Split (1)

train · 5.35k rows

text stringlengths 1.02k 3.02k
ems The plant body that develops after germination depends on the activities of meristematic tissues. Meristematic tissues are lumps of small cells with dense cytoplasm and proportionately large nuclei that act like stem cells in animals. That is, one cell divides to give rise to two cells. One remains meristematic, wh...
development, the leaf primordia cover the shoot apical meristem which is particularly susceptible to desiccation. The apical meristem gives rise to three types of embryonic tissue systems called primary meristems. Cell division continues in these partly differentiated tissues as they develop into the primary tissues o...
. Lateral Meristems Many herbaceous plants exhibit only primary growth, but others also exhibit secondary growth. Most trees, shrubs, and some herbs have active lateral meristems, which are cylinders of meristematic tissue within the stems and roots (figure 38.5). Although secondary growth increases girth in many nonwo...
size, and even structure of leaves and roots are often influenced by the environment. A vascular plant consists of a root system and a shoot system (figure 38.6). The root system anchors the plant and penetrates the soil, from which it absorbs water and ions crucial to the plant’s nutrition. The shoot system consists ...
m, which conducts water and dissolved miner- 756 Part X Plant Form and Function Apical meristem Terminal bud Primary growth zone Secondary growth zone (vascular cambium) Internode Blade Vein Petiole Leaf Axillary bud Node Vascular system Pith Lateral root Shoot Root Primary root Primary growth zone Apical meristem FIGU...
have become characteristic of vascular plants as a group. Sieve-tube members conduct carbohydrates away from areas where they are manufactured or stored. Vessel members and tracheids are thick-walled cells that transport water and dissolved minerals up from the roots. Both kinds of cells are elongated and occur in lin...
cells, which originate from the protoderm, cover all parts of the primary plant body. This is probably the earliest tissue system to appear in embryogenesis. The exposed outer walls have a cuticle that varies in thickness, depending on the species and environmental conditions. A number of types of specialized cells oc...
may be caused by a failure of developing stomata to suppress stomatal formation in neighboring cells (figure 38.9). The stomata open and shut in response to external factors such as light, temperature, and availability of water. During periods of active photosynthesis, the stomata are open, allowing the free passage o...
hairs should not be confused with lateral roots which are multicellular and have their origins deep within the root. In the case of secondary growth, the cork cambium (discussed in the section on stems in this chapter) produces the bark of a tree trunk or root. This replaces the epidermis which gets stretched and brok...
arenchyma tissue is called chlorenchyma. Collenchyma Collenchyma cells, like parenchyma cells, have living protoplasts and may live for many years. The cells, which are usually a little longer than wide, have walls that vary in thickness (figure 38.12b). Collenchyma cells, which are relatively flexible, provide support...
types of ground tissue. (a) Parenchyma cells. Only primary cell walls are seen in this cross-section of parenchyma cells from grass. (b) Collenchyma cells. Thickened side walls are seen in this cross-section of collenchyma cells from a young branch of elderberry (Sambucus). In other kinds of collenchyma cells, the thi...
resembling microscopic, squat coffee cans with both ends removed. Both vessel members and tracheids have thick, lignified secondary walls and no living protoplasts at maturity. Lignin is produced by the cell and secreted to strengthen the cellulose cell walls before the protoplast dies, leaving only the cell wall. Whe...
cell to cell by means of pits, (b) while in vessel members, it moves by way of perforation plates or between bars of wall material. In gymnosperm wood, tracheids both conduct water and provide support; in most kinds of angiosperms, vessels are present in addition to tracheids, or present exclusively. These two types o...
ieve tubes. Sieve cells are less specialized than sieve-tube mem- bers, and the pores in all of their sieve areas are roughly of the same diameter. In an evolutionary sense, sieve-tube members are more advanced, more specialized, and, presumably, more efficient. Each sieve-tube member is associated with an adjacent spe...
