Angiosperm Reproduction and Biotechnology Chapter 38 p. 771-780.

Angiosperm Reproduction and Biotechnology

Chapter 38p. 771-780

LE 38-2b

Haploid (n)Diploid (2n)

Key

Simplified angiosperm life cycle

Germinatingseed

Seed

Seed

Simple fruit

Embryo (2n)(sporophyte)

Zygote (2n)

FERTILIZATION

Egg (n)

Sperm (n)

Embryo sac (n) (femalegametophyte)

OvuleOvary

Germinated pollen grain(n) (male gametophyte)

Pollentube

Anther

Maturesporophyteplant (2n)

Flower Structure

Flowers are the reproductive shoots of the angiosperm sporophyte Stamen: (“male parts”)

Anther: where pollen is produced Filament: supports anther

Carpal: (“female parts”) Ovary: contains ovules (hold female

gametophytes) Stigma: where pollen lands Style: encloses ovary & supports the stigma

Time Lapse of Flowering Plant Life CycleFlower Blooming (time lapse)

LE 38-2a

Stamen Anther

Filament

An idealized flower

Receptacle

Petal

Carpel

Sepal

Ovary

Style

Stigma

Haploid (n)Diploid (2n)

Key

Flower Variations

Many flower variations have evolved during the 140 million years of angiosperm history A) Symmetry: radial/bilateral B) Ovary Location:

superior/semi-inferior/inferior C) Floral Distribution: individual

flowers/inflourescence (clusters) D) Reproductive Variations:

Monoecious: stamen & carpal on same flower Dioecious: stamen & carpal on different plants

Gametophyte Development and Pollination

Pollination is the transfer of pollen from an anther to a stigma Pollen grain produces a pollen tube that grows

down into the ovary and discharges sperm near the embryo sac

Pollen develops from microspores within the sporangia of anthers

Embryo sacs develop megaspores w/in ovules

Bat Pollinating Agave Plant Bee Pollinating

LE 38-4Development of a male gametophyte(pollen grain)

Pollen sac(microsporangium)

Micro-sporocyte

Micro-spores (4)

Generativecell (willform 2sperm)

Each of 4microspores

Malegametophyte(pollen grain)

Nucleus oftube cell

MITOSIS

(LM)75 µm

Ragweedpollengrain(colorizedSEM)

20 µm

Keyto labels

Haploid (n)

Diploid (2n)

MEIOSIS

Development of a female gametophyte(embryo sac)

Mega-sporangium

Ovule

Embryosac

Female gametophyte(embryo sac)

Mega-sporocyte

Integuments

Survivingmegaspore

Micropyle

Ovule Antipodalcells (3)

Polarnuclei (2)

Egg (1)

Synergids (2)Integuments

(LM)100

µm

Double Fertilization

The pollen tube discharges TWO sperm into the embryo sac One sperm fertilizes

the egg The other combines

with the polar nuclei of the embryo, giving rise to the food-storing endosperm

From Ovule to Seed

After double fertilization, each ovule develops into a seed

The ovary develops into a fruit enclosing the seed(s)

Endosperm Development: Stores nutrients that can be used by the

seedling OR Exports its food reserves to the cotyledons

Embryo Development

The first mitotic division of the zygote, splits it into a basal cell and a terminal cell Terminal cell →

embryo Basal Cell →

Suspensor → anchors & transports nutrients to embryo

Structure of the Eudicot Seed 1) Seed Coat: hard, protective shell that

encloses embryo & provides food supply 2) Radicle: embryonic root 3) Embryonic Axis

Hypocotyl: below cotyledon attachment Epicotyl: above cotyledon attachment

Contains shoot tip & 2 mini leaves

4) Cotyledon: “meat” of seed; stores food

Structure of Monocot Seed

Scutellum: thin, specialized cotyledon that absorbs nutrients during germination

Coleoptile: covers young shoot Coleorhiza: covers young root

From Ovary to Fruit

A fruit develops from the ovary Protects enclosed seeds and aids in seed

dispersal by wind or animals Types:

1) Simple: derived from 1 carpal/several fused (i.e. peach, pea, nut)

2) Aggregate: results from single flower w/ 2+ carpals (i.e. raspberry)

3) Multiple: results from inflourescence (i.e. pineapple)

Developmental Origin of Fruits

Seed Germination

As a seed matures, it dehydrates and enters a phase called dormancy ↓ metabolic rate growth & development suspended

↑ chances germination will occur at time & place most advantageous for seedling

Environmental cues required to break dormancy Change in temp or lighting

From Seed to Seedling

Germination depends on imbibition the uptake of water due to low water potential of

the dry seed 1) Radicle (embryonic root) emerges first 2) Shoot tip breaks through soil surface 3) In many eudicots, a hook forms in the

hypocotyl, and growth pushes the hook above ground

4) In maize & other grasses (monocots) coleoptile pushes up through soil

See

d G

erm

inat

ion