Ch 38 Bio

dormancy

-A condition typified by extremely low metabolic rate and a suspension of growth and development -During the last stages of its maturation, the seed dehydrates until its water content is only about 5-15% of its weight. The embryo, which is surrounded by a food supply (cotyledons, endosperm, or both), enters dormancy -The environmental conditions required to break seed dormancy vary among species. Some seed types germinate as soon as they are in a suitable environment. Others remain dormant, even if sown in a favorable place, until a specific environmental cue causes them to break dormancy; The requirement for specific cues to break seed dormancy increases the chances that germination will occur at a time and place most advantageous to the seedling -The length of time a dormant seed remains viable and capable of germinating varies from a few days to decades or even longer, depending on the plant species and environmental conditions

incomplete flower

-A flower in which one or more of the four basic floral organs such as sepals, petals, stamens, or carpels are either absent or nonfunctional. -most grass flowers lack petals. Some incomplete flowers are sterile, lacking functional stamens and carpels; others are unisexual (sometimes called imperfect), lacking either stamens or carpels.

simple fruit

-A fruit derived from a single carpel or several fused carpels -this group includes most fruits -ex: pea, lemon, peanut

multiple fruit

-A fruit derived from an entire inflorescence -develops from an inflorescence, a group of flowers tightly clustered together; When the walls of the many ovaries start to thicken, they fuse together and become incorporated into one fruit, as in a pineapple or fig

accessory fruit

-A fruit, or assemblage of fruits, in which the fleshy parts are derived largely or entirely from tissues other than the ovary -ex: in the apple fruit, the ovary is embedded in a fleshy receptacle; only the apple core develops from the ovary -ex: the strawberry, an aggregate fruit consisting of an enlarged receptacle studded with tiny, partially embedded fruits, each bearing a single seed.

inflorescence

-A group of flowers tightly clustered together -Flowers also vary in size, shape, color, odor, organ arrangement, and time of opening. Some are borne singly, while others are arranged in showy clusters called inflorescences -ex: a sunflower consists of a central disk composed of hundreds of tiny incomplete flowers, surrounded by sterile, incomplete flowers that look like yellow petals. Much of floral diversity represents adaptation to specific pollinators

fruit

-A mature ovary of a flower that protects dormant seeds and aids in their dispersal -While the seeds are developing from ovules, the flower develops into a fruit -Fertilization triggers hormonal changes that cause the ovary to begin its transformation into a fruit. If a flower has not been pollinated, fruit typically does not develop, and the flower usually withers and dies

fragmentation

-A means of asexual reproduction whereby a single parent breaks into parts that regenerate into whole new individuals -Detached root or stem fragments of some plants can develop into whole offspring; for example, pieces of a potato with an "eye" (bud) can each regenerate a whole plant -one of the most common modes of asexual reproduction -The adventitious plantlets on Kalanchoë leaves exemplify an unusual type of fragmentation -In other cases, the root system of a single parent, such as an aspen tree, can give rise to many adventitious shoots that become separate shoot systems

double fertilization

-A mechanism of fertilization in angiosperms, in which two sperm cells unite with two cells in the embryo sac to form the zygote and endosperm -ensures that endosperm develops only in ovules where the egg has been fertilized, thereby preventing angiosperms from squandering nutrients on infertile ovules. Near the time of double fertilization, the tube nucleus, the other synergid, and the antipodal cells degenerate

sepal

-A modified leaf in angiosperms that helps enclose and protect a flower bud before it opens. -a sterile modified leaf -enclose and protect unopened floral buds, usually resemble leaves more than the other floral organs do

petal

-A modified leaf of a flowering plant; petals are the often colorful parts of a flower that advertise it to insects and other pollinators. -sterile modified leaf -typically more brightly colored than sepals and advertise the flower to insects and other animal pollinators

scutellum

-A specialized type of cotyledon found in the grass family -Grasses, including maize and wheat, have a specialized cotyledon called a scutellum -has a large surface area and is pressed against the endosperm, from which it absorbs nutrients during germination

seed coat

-A tough outer covering of a seed, formed from the outer coat of an ovule. In a flowering plant, the seed coat encloses and protects the embryo and endosperm -formed from the integuments of the ovule

pollen tube

-A tube that forms after germination of the pollen grain and that functions in the delivery of sperm to the ovule -At the time of pollination, the pollen grain typically consists of only the tube cell and the generative cell. It then absorbs water and germinates by producing a pollen tube -As the pollen tube elongates through the style, the nucleus of the generative cell divides by mitosis and produces two sperm, which remain inside the tube cell. -The tube nucleus leads ahead of the two sperm as the tip of the pollen tube grows toward the micropyle in response to chemical attractants produced by the synergids. -The arrival of the pollen tube initiates the death of one of the two synergids, thereby providing a passageway into the embryo sac. The tube nucleus and the two sperm are then discharged from the pollen tube near the female gametophyte.

