BOT 313 Study Guide 2

Pine wood - bordered pits

A pit in which the secondary wall arches over the pit membrane, except in the area of the pit aperture

Classifying flower anatomy patterns

A complete flower has all of the major parts (sepals, petals, stamens, carpels). An incomplete flower lacks any one of the major parts. A perfect flower has both stamens (male) and carpels (female) within one flower; An imperfect flower lacks one of these parts. Therefore, imperfect flowers are unisexual. When stamens are present, the flower is staminate; When pistils are present the flower is pistillate.

Seed

A seed consists of an embryonic plant and a food reserve (typically endosperm or cotyledon, depending on the species) surrounded by a seed coat (testa). As a seed matures, its tissues lose water until the water content falls to 5 to 10%. In this dehydrated state, metabolism comes to a virtual, if not complete, halt. Seeds may remain in this quiescent stage until conditions are favorable for germination (resumption of growth).

Anthocyanins

A type of flavanoid pigment, are responsible for the coloration of red cabbage leaves. These pigments are water-soluble and are dissolved in the cell sap in the vacuole. Thus, they are a good marker to observe the size of the vacuole. In cabbage, anthocyanins may be synthesized in anthocyanoplasts which are tiny, transient, organelle-like structures found in the vacuole (look for discrete red spots or speckles).

Plant cells

A typical plant cell has a non-living, semi-rigid cell wall as its outer boundary. The cell wall encloses the living part of the cell, the protoplast. The protoplast has within it various organelles (membrane bound compartments, each with its own function).

Seedling

A young plant that develops from the embryo when a seed germinates.

Pollen tube growth

After the pollen grain has landed on the stigma, it begins to activate and undergoes hydration. Following this, the pollen tube begins to grow and emerge from the pollen grain. This tube will grow into and then down the stigma and style on its way to the ovule. The growth of the tube is achieved through elongation of the cytoskeleton and the transport of vesicles to the growing tip.

Observation of C-fern Gametophytes

After the spores have germinated, tiny, haploid gametophytes begin to grow out of the remnants of the spore casing. This casing may still be visible in some of the images you will observe. •You should be able to differentiate both hermaphrodite and male gametophytes. What are the visible differences between them? •At the base of the gametophytes are thin, thread like structures called rhizoids. What do the rhizoids resemble?

Lycophytes and ferns

Although there are exceptions among some ferns, most of the non-vascular plants and seed-free vascular plants (lycophytes and ferns) produce one kind of spore (they are "homosporous"). You should recall that this spore is haploid and develops into the gametophyte, which is the dominant phase in the bryophyte life cycle and is the heart-shaped structure called a prothallus in ferns.

Fruit

As mentioned earlier in this course, seeds are well adapted to survival, containing a protective seed-coat and a supply of food for the embryo (in angiosperms, this food is endosperm or, later, cotyledons; in gymnosperms, the food supply is the female gametophyte). Propagules of angiosperms are further protected by a fruit that encases the seeds. This fruit tissue is derived from flower parts, including the ovary and other tissue surrounding it. While this definition of fruit is very useful, it fails to convey the range of diversity of fruit types. To organize some of this diversity, fruits are classified based on specific characteristics of the mature ovary tissue, such as whether the tissue is fleshy or dry

Twig anatomy

At the tip of the twig is the terminal (apical) bud (an embryonic shoot of a plant). This is a primordial or immature shoot tip (p. 624). The bud is covered and protected by bud scales. Axillary buds grow along the sides of the twig in the axils (angles) between the stem and the leaves (now gone). They are like the terminal bud but smaller. Locate a node (where leaves are attached to the stem) and examine the leaf scar if present (Figure 10) - what remains on the stem after abscission - when the leaf falls off the plant. The size and shape of leaf scars can differ with various species. If there are no leaves attached, the location of the leaf scars will also tell you the type of leaf arrangement on the plant. Locate the internodes, the lengths of twig between the nodes. Vascular bundle scars are the tiny dots on the leaf scars ( Figure 10). They represent the broken ends of the vascular bundles that connect the leaf to the stem. The number and arrangement of vascular bundle scars may be characteristic of a species. Bud scale scars are rings of small transverse scars left by the bud scales when they fall from the terminal bud when it begins to grow. (Figure 11) Usually one terminal bud per year is produced on a twig, so these scars can be used to determine the age of the twig. Lenticels are small pores surrounded by masses of loosely compacted cork tissue. They allow gaseous exchange between the internal tissues of the stem and the atmosphere.

Shoot Apical Meristem of Coleus (Plectranthus scutellarioides)

Below are images of a longitudinal section though the apical tip of a Coleus (Figure 1). You should be able to locate the leaf primordia, apical meristem, and axillary buds/lateral buds ("bud primordium")—sites where stem branches and flowers are formed. Note the intensity of the staining in the apical meristem and the meristems in the axillary/lateral buds. Such stain intensity is characteristic of cells that are actively dividing. Compare your observations to that of Figure 25-2 in Raven's Biology of Plants(pg. 580).

Pinus mature male cone

Below are images of a prepared slide of a longitudinal section through a Pinus pollen-bearing male cone (microsporangiate strobilus). First view the images taken with the lower magnification and compare to Figure 18-17 in your textbook. Locate the microsporophylls and microsporangia located on either side of the central axis. Then at the higher magnification, observe the mature pollen grains within the microsporangia. The air sacs that confer buoyancy to the pollen grain (to keep it aloft on air currents for more efficient wind dispersal of the pollen) can be seen in Figure 1 within this lab; also note the different cells and nuclei inside the pollen grains. Figure 18-18 of your text should help.

Observation of Moss Capsule/Sporangium

Below are images of a prepared slide of a moss capsule. The slide shows a longitudinal section through a mature capsule in which arespores at various stages of development, including spore-tetrads and mature spores ready to be released. The spores are produced by meiosis.

