Angiosperm Reproduction and Biotechnology

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Flowers are the reproductive shoots of the angiosperm sporophyte; they attach to a part of the stem called the receptacle.

Flowers consist of four floral organs: sepals, petals, stamens, and carpels.

Slide 8

A stamen consists of a filament topped by an anther with pollen sacs that produce pollen.

A carpel / pistil has a long style with a stigma on which pollen may land.

At the base of the style is an ovary containing one or more ovules.

Slide 9

Complete flowers contain all four floral organs.

Incomplete flowers lack one or more floral organs, for example stamens or carpels.

Clusters of flowers are called inflorescences.

Slide 10

Development of Male Gametophytes in Pollen Grains

Pollen develops from microspores within the microsporangia, or pollen sacs, of anthers.

If pollination succeeds, a pollen grain: generative nucleus ---> 2 SPERM, and tube nucleus ---> produces a pollen tube that grows down into the ovary and discharges 2 sperm near the embryo sac.

The pollen grain consists of the two-celled male gametophyte and the spore wall.

Slide 11

(a)

Development of a male

gametophyte (in pollen grain)

Microsporangium

(pollen sac)

Microsporocyte (2n)

4 microspores (n)

Each of 4

microspores (n)

Male

gametophyte

Generative cell (n)

Ovule

(b)

Development of a female

gametophyte (embryo sac)

Megasporangium (2n)

Megasporocyte (2n)

Integuments (2n)

Micropyle

MEIOSIS

Surviving

megaspore (n)

3 antipodal cells (n)

2 polar nuclei (n)

1 egg (n)

2 synergids (n)

Female gametophyte

(embryo sac)

Ovule

Embryo

sac

Integuments (2n)

Ragweed

pollen

grain

Nucleus of

tube cell (n)

MITOSIS

100 µm

20 µm

75 µm

Slide 12

Development of Female Gametophytes (Embryo Sacs)

Within an ovule, megaspores are produced by meiosis and develop into embryo sacs, the female gametophytes.

Slide 13

Pollination

In angiosperms, pollination is the transfer of pollen from: anther to stigma (male -> female).

Pollination can be aided by environmental agents such as: wind, water, bee, moth and butterfly, fly, bird, bat, or water.

Slide 14

Abiotic Pollination by Wind

Hazel staminate flowers

(stamens / male sex organs only)