Gametophytic and Sporophytic Gene Expression in Helianthus annuus L.

Abstract

The life cycle of plants is characterized by an alternation of haploid and diploid generations. In the haploid organism (gametophyte), specific cells differentiate into male and/or female gametes which, upon fusion, yield a diploid zygote that develops into an adult diploid organism, the sporophyte. The sporophyte, in turn, generates special cells which, through meiosis, produce haploid spores developing into haploid gametophytes. In some plants, both the haploid and diploid forms are free-living green organisms of substantial size. In ferns, for example, both the gametophyte and sporophyte forms are independent green plants. In other plants, one phase dominates and becomes the recognizable plant while the other is reduced and inconspicuous and depends on the dominant one for nutrition and physical support. In some plants, such as mosses, the haploid gametophyte is the dominant phase. In seed plants, however, the diploid sporophyte is the dominant phase, whereas the gametophyte is reduced to a few cells: two or three for the male gametophyte, also known as pollen grain, and seven cells for the female gametophyte, or embryo sac.