Observation of a Living Moss

Below are images of living mass. Note the "leafy" green gametophytes and sporophytes. Compare these to a sample of moss you find. Can you identify the gametophyte and sporophyte in your sample? Check out the moss life cycle on pgs. 386-387 the textbook.

Observation of Moss Antheridia and Archegonia

Below are images of prepared slides (longitudinal section) of a moss antheridia ( Figure 4) and archegonia (Figure 5) which are part of the male and female gametophytes, respectively. Within the antheridia you will observe the haploid sperm and within the archegonia you will observe the haploid egg. Compare the images below to Figure 16-23 in the textbook.

Observation of Monocot and Dicot Stomata

Below are images of the epidermis from Corn (Zea mays) and Broad bean (Vicia faba) as well as other example monocots and eudicots. Note that fava beans have stomata on both the upper (adaxial) and lower (abaxial) surfaces of their leaves. For both the monocots and eudicots: •Note the distribution of the stomata within the epidermal tissue. Are they scattered or organized into regular "lines"? •Find all components of the stomatal complex: -Guard cells -Subsidiary cells (if present) -Stomatal pores (openings) •Note the shapes and arrangement of the "ordinary" epidermal cells, known as pavement cells. •Note the different shape of the guard cells in monocots versus dicots

Tracheary Elements, Sclereids, and Parenchyma Tissue in Wax plant (Hoya carnosa)

Below are images of thin cross sections of the stem of a wax plant (Hoya carnosa) stained with TBO (Figure 13). Parenchyma cells in the cortex (the outer ground tissue) and the pith (the ground tissue inside the ring of vascular tissue) differentiate into brachysclereids. The TBO will stain the sclereids and water-conducting cells (tracheary elements) in the xylem tissue blue or purple.

Observation of Moss Gametophyte Tissue

Below is a picture taken through a compound scope of one of the "leafy" structures from the living moss plants, stained with TBO. Note: this is not a true leaf; a true leaf has three different tissue systems, including dermal, ground, and vascular. This gametophyte tissue is NOT differentiated into three tissue systems and LACKS vascular tissue.

Buds

Buds are undeveloped or embryonic shoots that generally occur in the axils of leaves or at the tips of stems. Buds can remain dormant for extended periods or resume growth immediately. Buds can be specialized to develop flowers or short shoots, or they can give rise to entirely new stems/branches.

Angiosperms

By far the largest phylum and most diverse of photosynthetic organisms, the angiosperms (Phylum Anthophyta) include about 300,000 species. Angiosperms have traditionally been classified into two major groups: the monocotyledons, or monocots, and the dicotyledons, or eudicots. Recent systematic work has revealed that the monocots are a monophyletic group (consist of a common ancestor and all its descendants), but the dicots do not form a natural group (that is, they are not monophyletic). Refer to Table 19-1 in Raven's Biology of Plants(pg. 460) for a summary of some of the morphological differences between monocots and dicots.

Collenchyma cells (Ground tissue)

Collenchyma cells bear a strong resemblance to parenchyma (Figure 23.5 in Raven's Biology of Plants). This cell type is typically elongated and characterized by unevenly thickened, nonlignified primary cell walls and occur in groups just beneath the epidermis of the stem and associated with the vascular bundles in leaves. These cells are supportive in function and are alive at maturity. The primary cell walls become thickened with cellulose and pectin, often at their corners (see Figure 23-7 on pg. 543 in Raven's Biology of Plants). Locate the patches of collenchyma, which are rich in pectins and stain darkly.

Corn leaf (Zea mays), a C4 grass

Compare the upper and lower epidermis. Large cells in the upper epidermis are bulliform cells; these cells lose their turgor during dry periods and cause leaf rolling. Note the epidermal cells (shape, transparent, no chloroplasts). Locate a vein; veins consist of a few tracheary elements in the xylem and a small group of cells in the phloem. The vein will be surrounded with a conspicuous parenchyma bundle sheath, the cells of which will be large in comparison to the mesophyll cells in the leaf. The synthesis reactions of photosynthesis occur in these bundle sheath cells of this C4 plant.

Druses

Compound crystals (Figure 10); may be found in the cortical or pith parenchyma cells of stems of Begonia (Figure 11) or geranium, in the leaves of Hoya (Figure 12) or in the tissues of sweet potato root.

Dieffenbachiaand Idioblasts Primer

Dieffenbachiais a genus in the Arum family (Araceae), and the species D. picta (dumb cane) is a common houseplant, estimated to be found in millions of American homes (Arditti & Rodrigquez 1982) despite its propensity for causing harmful reactions in children and pets that may nibble on its leaves or stems. The irritant and toxic qualities of Dieffenbachiaare due to the presence of calcium oxalate crystals (particularly in the form of needle-shaped raphides) and a cocktail of chemical constituents located in cells containing the raphides. The raphides can pierce oral mucosa, and the toxic substances in the plant cells can cause burning in the mouth or throat, hoarse voice, nausea or vomiting, airway impairments, difficulty swallowing, and swelling and/or paralysis of the mouth or tongue. The identity of these toxic compounds has not been fully established, although a recent study by Oloyede et. al. (2011) detected 80 constituents in the essential oil from D. picta leaves and 54 in the stems. Distillates containing the essential oils from D. picta were found to anti-fungal properties and have antimicrobial activities against gram-positive and gram-negative bacteria. They were also found to be toxic to brine shrimp larvae, with leaf essential oils being more toxic than that from the stem. Bundles of raphides commonly occur in specialized cells called idioblasts, although they also can occur in extracellular bundles. The functional significance of calcium oxalate crystals is still under investigation, although hypotheses include: mechanical support, mineral balance, waste sequestration, and protection against herbivores (See discussion in Coté 2009). Raphides in Dieffenbachia and many other species with the Araceae have an unusual type of raphide-containing idioblast called a biforine that can forcibly expel the crystals when the cells are damaged (Coté 2009). Turgor pressure (hydrostatic pressure) is believed to be the driving force for ejecting crystals from the idioblasts of Dieffenbachia. The idioblasts contain a mucopolysaccaride material that is osmotically active. When the tip of the cell wall is broken, the mucopolysaccharides attract water. Turgor pressure presumably develops in the idioblasts because of this osmotic entry of water from the surroundings; the building water pressure forces the raphides out of the broken tip of the cell. Intact idioblasts do not release their raphides because the intact cell wall exerts wall pressure that prevents the cell from taking up additional water, therefore preventing sufficient turgor pressure to eject the raphides.