seed development

-After double fertilization, each ovule develops into a seed -The ovary develops into a fruit enclosing the seed -as the embryo develops from the zygote into a new sporophyte, the seed stockpiles proteins, oils, and starch to varying degrees, depending on the species. This is why seeds are such a major nutrient drain -Initially, carbohydrates and other nutrients are stored in the seed's endosperm, but later, depending on the species, the swelling cotyledons (seed leaves) of the embryo may take over this function. -When a seed germinates, the embryo develops into a new sporophyte. The mature sporophyte produces its own flowers and fruits: The life cycle is now complete

endosperm development

-After double fertilization, the triploid nucleus of the ovule's central cell divides, forming a multinucleate "supercell" that has a milky consistency. -This liquid mass, the endosperm, becomes multicellular when cytokinesis partitions the cytoplasm by forming membranes between the nuclei. -Eventually, these "naked" cells produce cell walls, and the endosperm becomes solid. -ex: Coconut "milk" and "meat" are examples of liquid and solid endosperm, respectively. The white fluffy part of popcorn is another example of endosperm. The endosperms of just three grains—wheat, maize, and rice—provide much of the food energy for human sustenance. -In grains and most other species of monocots, as well as many eudicots, the endosperm stores nutrients that can be used by the seedling after germination. In other eudicot seeds, the food reserves of the endosperm are completely exported to the cotyledons before the seed completes its development; consequently, the mature seed lacks endosperm.

vegetative reproduction

-Asexual plant reproduction based on the vegetative growth of stems, leaves, or roots

totipotent

-Describing a cell that can give rise to all parts of the embryo and adult, as well as extraembryonic membranes in species that have them -any cell that can divide and asexually generate a clone of the original organism -Totipotency is found in many plants, particularly but not exclusively in their meristematic tissues. Plant totipotency underlies most of the techniques used by humans to clone plants.

endosperm

-In angiosperms, a nutrient-rich tissue formed by the union of a sperm with two polar nuclei during double fertilization. Provides nourishment to the developing embryo in angiosperm seeds -One sperm fertilizes the egg, forming the zygote. The other sperm combines with the two polar nuclei, forming a triploid (3n) nucleus in the center of the large central cell of the female gametophyte. This cell will give rise to the endosperm

dioecious

-In plant biology, having the male and female reproductive parts on different individuals of the same species -plants cannot self-fertilize because different individuals have either staminate flowers (lacking carpels) or carpellate flowers (lacking stamens) -ex: Sagittaria latifolia (common arrowhead)

plant biotechnology

-In the general sense, it refers to innovations in the use of plants (or substances obtained from plants) to make products of use to humans -In a more specific sense, biotechnology refers to the use of GM organisms in agriculture and industry. Indeed, in the last two decades, genetic engineering has become such a powerful force that the terms genetic engineering and biotechnology have become synonymous in the media.

Opposition to GMOs: issues of human health

-Many GMO opponents worry that genetic engineering may inadvertently transfer allergens from a species that produces an allergen to a plant used for food. -However, biotechnologists are already removing genes that encode allergenic proteins from soybeans and other crops. -So far, there is no credible evidence that GM plants designed for human consumption have allergenic effects on human health. -In fact, some GM foods are potentially healthier than non-GM foods; ex: Bt maize (the transgenic variety with the Bt toxin) contains 90% less of a fungal toxin (fumonisin) that causes cancer and birth defects than non-Bt maize -Assessing the impact of GMOs on human health also involves considering the health of farmworkers, many of whom were commonly exposed to high levels of chemical insecticides prior to the adoption of Bt crops; ex: in India, widespread adoption of Bt cotton has led to a 41% decrease in insecticide use and an 80% reduction in the number of acute poisoning cases involving farmers.

what is one reason why vegetation reappears so rapidly after an environmental disruption such as fire?

-Most seeds are durable enough to last a year or two until conditions are favorable for germinating. -Thus, the soil has a bank of ungerminated seeds that may have accumulated for several years

plant tissue culture and genetic engineering

-Most techniques for the introduction of foreign genes into plants require small pieces of plant tissue or single plant cells as the starting material. -Test-tube culture makes it possible to regenerate genetically modified (GM) plants from a single plant cell into which the foreign DNA has been incorporated

vegetative growth

-Once a seed has germinated and started to photosynthesize, most of the plant's resources are devoted to the growth of stems, leaves, and roots, which is called vegetative growth -includes both primary and secondary growth and arises from activity of meristematic cells -During this stage, usually the best strategy is to photosynthesize and grow as much as possible before flowering, the reproductive phase

opposition to GMOs: possible effect on nontarget organisms

-One laboratory study indicated that the larvae (caterpillars) of monarch butterflies responded adversely and even died after eating milkweed leaves (their preferred food) heavily dusted with pollen from transgenic Bt maize, but this study was discredited when they found out the original researcher shook the male maize inflorescences onto the milkweed leaves in the laboratory, the filaments of stamens, opened microsporangia, and other floral parts also rained onto the leaves -it was these other floral parts, not the pollen, that contained Bt toxin in high concentrations; these floral parts would not be carried by the wind to neighboring milkweed plants when shed under natural field conditions. -Only one Bt maize line produced pollen with high Bt toxin concentrations -one must also weigh the effects of an alternative to the cultivation of Bt maize—the spraying of non-Bt maize with chemical pesticides. Subsequent studies have shown that such spraying is much more harmful to nearby monarch populations than is Bt maize production