of two types of cells, the inner columella (they look like columns) cells and the outer, lateral root cap cells that are continuously replenished by the root apical meristem. In some plants with larger roots it is quite obvious. Its most obvious function is to protect the delicate tissues behind it as growth extends t...
protoderm, epidermis, and ground meristem. The Zone of Cell Division The apical meristem is shaped like an inverted, concave dome of cells and is located in the center of the root tip in the area protected by the root cap. Most of the activity in this zone of cell division takes place toward the edges of the dome, whe...
increase in cell size occurs above the zone of elongation, and the mature parts of the root, except for an increase in girth, remain stationary for the life of the plant. (a) (b) FIGURE 38.16 Tissue-specific gene expression. (a) Epidermal-specific gene expression. The promoter of the WEREWOLF gene of Arabidopsis was a...
functions in food storage. The inner boundary of the cortex differentiates into a single-layered cylinder of endodermis (figure 38.17), whose primary walls are impregnated with suberin, a fatty substance that is impervious to water. The suberin is produced in bands, called Casparian strips that surround each adjacent ...
other plants with secondary growth, part of the pericycle and the parenchyma cells between the phloem patches and the xylem arms become the root vascular cambium, which starts producing secondary xylem to the inside and secondary phloem to the outside (figure 38.20). Eventually, the secondary tissues acquire the form ...
stem; these prop roots grow down to the ground and brace the plants against wind. Climbing plants such as ivy also produce roots from their stems; these anchor the stems to tree trunks or a brick wall. Any root that arises along a stem or in some place other than the root of the plant is called an adventitious root. A...
roots toward the base of the trunk, which provide considerable stability (figure 38.21c). Some plants have modified roots that carry out photosynthesis, gather oxygen, parasitize other plants, store food or water, or support the stem. Chapter 38 The Plant Body 767 38.4 Stems are the backbone of the shoot, transporting...
outer cells of the cortex containing chloroplasts. Herbaceous stems commonly have stomata, and may have various types of trichomes (hairs). Woody stems can persist over a number of years and develop distinctive markings in addition to the original organs that form. Terminal buds usually extend the length of the shoot ...
ylem and phloem, called a trace, branches off from the main cylinder of xylem and phloem and enters the developing leaf, flower, or shoot. These spaces in the main cylinder of conducting tissues are called gaps. In dicots, a vascular cambium develops between the primary xylem and primary phloem (figure 38.24). In many ...
. Rings in the stump of a tree reveal annual patterns of growth; cell size varies depending on growth conditions. In woody dicots, a second cambium, the cork cambium, arises in the outer cortex (occasionally in the epidermis or phloem) and produces boxlike cork cells to the outside and also may produce parenchyma-like ...
elike leaf bases of the long, green aboveground leaves. Corms. Crocuses, gladioluses, and other popular garden plants produce corms that superficially resemble bulbs. Cutting a corm in half, however, reveals no fleshy leaves. Instead, almost all of a corm consists of stem, with a few papery, brown nonfunctional leaves ...
axillary buds adjacent to leaf scars) Tuber (swollen tip of stolen) Runner (c) Runners (strawberry) (d) Tubers (potato) Leaves (modified as spines) Tendril Cladophyll (e) Tendrils (grape) (f) Cladophylls (prickly pear) FIGURE 38.28 Types of modified stems. Cladophylls. Cacti and several other plants produce flattened, ...
dicot leaves have a flattened blade, and a slender stalk, the petiole. The flattening of the leaf blade reflects a shift from radial symmetry to dorsal-ventral (top-bottom) symmetry. We’re just beginning to understand how this shift occurs by analyzing mutants like phantastica which prevents this transition (figure 38...
stem. (c) Palmately compound leaves of a Virginia creeper (Parthenocissus quinquefolia). (a) Leaf blades come in a variety of forms from oval to deeply lobed to having separate leaflets. In simple leaves (figure 38.31a), such as those of lilacs or birch trees, the blades are undivided, but simple leaves may have teeth...