Examination of the Parasitic Plant "Dodder"

Dodder (Cuscutasp.) is a parasitic plant that lacks chlorophyll and must obtain its food from other plants. Dodder plants are bright orange or yellow. They have specialized absorptive organs called haustoria that penetrate the tissues of their host plants. See page 460 in the textbook.

C-fern spores

Each spore is a single cell that is the product of meiosis; it contains a haploid set of chromosomes. Notice the ridges of the spore ornamentation and the trilete mark (Figure 14). Within each of the spores are several oil bodies. The oil bodies contain lipids that are broken down to provide energy and raw materials for growth of the fern gametophyte once the spore germinates and the gametophyte begins to grow.

Stem of Elodea (waterweed or anacharis),

Elodea (waterweed or anacharis) is an aquatic plant that is always submerged. Below are prepared cross-sections of the stem imaged at 40x, 100x and 400x in both black and white, and color. Examine its vascular tissue. •What do you see? •Locate the aerenchyma (spongy tissue containing air spaces, especially found in many aquatic plants), parenchyma, epidermis.

Examination of Aerial Roots of Orchid

Epiphytic orchids are characterized by aerial roots that are covered with a multiple epidermis, called velamen. Many orchids use these roots not only for absorption of water and dissolved minerals but also for photosynthesis. Epiphytic plants use other plants (or non-plant structures) as supports, but do not obtain any food/water from those plants (that is, epiphytes are NOT parasites).

Different cuts of wood

Examination of Wood (=Secondary Xylem) Cuts and Sections There are 3 different types of cuts we will examine: Cross-section, radiate section, and tangential section. Cross-section (cs) = Transverse section: a cut straight through a stem or root at a right angle to its axis. Growth rings are arranged in concentric circles. Rays radiate from the center, like spokes from the center of a wheel. Radiate section (rls):a longitudinal section that goes through the center of the stem. Cut runs parallel to the rays. Tangential section (tls): a longitudinal section that does not go through the centerof the stem. Rays appear as small circles as they come out at you from the cut.

Lilium (lily) young and older anther

Examine the images of prepared cross-sections through lily anthers. Each anther has four pollen sacs or microsporangia. Inside the microsporangium, early in development (Figure 9), are microspore mother cells (2n). These microspore mother cells will undergo meiosis to produce haploid (n) spores (Figure 10). Each spore will undergo mitosis to develop into a pollen grain (the male gametophyte, Figure 11).

Sclerenchyma of pear fruit (Pyrus communis)

Examine the images taken at 100x and 400x (Figure 4) of pear tissue stained with TBO. TBO stains lignified cell walls (such as those found in sclerenchyma cells and tracheary elements). In all four images you will see an example of a brachy sclereid ("stone cells") which give pears their gritty texture. MAKE A SKETCH of the sclereids in the pear fruit. You should be able to discern the thick, lignified cell walls, and you will likely notice pit canals, some of which are branched, running through the lignified cell walls.

Crystals

Excess inorganic substances, often calcium salts, in plant cells are often deposited in the vacuole in crystalline form. Raphides: needle like crystals that occur in bundles; may be found in the leaves and stems of Tradescantia zebrina (spiderwort or inch plant; Figure 8), leaves of Sansevieria (snake plant, Figure 9), or the peel or Musa (banana).

Pteris (Fern) leaf, cross-section

Ferns have complex leaves called megaphylls, that are more complex than the microphylls of clubmosses. In the images below, note how similar the leaf tissue looks to that of a dicot. You should be able to observe both spongy and palisade mesophyll, and stomata withguard cells.

Examine and label flowers

Flowers are the reproductive parts of angiosperms, involved in sexual reproduction. They typically consist of the receptacle, sepals (calyx collectively), petals (corollacollectively), stamens composed of filament and anther (androecium collectively) and the pistilcomposed of one or more carpels (gynoecium collectively). The calyx and corolla collectively are called the perianth. When the two cannot be distinguished from each other, they are called tepals.

Leaves

Leaves, in their morphology and anatomy, are perhaps the most variable of plant organs. The primary functions of leaves are photosynthesis and transpiration, and an understanding of these physiological processes is impossible unless it is correlated with an understanding of the anatomical features of the leaf. One must consider anatomical features such as the surface area, permeability of the epidermis to gases, the extent of the intercellular air spaces, and the distribution of vascular tissues.

Stem of Pelargonium sp. (geranium)

Geranium stems can show you how the single layer of epidermal cells of the primary plant body becomes replaced by multiple layers of periderm ("cork cells" or "phellem") as the stems undergo secondary growth (we will cover this more in module 5). Examine the numerous layers of phellem (cork) cells, which have suberin in their walls. The cork cambium ("phellogen") is the lateral meristem that is initiated in the outer cortex and divides to form the several rows of phellem ("cork") cells. In the black and white 40x image and in one of the 100x color images you can see a lenticel, which is a loose area in the phellem/cork cells that provides a pathway for gas exchange. You may also note that the cortex consists of several rows of collenchyma and sclerified parenchyma cells.

