microgametophyte

Microgametophyte refers to the male gametophyte in seed plants. It is derived from a microspore produced by meiosis in a microsporangium and develops within the pollen grain. In both gymnosperms and angiosperms, microsporocytes undergo microsporogenesis to produce haploid microspores, which then mature into microgametophytes. The pollen grain typically has an outer wall composed of exine and an inner layer called the intine, and it is adapted for dispersal by wind or animals. A typical microgametophyte is multi-cellular, consisting of a vegetative (tube) cell and one or more sperm-forming cells.

In many angiosperms, the microgametophyte begins as a two-celled structure—the tube cell and a generative cell—that later divides to form two sperm cells within the pollen tube. In many gymnosperms, a similar arrangement is common, with the generative cell giving rise to sperm cells inside the pollen grain or within a pollen tube during germination. The development is generally completed before or during pollen grain germination.

Lifecycle and function: after pollination, the tube cell forms a pollen tube that grows through the stigma and style toward the ovule, delivering the sperm cells to the female gametophyte. Fertilization occurs when a sperm nucleus fuses with the egg nucleus to form a zygote; in angiosperms, double fertilization can lead to endosperm formation, whereas in gymnosperms fertilization yields a zygote with development supported by the surrounding female tissues.

Evolutionarily, microgametophytes in seed plants are highly reduced and dependent on the sporophyte, contrasting with the free-living microgametophytes of many non-seed plants.