opposition to GMOs: transgene escape

-Perhaps the most serious concern raised about GM crops is the possibility of the introduced genes escaping from a transgenic crop into related weeds through crop-to-weed hybridization. -The fear is that the spontaneous hybridization between a crop engineered for herbicide resistance and a wild relative might give rise to a "superweed" that would have a selective advantage over other weeds in the wild and would be much more difficult to control in the field -In some instances, there are no weedy relatives nearby with which to hybridize; soybean, for example, has no wild relatives in the United States. -However, canola, sorghum, and many other crops do hybridize readily with weeds, and crop-to-weed transgene escape in a turfgrass has occurred. -ex: In 2003 a transgenic variety of creeping bentgrass (Agrostis stolonifera) genetically engineered to resist the herbicide glyphosate escaped from an experimental plot in Oregon following a windstorm. Despite efforts to eradicate the escapee, 62% of the Agrostis plants found in the vicinity three years later were glyphosate resistant

pathogenic viruses in vegetatively propagated varieties

-Plant tissue culture is important in eliminating weakly pathogenic viruses from vegetatively propagated varieties. -Although the presence of weak viruses may not be obvious, yield or quality may be substantially reduced as a result of infection. -ex: Strawberry plants are susceptible to more than 60 viruses, and typically the plants must be replaced each year because of viral infection. However, since the apical meristems are often virus-free, they can be excised and used to produce virus-free material for tissue culture.

breaking dormancy examples

-Seeds of many desert plants germinate only after a substantial rainfall. If they were to germinate after a mild drizzle, the soil might soon become too dry to support the seedlings -Where natural fires are common, many seeds require intense heat or smoke to break dormancy; seedlings are therefore most abundant after fire has cleared away competing vegetation -Where winters are harsh, seeds may require extended exposure to cold before they germinate; seeds sown during summer or fall will therefore not germinate until the following spring, ensuring a long growth season before the next winter -Certain small seeds, such as those of some lettuce varieties, require light for germination and will break dormancy only if buried shallow enough for the seedlings to poke through the soil surface. -Some seeds have coats that must be weakened by chemical attack as they pass through an animal's digestive tract and thus are usually carried a long distance before germinating from feces

self-incompatibility

-The ability of a seed plant to reject its own pollen and sometimes the pollen of closely related individuals -If a pollen grain lands on a stigma of a flower of the same plant or a closely related plant, a biochemical block prevents the pollen from completing its development and fertilizing an egg. -analogous to the immune response of animals because both are based on the ability to distinguish the cells of "self" from those of "nonself." The key difference is that the animal immune system rejects nonself while self-incompatibility in plants is a rejection of self. -Recognition of "self" pollen is based on genes called S-genes. In the gene pool of a population, there can be dozens of alleles of an S-gene. If a pollen grain has an allele that matches an allele of the stigma on which it lands, the pollen tube either fails to germinate or fails to grow through the style to the ovary. -two types: gametophytic and sporophytic

apomixis

-The ability of some plant species to reproduce asexually through seeds without fertilization by a male gamete -there is no joining or, indeed, production of sperm and egg. Instead, a diploid cell in the ovule gives rise to the embryo, and the ovules mature into seeds, which in the dandelion are dispersed by windblown fruits. -Thus, these plants clone themselves by an asexual process but have the advantage of seed dispersal, usually associated with sexual reproduction.

receptacle

-The base of a flower; the part of the stem that is the site of attachment of the floral organs -Flowers are determinate shoots; they cease growing after the flower and fruit are formed

embryo sac

-The female gametophyte of angiosperms, formed from the growth and division of the megaspore into a multicellular structure that typically has eight haploid nuclei; develops inside each ovule -embryo sac formation occurs in a tissue called the megasporangium within each ovule -Two integuments (layers of protective sporophytic tissue that will develop into the seed coat) surround each megasporangium, except at the micropyle. -Female gametophyte development begins when one megasporocyte (or megaspore mother cell), enlarges and undergoes meiosis, producing four haploid megaspores. Only one megaspore survives; the others degenerate. -The nucleus of the surviving megaspore divides by mitosis three times without cytokinesis, resulting in one large cell with eight haploid nuclei. The multinucleate mass is then divided by membranes to form the embryo sac. -Near the micropyle of the embryo sac, two cells called synergids flank the egg and help attract and guide the pollen tube to the embryo sac. At the opposite end of the embryo sac are three antipodal cells of unknown function. The other two nuclei, called polar nuclei, are not partitioned into separate cells but share the cytoplasm of the large central cell of the embryo sac. The mature embryo sac thus consists of eight nuclei contained within seven cells

