Anther- and Pollen-Specific Gene Expression in Sunflower

Abstract

Among the living organisms plants have a unique life cycle characterized by an alternation of diploid and haploid generations. The role of the diploid sporophytic generation is to produce, following meiosis, haploid spores that develop into haploid male or female gametophytes. Specific cells of the gametophytes then differentiate into male or female gametes which fuse to yield a diploid embryo that finally grows into mature sporophyte. In flowering plants, the diploid, sporophytic generation is the dominant phase, whereas the haploid gametophyte is microscopic and consists of a very reduced number of cells: two or three in the case of the male gametophyte and seven (one of which being binucleate) in the case of the female gametophyte. The haploid male gametophytes, or pollen grains, are produced in the anthers, while the female gametophytes, or embryo sacs, develop in the ovaries (anthers and ovaries are diploid, sporophytic structures). In higher plants, the development of the male and female gametophytes is therefore closely associated with the development of sporophytic tissues. This contrasts with the situation in lower plants where the gametophytes can develop and live as independent free organisms.