Plant Development Chapter 31 Part 1
Impacts, Issues Foolish Seedlings, Gorgeous Grapes Gibberellin and other plant hormones control the growth and development of plants environmental cues influence hormone secretion
31.1 Patterns of Development in Plants Germination Process by which a dormant mature embryo sporophyte in a seed resumes growth Certain species-specific conditions may be required to break dormancy Begins when water activates enzymes in the seed Ends when the embryo breaks the seed coat
Patterns of Development in Plants Growth (increase in cell number and size) occurs primarily at meristems Differentiation results in the formation of tissues and parts in predictable patterns Patterns of plant development are an outcome of gene expression and environmental influences
Anatomy of a Corn Seed
seed coat fused with ovary wall endosperm cells cotyledon coleoptile plumule (embryonic shoot) hypocotyl embryo radicle (embryonic root) Fig. 31-2, p. 524
Early Growth of Corn (Monocot)
Fig. 31-3a, p. 525
coleoptile branch root coleoptile primary root hypocotyl radicle A After a corn grain (seed) germinates, its radicle and coleoptile emerge. The radicle develops into the primary root. The coleoptile grows upward and opens a channel through the soil to the surface, where it stops growing. Fig. 31-3a, p. 525
Fig. 31-3b, p. 525
primary leaf coleoptile adventitious (prop) root branch root primary root B The plumule develops into the seedling s primary shoot, which pushes through the coleoptile and begins photosynthesis. In corn plants, adventitious roots that develop from the stem afford additional support for the rapidly growing plant. Fig. 31-3b, p. 525
coleoptile branch root primary root coleoptile hypocotyl radicle primary leaf coleoptile adventitious (prop) root branch root primary root A After a corn grain (seed) germinates, its radicle and coleoptile emerge. The radicle develops into the primary root. The coleoptile grows upward and opens a channel through the soil to the surface, where it stops growing. B The plumule develops into the seedling s primary shoot, which pushes through the coleoptile and begins photosynthesis. In corn plants, adventitious roots that develop from the stem afford additional support for the rapidly growing plant. Stepped Art Fig. 31-3, p. 525
Animation: Plant development
Early Growth of a Bean (Eudicot)
Fig. 31-4a, p. 525
seed coat radicle cotyledons (two) hypocotyl primary root A After a bean seed germinates, its radicle emerges and bends in the shape of a hook. Sunlight causes the hypocotyl to straighten, which pulls the cotyledons up through the soil. Fig. 31-4a, p. 525
Fig. 31-4b, p. 525
B Photosynthetic cells in the cotyledons make food for several days, then the seedling s leaves take over the task. The cotyledons wither and fall off. primary leaf primary leaf withered cotyledon primary root branch root root nodule Fig. 31-4b, p. 525
Summary: Eudicot Development
germination mature sporophyte (2n) zygote in seed (2n) fertilization DIPLOID HAPLOID meiosis in anther meiosis in ovary eggs (n) sperm (n) microspores (n) megaspores (n) male gametophyte (n) female gametophyte (n) Fig. 31-22, p. 535
31.1 Key Concepts Patterns of Plant Development Plant development includes seed germination and all events of the life cycle, such as root and shoot development, flowering, fruit formation, and dormancy These activities have a genetic basis, but are also influenced by environmental factors
31.2 Plant Hormones and Other Signaling Molecules Plant development depends on cell-to-cell communication mediated by plant hormones Plant hormones Signaling molecules that can stimulate or inhibit plant development, including growth Five types: Gibberellins, auxins, abscisic acid, cytokinins, and ethylene
Gibberellins Gibberellins induce cell division and elongation in stem tissue, and are involved in germination
Auxins Auxins promote or inhibit cell division and elongation, depending on the target tissue Auxin produced in a shoot tip prevents growth of lateral buds (apical dominance) Auxins also induce fruit development in ovaries, and lateral root formation in roots
Rooting Powder with Auxin
Abscisic Acid Abscisic acid (ABA) inhibits growth, is part of a stress response that causes stomata to close, and diverts products of photosynthesis from leaves to seeds
Cytokinins Cytokinins form in roots and travel to shoots, where they induce cell division in apical meristems Cytokinins also release lateral buds from apical dominance and inhibit leaf aging
Ethylene Ethylene The only gaseous hormone Produced by damaged or aging cells Induces fruit and leaves to mature and drop Used to artificially ripen fruit
Major Plant Hormones and Their Effects
Commercial Uses of Plant Hormones
Other Signaling Molecules Besides hormones, other signaling molecules are involved in plant development Brassinosteroids FT protein Salicylic acid Systemin Jasmonates
31.3 Examples of Plant Hormone Effects Gibberellins and barley seed germination Barley seed absorbs water Embryo releases gibberellin Gibberellin induces transcription of amylase gene Amylase breaks stored starches into sugars used by embryo for aerobic respiration
Gibberellins in Barley Seed Germination
Gibberellins in Barley Seed Germination
Gibberellins in Barley Seed Germination
aleurone endosperm embryo gibberellin A Absorbed water causes cells of a barley embryo to release gibberellin, which diffuses through the seed into the aleurone layer of the endosperm. Fig. 31-7a, p. 528
amylase B Gibberellin triggers cells of the aleurone layer to express the gene for amylase. This enzyme diffuses into the starch-packed middle of the endosperm. Fig. 31-7b, p. 528
sugars C The amylase hydrolyzes starch into sugar monomers, which diffuse into the embryo and are used in aerobic respiration. Energy released by the reactions of aerobic respiration fuels meristem cell divisions in the embryo. Fig. 31-7c, p. 528
A Absorbed water causes cells of a barley embryo to release gibberellin, which diffuses through the seed into the aleurone layer of the endosperm. aleurone endosperm embryo gibberellin B Gibberellin triggers cells of the aleurone layer to express the gene for amylase. This enzyme diffuses into the starchpacked middle of the endosperm. amylase C The amylase hydrolyzes starch into sugar monomers, which diffuse into the embryo and are used in aerobic respiration. Energy released by the reactions of aerobic respiration fuels meristem cell divisions in the embryo. sugars Stepped Art Fig. 31-7a, p. 528
Examples of Plant Hormone Effects Auxin (IAA) plays a critical role in all aspects of plant development First division of the zygote Polarity and tissue pattern in the embryo Formation of plant parts Differentiation of vascular tissues Formation of lateral roots Responses to environmental stimuli
Directional Transport of Auxin
auxin time time auxin A A coleoptile stops growing if its tip is removed. A block of agar will absorb auxin from the cut tip. B Growth of a de-tipped coleoptile will resume when the agar block with absorbed auxin is placed on top of it. C If the agar block is placed to one side of the shaft, the coleoptile will bend as it grows. Fig. 31-8, p. 529
time time A A coleoptile stops growing if its tip is removed. A block of agar will absorb auxin from the cut tip. B Growth of a de-tipped coleoptile will resume when the agar block with absorbed auxin is placed on top of it. C If the agar block is placed to one side of the shaft, the coleoptile will bend as it grows. Stepped Art Fig. 31-8, p. 529
Animation: Auxin s effects
Examples of Plant Hormone Effects Jasmonates signal plant defenses Wounding by herbivores cleaves peptides (such as systemin) in mesophyll cells Activated peptides stimulate jasmonate synthesis, which turns on transcription of several genes Some gene products slow growth Other gene products signal wasps to attack specific herbivores responsible for damage
Jasmonates in Plant Defenses
31.2-31.3 Key Concepts Mechanisms of Hormone Action Cell-to-cell communication is essential to development and survival of all multicelled organisms In plants, such communication occurs by hormones