Zivuku .M (2015)

• Outline the production of sex cells in ovary and the anther.
• Discuss various methods of pollination in angiosperms.
• Describe the development of pollen tube and including “double fertilisation”
• Outline the life cycle of an angiosperm.
• Evaluate pollen and stigma compatibility.

• The transfer of pollen from the anthers of a flower to the stigma of the same flower or of another flower.
• Pollen is typically transferred to stigma by pollination vectors (pollinators).

•
Cross-pollination - occurs when pollen is delivered to a flower from a different plant
•
Self-pollination - occurs when pollen from one flower pollinates the same flower or other flowers of the same individual

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 The collective term for the petals of a flower
Ovary The total of the carpels in a flower is the ovary
Pistil Each separate carpel when there are lots of them in the ovary
Perianth The floral envelope, it includes the calyx and corolla.
Stamen The anther and its supporting filament. The microsporophyll of the flower

… about meiosis, mitosis and cytokinesis?

• The life cycle of a plant is dominated by the sporophyte (2n).
• Spores that form by meisos develop into haploid spores (n)
• The production of female gametes starts when the mass of tissue in the inner ovary.

• One cell undergoes meiosis and cytoplasmic division to give four haploid cells
• Three of these disintegrate while the remaining undergoes mitosis without cytoplasmic division to give 8 haploid cells--- female gametophyte.

• Further division produces a mature embryo sac containing an egg and a large central cell containing two polar nuclei.

• The male structures or stamens, surrounds the pistil and consist of the filament.
• The mother cells, each of which undergoes meiotic division to form microspores.
• The micropore is subsequently become encased in heavy resistant walls. Pollen grain.

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

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 S
1
S
2 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

Nucleus of tube cell
Generative cell
Lilium pollen
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 excess pollen.
http://www.uri.edu/artsci/bio/plant_anatomy/images/153.gif

Separate petals
Magnolia grandiflora http://www.csdl.tamu.edu/FLORA/gallery4.htm

Flowers with a tubular corolla http://www.csdl.tamu.edu/FLORA/gallery4.htm
Gentiana algida
Rocky Mountain National Park CO

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