a leaf is covered by a transparent epidermis, most of whose cells have no chloroplasts. The epidermis itself has a waxy cuticle of variable thickness, and may have different types of glands and trichomes (hairs) present. The lower epidermis (and occasionally the upper epidermis) of most leaves contains numerous slit-l...
bags of epidermis containing vascular tissue and tightly packed palisade mesophyll rich in chloroplasts and loosely packed spongy mesophyll with many interconnected air spaces that function in gas and water vapor exchange. Vein Guard cell Stoma Cuticle Upper epidermis Palisade mesophyll Spongy mesophyll Lower epidermi...
regeneration is unique among just a few species. Window leaves. Several genera of plants growing in arid regions produce succulent, cone-shaped leaves with transparent tips. The leaves often become mostly buried in sand blown by the wind, but the transparent tips, which have a thick epidermis and cuticle, admit light ...
in a nitrogen-rich environment, perhaps a trade-off made in the intricate evolutionary process that resulted in its ability to capture and digest insects. The leaves of plants exhibit a variety of adaptations, including spines, vegetative reproduction, and even leaves that are carnivorous. Chapter 38 The Plant Body 77...
icot Root Structure • Roots 38.4 Stems are the backbone of the shoot, transporting nutrients and supporting the aerial plant organs. • Plants branch by means of buds derived from the primary apical meristem. They are found in the junction between the leaf and the stem. • The vascular cambium is a cylinder of dividing c...
is the result of movement between cells, across cell membranes, and through tubes of xylem. Water and Mineral Absorption. Water and minerals enter the plant through the roots. Water and Mineral Movement. A combination of the properties of water, structure of xylem, and transpiration of water through the leaves results...
sufficient for the synthesis of all the molecules a plant needs. Plants require a number of inorganic nutrients (table 39.1). Some of these are macronutrients, which the plants need in relatively large amounts, and others are micronutrients, which are required in trace amounts. There are nine macronutrients: carbon, h...
ADP and ATP, nucleic acids, phospholipids, several coenzymes Components of some amino acids and proteins, coenzyme A Chlorine Iron Manganese Zinc Boron Copper Molybdenum (Cl–) (Fe++, Fe+++) (Mn++) (Zn++) (BO3 (Cu++) (MoO4 =) – or B4O7 =) 100–10,000 Osmosis and ionic balance 25–300 15–800 15–100 5–75 4–30 0.1–5 Chlorop...
With increasing levels of CO2, the leaves of some plants increase in size, but the amount of nitrogen decreases relative to carbon. This decreases the nutritional value of the leaves to herbivores. The plant macronutrients carbon, oxygen, and hydrogen constitute about 94% of a plant’s dry weight; the other macronutrie...
lost because of erosion or poor landscaping, both the waterholding capacity and the nutrient relationships of the soil are adversely affected. About half of the total soil volume is occupied by spaces or pores, which may be filled with air or water, depending on moisture conditions. Some of the soil water, because of ...
turning the plant material into humus. Fertilizers are also used to replace nutrients lost in cultivated fields. The most important mineral nutrients that need to be added to soils are nitrogen (N), phosphorus (P), and potassium (K). All of these elements are needed in large quantities (see table 39.1) and are the mos...
secrete both sticky mucilage, which traps small animals, and digestive enzymes. Unlike Venus flytraps they do not close rapidly and it is possible that the two share a common ancestor. Pitcher plants attract insects by the bright, flowerlike colors within their pitcher-shaped leaves and perhaps also by sugar-rich secr...
rients is also enhanced. Functionally, the mycorrhizae extend the surface area of nutrient uptake substantially Carnivorous plants obtain nutrients, especially nitrogen, directly by capturing and digesting insects and other organisms. Nitrogen can also be obtained from bacteria living in close association with the root...
in getting water between many plant cells and the xylem. The greatest distances traveled by water molecules and dissolved minerals are in the xylem. Once water enters the xylem, it can move upward 100 m in the redwoods. Some “pushing” from the pressure of water entering the roots is involved. However, most of the forc...
