FLOWERS AND ANGIOSPERM REPRODUCTION
Most of the plant--roots, leaves, flowers--is diploid
The pollen and embryo sac
cells 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)
Pollen is formed in
the anthers
The embryo sac is in
the ovary
Formation of the male haploid
plant (pollen grain; gametophyte)
Pollen grains in pollen sacs within an anther
Pollen grains of Iris
and ragweed (Ambrosia)
Formation of the female
haploid plant (embryo
sac) and fertilization
by the sperm nucleus
in 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 fertilization
visualized by genetically
engineered fluorescence
Once fertilized, the egg cell divides by mitosis to form the embryo:
Below are some early stages of development of an embryo of
Arabidopsis (the favorite “fruit fly” of plant biologists)
Globular-stage
embryo
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 in
flowers
•Flower structures promote fertilization
•Seed structures promote dissemination of embryos