Class Tutorial B.Sc(Botany)Part-II Microsporogenesis

Dr. Devanand kumar Department of Botany B.N college, Patna University, Patna Microsporogenesis • The male and female reproductive structure in the flower is called androecium and the gynoecium respectively. • The androecium consists of a whorl of stamens representing the male reproductive organ of the flower. • Stamen or microsporophyll is the male reproductive structure of an angiosperms. • A typical stamen has three parts, the elongated stalk called filament, at the tip of filament the bilobed structure is called anther and connective which joins the lobes of the anther. Microsporogenesis Microsporogenesis • Each lobe of anther has two pollen sacs or microsporangia. A complite anther has four microsporangia, thus tetrasporangiate or dithecous. • Microspores or pollen grains are developed within the microsporangia i.e. anther lobe of stamen. • A very young anther is made up of homogeneous meristematic cells. • Gradually the anther becomes a four lobed structure. Microsporogenesis Microsporogenesis • The hypodermal cells of each lobe become differentiated by their shape and dense contents with distinct nucleus, and are called archesporium or archesporial cells. • The archesporial cells divide to form an outter primary partietal cell layer and inner primary sporogenous cell layer. • Cells of primary partietal layer divide periclinally and anticlinally giving rise to multilayered anther wall-i.e. epidermis, endothecium, middle layer and tapetum Microsporogenesis • Epidermis-outtermost layer, single layered flattened cells. • Endothecium-Single layered, radially elongated cells, has thin layer area called stomium helps in dehisence of anther. • Middle layer-2-3 layers of flattened cells inner to endothecium. • Tapetum-Innermost layer, single layer of cells with dense cytoplasm and prominent nuclei, provide nutrition to developing microspores. Microsporogenesis Microsporogenesis • The cells of primary sporogenous layer direcly functions as spore mother cell or may divide further by mitosis to form diploid sporogenous tissue which then forms microspore mother cells or pollen mother cell (MMC or PMC) • PMC divide by meiosis to haploid microspores or pollen grains arranged. • Microspores are arranged tetraheadrally. • Cells of the tetrad completely separate from each other and develop into mature pollen grains or microspores. • These microspores germinate and produce male gametophyte. Microsporogenesis References

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