or osmotic) potential of the solution. Water will enter a cell osmotically until it is stopped by the pressure potential caused by the cell wall. The water potential of a plant cell is, in essence, the combination of its pressure potential and solute potential; it represents the total potential energy of the water in a...
go directly through the plasma membranes and the protoplasm of adjacent cells (figure 39.9). When mineral ions pass between the cell walls, they do so nonselectively. Eventually, on their journey inward, they reach the endodermis and any further passage through the cell walls is blocked by the Casparian strips. Water ...
ascular bundle Spongy mesophyll Intercellular space (100% humidity) Stoma Epidermis Water molecule Water exits plant through stomata Water moves up plant through xylem Water enters plant through roots FIGURE 39.10 Transpiration. Water evaporating from the leaves through the stomata causes the movement of water upward i...
y larger than the openings, so they cannot pass through them. Furthermore, the cohesive force of water is so great that the bubbles are forced into rigid spheres that have no plasticity and therefore cannot squeeze through the openings. Deformed cells or freezing can cause small bubbles of air to form within xylem cell...
like humidity and the time of day. After the sun sets, transpiration from the leaves decreases. The sun is the ultimate source of potential energy for water movement. The water potential that is responsible for water movement is largely the product of negative pressure generated by transpiration, which is driven by th...
each guard cell bowing outward, thereby opening the stoma. (b) When the potassium ions leave the guard cells and their solute potential becomes low, they lose water and turgor, and the stoma closes. duct tape on the inside edge of both balloons and inflate each one a bit more. Hold the open ends together. You should n...
Abscisic acid, a plant hormone discussed in chapter 41, plays a primary role in allowing K+ to pass rapidly out of guard cells, causing the stomata to close in response to drought. This hormone is released from chloroplasts and produced in leaves. It binds to specific receptor sites in the plasma membranes of guard ce...
can also receive too much water, and ultimately “drown.” Flooding rapidly depletes available oxygen in the soil and interferes with the transport of minerals and carbohydrates in the roots. Abnormal growth often results. Hormone levels change in flooded plants—ethylene (the only hormone that is a gas) increases, while...
respond to flooded conditions by forming larger lenticels (which facilitate gas exchange) and additional adventitious roots. O2, CO2 Gas exchange Stoma Vein Upper epidermis of leaf Gas exchange (a) (b) FIGURE 39.14 Aerenchyma tissue. Gas exchange in aquatic plants. (a) Water lilies float on the surface of ponds where ...
oxygen because these roots emerge above the water and have large lenticels. Oxygen can enter the roots through the lenticels, pass into the abundant aerenchyma, and move to the rest of the plant. Chapter 39 Nutrition and Transport in Plants 789 39.4 Dissolved sugars and hormones are transported in the phloem. Phloem T...
flow hypothesis, pressure flow hypothesis, or bulk flow hypothesis. Experimental evidence supports much of this model. Dissolved carbohydrates flow from a source and are released at a sink where they are utilized. Carbohydrate sources include photosynthetic tissues, such as the mesophyll of leaves, and food-storage tis...
throughout the plant’s system of sieve tubes. At the sink, carbohydrates are actively removed. Water moves from the sieve tubes by osmosis and the turgor pressure there drops, causing a mass flow from the higher pressure at the source to the lower pressure sink (figure 39.17). Most of the water at the sink diffuses th...
ids is the sun. • Water leaves the plant through openings in the leaves called stomata. Stomata open when their guard cells are turgid and bulge, causing the thickened inner walls of these cells to bow away from the opening. • Plants can tolerate long submersion in water, if they can deliver oxygen to their submerged t...
ates central pattern formation in the plant kingdom? Almost nothing was known of these mechanisms a decade ago, but intensive research is now rapidly painting in the blank canvas. Much of the most exciting research on plant pattern formation is being performed on a small weedy relative of the mustard plant, the wall cr...
rate at which the cell types differentiate. Schiefelbein set out to learn how the root apex coordinates these two processes. To get a handle on the process, Schiefelbein seized on a recently characterized root pattern mutant called transparent testa glabra (TTG). This mutant changes the pattern of root hairs in Arabid...