embryo development

-The first mitotic division of the zygote is asymmetrical and splits the fertilized egg into a basal cell and a terminal cell. The terminal cell eventually gives rise to most of the embryo. -The basal cell continues to divide, producing a thread of cells called the suspensor, which anchors the embryo to the parent plant. The suspensor helps in transferring nutrients to the embryo from the parent plant and, in some species, from the endosperm. -As the suspensor elongates, it pushes the embryo deeper into the nutritive and protective tissues. -Meanwhile, the terminal cell divides several times and forms a spherical proembryo (early embryo) attached to the suspensor. The cotyledons begin to form as bumps on the proembryo. A eudicot embryo, with its two cotyledons, is heart-shaped at this stage -Soon after the rudimentary cotyledons appear, the embryo elongates. Cradled between the two cotyledons is the embryonic shoot apex. At the opposite end of the embryo's axis, where the suspensor attaches, an embryonic root apex forms. After the seed germinates—indeed, for the rest of the plant's life—the apical meristems at the apices of shoots and roots sustain primary growth

seed germination

-The first organ to emerge from the germinating seed is the radicle, the embryonic root. The development of a root system anchors the seedling in the soil and supplies it with water necessary for cell expansion -ready supply of water is required for the emergence of the shoot tip into the drier conditions encountered above ground ex: garden beans, a hook forms in the hypocotyl, and growth pushes the hook above ground. In response to light, the hypocotyl straightens, the cotyledons separate, and the delicate epicotyl spreads its first true leaves. These leaves expand, become green, and begin making food by photosynthesis. The cotyledons shrivel and fall away, their food reserves having been exhausted by the germinating embryo -ex: maize/grasses, the shoot grows straight up through the tube of the coleoptile; The coleoptile pushes up through the soil and into the air. The shoot tip grows through the tunnel provided by the coleoptile and breaks through the coleoptile's tip upon emergence.

flowering

-The flowers of a given plant species typically appear suddenly and simultaneously at a specific time of year -Flower formation involves a developmental switch in the shoot apical meristem from a vegetative to a reproductive growth mode. This transition into a floral meristem is triggered by a combination of environmental cues (such as day length) and internal signals -Once the transition to flowering has begun, the order of each organ's emergence from the floral meristem determines whether it will develop into a sepal, petal, stamen, or carpel

carpel

-The ovule-producing reproductive organ of a flower, consisting of the stigma, style, and ovary -a single carpel is called a simple pistil; many species have multiple carpels (compound pistils=group of fused carpels) -pistils can be a group of multiple simple pistils/multiple carpels that are not fused, or they can be compound pistils where multiple pistils/carpels are fused together -one of the sporophylls in angiosperms (the megasporophyll) -has an ovary at its base and a long, slender neck called the style. At the top of the style is a sticky structure called the stigma that captures pollen. Within the ovary are one or more ovules, which become seeds if fertilized; the number of ovules depends on the species -In most species, the carpels are fused, resulting in a compound ovary with two or more chambers, each containing one or more ovules

stamen

-The pollen-producing reproductive organ of a flower, consisting of an anther and a filament. -one of the sporophylls (the microsporophyll) -consists of a stalk called the filament and a terminal structure called the anther; within the anther are chambers called microsporangia (pollen sacs) that produce pollen

test tube cloning

-Whole plants can be obtained by culturing small pieces of tissue from the parent plant on an artificial medium containing nutrients and hormones. -The cells or tissues can come from any part of a plant, but growth may vary depending on the plant part, species, and artificial medium. In some media, the cultured cells divide and form a callus of undifferentiated totipotent cells. When the concentrations of hormones and nutrients are manipulated appropriately, a callus can sprout shoots and roots with fully differentiated cells -If desired, the cloned plantlets can then be transferred to soil, where they continue their growth.

ripening of fruit

-a fruit usually ripens about the same time that its seeds complete their development. -Whereas the ripening of a dry fruit, such as a soybean pod, involves the aging and drying out of fruit tissues, the process in a fleshy fruit is more elaborate. -Complex interactions of hormones result in an edible fruit that entices animals that disperse the seeds. The fruit's "pulp" becomes softer as enzymes digest components of cell walls. The color usually changes from green to another color, making the fruit more visible among the leaves. -The fruit becomes sweeter as organic acids or starch molecules are converted to sugar, which may reach a concentration of 20% in a ripe fruit

abiotic pollination by wind

-about 20% of angiosperms are pollinated in this way; includes most grasses and temperate trees -Flowers are small, green, neither nectar nor scent is produced; no selective pressure favoring colorful or scented flowers -ex: flowers of hazel (Corylus avellana) and many other temperate wind-pollinated trees appear in the early spring when there are no leaves to interfere with pollen movement -because wind pollination is relatively inefficient, wind-pollinated plants produced huge amounts of pollen grains -wind pollination is often more efficient than it seems because floral structures can create eddy currents that aid in pollen capture

pollination by bees

-about 65% of flowering plants require insects for pollination -Bees eat nectar & pollen -bees attracted to bright colors (yellow & blue; red appears dull to them) -bees can see UV radiation: common dandelion (Taraxacum vulgare) have UV markings called nectar guides that help insects locate the glands that produce nectar (nectaries), but these are only visible to the human eye under UV light -flowers have a delicate, sweet fragrance

natural genetic modification of plants

-an early ancestor of the sweet potato (Ipomoea batatas) came into contact with the soil bacterium Agrobacterium (the vector commonly used to genetically engineer plants), upon which a horizontal gene transfer event occurred. Thus, sweet potato is a naturally genetically modified plant -the wheat species we rely on for much of our food evolved by natural hybridization between different species of grasses. Such hybridization is common in plants and has long been exploited by breeders to introduce genetic variation for artificial selection and crop improvement.

