Outline: Plant Reproduction and Development (Angiosperms) Chpt 38 Bio 102 (Vogt)

I. Review - Life Cycle of Flowering Plants

II. Anatomy of Flowers

III. Reproduction: Asexual vs. Sexual

IV. POLLEN GRAIN (sperm) Male Gametogenesis.

V. OVULE (egg): Female Gametogenesis.

VI. Pollination and Fertilization; Self Recognition

VII. Embryogenesis: formation of Seed & Fruit

VIII. Germination

IX. Growth, Morphogenesis

Lecture Notes: Plant Reproduction and Development Chpt 38

I. Review - Life Cycle of Flowering Plant (Fig. 38.1)

A. sporophyte (2N) dominant

1. reproductive structures (flowers) > meiosis

a. male gametophyte: pollen (N)
b. female gametophyte: ovary / egg (N)

2. pollination > fertilization > embryo (2N)
3. germination > sporophyte (2N)

B. Specialized Diversity

1. flower parts: attract animals to transfer pollen
2. fruit: seed dispersal

II. Anatomy of Flowers (Fig. 38.2, also 21.17, 21.18)

A. Four major parts - on central axis - evolved as modified leaves

1. Sepal
2. Petals
3. Stamen (male reproductive organ)

a. filament
b. anther: produces pollen

4. Carpel (female reproductive organ)

a. ovary - site of fertilization
b. style - tissue between stigma and ovary
c. stigma - pollination site

B. Missing flower parts : variations


1. complete / incomplete : any missing parts
2. perfect / imperfect : missing stamen or carpel
3. monoecious / dioecious : M/F plant, M plant - F plant

C. Evolution of Flowers - read the book

1. Natural selection on flowers to ensure pollination
2. diversity as selective pressure is specific to...

a. flower species
b. means / organism of pollination

III. Reproduction: Asexual vs. Sexual

A. Asexual Reproduction (vegetative reproduction)

(useful in agriculture, agricultural research)

B. Sexual Reproduction

C. If you can reproduce asexually, why have sex?


World is not homogeneous in time or space
Genetic diversity: yields different solutions.

D. Assignation of Male - Female

1. female: large, "expensive", immovable -- egg
2. male: cheap, small, motile -- sperm

IV. POLLEN GRAIN (sperm) Male Gametogenesis (Fig. 38.4).

A. Anther (2N) > pollen sacs >

microspore mother cell (2N) (microsporocyte) > meiosis >
4 microspores (N) > mitosis > four 2 cell male gametophytes >
3 cell POLLEN GRAIN:

cell I: tube cell
cell II: divides to two sperm cells

B. Digression: Mitosis / Meiosis Revisited. Somatic vs. Germ Cells

1. Mitosis - somatic cells (2N) (Review Chapter 12)

a. homologous chromosomes replicate - centromere
b. replicates are identical (chromatids)
c. replicates segregate > new cells (2N)

2. Meiosis - germ cells only (Review Chapter 13)

a. homologous chromosomes replicate - centromere
b. homologous pairs align - cross over

(genetic mixing / recombination of mother and father genomes)

c. joined replicates segregate > new cells
d. replicates segregate > new cells (N) - gametes

3. Growth can come from mitosis,

or from changes in cell size or shape.

V. OVULE (egg): Female Gametogenesis (Fig. 38.4)

Ovary (2N) > ovule > megaspore mother cell (2N) (megasporocyte)

meiosis > megaspore (N) (4 produced, 3 degenerate) >
mitosis (3 rounds) > female gametophyte (N):

first 8 nuclei, then cellularization (EMBRYO SAC):

1 egg cell + 2 synergid cells
1 primary endosperm cell with 2 nuclei (polar nuclei)
3 additional cells (antipodal)

Ovule: embryo sac (N) + integuments (2N, surrounding tissue)

VI. Pollination and Fertilization (Fig. 38.7)

A. Pollination:

1. Pollen lands on Stigma
2. Pollen tube grows down Style to ovary
3. Sperm cells move down pollen tube to ovary

B. Fertilization - Double Fertilization

1. One sperm cell (N) fuses with egg (N) > zygote (2N)
2. One sperm cell joins two polar nuclei > endosperm cell (3N)

endosperm cell (3N): plant equivalence of yolk
contents exported to cotyledons (zygote) which serve as nutrient
supply in developing embryo before photosynthesis starts.

C. Preventing Self Fertilization - Self Recognition?
• While certain plants will self fertilize (accept pollen from the same individual), others will not (accept pollen only from other individuals.

• Ability to reject on pollen implies mechanism for "self recognition".

• Known recognition mechanisms occur at the level of pollen-stigma interaction.
  
  • S-genes - Self incompatibility genes - multiple alleles (example >50).
    
  • If Pollen (N) and Sigma (2N) present identical S-gene allele products (proteins), then they are recognized as deriving from the same individual. (Fig. 38.5).

• Recognition of same identitiy activates processes which block fertilization.
  
  Gametophytic self-incompatibility - block occurs in pollen grain
  
  • tobacco, rose, legume
    
  • enzymatic distruction of RNA within a rudimentary pollen tube; RNases are in carpel, but can enter pollen tube and attack RNA if self
    
  Sporophytic self-incompatibility - block occurs in carpel
  
  • mustard
    
  • activation of signal-transduction pathway in epidermal cells of stigma that prevents germination of the pollen grain when it lands on stigma.
    

VII. Embryogenesis: formation of Seed & Fruit (Fig. 38.8, 38.9)

A. zygote >> embryo (Fig. 38.8)

Assymetrical cell divisions >>> embryo

1. shoot tip
2. hypocotyl
3. cotyledons - food source for sprout
4. epicotyl
5. root tip

B. Primary endosperm cell (3N) > endosperm

1. grows rapidly
2. non-genetic inheritance (dependent on nutritional health of parent)
3. dicots: most is transferred to cotyledons
4. monocots: most remains as endosperm (consider corn kernel)

C. Ovary > Fruit

1. Fruit derives from parental integument tissue surrounding embryo sac

generic / it is whatever tissue derives from the ovary

- contrast dandylion fluff with the "edible" part of an apple
- both are fruit

2. non-genetic inheritance, a bit of the parent carried on
3. FUNCTION? seed dispersal
4. diversity - selection based on mode of dispersal

a. wind
b. animal (burr, eat and digest, etc.)
c. etc.

VIII. Germination (Figs. 38.12, 38.11)

A. Germination

1. Embryo absorbs water, swells, bursts open seed coat.
2. Shoot tip pushes up through soil -

- Monotcots: Coleoptile : cap protecting apical meristem
- Dicots: embryonic stem bends and the bend leads, protecting tip

3. QUESTION: why does stem grow up and roots grow down?

B. Dormancy / Breaking Dormancy

1. Function:

a. allow seed time to develop : embryonic arrest
b. over "season": winter; dry season; etc.

2. Specific Mechanisms Induce Dormancy

- freeze tolerance - drought tolerance
- physiological change

3. Environmental Cues /

Experience Required for Breaking Dormancy

a. Seed may require drying out.
b. Cold / Warm cycle.
c. Seed coat must be disrupted - could require gut passage.

IX. Growth, Morphogenesis

• Consider specific sites of growth: apical and lateral meristems
  
• Undifferentiated Cambium cells (one cell type) divide and differentiate into all other cell types.
  
• Requirement for cell-cell communication
  
• Cells must acquire self identity, self awareness
  
• Mechanisms of growth: cell shape change guided by cytoskeleton
  
• Cellular Differentiation and Pattern Formation Depend on Differentially Regulated Gene Expression (p. 746-748)
  

Vocabulary