Gymnosperms and angiosperms

Gymnosperms and angiosperms, however, produce two distinct kinds of spores (that is, they are "heterosporous"): the microspore that develops into a male gametophyte (pollen grain), and the megaspore that develops into the female gametophyte (including egg). Also, unlike ferns and mosses that disperse primarily by spores, dispersal of gymnosperms and angiosperms is primarily by means of seeds, which are much larger and more complex than spores. While these differences are significant and have important consequences for the migration of plants to different habitats, gymnosperms and angiosperms still share the same general alternation of generations described for mosses and ferns. In seed plants (gymnosperms & angiosperms) the gametophyte phase is proportionally much more reduced and doesn't grow independently of the sporophyte. The female gametophyte, for example, is produced inside a special structure called an ovule that contains the megasporangium, which is fleshy (and called the nucellus). After fertilization by a pollen grain (male gametophyte), the ovule then develops into a seed, which is the distinguishing characteristic that separates gymnosperms and angiosperms from other spore-producing plants; keep in mind that like all plants, seed plants produce spores as well. Seeds are particularly well-suited for dispersal because they have a protective seed-coat and a supply of food for the embryo. These structures enable seeds to survive in many different environments, which undoubtedly aided seed plants in becoming the dominant vegetation on earth today

Splitting corn kernel longitudinally

Imagine we have cut the corn kernel longitudinally (Figure 2 and 3) and bisected the embryonic axis and cotyledon. This slice will give two mirror images showing the pericarp, aleurone (outermost layer of endosperm, see page 533 in the text), endosperm, and embryo (including cotyledon, epicotyl, hypocotyl, and radicle; see Figure 3).

Fruit organization

In fruits comprised of fleshy ovary tissue, there are usually three distinct regions: the exocarp (skin), mesocarp (fleshy part), and endocarp (directly adjacent to seed) (Figure 1). In dry fruits, these three layers are fused into one pericarp, surrounding the seed. As always, there are many exceptions to this simple classification system. For example, the fleshy part of a strawberry is derived from the flower's receptacle tissue. Fruits such as strawberries that are composed of more than just ovary tissue are called accessory fruits. As you examine some of the diversity in fruit morphology, try to imagine the type of dispersal mechanisms that might be involved. Since part of successful reproduction (i.e., "fitness") involves transport of seeds or fruits to preferable habitats, fruits can be subject to selection pressures that favor one form over another. This type of natural selection has resulted in fruits that are modified to be dispersed by water (coconut), wind (maple 'helicopters'), or animals (many fruits we eat).

Shoot tip

In this exercise, we concentrate our observation on the shoot apical meristem and the stem apex. This region is dominated by cells undergoing mitosis to produce daughter cells, which — once they've reached maturity — begin to expand, automatically pushing the meristem upward. This extension, or growth, initiated in the apical meristem is termed primary growth and the tissues produced are termed primary tissues. These primary tissues consist of the complex tissues of the dermal tissue system (epidermis) and the vascular tissue system (primary xylem and primary phloem), as well as the simple tissues of the ground tissue system (parenchyma, collenchyma, and sclerenchyma).

Germination

Involves absorption of water and oxygen by the seed, rapid growth of the embryo, rupture of the seed coat and emergence of the seedling.

Leaves

Leaves are attached to stems at nodes. The upper angle between the petiole and the stem is the axil. In the axil is usually a bud—an embryonic branch shoot, protected by bud scales, that has the potential to give rise to a new leaf or a branch shoot. The presence of a bud delimits a leaf: everything immediately below the bud is a leaf; leaflets of compound leaves never have buds at their base (Raven's Biology of Plants page 591 and 593; 'Leaf Terminology' available on the lab assignment page in Canvas). Leaves may be simple or compound. Simple leaves may have an entire margin to one that is variously toothed to pinnately or palmately lobed. Compound leaves are deeply divided into segments—leaflets—and may be pinnately to palmately compound. The leaves of some monocots are sessile (lack a petiole) and consist of a basal sheath which wraps around the stem and blade projecting outward from the stem. Leaves on conifers (gymnosperms) are usually needle-like or scale-like or awl-shaped (short and narrowly triangular). Leaves are borne singly or in clusters (fascicles); when in fascicles, the leaf base is often sheathed by more or less persistent scale leaves.

Sclerenchyma fibers of Snake Plant (Sansevieria trifasciata)

Leaves of the snake plant contain bundles of fibers that provide strength to the elongated leaves. Below are several thin cross-sections from the leaf of a snake plant stained with TBO (Figure 5, 6 and 7). Observe the bundles of fibers located in the mesophyll; the thickened secondary cell walls of the fibers will stain blue or blue-green because of the presence of lignin. You may also observe veins (vascular bundles), photosynthetic parenchyma cells of the mesophyll, and epidermis cells (generally colorless). The following are thin longitudinal-sections of a portion of snake plant leaf stained with TBO (Figures 8, 9 and 10). Observe the narrow, elongated shape of the fibers, which are located in bundles.

Observation of fern

Locate a fern. This can be out in the field or one at home or at a garden center. Locate the rhizome and fronds (a fern leaf). On a frond find a sorus—a cluster of sporangia. In some species a flap of tissue will be partially covering the sorus, this is called an indusium. Do you see any spores? If a sorus is not present on your fern frond, find an image online. Read the section titled 'Most Polypodiopsida Are Homosporous Leptosporangiate Ferns' (pages 417 to 419) and consult Figures 17-32 and 17-35 in your text.

Examination of Mycorrhizae (symbiosis between roots and fungi)

Mycorrhizal fungi benefit plants by increasing plants' abilities to capture water and essential elements, especially phosphorus. See textbook, pages 312-315. 1. Endomycorrhizae Examine the prepared slide showing roots containing endomycorrhizae. Locate the epidermis, cortex, and stele of the root. •Where are the fungal hyphae found? 2. Ectomycorrhizae Examine the prepared slide showing roots containing ectomycorrhizae. Locate the plant roots, epidermis, cortex, and stele. •Where are the fungal hyphae found?

Myriophyllum sp. (watermilfoil)

Myriophyllum are a genus of submerged aquatic plants. These are a type of hydrophytic leaves - note the aerenchyma tissue within the leaf.