vegetative propagation

-asexual reproduction in plants that is facilitated or induced by humans -Vegetative reproduction that is facilitated or induced by humans -Most houseplants, landscape shrubs and bushes, and orchard trees are asexually reproduced from plant fragments called cuttings. In most cases, shoot cuttings are used. At the wounded end of the shoot, a mass of dividing, undifferentiated totipotent cells called a callus forms, and adventitious roots develop from the callus. If the shoot fragment includes a node, then adventitious roots form without a callus stage.

sporophytic self-incompatibility

-blocked by S-allele gene products in tissues of the parental sporophyte. For example, neither an S1 nor an S2 pollen grain from an S1S2 parental sporophyte can fertilize eggs of an S1S2 flower or an S2S3 flower, due to the S1S2 parental tissue attached to the pollen wall -involves a signal transduction pathway in epidermal cells of the stigma that prevents germination of the pollen grain

pollination by birds

-columbine flowers are large and bright red or yellow with little odor b/c birds don't have good sense of smell -the nectar meets the high energy demands of the bird and rewards the pollinator -petals are often fused, forming a floral tube that fits the bird's curved beak

male gametophyte development

-each anther develops four microsporangia aka pollen sacs, which each contain many microsporocytes -Each microsporocyte undergoes meiosis, forming four haploid microspores, each of which eventually gives rise to a haploid male gametophyte. -Each microspore then undergoes mitosis, producing a haploid male gametophyte consisting of only two cells: the generative cell and the tube cell. Together, these two cells and the spore wall constitute a pollen grain -The spore wall, which consists of material produced by both the microspore and the anther, usually exhibits an elaborate pattern unique to the species. During maturation of the male gametophyte, the generative cell passes into the tube cell: The tube cell now has a completely free-standing cell inside it.

cotyledon

-first leaf or first pair of leaves produced by the embryo of a seed plant -The cotyledons of the common garden bean are packed with starch before the seed germinates because they absorbed carbohydrates from the endosperm when the seed was developing. -However, the seeds of some eudicot species, such as castor beans (Ricinus communis), retain their food supply in the endosperm and have very thin cotyledons. The cotyledons absorb nutrients from the endosperm and transfer them to the rest of the embryo when the seed germinates.

pollination by moths and butterflies

-flower and fragrance are key; flowers they pollinate are sweetly fragrant -butterflies like all bright colors -moths like white and yellows, which stand out at night when moths are active -ex: yucca plant is typically pollinated by a single species of moth with appendages that pack pollen onto the stigma; the moth deposits its eggs directly into the ovary, and the larvae eat some developing seeds; if a moth deposits too many eggs, the flower aborts and falls off, selecting against individuals that overexploit the plant

pollination by flies

-flowers are reddish and fleshy, with an odor like rotten meat -blowflies visiting carrion flowers (Stapelia species) mistake the flower for a rotting corpse and lay eggs on it -blowflies become dusted with pollen, but when those eggs hatch, they find no carrion to eat and die

preventing transgene escape

-if male sterility could be engineered into plants, these plants would still produce seeds and fruit if pollinated by nearby nontransgenic plants, but they would produce no viable pollen -A second approach involves genetically engineering apomixis into transgenic crops. When a seed is produced by apomixis, the embryo and endosperm develop without fertilization. The transfer of this trait to transgenic crops would therefore minimize the possibility of transgene escape via pollen because plants could be male-sterile without compromising seed or fruit production -A third approach is to engineer the transgene into the chloroplast DNA of the crop. Chloroplast DNA in many plant species is inherited strictly from the egg, so transgenes in the chloroplast cannot be transferred by pollen -A fourth approach for preventing transgene escape is to genetically engineer flowers that develop normally but fail to open. Consequently, self-pollination would occur, but pollen would be unlikely to escape from the flower

life cycle of an angiosperm

-in the megasporangium of each ovule, the megasporocyte divides by meiosis, and one of the four megaspores produced survives and give rise to the female gametophyte -in the anther of a stamen, each microsporangium divides by meiosis and produces microspores -a microspore develops into a pollen grain; the generative cell will split and form 2 sperm, and the tube cell will produce the pollen tube -after pollination, two sperm cells are discharged in each ovule -double fertilization occurs; one sperm fertilizes the egg, forming a zygote and the other one fertilizes the central cell, forming the endosperm (food supply) -the zygote develops into an embryo packaged along with food into a seed -when a seed germinates, the embryo develops into a mature sporophyte

glyphosate

-lethal to a wide variety of plants because it inhibits a key enzyme in a biochemical pathway that is found in plants (and most bacteria) but not in animals. Researchers discovered a bacterial strain that had undergone a mutation in the gene encoding this enzyme that rendered it glyphosate-resistant. When this mutated bacterial gene was spliced into the genome of various crops, these crops also became glyphosate-resistant -Farmers achieved almost total weed control by spraying glyphosate over their fields of glyphosate-resistant crops, but the overuse of glyphosate created a huge selective pressure on weed species, resulting in many weed species evolving resistance to glyphosate. -claims have been made that glyphosate may be having negative effects on the health of humans and livestock by interfering with beneficial gut bacteria, and in 2015 the World Health Organization deemed glyphosate a probable cause of cancer.

