Microsporogenesis

Microsporogenesis is the process by which the diploid microspore mother cells contained in the sporogenous tissue of the anther undergo meiotic division to produce a tetrad of four haploid microspores, the cells that will go on to become pollen grains. Because meiosis, not mitosis, drives this division, each resulting microspore carries only half the parental chromosome number, and the process is the direct source of genetic variation transmitted through the male line.

Structure of microspore : A mature, released pollen grain is a non-motile, unicellular, haploid structure containing a single nucleus. It is enclosed by a two-layered wall known collectively as the sporoderm:

• The exine, the tough outer layer, is built from an extremely resistant, chemically inert biopolymer called sporopollenin, which does not degrade under normal chemical or biological attack. Its surface may be smooth or elaborately sculptured in a pattern characteristic of the species, which is why fossilised pollen grains can survive largely intact for very long periods and are useful in palynology. At certain points the exine is markedly thin, leaving thin regions called germ pores; these are the sites through which the pollen tube will later emerge during germination.
• The intine, the inner wall layer, is thinner and composed of cellulose and pectin, materials that are readily broken down when the pollen tube needs to emerge through a germ pore.