EFFECTS OF WATER-STRESS ON MALE GAMETOPHYTE DEVELOPMENT IN PLANTS

Male reproductive development in plants is highly sensitive to water d eficit during meiosis in the microspore mother cells. Water deficit du ring this stage inhibits further development of microspores or pollen grains, causing male sterility. Female fertility, in contrast, is quit e immune to stress. The injury is apparently not caused by desiccation of the reproductive tissue, but is an indirect consequence of water d eficit in the vegetative organs, such as leaves. The mechanism underly ing this stress response probably involves a long-distance signaling m olecule, originating in the organs that undergo water loss, and affect ing fertility in the reproductive tissue, which conserves its water st atus. Much research has been focused on the involvement of abscisic ac id in this regard, but the most recent evidence tends to reject a role for this hormone in the induction of male sterility. Stress-induced a rrest of male gametophyte development is preceded by disturbances in c arbohydrate metabolism and distribution within anthers, and an inhibit ion of the key sugar-cleaving enzyme, acid invertase. Since invertase gene expression can be modulated by sugar concentration, it is possibl e that decreased sugar delivery to reproductive tissue upon inhibition of photosynthesis by stress is the signal that triggers metabolic les ions leading to failure of male gametophyte development.