Question

Describe in sequence the events that lead to the development of a 3 celled pollen grain from microspore mother cell in angiosperms.

Answer 1

When the anther is young, a group of compactly arranged homogenous cells called the sporogenous tissue occupies the center of each microsporangium. As the anther develops, the cells of sporogenous tissue undergo meiotic divisions to form microspore tetrads. As each cell of the sporogenous tissue is capable of giving rise to a microspore tetrad. Each one is potential pollen or microspore mother cell(PMC). The process of formation of microspores from a mother cell through meiosis is called microsporogenesis. The microspores, as they are formed, are arranged in a cluster of four cells- the microspore tetrad. As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains. Inside each microsporangium, several thousands of microspores or pollen grains are formed that are released with the dehiscence of anther. The cytoplasm of the pollen grain is surrounded by a plasma membrane. When the pollen grain is mature it contains two cells, the vegetative cell, and a generative cell. The pollen grain germinates on the stigma to produce a pollen tube through one of the germ pores. In over 60% of angiosperms, pollen grains are shed at this 2- celled stage. In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed(3-celled stage).