FLOWERS AND ANGIOSPERM REPRODUCTION

Most of the plant--roots, leaves, flowers--is diploid

The pollen and embryo saccells are haploid

Flowering plants arose recently, diversified rapidly

Million years ago

Angiosperms—flowering plants

First fossil angiosperms are 140 million years old

Diversified quickly: 250,000 species named (maybe

2,500,000 extant), compared to 550 species of

conifers, 10,000 species of ferns

Evolved first in dry, hilly areas (Mediterranean

climates?); now present everywhere with the

most diversity in tropics

Why the success?

Continued to refine vegetative adaptations to dry

land and cold: e.g., developed vessels vs

tracheids; sieve tubes (with larger diameter,

larger pores, companion cells, and no big

organelles) vs sieve cells

Invented flower and fruit: better protection of

megasporocytes, megaspores and

megagametophytes (embryo sac); better

distribution of microgametophytes (pollen); better

distribution of seeds

Double fertilization and endosperm: better nutrition

of developing embryo

The parts of the flower(exploded) The embryo sac is in

the ovary

Pollen is formed inthe anthers

Formation of the male haploidplant (pollen grain; gametophyte)

Pollen grains in pollen sacs within an anther

Pollen grains of Iris

and ragweed (Ambrosia)

Formation of the female haploid plant (embryosac) and fertilizationby the sperm nucleusin the pollen tube

Flower with a superior ovary

Flower with an inferior ovary

This daffodil has a (an) ? ovary

Ovules within a lily ovary

Within the ovule, a megasporocyte

After two meiotic divisions and three mitotic divisions, an embryo sac

Pollen tube and fertilizationvisualized by geneticallyengineered fluorescence

Once fertilized, the egg cell divides by mitosis to form the embryo:Below are some early stages of development of an embryo ofArabidopsis (the favorite “fruit fly” of plant biologists)

Globular-stageembryo Heart-stage

embryo

Seeds in a “silique”

Once fertilized, the egg cell divides by mitosis to form the embryo

Summary

•Reproduction in flowering plants involves male and female gametes(formed from microsporophytes and megasporophytes,the haploid plants resulting from meiosis)

•Formation of gametes, fertilization, and embryo growth take place inflowers

•Flower structures promote fertilization

•Seed structures promote dissemination of embryos