pollination by bats

-light colored and aromatic to attract the nocturnal bats -long-nosed bat feeds on pollen of agave and cactus in SW United States and Mexico

structure of mature maize (grasses, including maize and wheat) seed

-maize has only one cotyledon -Maize and other grasses have a large cotyledon called a scutellum. The rudimentary shoot is sheathed in a structure called the coleoptile, and the coleorhiza covers the young root.

grafting

-method of propagation -a severed shoot from one plant is permanently joined to the truncated stem of another -usually limited to closely related individuals, can combine the best qualities of different species or varieties into one plant. -The plant that provides the roots is called the stock; the twig grafted onto the stock is known as the scion. -ex: scions from varieties of vines that produce superior wine grapes are grafted onto rootstocks of varieties that produce inferior grapes but are more resistant to certain soil pathogens. -The genes of the scion determine the quality of the fruit. -a callus first forms between the adjoining cut ends of the scion and stock; cell differentiation then completes the functional unification of the grafted individuals

reducing world hunger

-plant biotechnology can help increase crop yields since there really isn't anymore extra land to plant crops on -ex: Crops that have been genetically modified to express transgenes from Bacillus thuringiensis, a soil bacterium, require less pesticide. The "transgenes" involved encode a protein (Bt toxin) that is used in crops and is produced in the plant as a harmless protoxin that only becomes toxic if activated by alkaline conditions, such as in the guts of most insects. Because vertebrates have highly acidic stomachs, protoxin consumed by humans or livestock is rendered harmless by denaturation; non-Bt maize is heavily damaged by insect feeding and Fusarium mold infection, whereas Bt maize suffers little or no damage.

seed dispersal by animals

-puncture vine (Tribulus terrestris) has sharp, tack-like spines on its fruits that can injure animals/pierce bike tires; when the "tacks" are removed/discarded, the seeds are dispersed -squirrels hoard seeds or fruits in underground caches; if the animal dies or forgets the location of the cache, the buried seeds are well-positioned to germinate -seeds in edible fruits are often dispersed through feces, which may carry seeds far from the parent plant -ants are chemically attracted to seeds with "food bodies" rich in fatty acids, amino acids, and sugars; the ants carry the seed to the underground nest, where the food body is removed and fed to larvae; the remainder is usually left intact in the nest, where it germinates

biofuel crops from wild precursors

-scientists are focusing their domestication efforts on fast-growing plants, such as switchgrass (Panicum virgatum) and poplar (Populus trichocarpa), that can grow on soil that is too poor for food production. -the polymers in cell walls, such as cellulose and hemicellulose, which constitute the most abundant organic compounds on Earth, would be broken down into sugars by enzymatic reactions. These sugars, in turn, would be fermented into alcohol and distilled to yield biofuels. -In addition to increasing plant polysaccharide content and overall biomass, researchers are trying to genetically engineer the cell walls of plants to increase the efficiency of the enzymatic conversion process.

using genetic engineering to improve malnutrition

-some 250,000 to 500,000 children go blind each year because of vitamin A deficiencies. More than half of these children die within a year of becoming blind, so genetic engineers created "Golden Rice," a transgenic variety supplemented with transgenes that enable it to produce grain with increased levels of beta-carotene, a precursor of vitamin A. -cassava: This starchy root crop is the primary food for 800 million of the world's poor, but it does not provide a balanced diet. Transgenic cassava plants have been developed with greatly increased levels of iron and beta-carotene (a vitamin A precursor). Researchers have also created cassava plants with root masses twice the normal size and others containing almost no cyanide-producing chemicals (chemicals that release cyanide must be removed) -a transgenic papaya that is resistant to a ring spot virus was introduced into Hawaii, thereby saving its papaya industry.

Seed dispersal by water

-some buoyant seeds and fruits can survive months or years at sea -in coconut, the seed embryo and fleshy white "meat" (endosperm) are within a hard layer (endocarp) surrounded by a thick and buoyant fibrous husk

Gametophytic self-incompatibility

-the S-allele in the pollen genome governs the blocking of fertilization -ex: an S1 pollen grain from an S1S2S1S2 parental sporophyte cannot fertilize eggs of an S1S2 flower but can fertilize an S2S3 flower. An S2 pollen grain cannot fertilize either flower. -In some plants, this self-recognition involves the enzymatic destruction of RNA within a pollen tube. RNA-hydrolyzing enzymes are produced by the style and enter the pollen tube. If the pollen tube is a "self" type, they destroy its RNA.

what are the two variations of compound pistils?