To do this, roots were selected that contained clones of trichoblast and atrichoblast produced by longitudinal cell divisions perpendicular to the surface of the root. Called longitudinal anticlinal cell divisions, these clones are rare but easily recognized when stained with propidium iodide. Careful mapping of indiv...
(see graph b above). The percent of clones in the A file of the TTG mutants exhibiting this type of cell division was twice that seen in the wild-type or gl2 mutants. This observation directly supports the hypothesis that the TTG gene is not only required for cell division in the T cell file, but also controls longitu...
ophyte, where most of these innovations occurred. In the next few chapters, we continue our focus on the sporophyte generation of the angiosperms. In many cases, we will use the model plant Arabidopsis, a weedy member of the mustard family. Its very small genome has allowed plant biologists to study how genes regulate ...
a dormant phase, signaling the end of embryogenesis. Environmental signals (for example, water, temperature, and light) can break dormancy and trigger a cascade of internal events resulting in germination. Early Cell Division and Patterning The first division of the fertilized egg in a flowering plant is asymmetric an...
other end of the axis ultimately become a shoot. Investigating the asymmetry of the first cell division is difficult because the fertilized egg is embedded within the gametophyte, which is surrounded by sporophyte tissue (ovule and carpel tissue). One approach has been to use the brown algae Fucus as a model system. A...
Plant Development 797 Establishing Three Tissue Systems Three basic tissues differentiate while the plant embryo is still a ball of cells, the globular stage (figure 40.5), but no cell movements are involved. The protoderm consists of the outermost cells in a plant embryo and will become dermal tissue. These cells alm...
d) Heart-shaped stage. 798 Part XI Plant Growth and Reproduction gene in Arabidopsis is active in early and late embryo development and may be responsible for maintaining an embryonic environment. It is possible to turn this gene on later in development using recombinant DNA techniques (see chapter 43). In that case, e...
ms, although double fertilization has been observed in the gymnosperm Ephedra) which may be extensive or minimal. Endosperm in coconut is the “milk” and is in liquid form. In corn the endosperm is solid and in popping corn expands with heat to form the edible part of popcorn. In peas and beans, the endosperm is used up...
impermeable seed coat, which encloses the seed with its dormant embryo and stored food. Seeds are important adaptively in at least four ways: 1. They maintain dormancy under unfavorable conditions and postpone development until better conditions arise. If conditions are marginal, a plant can “afford” to have some seed...
ared habitat; nutrients will be relatively abundant, having been released from plants burned in the fire. Seeds of other plants will germinate only when inhibitory chemicals have been leached from their seed coats, thus guaranteeing their germination when sufficient water is available. Still other plants will germinate...
, tomatoes, grapes, peppers. More than one seed and a leathery skin; oranges, lemons, limes. FIGURE 40.11 Examples of some kinds of fruits. Distinguishing features of each of these fruit types are listed below each photo. Follicles, legumes, and samaras are examples of dry fruits. Drupes, true berries, and hesperidiums...
fruits, such as those of maples, elms, and ashes, have wings which aid in their distribution by the wind. The dandelion provides another familiar example of a fruit type that is dispersed by wind (figure 40.13), and the dispersal of seeds from plants such as milkweeds, willows, and cottonwoods is similar. Orchids have...
embryonic phase of growth and development is underway. Mechanisms of Germination Germination is the first step in the development of the plant outside of its seed coat. Germination occurs when a seed absorbs water and its metabolism resumes. The amount of water a seed can absorb is phenomenal and creates a force strong...
