Process of Development of Zygote in Flowering Plants

Topic Content:

Flowers are modified shoots of plants for sexual reproduction. Male reproductive organs are androecium while gynoecium represents female reproductive organs.

The gynoecium encloses ovules or megasporangia. Pollen may spread from plant to plant but can only reproduce with the same species of plants.

Pollen Grains:

Pollen grains (from the Greek word palynos for dust or pollen) are male gametophyte – spherical in shape.

Pollen grains are produced by meiosis of microspore mother cells that are located along the inner edge of the anther sacs (microsporangia). They are usually spherical measuring about 25-50 micrometers in diameter. It has two-layered walls, exine, and intine.

The outer part of the pollen is the exine, which is composed of a complex polysaccharide, sporopollenin. Inside the pollen are two (or, at most, three) cells that comprise the male gametophyte. The tube cell (also referred to as the tube nucleus) develops into the pollen tube.

A pollen tube is a special structure that grows within the style from the pollen grain to the ovary of a flower.

The two nuclei present on the pollen tube are the tube nucleus and the generative nucleus .