Alfalfa (Medicago sativa) and Privet (Ligustrum), C3 dicots

Note how the mesophyll is differentiated into a palisade layer below the upper epidermis and a spongy layer above the lower epidermis. Find stomata; note the size of the guard cells and the substomatal space above the stomata (this minimizes water loss by increasing the distance that water must diffuse after evaporating from the wet surfaces of spongy mesophyll cells and diffusing out of the leaf. Note the presence of intercellular spaces within the spongy mesophyll; these aid the diffusion of gases through the leaf. Identify the upper epidermis, lower epidermis, vein, xylem, phloem, palisade mesophyll, and spongy mesophyll.

The major organelles in plant cells that can be seen with a compound microscope are the...

Nucleus, vacuole (surrounded by its membrane, the tonoplast), and various plastids. Proplastids are found in actively dividing cells and differentiate into the following types: leucoplasts, which are colorless; chloroplasts, which contain chlorophyll pigments (green) and carry out photosynthesis; and chromoplasts, which contain red or yellow pigments and are often found in cells of fruits or flowers. Amyloplasts are a type of leucoplast that store starch. Water-soluble pigments, such as anthocyanins (blue-red), are located in the vacuole.

Nerium (Oleander) leaf, cross-section

Oleander is a small shrub or tree whose flowers grow in pairs or whorls of three. It is considered a good example of a xerophytic leaf. Of the most commonly grown garden plants, it is one of the most poisonous. Notice the crypts which house trichomes and stomata. Compare the images below to Figure 25-23 in the text.

Parenchyma cells (Ground tissue)

Parenchyma cells vary in their morphology (form and structure) and physiology (function), but generally they have thin walls and a polyhedral (many-sided) shape (Figure 23-5 on pg. 542 in Raven's Biology of Plants). The parenchyma cell is the principal site of photosynthesis, assimilation, and storage — activities that depend on living cytoplasm. Intercellular spaces should be apparent within the parenchyma tissue

Examination of Gymnosperm Reproductive Structures in Pinus (pine)

Pine trees possess both male and female cones. The structure of the male cone (microstrobilus or pollen cone) is very similar across species. The pollen cone consists of microsporangia (pollen sacs) tucked under microsporophylls, which contain the developing and mature pollen. The structure of the female cone (megastrobilus, seed, or ovulate cone) varies quite a bit more between species. The scales of the female cone hold the exposed ovules and later the seeds after fertilization. In pine, there are two depressions on the upper surface at the base of each woody scale in the female cone. These depressions are where the exposed ovules are located. If you have access to a female cone, try to find these depressions.

Pinus (Pine) leaf, cross-section

Pines have evergreen leaves (needles) that are adapted to areas where little moisture is available to them in the winter (think about the environments where pines are abundant: boreal forests where water is frequently unavailable, because it is frozen, or arid environments or nutrient poor regions in the subtropics or tropics). The number of vascular bundles per needle can vary—usually one or two. See Figure 18-14 on page 438. The vascular region is surrounded by transfusion tissue (parenchyma & tracheids) which in turn is delimited by an endodermis. The mesophyll is most of the remaining tissue of the leaf. The cells have a characteristic rosette shape — this facilitates expansion and contraction of the needle. Note the resin canals, hypodermis, epidermis and cuticle. You may also notice sub-stomatal chambers and tannins in vacuoles of mesophyll.

Protoplasts

Plant cells without walls, are important tools in the study of plant physiological activities. Viable protoplasts are generally spherical and exhibit cytoplasmic streaming (cyclosis). Cytoplasmic streaming, often easiest to see in the transvacuolar strands, also called cytoplasmic bridges. They have been used to: (1) separate cell types; (2) study the intracellular location of particular metabolites; (3) gently isolate organelles from plant cells; (4) study cell wall and plasma membrane biosynthesis; (5) produce somatic cell hybrids (fusion of protoplasts); (6) introduce foreign genetic material and organelles into recipient plants; and (7) achieve highly efficient virus infections

Root tip

Primary growth of the root occurs near the root tip, in the apical meristem region (the "region of cell division").

Isolating protoplasts

Protoplasts are most easily isolated by enzymatically digesting the cell wall. The general procedure is: (1) surface sterilize the leaf; (2) rinse the tissue in the proper osmotic agent such as sorbitol or mannitol (protoplasts must be maintained in an isotonic medium so they don't burst); (3) cut the leaf into strips or peel the epidermis to expose the tissue for enzymatic digestion; (4) treat with enzymes, sequentially or mixed, typically a combination of cellulase, pectinase and hemicellulase; (5) rinse the preparation to remove the enzymes; and (6) isolate and purify the protoplasts. An alternative method to isolate protoplasts is to mechanically chop up the plant tissue in isotonic medium

Rupturing protoplasts

Protoplasts can be ruptured in a variety of ways to release the cell contents. Three commonly used methods include: (1) mechanical shear; (2) osmotic shock; and (3) mild detergent. Each method has specific advantages and disadvantages and the method selected depends upon the application. For example, forcing protoplasts through a syringe or fine nylon mesh (~ 20 μm) will rupture protoplasts including the vacuoles. Osmotic shock will gently disrupt the protoplast releasing intact vacuoles. Treating protoplasts with K2HPO4 causes the cytoplasm to congeal and release vacuoles.

Stem of Psilotum (whisk fern) and Equisetum (horsetail)

Psilotum and Equisetum don't appear very "fern-like" but are found among more "typical" ferns like sword fern (Polystichum munitum) or licorice fern (Polypodium glycyrrhiza) in a monophyletic lineage of seed-free vascular plants that is sister to the seed plants (gymnosperms and angiosperms). Below are prepared cross-sections of Psilotum (Figure 1) and Equisetum stems (Figure 2 and 3). Compare the Equisetum images to Figure 17-38 in the text.

