription factors. This results in the production of new classes of mRNA and the translation of those mRNAs result in novel proteins that can mediate hormonal responses
How do brassinosteroids play a role in tracheary element differentiation?
This was discovered in Zinnia elegans. - putting zinnia mesophyll cells into a media that contained auxin and cytokinins leads the cells to differentiate and then re-differentiate into tracheary elements. This maturation phase is preceded by a rapid increase in the levels of brassinosteroids. These are necessary for the final stage of element differentiation - These three different hormones work in combination to produce a desired response.
What were the three possibilities for the effect of light as a phototropism on plants?
This was tested in an experiment where a scientist wanted to find out which of the three possibilities was occurring: 1. Light decreases auxin sensitivity to the lighted side 2. Light destroys auxin 3. Light drives auxin to the shaded side of the tip
Why are gibberellins routinely applied to grapes?
To create a larger, seedless fruit with a loose cluster in order to look more attractive to consumers
Where does far red light and red light come from?
Under natural light there is both red light and far red light. This results in an equilibrium being reached of around 60% PFR being produced in the sunshine whereas in darkness the PFR level decreases due to dark reversion. It is then lost through a catalyzed process known as destruction
How does the cambium grow?
Using anticlinal divisions which go perpendicular to the surface of the stem or the roots
What is ethylene's role in fruit ripening?
When fleshy fruits ripen, the chlorophyll is degraded and other pigments form, changing the color of the fruit. The fleshy part of the fruit softens due to the enzymatic action of pectin. Next, the starches are metabolized into sugars.
When do signal transduction pathways occur?
When the binding of hormones to protein receptors initiates a chain reaction (a series of biochemical events)
How do PR and PFR work as a biological on and off switch?
When the lettuce seeds get the final flash of red light, this is when PR is converted into PFR. This is biologically active. This results in the biological response of germination. The lettuce seeds that end with a flash of far red light end up with PFR converted into PR and nothing happens because PR is biologically inactive.
How does auxin play a role in induction and arrangements of leaves?
When the polar transport of auxin is inhibited, leaf formation is blocked. This leaves the plants with naked stems and an intact apical meristem at the top. When auxin is then added to the apical meristem, leaf formation can resume.
Where do mitochondria congrgate?
Where most energy is needed in a cell Ex. many might be located in flagella or on the outside of the plasma membrane
Describe the role that auxin has in maintaining apical dominance.
Where there is apical dominance, the terminal bud at the tip is releasing auxin. The auxin goes and inhibits the growth of the lateral buds. This results in a tall and thin plant.
What role does auxin play in lateral and adventitious root growth?
While auxin inhibits lateral stems, it promotes the growth of lateral and adventitious roots.
What don't we know about synthetic auxins used as weed killers?
Why they are selective to kill broad leaved weeds over plants that w want such as grasses.
Do long-day plants measure darkness?
Yes, long-day plants like henbane are also measuring the darkness. A long day plant that flowers with 16 hours light and 8 hours of dark will flower on just 8 hours of light and 16 hours of darkif that dark period is interrupted by a short period of light.
Why is using mutants to study plants helpful?
You can look at the differences between the ones that do it weirdly and the ones that do it normally in the wild type
What is one way in which we can learn about biochemical events initiated by hormones binding to protein receptors?
You can study the mutants in which these pathways seem to be disrupted and see exactly what the difference is in these mutants.
What are polysomes?
a cluster of ribosomes held together by a strand of mRRNA that each ribosome is translating
What surrounds plant plastids?
a double membrane envelope
What is a vacuole?
a fluid filled organelle which is surrounded by a membrane called a tonoplast
what is the endomembrane system?
a group of continuous membranes and organelles that work together to modify, package and transport lipids and proteins - plasma membrane - nuclear envelope - endoplasmic reticulum - glogi apparatus - tonoplast - vesicles
How do primary and secondary stem development come together in a woody angiosperm?
