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

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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 • www.slm.ignou.com • www.biologydiscussion.com • www.askiitians.com.

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Topic: Microsporogenesis and Microgemetogenesis B.Sc. Botany (Hons.) II Paper: IV Group: B Dr
1 Topic: Microsporogenesis and Microgemetogenesis B.Sc. Botany (Hons.) II Paper: IV Group: B Dr. Sanjeev Kumar Vidyarthi Department of Botany Dr. L.K.V.D. College, Tajpur Microsporogenesis and Microgametogenesis Microsporogenesis Microspores i.e., the pollen grains are developed inside microsporangia. The microsporangia are developed inside the corners of the 4-lobed anther. Young anthers are more or less oblong in shape in section and made up of homogeneous mass of meristematic cells without intercellular space with further development, the anther becomes 4-lobed. The outer layer of anther is called epidermis. Below the epidermis, at each corner, some cells become differentiated from others by their dense protoplasm- archesporium or archesporial cells. Each archesporial cell then divides mitotically and forms an outer primary parietal cell and an inner primary sporogenous cell. The outer primary parietal cells form primary parietal cell layer at each corner. Below the parietal cell layer, the primary sporogenous cells remain in groups i.e., the sporogenous tissue. The cells of primary parietal layer then divide both periclinally and anticlinally and form multilayered antheridial wall. The innermost layer of antheridial wall, which remains in close contact with the sporogenous tissue, functions as nutritive layer, called tapetum. The primary sporogenous cells either directly function as spore mother cells or divide mitotically into a number of cells which function as spore mother cells. The spore mother cell undergoes meiotic division and gives rise to 4 microspores arranged tetrahedrally. Structure of Microspores Dr. Sanjeev Kumar Vidyarthi, Dept. of Botany, Dr. L.K.V.D. College, Tajpur 2 Microspore i.e., the pollen grain is the first cell of the male gametophyte, which contains only one haploid nucleus.
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