ABSTRACT
Pollen grain, the male gametophyte, in flowering plants is a microscopic two-or threecelled structure, and its primary function is to deliver male gametes (sperm cells) to the female reproductive organ, the carpel. Pollen grains are highly desiccated structures when mature and contain either two cells, a vegetative cell and a generative cell; the latter divides to form two sperm cells before germination, or three cells: a vegetative cell and two sperm cells. Pollen are produced in large numbers in the anther of a stamen and may be carried long distance by wind, insects, or other animals for fertilization. Pollen grains have a thick outer protective wall, the exine (1,2), which contains sporopollenin, a complex polymer that makes the pollen resistant to decay, a useful feature for pollen storage and function. The exine also forms a distinct sculpturing pattern on the pollen surface that is characteristic of a plant species (2). Since plants are sedentary organisms, they are entirely dependent on pollen for the transport of sperm cells either to the carpel of the same flower in which they are produced (self-pollination) or to a flower of another plant (cross-pollination) of the same species. Thus, pollen development is crucial for successful sexual reproduction in angiosperms, and for subsequent fruit and seed development. In addition, pollen grains are of direct, or indirect, importance in several areas of human interest, e.g., in honey production, in pharmaceutical products, in pollen allergens, and as food supplement (see e.g., 3-5).
