BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VIII. BASICS OF PLANT MORPHOLOGY AND ANATOMY

Features of reproduction in angiosperms

Development of the male gametophyte

As a result of two mitotic divisions, the male gametophyte (pollen) develops from the microspore, forming two male Gametes. During the first division, the microspore Cell gives rise to a pollen grain consisting of two Cells of different sizes. The smaller (generative) cell is embedded within the larger (vegetative), highly vacuolated tube cell.

The microspore wall (sporoderm) differentiates into the intine and exine. The intine is the inner layer of the pollen grain wall from which the pollen tube wall is formed.

The exine is the outer layer of the pollen grain wall, consisting of the ectexine, mesexine, and endexine. The ectexine is the most resistant part of the exine, and its surface is characterized by a specific sculpture. The exine features unthickened areas known as apertures (pores or furrows), through which the intine protrudes during pollen tube germination. Apertures can appear as pores or furrows. Depending on the number of pores, pollen is classified as monoporate, triporate, or multiporate, and based on the number of furrows, as monosulcate, trisulcate, or multisulcate.

The subsequent fate of these cells differs. During pollen germination, the vegetative cell exerts pressure on the inner wall of the pollen grain, causing it to protrude through a pore in the outer wall and form the walls of the pollen tube, which grows at the expense of the vegetative cell. Its precise role after entering the pollen tube remains unclear; the hypothesis that it stimulates the apical growth of the pollen tube has not been confirmed. The generative cell moves into the pollen tube following the vegetative cell and undergoes mitotic division to form two non-flagellated male gametes, or sperm cells. In some cases, sperm cells are formed while still inside the pollen grain.