15), from the Latin word meaning “shield.” The abundant food stored in the scutellum is used up first because these plants do not need to use the endosperm during germination. Later, while the seedling is becoming established, the scutellum serves as a nutrient conduit from the endosperm to the embryo. This is one of t...
ellum Embryo Starch -amylase Sugars Gibberellic acid FIGURE 40.16 Hormonal regulation of seedling growth. The germinating barley embryos utilize the starch stored in the endosperm by releasing the hormone gibberellic acid (GA) that triggers the outer layers of the endosperm (aleurone layers) to produce the starch-diges...
otype of the embryo? How does the genotype of the seed wall compare with the fruit wall? 5. Explain how the embryo signals the endosperm to obtain sugars for growth during germination. 6. Why does the root (actually the radicle) of the embryo emerge first? 40.3 Fruit formation enhances seed dispersal. • Fruits are an a...
shoot meristem from vegetative to adult is called phase change. Pathways Leading to Flower Production. Photoperiod is regulated in complex ways. Identity Genes and the Formation of Floral Meristems and Floral Organs. Floral meristem identity genes activate floral organ identity genes. 41.4 Many short-term responses to...
because they challenge us to connect environmental signals with cellular perception of the signal, transduction into biochemical pathways, and ultimately an altered growth response. Phototropism Phototropic responses involve the bending of growing stems and other plant parts toward sources of light (figure 41.2). In g...
to bring about reactions to light. The existence of phytochrome was conclusively demonstrated in 1959 by Harry A. Borthwick and his collaborators at the U.S. Department of Agriculture Research Center at Beltsville, Maryland. It has since been shown that the molecule consists of two parts: a smaller one that is sensiti...
necessary for brassinosteroid biosynthesis. Researchers suspect that brassinosteroids play a role in how plants respond to light through phytochrome. Thus, because det2 mutants lack brassinosteroids, they do not respond to light, or lack of light, as normal plants do, and the det2 mutants grow normally in the dark. Re...
d. FIGURE 41.4 Plant response to gravity. This plant (Zebrina pendula) was placed horizontally and allowed to grow for 7 days. Note the negative gravitational response of the shoot. Glenn made his second trip into space, he was accompanied by an experiment designed to test the role of gravity and electrical signaling i...
aboard the space shuttle. So far the verdict is still not in on the exact mechanism. It may surprise you to learn that in tropical rain forests, roots of some plants may grow up the stems of neighboring plants, instead of exhibiting the normal positive gravitropic responses typical of other roots. The rainwater dissol...
otropism (response to chemicals); traumotropism (response to wounding which we discuss on page 834); thermotropism (response to temperature); aerotropism (response to oxygen); skototropism (response to dark); and geomagnetotropism (response to magnetic fields). Roots will often follow a diffusion gradient of water comi...
promoting growth in seasonally dry areas. Whenever rains occur, they will leach out the chemicals from the seed coats, and the hard coats of other seeds may be cracked when they are being washed down along temporarily flooded arroyos (figure 41.6). Seeds may remain dormant for a surprisingly long time. Many legumes (p...
one part of an organism and then transported to another part, where they bring about physiological or developmental responses. The activity of hormones results from their capacity to stimulate certain physiological processes and to inhibit others (figure 41.7). How they act in a particular instance is influenced both ...
ment of ethylene production; promotion of lateral bud dormancy Stimulation of cell division, but only in the presence of auxin; promotion of chloroplast development; delay of leaf aging; promotion of bud formation Where Produced or Found in Plant Apical meristems; other immature parts of plants Root apical meristems; i...
If they covered the tip of the shoot with a thin glass tube, the shoot would bend as if it were not covered. However, if they used a metal foil cap to exclude light from the plant tip, the shoot would not bend (figure 41.8). They also found that using an opaque collar to exclude light from the stem below the tip did n...
been removed. (3) The seedlings bent away from the side on which the agar block was placed. Went concluded that the substance that he named auxin promoted the elongation of the cells and that it accumulated on the side of an oat seedling away from the light. Auxin in tip of seedling Auxin Agar Auxin diffuses into agar...
side of seedling Light Lighted side of seedling FIGURE 41.10 Auxin causes cells on the dark side to elongate. Went determined that a substance called auxin enhanced cell elongation. Plant cells that are in the shade have more auxin and grow faster than cells on the lighted side, causing the plant to bend toward light....