Root nodules

Root nodules are nitrogen-fixing organs that result from a symbiotic interaction between the plant and nitrogen-fixing bacteria; they are a characteristic feature of plants in the pea/bean family, Fabaceae. The nodules provide a favorable environment for the enzyme nitrogenase that catalyzes the fixation of nitrogen. The level of oxygen in the nodules must be carefully regulated, because the plant cells and the nitrogen-fixing bacteria require oxygen for their respiration, but oxygen can irreversibly inhibit nitrogenase. Oxygen levels are regulated by the oxygen-binding heme protein leghemoglobin, which is found in the cytosol of infected cells. This protein imparts a pink color to the central region of the nodule. Note in the prepared slides below it appears as a dark purplish pink color. The nitrogen-fixing bacteria, rhizobia, are each surrounded by a "halo" of polysaccharides and are encased in a membrane derived from the root-nodule cell. Compare the images above to Figure 29-10 and 29-11 on pages 696-697 of the textbook.

External Features and Structures of Roots

Roots have many functions: 1) anchoring the plant firmly to a substrate, 2) absorbing water and minerals, 3) conduction of water, minerals, and carbohydrates, and 4) storage of carbohydrates, in addition to playing a role in asexual reproduction. The structure of roots is important to how they ultimately carry out these functions. Roots have an enormous absorptive surface made possible, in part, by their extensive branching. Plants are characterized by two types of highly branched root systems: taproot systems and fibrous root systems(Figure 24-2 on pg. 560 in Raven's Biology of Plants). 1. Taproot systems are typical for dicots and gymnosperms, while 2. fibrous root systems are typical for monocots. Regardless of the type of root system exhibited by a plant, root origins are the same. The primary root—the plant's first root—develops in the root apical meristem of the embryo, from the embryonic root called the radicle. In taproot systems, the primary root develops as a taproot, which gives rise to secondary or lateral (branch) roots. The primary roots of monocots are commonly short-lived, so the fibrous root system is composed of adventitious roots ("shoot-borne roots") and their branches.

Sclerenchyma cells (ground tissue)

Sclerenchyma, another basic type of cell and tissue, has both a primary wall and a thick secondary cell wall that is usually highly impregnated with lignin (Figure 23-8 on page 543 in Raven's Biology of Plants). These lignified cells have the property of elasticity. They can be deformed, but snap back to their original size and shape when the pressure and tension is released. Sclerenchyma cells develop mainly in mature organs that have stopped growing and have achieved their proper size and shape. When strength and resistance is the only selective advantage of sclerenchyma, the cytoplasm usually dies once the secondary wall has been deposited. But in some species, the cells remain alive at maturity and carry out metabolism. Types are classified according to cell shape and include: 1. fibers, which are long, straight and thin, often occurring in bundles (e.g. phloem or xylem fibers); and 2. sclereids, which are typically short and variable in shape, and are classified according to shape (e.g. astrosclereids: star shaped, with several projecting arms). See Figures 23-8, 23-9, and 23-10 in Raven's Biology of Plants.

Spores

Spores are dispersed in mosses (non-vascular plants) and ferns (seed-free vascular plants). The nonvascular plants, commonly referred to as the "bryophytes," are made up of three groups: true mosses, liverworts, and hornworts. These groups are considered nonvascular because they do not produce lignin and do not have specialized conducting tissues for the transport of water and sugars (i.e., no xylem or phloem). Without these tissues, they cannot efficiently conduct water long distances, which is one reason why most bryophytes are small and live in moist habitats. The single-celled, root-like structures of "bryophytes" are called rhizoids and only function to anchor the organism to the substrate. The nonvascular plant body is not differentiated into true roots, stems, and leaves, and therefore it is called a thallus. The more dominant (or conspicuous) phase of "bryophytes" is the haploid, green gametophyte. The sporophyte, or spore-producing phase, is often not green (i.e. non-photosynthetic) and is nutritionally dependent on the gametophyte.

Stems

Stems provide support as well as transportation of water and nutrients. The evolutionary trends of stems in the angiosperms has led to two basic patterns of primary organization and structure (dicots and monocots). With the exceptions of a few taxa, dicots are characterized by primary vascular tissues represented by discrete bundles, separated from one another by ground tissue (mostly parenchyma cells) and arranged in a ring. Monocots have vascular tissues that occur in more than one ring of bundles or, most frequently, scattered throughout the ground tissue.

C-fern sex

The C-fern, and many other species of ferns, produces mixed populations of large hermaphroditic (bisexual) gametophytes and dwarf male gametophytes. The differentiation of distinct sexual forms (hermaphrodites and males) is controlled by a pheromone-like substance—"antheridiogen"—that is secreted by developing gametophytes. In the absence of antheridiogen, gametophytes develop into mitten-shaped hermaphrodites bearing both archegonia (female sex organs) and antheridia (male sex organs). In the presence of antheridiogen, gametophytes develop into tongue-shaped males that are much smaller than hermaphrodites and bear large numbers of antheridia. Therefore, early germinating spores typically develop into hermaphrodites, while later germinating spores develop into males. In cultures with high population densities, the antheridiogen concentrations are high, which leads to an increase in the proportion of males.When in the presence of water, antheridia on mature gametophytes burst open and release the sperm, which swim using their many flagella. The sperm swim toward high concentrations of a chemical released by the archegonium; the concentration gradient guides the sperm to the egg within the archegonium. One sperm will fertilize the egg; the resultant zygote (a diploid cell) will undergo embryogenesis and develop into the new sporophyte—which will grow right out of the archegonium. Sporophyte emergence occurs within 2 weeks of fertilization.