a. This is early and primary growth. There are the three primary meristems: the ground meristem, the procambium and the protoderm b. Shows what everything looks like at the end of primary growth. The procambium, the primary phloem and the primary xylem, the epidermis which is created by the protoderm and we have the cortex and the pith ray which was created by the ground meristem. c. This is were you can see the origin of the vascular cambium. This is what results when the interfascicular cambium and the fascicular cambium meet to join as the vascular cambium. d. This is where you can see secondary growth. This shows how things look after the formation of secondary xylem (pink) toward the center of the stem. There is also secondary phloem on the outside (blue). e. This is the stem after the first year of secondary growth. It is enlarged in diameter and a periderm has formed just below the ruptured epidermis. The primary phloem are mostly lost, leaving thick-walled phloem fibers
In times of water stress or shortage, the roots increase their production of ________?
abscisic acid
What is associated with cell wall deposition tip growth or pollen tubed and movement of the nucleus?
actin filaments
What hormones have a positive role in differentiation (gene expression)?
all of them: - auxins - cytokinins - ethylene - abscisic acid - gibberellins
Primary growth results in an increase in length while secondary growth results in...
an increase in diameter
You can think of circadian clocks as...
an oscillator which generates a rhythmic behavior - this oscillator is regulated by input pathways with environmental information. Together the oscillator and the input pathways are able to produce their behavior or the response of the output pathways. circadian clock + environments = response or oscillator + input pathways = output pathways
Auxins: examples of effects
apical dominance, vascular tissue differentiation, inhibition of leaf and fruit abscission
Lateral movement of auxin occurs...
at the tip
Polar transport of auxins from shoot apex is ______ until the root-shoot junction, and ____ from the root-shoot junction to the root tips.
basipetal, acropetal - As auxins move from the shoot apex and down towards the center, this is basipetal. Once auxins pass the root-shoot junction the auxins are moving toward the root apex resulting in acropetal transport.
Where can you find pith rays?
between the vascular bundles
What is the most common, naturally occurring brassinosteroid?
brassinolide
brassinosteroids: examples of effects
cell division and cell expansion, branching, seed germination, leaf senescence
What fills the vacuoles?
cell sap, which is water dissolved in organic ions
Hormones control coordination of...
cellular processes - this allows them to stimulate or repress specific genes in the nucleus.
What is the primary component of the cell wall?
cellulose - repeating monomers of glucose
What makes up secondary cell walls?
cellulose and hemicellulose
How does cellulose make up the cell wall?
cellulose consists of repeating monomers of glucose which are then bundled together into microfibrils which wind together to provide extreme strength
What is interlocked with hemicelluloses and pectins?
cellulose microfibrils
List the chloroplast, peroxisome and mitochondria, from biggest to smalledt.
chloroplast>mitochondria>peroxisome
Where is the site of photosynthesis?
chlorplasts as they are the ultimate source of food and fuel supplies that we use today
What forms distinct chromosomes during cell division?
chromatin
The color of _____ is also used to attract pollinators to angiosperms.
chromoplasts
What is responsible for the red, yellow and orange colors found in flowers and aging leaves?
chromoplasts
Where are naturally occurring cytokinins found?
coconut milk, angiosperms, algae, mosses, horse tails and conifers
What type of periderm cells provide an impermeable barrier to water and grasses?
cork cells - this is great for protection - problem with gas exchange
Primary growth creates an epidermis, cortex and primary vascular tissues while secondary growth...
creates bark, periderm, lenticels, secondary phloem and secondary xylem
What are the folds of the inner membrane of the mitochondria called?
cristae which increase the surface area of the mitochondria that is available to proteins
What hormones have little or no effect on the rate of cell expansion?
cytokinins
What is the most important characteristic of wood?
density - it can be used to predict hardness and what we can use it for - dense woods make less fuel because they shrink less than lighter woods
Diffusion alwsya occurs..
down a conc. gradient
What are plant chromosomes surrounded by?
envelopes made of two membranes
What are some external factors that effect plants?
environmental things such as excess to light, excess to rainfall
What hormones can have either a positive or negative influence on the rate of cell expansion?
ethylene
cytoplasmic streaming
facilitates the transport of materials and molecules through the cell and between the cell and the environment. This is where the cytoplasm is in constant movement
What makes estimates of aging growth rings inaccurate?
false rings created by environmental factors such as abrupt changes in water availability
Primary growth occurs at the beginning and secondary growth...
follows primary growth
ethylene: examples of effects
fruit ripening, leaf and flower senescence, leaf and fruit abscission
What triggers the fueling of growth as well as roots and seeds breaking the seed dormancy?
