Flowers
Basic structure of the angiosperm flower
The fertilization process
Pollen and stigma self-incompatibility
The efficiency of animal pollination
Some basic types of flower
Reproduction and diversity of angiosperms
Basic structure of the angiosperm flower
Collective nouns that can cause confusion!
Calyx
The outer whorl of a flower made up of sepals
that are usually green, and protect the flower
in bud.
Carpel
Bears the stigma, and frequently an elongated
style, and encloses the ovules (sometimes gynaecium).
The megasporophyll of the flower
Corolla
Ovary
Pistil
The collective term for the petals of a flower
Perianth
The floral envelope, it includes the calyx and
corolla.
Stamen
The anther and its supporting filament. The
microsporophyll of the flower
The total of the carpels in a flower is the ovary
Each separate carpel when there are lots of
them in the ovary
Ways in which Angiosperms are different from Gymnosperms
Angio-Gymno 4 Ovules protected within an enclosed structure
Evolution of the pistil
… about meiosis, mitosis
and cytokinesis?
Life cycle of angiosperms
Fig. 17.12
The fertilization process
in Angiosperms
(Equivalent to Fig 31.10)
Development of gametophytes
Ways in which Angiosperms are different from Gymnosperms
Angio-Gymno 5.
Double fertilization to
produce diploid zygote and triploid
endosperm nucleus
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. The developing embryo
uses the nutrients stored in the endosperm, as
does the moncot seedling after germination. In
most dicots, food reserves are moved to the
cotyledons and the endosperm is not present in a
mature seed.
Somatic cell division involves two
successive steps: mitosis and cytokinesis.
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.
Ways in which Angiosperms are different from Gymnosperms
Angio-Gymno 5. Generally angiosperms have
hermaphrodite flowers and cross pollinate
(70%)
… how many alleles
there are at a locus?
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. What happens when
pollen from plants with three different allele pairs is crossed
with an S1S2 plant? This system prevents self-fertilization
AND fertilization from close relatives.
Pollen Grain Size and Surface Morphology in a Perennial Rye
Grass Hybrid
Rye grass incompatibility
Pollen grain on stigma
Attempts to hybridize
between particular
varieties resulted in
production of a web-like
substance and
incompatibility
Stacey Lacoste
The efficiency of
animal pollination
Nucleus of tube cell
Generative cell
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 excess pollen.
Lilium pollen
http://www.uri.edu/artsci/bio/plant_anatomy/images/153.gif
Some basic types of flower
Separate petals
Magnolia grandiflora
http://www.csdl.tamu.edu/FLORA/gallery4.htm
Flowers with a tubular corolla
Gentiana algida
Rocky Mountain National Park CO
http://www.csdl.tamu.edu/FLORA/gallery4.htm
A head with many florets
http://www.csdl.tamu.edu/FLORA/gallery4.htm
Monocotyledons
Flower parts in threes
Narcissus spp.
http://www.csdl.tamu.edu/FLORA/gallery4.htm
Monoecious, wind pollinated
Oaks, have separate male and female flowers.
The female flower (upper left) consists only of
carpels and a calyx (collection of sepals).
The male flowers are in elongated clusters, called
catkins, and consist only of anthers and a calyx.
Both sexes are found on the same tree, and thus
oaks are monoecious (meaning same house).
Some trees, e.g., poplars and willows are dioecious
(meaning two houses), and there are male and
female trees.
Other monoecious genera include birch, walnut,
ash, hickory, and most maples.
http://forest.wisc.edu/forestry415/INDEXFRAMES.HTM
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
Sections you need to have read
17.10 through 17.14 and 31.9 and 31.10
Courses that deal with this topic
Botany 113 Plant identification and classification