How Auxin Works In spite of this long history of research on auxin, its molecular basis of action has been an enigma. The chemical structure of IAA resembles that of the amino acid tryptophan, from which it is probably synthesized by plants (figure 41.12). Unlike animal hormones, a specific signal is not sent to speci...
principal naturally occurring auxin. (b) Tryptophan, the amino acid from which plants probably synthesize IAA. (c) Dichlorophenoxyacetic acid (2,4-D), a synthetic auxin, is a widely used herbicide. 816 Part XI Plant Growth and Reproduction FIGURE 41.13 Acid growth hypothesis. Auxin stimulates the release of hydrogen i...
olly that is being prepared for shipping. Synthetic auxins are also used to promote flowering and fruiting in pineapples and to induce the formation of roots in cuttings. Synthetic auxins are routinely used to control weeds. When used as herbicides, they are applied in higher concentrations than IAA would normally occu...
culture later led to their discovery. Subsequent studies have focused on the role cytokinins play in the differentiation of tissues from callus. A cytokinin is a plant hormone that, in combination with auxin, stimulates cell division and differentiation in plants. Most cytokinins are produced in the root apical merist...
in ratios favor shoot development; and (c) intermediate concentrations result in the formation of undifferentiated cells. These developmental responses to cytokinin/auxin ratios in culture are species specific. versely, cytokinins inhibit formation of lateral roots, while auxins promote their formation. As a consequenc...
that are related to or derived from adenine. Chapter 41 How Plants Grow in Response to Their Environment 819 Gibberellins Gibberellins are named after the fungus Gibberella fujikuroi, which causes rice plants, on which it is parasitic, to grow abnormally tall. Japanese plant pathologist Eiichi Kurosawa investigated Ba...
layer surrounding the endosperms of cereal grains have shown that transcription occurs when the gibberellins initiate a burst of messenger RNA (mRNA) and protein synthesis. GA somehow enhances DNA binding proteins, which in turn allow DNA transcription of a gene. Synthesis of DNA does not seem to occur during the earl...
similarities to animal steroid hormones (figure 41.20). One of the genes coding for an enzyme in the brassinosteroid biosynthetic pathway has significant similarity to an enzyme used in the synthesis of testosterone and related steroids. Brassinosteroids have been identified in algae and appear to be quite ubiquitous ...
many effects on plant growth and development that parallel those of auxins and gibberellins. Oligosaccharins are complex carbohydrates that are released from cell walls and appear to regulate both pathogen responses and growth and development in some plants. Chapter 41 How Plants Grow in Response to Their Environment ...
cloned, and its antisense copy has been inserted into the tomato genome. The antisense copy of the gene is a nucleotide sequence that is complementary to the sense copy of the gene. In this transgenic plant, both the sense and antisense sequences for the ethylene biosynthesis gene are transcribed. The sense and antise...
appear to stimulate leaf senescence (aging) and abscission, but there is little evidence that it plays an important role in this process. In fact, it is believed that abscisic acid may cause ethylene synthesis, and that it is actually the ethylene that promotes senescence and abscision. When abscisic acid is applied t...
survival under environmental stress, especially water stresses. (a) (b) FIGURE 41.22 Effects of abscisic acid. (a) Abscisic acid plays a role in the formation of these winter buds of an American basswood. These buds will remain dormant for the winter, and bud scales— modified leaves—will protect the buds from desiccat...
initiated by a juvenile meristem. The fact that they did not respond to environmental cues and drop their leaves indicates that they are young branches and have not made a phase change. Ivy also has distinctive juvenile and adult phases of growth (figure 41.24b). Stem tissue produced by a juvenile meristem initiates a...
occurs in weeks instead of years (figure 41.26). Phase change requires both sufficient signal and the ability to perceive the signal. Some plants acquire competence in the shoot to perceive a signal of a certain intensity. Others acquire competence to produce sufficient promotive signal(s) and/or decrease inhibitory s...

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.