-the carpels are fused, but there are multiple stigmas (one stigma from each carpel) -OR having a lobed stigma, with one lobe from each carpel -the cross section of a compound ovary shows a chamber from each carpel, while the cross section of a simple ovary isn't separated into chambers

embryonic axis

-the embryo consists of an elongate structure, the embryonic axis, attached to two thick, fleshy cotyledons -Below where the cotyledons are attached, the embryonic axis is called the hypocotyl. The hypocotyl terminates in the radicle, or embryonic root -The portion of the embryonic axis above where the cotyledons are attached and below the first pair of miniature leaves is the epicotyl. The epicotyl, young leaves, and shoot apical meristem are collectively called the plumule.

seed dispersal by wind

-the giant seed of the tropical Asian climbing gourd Alsomitra macrocarpa glides through the air of the rain forest in wide circles when released -the winged fruit of maple spins like a helicopter blade, slowing descent and increasing the chance of being carried farther by horizontal winds -tumbleweeds break off at the ground and tumble across the terrain, scattering their seeds -some seeds and fruits are attached to umbrella-like "parachutes" that are made of intricately branched hairs and often produced in puffy clusters; these dandelion "seeds" (actually one-seeded fruits) are carried by the slightest gust of wind

coevolution

-the joint evolution of two interacting species, each in response to selection imposed by the other -natural selection favors deviations in floral structure or physiology that make it more likely for a flower to be pollinated regularly by an effective animal species. If a plant species develops traits that make its flowers more prized by pollinators, there is a selective pressure for pollinators to become adept at harvesting food from these flowers -ex: some species have fused flower petals that form long, tubelike structures bearing nectaries tucked deep inside. Charles Darwin suggested that a race between flower and insect might lead to correspondences between the length of a floral tube and the length of an insect's proboscis, a straw-like mouthpart. Based on the length of a long, tubular flower that grows in Madagascar (Angraecum sesquipedale), Darwin predicted the existence of a pollinating moth with a 28-cm-long proboscis. Such a moth (hawk moth, Xanthopan morganii praedicta) was discovered two decades after Darwin's death

plant breeding with genetic engineering

-the natural rate of mutation is too slow and unreliable to produce all the mutations that breeders would like to study. Breeders sometimes hasten mutations by treating large batches of seeds or seedlings with radiation or chemicals -While most breeders cross-pollinate plants of a single species, some breeding methods rely on hybridization between two distant species of the same genus. Such crosses sometimes result in the abortion of the hybrid seed during development. Often in these cases the embryo begins to develop, but the endosperm does not. Hybrid embryos are sometimes rescued by surgically removing them from the ovule and culturing them in vitro -not limited to the transfer of genes between closely related species or genera -ex: inserting a desired gene from daffodil into rice can be done more quickly, more specifically, and without the need for intermediate species

biomass

-the total mass of organic matter comprising a group of organisms in a particular habitat -The use of biofuels from plant biomass would reduce the net emission of CO2. Whereas burning fossil fuels increases atmospheric CO2 concentrations, biofuel crops reabsorb by photosynthesis the CO2 emitted when biofuels are burned, creating a cycle that is carbon neutral.

pollination

-the transfer of pollen to the part of a seed plant that contains the ovules, a process required for fertilization -in angiosperms its from anthers to stigmas -can occur by wind, water, or animals; In wind-pollinated species, including grasses and many trees, the release of enormous quantities of smaller-sized pollen compensates for the randomness of dispersal by the wind; Some species of aquatic plants rely on water to disperse pollen. Most angiosperm species, however, depend on insects, birds, or other animal pollinators to transfer pollen directly from one flower to another. -about 80% of all angiosperms depend on animals/biotic factors for pollination; 98% of the species that use abiotic pollination factors rely on wind, and the other 2% rely on water

imbibition

-the uptake of water by a seed or other structure, resulting in swelling; uptake of water due to the low water potential of the dry seed -initiates seed germination -causes the seed to expand and rupture its coat and triggers changes in the embryo that enable it to resume growth (after being dormant). Following hydration, enzymes digest the storage materials of the endosperm or cotyledons, and the nutrients are transferred to the growing regions of the embryo.

traditional plant breeding method

-when a desirable trait is identified in a wild species, the wild species is crossed with a domesticated variety. -Generally, those progeny that have inherited the desirable trait from the wild parent have also inherited many traits that are not desirable for agriculture, such as small fruits or low yields. -The progeny that express the desired trait are again crossed with members of the domesticated species and their progeny examined for the desired trait. -This process is continued until the progeny with the desired wild trait resemble the original domesticated parent in their other agricultural attributes -ex: traditional breeding techniques could not be used to insert a desired gene from daffodil into rice because the many intermediate species between rice and daffodil and their common ancestor are extinct. In theory, if breeders had the intermediate species, over the course of several centuries they could probably introduce a daffodil gene into rice by traditional hybridization and breeding methods

Mechanisms that prevent self-fertilization

1.) self-incompatibility 2.) Some species have staminate and carpellate flowers on separate plants (dioecious species) 3.) Others have stamens and carpels that mature at different times or are arranged such that it is unlikely that an animal pollinator could transfer pollen from an anther to a stigma of the same flower

complete flower

A flower that has all four basic floral organs: sepals, petals, stamens, and carpels.