gibberellins
In normal development, when grass seeds begin to germinate, their embryo releases....
gibberellins (GA's)
Example of elderberry in two stages of secondary growth
green: beginning - at the start you can see small amounts of secondary phloem and small amounts of secondary xylem - the dark line of cells in the blue picture is the vascular cambium orange: after the first year of secondary growth - by the end of the first year of secondary growth, you can see much more secondary phloem and much more secondary xylem being produced. - the epidermis is crushed and the periderm has begun to form
Primary growth means growth longitudinally while secondary growth means...
growth in a radial axis moving outwards
How do we classify woods?
hardwoods and softwoods
Non-conducting wood is known as...
heartwood - a darker color
How do cellulose microfibrils interact with hemicelluloses?
hemicelluloses hydrogen bond to cellulose microfibrils
How is the internal environment of a plant regulated?
hormones
What allows for communication between cells, tissues and organs in the plant's body?
hormones
gibberellins: examples of effects
hypo elongation of shoots, induction of seed germination, stimulation of flowering
Where in a plant are growth rings created?
in both the secondary xylem (the wood) as well as the secondary phloem
Where are lateral roots initiated?
in the pericycle
What filament of the cytoskeleton has an unknown purpose?
intermediate filaments
What us M phase of the cell cycle?
it consists of mitosis and cytokinesis. During mitoosis there is a complete set of chromosomes which is allocated to daughter cells. Cytokinesis is when the cells divide into two.
What does the smooth endoplasmic reticulum consist of?
it does not have any ribosomes, is tubular and is often involved in lipid synthesis
Where does the word hormone come from?
it is Greek and means "to stimulate" - in reality hormones can both stimulate a response or inhibit a response
What happens when PR absorbs red light?
it is converted into PFR
What is callose?
it is embedded in the cell wall and is a polysaccharide that assists in wound-healing and pollen tube development
What are the pro and cons of diffusion?
it is passive, no energy required, but may be slow over long distances
What is the cortical ER?
it lays beneath the plasma membrane and is linked between adjacent plant cells by the plasmodesmata
Plants have ______ DNA bound to ______ to form chromosomes
linear; histones
Sapwood is...
living and conducting wood - lighter colored
What is outer bark made up of?
made up of the periderm layers - another layer of periderm is added annually - also contains any cortical and phloem tissues - made up of all dead cells, so the outer bark is a dead structure
What does the vacuole store?
metabolites and pigments such as anthocyanins which are responsible for blue, red and purple colorations in angiosperm flowers as well as the red in autumn leaves.
What forms the spindle fibers in cell plate formation during cell division?
microtubules
What is a component (structurally) of cilia and flagella?
microtubules
What are the filaments that make up the cytoskeleton?
microtubules, actin filaments, and intermediate filaments
What is the essential role of brassinosteroids?
normal plant growth
Which is the most visble portion of the nucleus?
nucleolus
The nuclear envelope binds to the _____ and the _____.
nucleus; endoplasmic reticulum
Primary growth occurs in all parts of all plants and secondary growth...
occurs in some angiosperms and gymnosperms
Primary growth stops after the completion of tissue differentiation while secondary growth...
occurs only in mature parts of the plant
Cambial initials produce _______ cells toward the outside and ______ cells towards the inside
phloem; xylem
Peroxisomes play an important role in...
photorespiration
What is a plant's growth response toward light?
phototropism
What are the three major features that make up a plant cell?
plastids, the cell wall and the vacuole
WHat can create water potential?
pressure
cytokinins: examples of effects
promotion of cell division and shoot formation, delay of leaf senescence
What does auxin alone lead to in regards to root and shoot production?
rapid cell expansion and differentiation - lots of root production
The vacuole is the ______ of the cell.
recycling center; organelles and macromolecules are sent here to be broken down
Where are proteins formed from aminoacids?
ribosomes
Some cells might have a secondary cell wall, why?
secondary cell walls are found in cells involbed in strengthening and conducting
Wood is actually...
secondary xylem
On stems you can distinguish lenticels as?
small, dotted, raised bumps visible to the naked eye
What is the specific gravity equation?
specific gravity is = (oven-dry weight of wood) / (weight of the displaced volume of water) - this is the ratio of the weight of a substance relative to an equal volume of water
What is an example of a long day plant?
spinach
What are cucurbits?
squashes, cucumbers, etc. - these plants are monoecious meaning they have both male and female flowers as separate structures on the same plant.
