Flowers

Basic structure of the angiosperm flower

The fertilization process

Pollen and stigma self-incompatibility

Reproduction and diversity of angiosperms

The efficiency of animal pollination

Some basic types of flower

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

Ovary The total of the carpels in a flower is the ovary

Corolla 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

Pistil Each separate carpel when there are lots of them in the ovary

Evolution of the pistil

Ways in which Angiosperms are different from Gymnosperms

Angio-Gymno 4 Ovules protected within an enclosed structure

… 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

Angio-Gymno 5. Double fertilization to produce diploid zygote and triploid endosperm nucleus

Ways in which Angiosperms are different from Gymnosperms

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.

What goes on in the endosperm?

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.

Angio-Gymno 5. Generally angiosperms have hermaphrodite flowers and cross pollinate (70%)

Ways in which Angiosperms are different from Gymnosperms

… 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.

Rye grass incompatibility

Pollen Grain Size and Surface Morphology in a Perennial Rye Grass Hybrid

Stacey LacostePollen grain on stigma

Attempts to hybridize between particular varieties resulted in production of a web-like substance and incompatibility

The efficiency of animal pollination

Lilium pollen

Pollen is up to 30% protein

Pollen is important for animals – and many animal pollinated plants do produce excess pollen.

Animal pollination is targeted and so is more efficient than wind pollination.

Animal pollinated flowers generally produce much less pollen than wind pollinated flowers.

Generative cell

Nucleus of tube cell

http://www.uri.edu/artsci/bio/plant_anatomy/images/153.gif

Some basic types of flowerSeparate petals

http://www.csdl.tamu.edu/FLORA/gallery4.htm

Magnolia grandiflora

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

http://www.csdl.tamu.edu/FLORA/gallery4.htm

Flower parts in threes

Narcissus spp.

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

Monoecious, wind pollinated

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