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

VIII. BASICS OF PLANT MORPHOLOGY AND ANATOMY

Features of angiosperm reproduction

Structure of the anther, microsporogenesis, formation of the male gametophyte, and gametogenesis

The anther and microsporogenesis. As the stamen develops, processes that lead to The formation of the anther begin very early within it (Fig. 82). Beneath the epidermis of the future anther, four groups of Cells with large nuclei and dense Cytoplasm appear. These cells give rise to four microsporangia. The division and growth of the microsporangium cells are accompanied by their subsequent differentiation: the peripheral cells remain sterile, while the internal ones give rise to primary sporogenous cells. The peripheral cells form the wall of the microsporangium, the cells of which differentiate into three layers: the outer (endothecium), the middle, and the inner (tapetum).

The endothecium cells lie immediately beneath the epidermis on the inner side. They have uneven (horseshoe-shaped) thickenings that facilitate anther dehiscence. The endothecium is also referred to as the fibrous layer.

The Cells of the middle layer are tabular and thin-walled. During microspore formation, they stretch, become compressed, and in many plants disintegrate altogether.

The tapetum consists of a single layer, or less frequently multiple layers, of tabular, thin-walled, uni-, bi-, or multinucleated cells with dense cytoplasm. Two MAIN TYPES OF tapetum are distinguished: secretory or glandular (granular), and amoeboid or periplasmodial.

Microsporogenesis occurs in parallel with the Differentiation of the microsporangium wall cells. At the same time, through a series of successive mitotic divisions, the primary sporogenous cells transform into microsporocytes, or microspore mother (archesporial) cells. As a result of Meiosis, the latter form tetrads of haploid microspores. By the end of meiosis, the sporoderm—the microspore wall—is formed.