What do chloroplasts contain?
starch
abscisic acid: examples of effects
stomatal closure, induction of photosynthate transport from leaves to seeds, embryogenesis
What happens during the G1 phase?
synthesizes organelles, rbosomes , cytoplasm and grows in size
Often peroxisomes are associted with...
the ER
When is DNA replicated and associated protein are synthesized?
the G1 phase
When is DNA replicated and associated proteins are synthesized?
the S phase
What determines the overall structure and size of the plant cell?
the cell wall
What encloses the cell?
the cell wall and the plasma membrane]
What does the specific gravity of wood depend on?
the cellular properties of that wood - it depends on the proportion of cell wall to lumen (the space bordered by the cell wall) - woods with very thick-walled fiber and narrow lumens tend to have a very high specific gravity
What is etaphasic?
the chromosomes become aligned on te equitrial plane of teh mitotic spindel
Root: What types of secondary tissues are created from the cork cambium?
the cork and the phelloderm
Stem: What makes up the periderm?
the cork, cork cambium and phelloderm
Root: What structures constitute the periderm?
the cork, the phelloderm, the cork cambium
Root: What primary tissues are produced by the ground meristem?
the cortex
Stem: The cortex gives rise to what secondary tissues?
the cortex gives rise to the cork cambium which produces secondary tissues known as the cork and the phelloderm
Experiments involving chrysanthemums and the floral stimulus:
the defoliated plants would never flower. If the leaf was removed, directly after light exposure then the flowering would not occur. Flowering would occur if the leaf was removed an hour after light exposure. This implies the some substance (florigen) was moving from the leaves to the shoot apex in order to initiate flowering.
What happens after there are more and more periclinal divisions?
the diameter of the stem or the root increases - this means that the cambium is being pushed outwards by the expanding secondary xylem and must also grow in diameter
Root: What primary tissues are produced by the protoderm?
the epidermis
Stem: What primary tissues arise from the protoderm?
the epidermis
Stem: The undifferentiated procambium results in which structure?
the fascicular cambium
What does the rough endoplasmic reticulum consist of?
the flattened membrane disks called cisterna which have polysomes on its surface and is abundant in cells that store alot of protein
Stem: Pith rays result in what structure?
the interfascicular cambium
What part of plants is perceiving the day length?
the leaf blade
What are stroma?
the matrix of the plastid
Where is the site of respiration?
the mitochondria
Where else is molecular information found in the cell, other than the nucelus?
the mitochondria and the plastids
What is osmosis?
the movement of water through a selectively permeable membrane
What is diffusion?
the net movement of anything from a region of higher conc. to a region of lower conc. This is drive by a conc. gradient
Where are the large and small ribosomal subunits formed?
the nucleolus
What does the nuclear envelope enclose?
the nucleus and the nucleolu
What provides links between cells through the cell wall?
the plasmodesmata
What is the cell cycle?
the process by which cells divide mitotically
What is an example of pressure creating water potential in plants?
the sap in tress moves via bulk flow from the leaves where the sugars are produced to other parts of the plant body where they are used for growth and maintenace
When the derivative of the cambial initial is towards the outside of the roots or the stem it becomes...
the secondary phloem
Root: What does the vascular cambium produce?
the secondary phloem and the secondary xylem
Normally we look at what structure when we talk about growth rings?
the secondary xylem
When the derivative of the cambial initial is toward the inside of the roots or the stem it becomes...
the secondary xylem
What happens during anaphase?
the sister chromatids separate and move to opposite poles of the spindle
Stem: The secondary phloem and the secondary xylem come from...
the vascular cambium
Stem: What is created from a combination of the fascicular cambium and the interfascicular cambium?
the vascular cambium
What adds secondary phloem to the inner bark?
the vascular cambium
What adds secondary xylem to the inside of the plant, to the core of the stem each growing season?
the vascular cambium
The ray initials make horizontally oriented ray cells which make up...
the vascular rays or the radial system. The rays are mostly made up of parenchyma and they are pathways for the movement of food between the secondary phloem to the secondary xylem and water from the secondary xylem to the secondary phloem.
