Flowers

1
Flowers
2
Remember
Three more differences between gymnosperms and
angiosperms
4. Angiosperm ovules are protected within an
enclosed structure rather sitting on a modified
leaf
5. Double fertilization in the angiosperms
produces a diploid zygote and triploid endosperm
nucleus
6. In the angiosperms there are generally
hermaphrodite flowers and cross pollinating
(70). Wind pollination is typical in the
gymnosperms animal pollination widespread in
angiosperms
First some basic naming of parts
3
Basic structure of the angiosperm flower
This is a hermaphrodite flower with a single
carpel
Fig. 31.3, p. 532
4
Collective nouns that can cause confusion!
5
Collective nouns that can cause confusion!
6
Evolution of the pistil
4. Angiosperm ovules are protected within an
enclosed structure rather sitting on a modified
leaf
Remember, angeion case this is how we think it
evolved
7
Life cycle of Angiosperms
The basic life cycle appears similar to that of
the Gymnosperms
there is a well developed receiving system for
the pollen so that the male gametophyte can
penetrate the angion,
the female gametophyte has a more complex
structure that results in an endosperm, nutritive
material for the embryo
8
Overview of cherry life cycle
Flower
Ovule formation
Seedling
Seed
Diploid Stage
Meiosis
Meiosis
Double Fertilization
Haploid Stage
Pollen development
Development of embryo sac
Pollination
9
How pollen grains develop and germinate
(see next slide)
Diploid Stage
Meiosis
Haploid Stage
(see next slide)
mature male gametophyte
Fig. 31.6a, p. 534
10
5. Double fertilization in the angiosperms
produces a diploid zygote and triploid endosperm
Ways in which Angiosperms are different from
Gymnosperms
11
Somatic cell division involves two successive
steps
mitosis and cytokinesis.
Now, remind me, what is cytokinesis again ?
In mitosis, the nuclear DNA duplicates and
chromosomes segregates equally between the two
daughter nuclei
cytokinesis divides these two nuclei and
cytoplasm, including related cytoplasmic
organelles, into two individual cells.
12
The fertilization process in Angiosperms
seedling (2n)
How many ovules in a cherry?
Diploid Stage
Double Fertilization
Meiosis
Haploid Stage
One sperm nucleus to the egg, one to the
endosperm mother cell
Cytoplasmic division then gives 7 cells the
endosperm mother cell with 2 nuclei
Fig. 31.6b, p. 535
13
What goes on in the endosperm?
The triploid nucleus divides and the endosperm
cell becomes a supercell with many nuclei and a
milky consistency.
Cyotkinesis forms membranes and walls between the
nuclei and makes the endosperm more solid.
In most dicots the developing embryo moves the
nutrients stored in the endosperm to the
cotyledons and the endosperm is not present in a
mature seed.
In moncots the endosperm remains and is used by
the seedling after germination.
14
Look what happens when you eat your endosperm!
15
6. In the angiosperms there are generally
hermaphrodite flowers and cross pollinating
(70). Wind pollination is typical in the
gymnosperms animal pollination widespread in
angiosperms
Ways in which Angiosperms are different from
Gymnosperms

Hermaphrodite organism with the organs of both
sexes.
16
That should make fertilization easier. Pollen
can fertilize the egg and endosperm mother cell
of the same flower.
Hmm! Im not so sure that is such a good idea.
How can self-fertilization be prevented for
hermaphrodite flowers?
1 Differences in timing of maturity of male and
female parts
2 Incompatibility mechanisms
17
Pollen and stigma incompatibility
There can be dozens of alleles of the S-gene. If
a pollen grain has an allele that matches an
allele of the stigma upon which it lands, then
the pollen tube fails to grow.
This system prevents self-fertilization AND
fertilization from close relatives.
18
Rye grass incompatibility
Pollen Grain Size and Surface Morphology in a
Perennial Rye Grass Hybrid
Attempts to hybridize between particular
varieties resulted in production of a web-like
substance and incompatibility
Pollen grain on stigma
Stacey Lacoste
19
The efficiency of animal pollination
Pollen is up to 30 protein
Animal pollination is targeted and so is more
efficient than wind pollination.
Animal pollinated flowers generally produce much
less pollen than wind pollinated flowers.
Pollen is important for animals and many animal
pollinated plants do produce some excess pollen.
http//www.uri.edu/artsci/bio/plant_anatomy/images
/153.gif
20
Reproduction and diversity of angiosperms
Animal pollination is efficient and associated
with the development of the hermaphrodite
reproductive axis
The diversity of flowers represent mechanisms
promoting efficient pollination
Prevention of self-fertilization maintains
genetic variation by promoting cross pollination
Sophistication of the reproductive process
enables a large number of ways reproductive
isolation can occur and so maintains genetic
diversity