DIFFERENTIATION OF GENERATIVE AND VEGETATIVE CELLS IN ANGIOSPERM POLLEN

Cellular differentiation of a generative and a vegetative cell is an i mportant event during microspore and pollen development and is requisi te for double fertilization in angiosperms. The generative cell produc es two sperm cells, or male gametes, whereas the vegetative cell produ ces an elongated pollen tube, a gametophytic cell, to deliver the male gametes to the embryo sac. For typical differentiation of the gametic and gametophytic cells, cell polarity, including nuclear positioning, must be established prior to microspore mitosis and be maintained dur ing mitosis. Microtubules are closely involved in the process of asymm etric cell division. On the other hand, alteration of the chromatin co mposition seems to be responsible for the differential gene expression between the generative and vegetative cells. Cytoplasmic regulatory m olecules, which affect chromatin configuration, are postulated to be u nequally distributed to the two cells at the asymmetric cell division. Thus, typical differentiation of the cells is accomplished by a cellu lar mechanism and a molecular mechanism, which might be independent of each other. These results are discussed in relation to one model that accounts for the different fates of generative and vegetative cells d uring sexual plant reproduction.