Question

Class XII problem

What is microsporogenesis? Where does it occur in angiosperms?

Answer 1

Microsporogenesis The pollen sacs represent microsporangia. Thus each anther has four microsporangia, two in each anther lobe. These are covered by the common epidermis of the anther. They contain pollen grains or microspores 1.  Very young anther consists of group of actively dividing parenchymatous cells surrounded by a layer of epidermis.
2.   It becomes two lobed; each anther lobe develops into two microsporangia in its two corners.
3.  In each lobe in the two corners one cell becomes conspicuous from the rest- archesporial cell.
4.  Archesporial cell divides to form an outer parietal cell and an inner sporogeneous cell
5.   Parietal cell divides to form concentric layers of pollen sac wall
6.  The pollen wall externally is made up of a single layered epidermis. Inner to the epidermis is a single layer of radially elongated cells with fibrous thickenings which help in dehiscence. The cells in the shallow groove between two microsporangia remains thin walled and form stomium. Inner to the endothecium lie three to four layers of thin walled cells occur in between which disintegrates in mature anthers. The innermost layer of cells with dense cytoplasm which nourishes developing pollen grains is called Tapetum.
7.       The primary sporogeneous cell divides to produce a mass of sporogeneous cell or microscopore mother cell.
8.       Microspore mother cell undergoes meiosis to give rise to four haploid microspores. The microspores are arranged in a cluster of four cells to form tetrad. As the anthers mature and dehydrate, microspore dissociates from each other and form pollen grains. In some microspores do not separate but together form compound pollen grains.