1) A seed is formed through the processes of megasporogenesis and megagametogenesis within the ovule of a flower, leading to double fertilization and the formation of an embryo and endosperm within the seed. 2) A seed becomes a seedling through germination, which begins with water uptake by the dry seed and involves embryonic growth and the emergence of the radicle and plumule from the seed coat. 3) Flowers are formed through the processes of flower evocation and meristem identity genes that commit the shoot apical meristem to produce floral meristems and initiate the development of floral organs according to the ABC model of flower development.

1. Plant Development
PS452
Feng Chen
Department of Plant Sciences
University of Tennessee
01/21/2014

2. Plant Growth: an irreversible change in the size of a cell, organ or
whole organism.
Differentiation: Cells taking on specialized form and function.
Plant Development: the orderly and progressive change from seed
germination through juvenility, maturity, flowering and fruiting.

3. Seed
Seedling
Mature plants
Flowering
Fruiting
Plant Life Cycle
(1) How is a seed formed? (2) How does a seed
become a seedling?
(3) How is shoot formed?
(4) How is root formed?
(5) How is a flower
formed?

4. (1) How is a seed formed?
(2) How does a seed become a seedling?
(3) How is shoot is formed?
(4) How is root is formed?
(5) How is a flower formed?

5. Flower Structure

6. Figure 4.2

7. Male and Female Gametophyte
Gametophyte – embryo sac
Gametophyte – anther
Gamete – egg
Gamete – two sperm cells (in pollen grain or tube)
Male
Female

8. 21-14
Anther
Tapetum
(nutritive)
Epidermis
Raven et al., 1999; Biology of Plants
Anther
(lily)
Pollen sac Pollen mother cells
(Microsporocytes)

9. Tetrad
(n)
Free microspores
(n)
Mature pollen
(n)
Nucleus of
vegetative cell
Generative cell
Pollen mother cell (Microsporocyte)
(2n)
Meiosis
Pollen Development
“‘diploid’”
“‘haploid’”

10. Ovule Development
micropyle
funiculus
outer
integument
inner
integument nucellus 20.8
Esau, 1977; Anatomy of Seed Plants
embryo
sac

11. Megasporogenesis
(2n) (n) (n) (n)
Meiosis
Megasporocyte
(mother cell)
“Megasporogenesis”

12. Egg Cell Differentiation
Buchanan et al., 2000’ Biochemistry and Molecular Biology of Plants

13. Haploid Egg
Antipodal cells
Egg cell
Synergid
cells
Central nuclei

14. ovule
stigma
Pollen tube
Fertilization
Fertilization

15. Double Fertilization
Antipodal cells
Central nuclei
Egg cell
Synergid cell
Sperm nuclei
Endosperm
Embryo

16. Figure 4.4
Embryogenesis

17. Simplified Structure of A Mature Seed
Seed coat
Embryo
Endosperm
Seed coat is dead tissue.
It protects everything
inside it.
Embryo is a minute
plant .
Endosperm provides energy
for seed germination and
early seedling growth.

18. (1) How is a seed formed?
(2) How does a seed become a seedling?
(3) How is shoot formed?
(4) How is root formed?
(5) How is a flower formed?

19. Dry seeds Imbibed seeds
Water Uptake: the First Event in Germination

20. Bewley, Plant Cell
Events Occur during Seed Germination

21. Water Relations and Seed Germination
High water availability
Medium water availability
Low water availability

22. Temperature and Seed Germination

23. Some Seeds Require Light for Germination
Dark Dark
Light

24. Tomato Seed Anatomy
Endosperm
Seed coat
Embryo
0.5 mm

25. Embryo
Endosperm
Embryo
Endosperm
Seed Coat Seed Coat

26. Embryo
Endosperm
Growth Potential
Constraint
Seed Coat

27. Involvement of Expansin Genes in Seed Germination
LeEXP4
Dissecting seed
LeEXP8

28. (1) How is a seed formed?
(2) How does a seed become a seedling?
(3) How is shoot formed?
(4) How is root formed?
(5) How is a flower formed?

29. Figure 4.1

30. Formation of SAM
Taiz and Zeiger, Plant Physiology

31. CZ: central zone; PZ: peripheral zone; RZ: rib zone
Shoot Apical Meristem (SAM)
Taiz and Zeiger, Plant Physiology

32. Leaf Formation: Leaf Primordium

33. Figure 4.7

34. Leaf Anatomy
Taiz and Zeiger, Plant Physiology

35. From: PM Ray, “The Living Plant”
Apical dominance is a
phenomenon in which the
apical bud tends to
“dominate” stem growth in
the sense that all of the
axillary buds immediately
below it do not grow out to
form branches. Thus the
stem grows tall, not wasting
resources by growing wide.
The idea is that auxin
produced in the apical bud is
transported down the stem
and suppresses the
outgrowth of the lateral
(axillary) buds. If the tip is
cut off the auxin source is
removed and the buds begin
to develop into branches.

36. (1) How is a seed formed?
(2) How does a seed become a seedling?
(3) How is shoot formed?
(4) How is root formed?
(5) How is a flower formed?

37. Root Systems
Taproot system: characterized by
having one main root (the taproot)
from which smaller branch roots
emerge. When a seed germinates,
the first root to emerge is the radicle,
or primary root. In conifers and
most dicots, this radicle develops
into the taproot.
Fibrous root system: characterized by
having a mass of similarly sized roots. The
radicle from a germinating seed is short lived
and is replaced by adventitious roots.
Adventitious roots are roots that form on
plant organs other than roots. Most monocots
have fibrous root systems.

38. Root tip has 4 developmental zones
Root cap: Protects RAM and push
Meristematic zone: Primary root
Elongation zone: Rapid cell
elongation, rate of division
decreases with distance from
meristem
Maturation zone: Cells get their
mature differentiated features.
No lateral organs produced from apical
meristem to avoid hindrance in soil
penetration
Branch roots arise from non
growing region
Root System development

39. Cells of the root epidermis develop projections called root hairs. These
elongate by “tip growth” and increase surface area for water and mineral
uptake. Root hairs are found away from the root tip, in the region of
maturation.
Note that the root hair develops as an
outgrowth from individual epidermal
cells; that is, the root hair is not a cell
separate from the epidermal cell. The
Figure shows (bottom to top) four
stages of root hair development: cell
specification, root hair initiation, tip
growth, and maturation.

40. (1) How is a seed formed?
(2) How does a seed become a seedling?
(3) How is shoot formed?
(4) How is root formed?
(5) How is a flower formed?

41. Flower Structure

42. Internal factors
Phase change
Hormones
External factors
Light
Temperature
Total light radiation
Water availability
Cues for Flower Evocation
Flower Evocation: The events occurring in the shoot apex that
specifically commit the apical meristem to produce flowers.

43. Vegetative SAM Reproductive SAM
Formation of Floral Meristems

44. Genetic Control of Flower Development
Taiz and Zeiger, Plant Physiology

45. Three Types of Genes Control Floral Identify
1. Gene A activity controls the first and second whorls
2. Gene B activity controls the second and third whorls
3. Gene C activity controls the third and fourth whorls.

46. ABC Model for Flower Development
Taiz and Zeiger, Plant Physiology

49. Figure 4.8
Mutations in Floral Organ Identify Genes

50. Seed
Seedling
Mature plants
Flowering
Fruiting
Plant Life Cycle
(1) How is a seed formed? (2) How does a seed
become a seedling?
(3) How is shoot formed?
(4) How is root formed?
(5) How is a flower
formed?