Elodea cells

The Elodea leaf is especially suited for the study of chloroplasts, which are the numerous green organelles that you see in the cells. In many fresh preparations of these leaves, numerous dark lines may be seen extending parallel with the long axis of the leaf. These are intercellular spaces that normally contain air in this aquatic plant (we will see more if this later in the quarter). Elodea are also a handy species to observe cytoplasmic streaming or cyclosis - the orderly movement of the relatively large chloroplasts within the cell. Cytoplasmic streaming facilitates the exchange of materials within the living cell; although most of the movement is around the vacuole, cytoplasmic bridges allow for some movement across the vacuole. We will first examine a trichome (hair) at the edge of the Elodea leaf; these cells have few chloroplasts, so it is often easier to see nuclei in these cells (Figure 1).

Angiosperm

The angiosperms comprise more than 300,000 species, of which around 65,000 are classified as monocots and the rest are dicots. Previous lab exercises have allowed you to become acquainted with a number of differences between monocots and dicots. In this lab we complete our observations of these differences by looking at reproductive structures (flowers).

External and internal structure of a kidney bean seed (Phaseolus vulgaris, a dicot) and a corn kernel (Zea mays, a monocot)

The bean seed is from a legume, like the pea you just examined. The corn kernel is actually an entire fruit, called a caryopsis or grain; in this type of fruit, the seed coat is fused with the pericarp. Using the resources from the textbook, lecture and/or research, MAKE LABELED SKETCHES of the parts of these seeds. Use these labels (all of them) •Labels for the external structure of bean: seed coat, hilum, and micropyle. •Labels for external structure of corn kernel: pericarp, pedicel, and silk scar (remains of style) Now examine the internal structure of the seeds using the seeds that were soaked. For the bean seed, remove the seed coat and gently pull the two halves apart. Find the embryo and cotyledons. Take a picture and locate the cotyledons, epicotyl, hypocotyl, radicle, and plumule. For the corn kernel, use a razor blade to make a longitudinal section of the seed parallel to the narrow surface of the seed (Figure 2). Take a picture of both bisected seeds and locate the endosperm and embryo. Can you find the scutellum/cotyledon and plumule? •Labels for interior structure of bean: cotyledon, embryo (plumule, radicle), and seed coat. •Labels for internal structure of corn kernel: endosperm and embryo (scutellum/cotyledon and plumule if visible).

Dermal tissues

The epidermis is the outer covering of the primary plant body. This tissue is a complex tissue that may include guard cells, subsidiary cells, trichomes, or other specialized cells, in addition to the "pavement cells" that make up the bulk of the epidermis. See Figures 23-26a and 25-24, in Raven's Biology of Plants.

C-fern

The female sex organs—the archegonia—are located at the notch of the large, hermaphroditic gametophytes (the mitten-shaped haploid plants you have observed before). After a sperm fertilized the egg cell within an archegonium, a zygote was formed (a zygote is the first cell of the diploid generation). The zygote has been growing via mitosis, first developing as an embryo that was retained and protected within the archegonium. Shortly thereafter, the embryo outgrew the archegonium and the first true leaf of the fern emerged from under the gametophyte. Right now, we will be able to see both the gametophyte and the sporophyte still co-existing; both are green and photosynthetic, but soon the gametophyte will start to senesce and die, and the sporophyte will continue to grow.

Sporic life cycleor alternation of generation

The gametangia—multicellular structures that produce gametes—are protected by a sterile jacket of cells and are located on the gametophyte, a multicellular haploid (n) individual. The gametangia give rise to gametes — eggs and sperm — by way of mitosis. The egg and sperm unite through fertilization giving rise to a zygote (a diploid cell, 2n), which divides via mitosis to form the multicellular sporophyte, a diploid (2n) individual. Spores (n) are produced by certain cells in the sporophyte by meiosis, and eventually the spores form new multicellular gametophytes (via mitosis), thus completing the life cycle. Even though all land plants exhibit the sporic life cycle, there are differences in how this sexual reproduction takes place.

C-fern: Gametophytes and attached sporophyte

The gametophyte is a multicellular haploid plant that is characterized by an undifferentiated thallus—the body of the gametophyte is not differentiated into different tissue layers. The gametophyte, therefore, does not have vascular tissue, or separate ground and dermal tissue layers. On the other hand, the sporophyte is a multicellular diploid plant that is characterized by the three distinct tissue systems we have discussed in class—the body of the sporophyte has vascular tissue, ground tissue, and dermal tissue. There are small veins in the leaves, which are denser and more structured than in the thallus of the gametophyte. The primary root of the sporophyte will grow downwards and contain. Contrast the structure and size of this true root with the tiny rhizoids that are present on the gametophyte. Recall that a root has ground tissue, dermal tissue, and vascular tissue. Rhizoids are simply elongated cells that function to anchor the gametophyte to the substrate; rhizoids do not contain any tissue layers.

Lycopodium (clubmoss) leaf, cross-section

This leaf is an example of the earliest type leaves to evolve—a "microphyll".

Parenchyma of Solanum tuberosum (Potato), Ipomoea batatas (Sweet potato) and Musa sp. (Banana)

The most abundant of plant cells are parenchyma cells. They are thin walled and occur in various sizes. They usually have several sides at maturity. Below is an example of parenchyma cells in potato (Solanum tuberosum, Figure 3), in sweet potato (Ipomoea batatas, Figure 4), and in banana (Musa sp., Figure 5). In all cases you will also see good examples of amyloplasts which are plastids that produce and store starch.

Flower ovary

The ovary has one or more chambers, called locules, that contain the ovules (immature seeds). The ovary will develop into the fruit. A flower often has a single pistil (=carpel) but sometimes it may have 2 to many individual pistils. A cross section of the ovary will allow you to determine the number of locules (one to several). This cross-section along with a longitudinal section will allow you to determine placentation type — the way the ovules are attached to the placenta. The main placentation types are marginal, axile, parietal, free-central, basal and apical (See page 463 in Raven's Biology of Plants).

