1. Plant Development
Chapter 31 Part 1

2. Impacts, Issues Foolish Seedlings, Gorgeous Grapes
Gibberellin and other plant hormones control the growth and development of plants – environmental cues influence hormone secretion

3. 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

4. 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

5. Anatomy of a Corn Seed

6. seed coat fused with ovary wall
endosperm cells
cotyledon
coleoptile
plumule (embryonic shoot)
embryo
Figure 31.2
Anatomy of a corn seed (Zea mays). During germination, cell divisions resume mainly at apical meristems of the plumule (the embryonic shoot) and radicle (the embryonic root). A plumule consists of an apical meristem and two tiny leaves. In grasses such as corn, the growth of this delicate structure through soil is protected by a sheathlike coleoptile.
hypocotyl
radicle (embryonic root)
Fig. 31-2, p. 524

7. Early Growth of Corn (Monocot)

8. Figure 31.3
Early growth of corn (Zea mays), a monocot.
Fig. 31-3a, p. 525

9. coleoptile branch root primary root coleoptile hypocotyl radicle
Figure 31.3
Early growth of corn (Zea mays), a monocot.
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

10. Figure 31.3
Early growth of corn (Zea mays), a monocot.
Fig. 31-3b, p. 525

11. adventitious (prop) root
primary leaf
coleoptile
adventitious (prop) root
branch root
Figure 31.3
Early growth of corn (Zea mays), a monocot.
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

12. adventitious (prop) 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.
coleoptile
primary leaf
branch root
adventitious (prop) root
primary root
hypocotyl
radicle
Figure 31.3
Early growth of corn (Zea mays), a monocot.
Stepped Art
Fig. 31-3, p. 525

13. Animation: Plant development

14. Early Growth of a Bean (Eudicot)

15. Figure 31.4
Early growth of the common bean plant (Phaseolus vulgaris), a eudicot.
Fig. 31-4a, p. 525

16. A After a bean seed germinates, its radicle emerges
seed coat
radicle
cotyledons (two)
hypocotyl
Figure 31.4
Early growth of the common bean plant (Phaseolus vulgaris), a eudicot.
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

17. Figure 31.4
Early growth of the common bean plant (Phaseolus vulgaris), a eudicot.
Fig. 31-4b, p. 525

18. primary leaf primary leaf withered cotyledon
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
branch root
Figure 31.4
Early growth of the common bean plant (Phaseolus vulgaris), a eudicot.
primary root
root nodule
Fig. 31-4b, p. 525

19. Summary: Eudicot Development

20. female gametophyte (n)
mature sporophyte (2n)
germination
zygote
in seed (2n)
meiosis in anther
meiosis in ovary
DIPLOID
fertilization
HAPLOID
eggs (n)
sperm (n)
microspores (n)
megaspores (n)
Figure 31.22
Summary of development in the life cycle of a typical eudicot.
male gametophyte (n)
female gametophyte (n)
Fig , p. 535

21. 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

22. 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

23. Gibberellins
Gibberellins induce cell division and elongation in stem tissue, and are involved in germination

24. 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

25. Rooting Powder with Auxin

26. 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

27. 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

28. 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

29. Major Plant Hormones and Their Effects

30. Commercial Uses of Plant Hormones

31. Other Signaling Molecules
Besides hormones, other signaling molecules are involved in plant development
Brassinosteroids
FT protein
Salicylic acid
Systemin
Jasmonates

32. 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

33. Gibberellins in Barley Seed Germination

34. Gibberellins in Barley Seed Germination

35. Gibberellins in Barley Seed Germination

36. gibberellin aleurone endosperm embryo
Figure 31.7
Action of gibberellin in barley seed germination.
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

37. amylase
Figure 31.7
Action of gibberellin in barley seed germination.
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

38. sugars
Figure 31.7
Action of gibberellin in barley seed germination.
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

39. 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.
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.
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
Figure 31.7
Action of gibberellin in barley seed germination.
Stepped Art
Fig. 31-7a, p. 528

40. 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

41. Directional Transport of Auxin

42. 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.
Figure 31.8
A coleoptile lengthens in response to auxin produced in its tip. Auxin moves down from the tip by passing through cells of the coleoptile. The directional movement is driven by different types of active transporters positioned at the top and bottom of the cells’ plasma membranes (right).
Fig. 31-8, p. 529

43. A A coleoptile stops growing if its tip is removed
A A coleoptile stops growing if its tip is removed. A block of agar will absorb auxin from the cut tip.
time
B Growth of a de-tipped coleoptile will resume when the agar block with absorbed auxin is placed on top of it.
time
C If the agar block is placed to one side of the shaft, the coleoptile will bend as it grows.
Figure 31.8
A coleoptile lengthens in response to auxin produced in its tip. Auxin moves down from the tip by passing through cells of the coleoptile. The directional movement is driven by different types of active transporters positioned at the top and bottom of the cells’ plasma membranes (right).
Stepped Art
Fig. 31-8, p. 529

44. Animation: Auxin’s effects

45. 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

46. Jasmonates in Plant Defenses

47. 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