Tag: introduction to flower

Apical zone of pollen tube contains abundant vesicles but lacks cell organelles. It is hemisphere in shape and transparent in nature. This transparent apical growing region of pollen tube is called as cap block. It exists only until the tube is growing. It disappears as soon as the growth ceases. 

Callose is a beta-1,3-glucan. It is the major component of the pollen tube cell wall. It is also deposited within the cytoplasm as distinct callose grains. This leads to the formation of callose plugs. Callose plugs separate the living, growing and functional part of the pollen tube in the tip from the remaining degenerating part.

Site of meiosis in Angiosperms is the spore mother cell. 

In plants, meiosis can be observed in sporangia. A microsporangium is the part of plant is suitable for the study of meiosis. A typical anther contains four microsporangia. The microsporangia form sacs or locules in the anther. The two separate locules on each side of an anther may fuse into a single locule. Each microsporangium is lined with a nutritive tissue layer called the tapetum and initially contains diploid pollen mother cells. These undergo meiosis to form haploid spores. The spores may remain attached to each other in a tetrad or separate after meiosis.

The site of meiosis in higher plants is the spore mother cell.  In land plants and some algae, there is an alternation of generations such that meiosis in the diploid sporophyte generation produces haploid spores. These spores multiply by mitosis, developing into the haploid gametophyte generation, which then gives rise to gametes directly. In both animals and plants, the final stage is for the gametes to fuse, restoring the original number of chromosomes.

Meiosis occurs in microspores mother cells which are diploid cells; to produce microspores or pollen grains. Each microspore mother cell produces four microspores after a meiotic division.

Anther is the part of plant is suitable for the study of meiosis. A typical anther contains four microsporangia. The microsporangia form sacs or locules in the anther. The two separate locules on each side of an anther may fuse into a single locule. Each microsporangium is lined with a nutritive tissue layer called as the tapetum and initially contains diploid pollen mother cells. These undergo meiosis to form haploid spores. The spores may remain attached to each other in a tetrad or separate after meiosis.

Meiosis occurs in reproductive cells. Microsporocytes (pollen mother cells) are the cells that undergo meiosis to produce microspores.

In flowering plants like tomatoes, meiosis occurs in the microspore mother cells (within the anther) and megaspore mother cells (within the ovule) to produce haploid spores.

One meiotic division of a microspore mother cell produces 4 pollen grains. Therefore, 1000 pollen grains require 1000 / 4 = 250 meiotic divisions.