Anatomy of a sugar snap pea pod

The pod is a type of fruit called a legume. A fruit is a ripened ovary and the legume is a dehiscent fruit (dehiscent means "splitting open at maturity") derived from a single carpel and usually opening along two seams (lines of dehiscence). At one end of the pod (legume), you may notice the remnants of the peduncle (stalk) that supported the flower from which the fruit developed. At the opposite end of the pod, you may be able to discern the remnants of the stigma (the receptive structure found at the top of the female part of the flower, the carpel). Make a quick sketch of the intact (unopened) pea fruit, labeling the pericarp (wall of the fruit), the peduncle, and the remnants of the stigma. Next, gently open the pod along one of the seams. Lay the pod open flat. Observe the seeds inside; note that the seeds are attached to the wall of the ovary (the pericarp) with a short stalk called a funiculus. You should notice the vestigial aril where the seed and funiculus meet. The seeds are attached to only one edge of the pericarp, along the placenta.

Vascular tissues

The principal water-conducting tissue in vascular plants is xylem, a complex tissue derived from the procambium in the primary plant body and from the vascular cambium in plants undergoing secondary growth. Conducting cells of the xylem include two types of tracheary elements—tracheids and vessel elements (Figures 23-12, 23-13, and 23-14). Xylem tissue also contains parenchyma cells, which store various substances, and fibers, which function mostly in support. Review Table 23-1 in Raven's Biology of Plants. The principal food-conducting tissue in vascular plants is phloem, a complex tissue comprised of two types of sieve elements—sieve cells and sieve-tube elements—and specialized parenchyma cells known as companion cells, other parenchyma cells, and fibers and sclereids. The phloem transports amino acids, lipids, micronutrients, hormones, and other signaling molecules, in addition to its role in the transport of sugars through the plant.

Variety of pollen types

The shape and exine patterning of pollen vary greatly from plant to plant and can even be used to identify a species.

Examination of the Azolla-Anabaena Symbiosis

The small aquatic fern Azolla has a symbiosis with the nitrogen-fixing cyanobacterium Anabaena. The cyanobacterium lives in cavities within the leaves of this fern and this relationship is sustained throughout the life cycle of the fern, beginning when it is a gametophyte. See textbook, page 698 (photo of Azolla), 419, and 265 (photo, of Anabaena).

Nymphaea (waterlily) leaf, cross-section

These leaves float on the surface of still bodies of water. These are typically considered an example of a hydrophytic leaf. Note the epidermis, stomata, mesophyll.

Wheat (Triticum), a C3 grass

This grass is an important agricultural crop on which humans depend. Note the epidermal cells, the mesophyll, and the veins. The veins are surrounded with bundle sheath cells, compare them to the bundle sheath cells of corn. There is no spatial separation between the photo (light-harvesting) reactions of photosynthesis and the synthesis (carbon-reduction) reactions; they both take place in the mesophyll cells of C3 plants. Compare these images to Figures 25-27 and 25-28 in the text.

Tissues

Tissues may be defined as groups of cells that are structurally and/or functionally distinct. Simple tissues are tissues composed of cells that are of one type, whereas complex tissues are composed of two or more types of cells. The ground tissues — parenchyma, collenchyma, and sclerenchyma—are simple tissues. Complex tissues include the xylem, phloem, and epidermis.

Epidermal Hairs (Trichomes)

Trichomes or epidermal hairs come in different types and shapes. See Figure 1 in addition to the following images.

Vascular plants

Unlike the nonvascular plants, vascular plants (including ferns, gymnosperms, and angiosperms) have specialized tissues responsible for transport of water and nutrients throughout the plant body. As expected, this specialization is met with differentiation of the plant body into organs such as roots, stems, and leaves. In the ferns, the stems are usually horizontal and are called rhizomes; the leaves are called fiddleheads when young and curled, and fronds when mature. Just as in all members of the plant kingdom, the vascular plants exhibit a sporic life cycle but the dominant generation (larger, most conspicuous) differs from that of the nonvascular plants; while nonvascular plants are characterized by a dominant gametophyte generation (n), the vascular plants are characterized by a dominant, independent sporophyte generation (2n). The oldest lineages of the vascular plants are the seed-free vascular plants—the lycophytes and the ferns.

Roots

We will continue our study of roots by examining a couple of modified roots and by exploring two important root symbioses: mycorrhizae (a symbiosis between roots and fungi) and nodules (a symbiosis between roots and nitrogen-fixing bacteria). Nitrogen fixing bacteria are also found in symbiosis with the mosquito-fern Azolla, where the cyanobacteria are housed within small cavities within the leaves of the aquatic fern. We will also examine the structural interaction between the parasitic plant known as "Dodder" (Cuscuta) to determine where in the tissue of its host plant the Dodder sinks its "rootlike" structures called haustoria.

Observation of C-fern Sperm

When the male sex organs— the antheridia— are mature, they will burst and release the flagellated sperm cells they contain. View the video under 'Chemotaxis fertilization' on the C-fern life cycle site. •How do the sperm cells appear to move?

C-fern

With this lab we will start our exploration of an organism known as "C-fern." C-fern (a trademarked name) is a special strain of the fern Ceratopteris richardii. Members of the genus Ceratopteris grow in aquatic or semi-aquatic habitats in the tropics. C-fern has been developed as a model plant system for use in the biology laboratory because it possesses several characteristics that make it suitable for classroom use, including a very short life cycle that takes less than twelve weeks to complete

Reagents that can be used to test for different substances or metabolic activity

•To check for the presence of starch, I2KI (Lugol's iodine) can be used. The I2KI solution turns starch black or dark purple. Note if you have iodine at home you can try staining your bisected seeds - briefly expose the seeds to iodine, then rinse with water. •The reagent Sudan IV will indicate areas with oil. The Sudan IV solution is taken up into oleosomes (oil bodies) in the cut cells leaving dark or light pink areas. •Methylene blue will stain areas of active respiration. Methylene blue is taken up into cells with active metabolism turning them dark blue-green (the dye responds to electrons from the electron transport system of active mitochondria); less-blue areas have less-active metabolism.