The xylem and phloem produced by the long and thin fusiform initials have...
their long axes oriented vertically and they make up the axial system of secondary vascular tissues.
How does cytokinesis occur in plants?
there is formation of a cell plate which starts in the middle of the cell and grows outwards
How are growth rings created?
these are made through the periodic activity in the vascular cambium that we see in temperate zones
What are desmotubules?
these are modified endoplasmic reticulum which cross the plsmdesmata
What are microtubules?
these are polymers of tubulin that form part of the cytoskeleton. They form a cylindrical helix and play a role in cell enlargement and cell differentiation
What are plasmodesmata?
these are structures that connect adjacent cells by crossing cell walls
What are thylakoids?
these form stacks of disks called grana and are the site of light dependent reactions of photosynthesis
What is the purpose of the cell walls cutin, suberina and waxes?
these protect the cell and reduce water loss
How do cells keep steep conc. gradients?
thet are maintained by cells doing different metabolic acivities
What is the job of the desmotubules?
they aid in transporation and cell to cell communication
What is the purpose of pectin in the cell?
they are very hydrophilic and attract water to the cell
How are mitochondria semi-autonomous?
they contain some of their own DNA within nucleoids
How do plastids reproduce?
they divide into equal halves during the fission process
What is the purpose of the nuclear pores?
they let mitochondria in and out of the nucleus
What is the preprophase hand?
this band appears in G2 when the microtubules encircle the nucleus
What is the Golgi apparatus?
this is the collection of golgi bodies within the cell
What is the region of primary cell wall where adjacent cells meet?
this is the middle lamella and it is composed of pectin
What is dendrochonology?
this is the science of dating things using tree growth rings - as tree growth varies with environmental conditions (larger rings are made during times of favorable growth conditions and smaller in times of water shortage). This means that the tress can provide an accurate index of rainfall going far back into the past. - this is very useful in semi arid areas where tree growth is a very accurate rain gauge - the bristle cone pine is an extremely long lived tree species - these scientists have used growth rings from a mixture of dead and living bristlecone pines to build up a continuous dataset of environmental conditions going back for more than 8 thousand years
What is abscission?
this is the shedding of roots and leaves
What happens during cytokinesis?
this is the stage where the cytoplasm divides following mitosis
What is water potential
this is the stored energy that water possesses because of its position
What is bolting?
this is when a plant prematurely goes to flower before its vegetative parts are completely developed Ex: cabbages may bolt which lead to it no longer being harvestable. This is because a lot of the energy has been diverted into flowering while we want it in the vegetative parts
What is bulk flow?
this is when water molecules move from a place of high energy to a place of low potential energy
What is an annual ring?
this is where a growth layer represents one season's growth
What happens during telophase?
this is where the chromosomes lengthen and become indistinct
Why is it difficult to see growth rings in the secondary phloem?
this layer tends to get crushed by the expansion of the xylem and therefore it is much narrower
What happens during G2 phase?
this phase checks chromosome replication
What is the purpose of interphase?
this prepares the cell for replication
Within a chloroplast, chlorophylls and carotenoid pigments are embedded in the...
thylakoid membrane
What do plant plastids consist of?
thylakoids and stroma
Why must plant cells regulate its concentration of ions and water?
to be able to make their own internal condutuons different from that of the environmet For example; water has a much lower conc for all the ions that they need to maintain. They manage this through the use of membranes
What is the primary role of the cell wall?
to constrain the protoplast and prevent the cell from rupturing during water uptake
The single membrane of the vacuole is called the...
tonoplast
Root: What primary tissues are produced by the procambium?
vascular cylinder: - pericycle - undifferentiated procambium - primary phloem - primary xylem
What are one of the main differences between the stem and the root?
where the vascular cambium originates: - in the stem, the vascular cambium originates from the undifferentiated procambium. The procambium goes on to create the fascicular cambium and the pith rays. The pith rays then create the interfascicular cambium
Diffusion is highly inefficient...
without a steep conc. gradient
What might stimulate the formation of resin ducts?
wounding, pressure and injuries