aggregate fruit

A fruit derived from a single flower that has more than one separate carpel, each forming a small fruit. These "fruitlets" are clustered together on a single receptacle, as in a raspberry -ex: raspberry, blackberry, strawberry

agricultural adaptations of self-incompatibility

Breeders often hybridize different genetic strains of a crop to combine the best traits of the two strains and to counter the loss of vigor that can often result from excessive inbreeding. To prevent self-fertilization within the two strains, breeders must either laboriously remove the anthers from the parent plants that provide the seeds (as Mendel did) or use male-sterile strains of the crop plant, if they exist. If self-compatibility can be genetically engineered back into domesticated plant varieties, these limitations to commercial hybridization of crop seeds could be overcome.

epicotyl

In an angiosperm embryo, the embryonic axis above the point of attachment of the cotyledon(s) and below the first pair of miniature leaves.

hypocotyl

In an angiosperm embryo, the embryonic axis below the point of attachment of the cotyledon(s) and above the radicle (embryonic root of a plant)

artificial selection of maize

Left on its own in nature, maize would soon become extinct for the simple reason that it cannot spread its seeds. Maize kernels are not only permanently attached to the central axis (the "cob") but also permanently protected by tough, overlapping leaf sheathes (the "husk"). These attributes arose by artificial selection by humans -Modern maize was derived from teosinte. Teosinte kernels are tiny, and each row has a husk that must be removed to get at the kernel. The seeds are loose at maturity, allowing dispersal, which probably made harvesting difficult for early farmers. -Neolithic farmers selected seeds from plants with larger cob and kernel size as well as the permanent attachment of seeds to the cob and the encasing of the entire cob by a tough husk.

transgenic

Pertaining to an organism whose genome contains a gene introduced from another organism of the same or a different species.

coleorhiza

The covering of the young root of the embryo of a grass seed -The embryo of a grass seed is enclosed within two protective sheathes: a coleoptile, which covers the young shoot, and a coleorhiza, which covers the young root. Both structures aid in soil penetration after germination.

coleoptile

The covering of the young shoot of the embryo of a grass seed. -The embryo of a grass seed is enclosed within two protective sheathes: a coleoptile, which covers the young shoot, and a coleorhiza, which covers the young root. Both structures aid in soil penetration after germination.

asexual reproduction

The generation of offspring from a single parent that occurs without the fusion of gametes (by budding, division of a single cell, or division of the entire organism into two or more parts). In most cases, the offspring are genetically identical to the parent.

callus

a mass of dividing, undifferentiated cells growing at the site of a wound or in a culture

Advantages and disadvantages of asexual reproduction

advantages: -no need for a pollinator -allows the plant to pass on all its genetic legacy intact to its progeny, compared to in sexual reproduction when a plant passes on only half of its alleles -If a plant is superbly suited to its environment, asexual reproduction can be advantageous. A vigorous plant can potentially clone many copies of itself, and if the environmental circumstances remain stable, these offspring will also be genetically well adapted to the same environmental conditions under which the parent flourished -Generally, the progeny produced by vegetative reproduction (which is asexual) are stronger than seedlings produced by sexual reproduction disadvantages: -genotypic uniformity of asexually produced plants puts them at great risk of local extinction if there is a catastrophic environmental change, such as a new strain of disease

The germination of seeds _____.

depends on imbibition -Imbibition, the absorption of water by the seed, causes the seed to expand and rupture.

Advantages and disadvantages of sexual reproduction

disadvantages: -seed germination is a precarious stage of life in the plant; the tough seed gives rise to a fragile seedling that may face exposure to predators, parasites, wind, and other hazards. In the wild, few seedlings survive to become parents themselves -production of enormous numbers of seeds compensates for the odds against individual survival and gives natural selection ample genetic variations to screen. However, this is an expensive means of reproduction in terms of the resources consumed in flowering and fruiting. -Although sexual reproduction involving two genetically different plants produces the most genetically diverse offspring, some plants, such as garden peas, usually self-fertilize. This process, called "selfing," is a desirable attribute in some crop plants because it ensures that every ovule will develop into a seed advantages: -genetic variation can be advantageous in unstable environments where evolving pathogens and other fluctuating conditions affect survival and reproductive success -seeds (which are almost always produced sexually) facilitate the dispersal of offspring to more distant locations; seed dormancy allows growth to be suspended until environmental conditions become more favorable

Which of the following is an advantage of asexual reproduction in plants?

enhanced survival of genetically favorable offspring -In constant environments, asexually produced offspring have higher survival rates. -no need for a pollinator is also correct, but enhanced survival is the better answer

Self-incompatibility _____.

helps maintain genetic variability in a population -By preventing self-pollination or pollination by closely related individuals, variability is maintained.

In grafting, the plant that provides the root system is the _____ and the twig is the _____.

stock ... scion

fruit development

the ovary wall becomes the pericarp, the thickened wall of the fruit. In some fruits, such as soybean pods, the ovary wall dries out completely at maturity, whereas in other fruits, such as grapes, it remains fleshy. In still others, such as peaches, the inner part of the ovary becomes stony (the pit) while the outer parts stay fleshy. As the ovary grows, the other parts of the flower usually wither and are shed.