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a, oi ae, 4, = SEXUAL REPRODUCTION | IN FLOWERING PLANTS SEXUAL REPRODUCTION IN FLOWERING PLANTS bankofbiology.com > All flowering plants (angiosperms) show sexual reproduction. » Flowers are the sites of sexual reproduction. int chide heed en aaa PRE- FERTILIZATION: STRUCT URES & EVENTS” STRUCTURE OF A FLOWER A typical flower has 2 parts: ELLKOTLICLOGV.CCLu t PRE-FERTILIZATION: STRUCTURES & EVENTS Stigma bankofbiology.com : Style > Itis the male Filament reproductive part of the flower. » It consists of awhorl (o of stamens. Their a Anther number and I length are re variable in different species. Connective Microsporangium —— Filament Floral axis Articulation Nectary Pedicel Stamen PRE-FERTILIZATION: STRUCTURES & EVENTS / ~~ "y aN he oF) KX \ Ml ae J eS OW MA it \ WWW YY i] Vi i> My i i \ } f Filament t | bs (tally 7] © y « Filament is long and slender stalk. = Its proximal end is attached to the thalamus or the petal of flower. |, Line of dehiscence q PRE-FERTILIZATION: STRUCTURES & EVENTS Parts of a stamen — =) Filament \\HY « Terminal and typically bilobed. Each lobe has 2 thecae (dithecous). * Often a longitudinal groove runs lengthwise separating the theca. | Line of dehiscence | PRE-FERTILIZATION: STRUCTURES & EVENTS STRUCTURE OF AFLOWER > __1-Androscium | » Atypical microsporangium is near circular in outline. > It is surrounded by 4 wall layers: Epidermis “+ Endothecium “+ Middle layers : “ Tapetum > The outer 3 layers give protection and help in dehiscence of anther to release the pollen. _ Wanorate te __ PRE-FERTILIZATION: STRUCTURES & EVENTS i ronsen aan i Structure of Microsporangium > The tapetum (innermost layer) nourishes the developing pollen grains. » Cells of the tapetum contain dense cytoplasm and generally have more than one nucleus. » In young anther, each microsporangium has sporogenous tissue at centre. It consists of compactly arranged homogenous diploid cells (sporogenous cells). PRE-FERTILIZATION: STRUCTURES & EVENTS Microsporogenesis bankofbiology.com » As the anthers mature and dehydrate, the microspores dissociate from each other and develop into pollen grains. » Each microsporangium contains thousands of pollen grains. They are | : released with the dehiscence of any Warioustypes sof pollen anther. 5 grains- microscopic ‘ ) A mature dehisced anther | PRE-FERTILIZATION: STRUCTURES & EVENTS | Pollen grain (male gametophyte) >» Generally spherical. >» 25-50 mm in diameter. thickening » Cytoplasm is surrounded bya of cellulose plasma membrane. Exine >» Apollen grain has a two-layered ae wall: exine and intine. A pollen grain PRE-FERTILIZATION: STRUCTURES & EVENTS | Pollen grain (male gametophyte) Intine > The inner wall. thickening 7 =, Hy of cellulose > It is a thin and continuous layer made up of cellulose and pectin. A pollen grain | PRE-FERTILIZATION: STRUCTURES & EVENTS | Pollen grain (male gametophyte) bankofbiology.com A matured pollen grain contains 2 cells: * Vegetative cell: It is bigger, has abundant food reserve and a large shai irregularly shaped nucleus. of cellulose * Generative cell: It is small and floats in the cytoplasm of the vegetative cell. It is spindle shaped with dense Generative cell cytoplasm and a nucleus. Intine & xine A pollen grain PRE-FERTILIZATION: STRUCTURES & EVENTS STRUCTURE OF A FLOWER 1. Androecium : Pollen grain (male gametophyte) > The shed pollen grains have to land on the stigma before they lose viability. > The viability period of pollen grains is variable. It depends on temperature and humidity. > Viability of pollen grains of some cereals (rice, wheat etc.) is 30 minutes. Some members of Leguminoseae, Rosaceae & Solanaceae have viability for months. | PRE-FERTILIZATION: STRUCTURES & EVENTS mh, Vw Economic importance of pollen grains >» These are rich in nutrients. Pollen tablets are used as food supplements. Pollen / tablets & syrups increase performance of , athletes and race horses. » They are stored for years in liquid nitrogen (-196°C). They are used as pollen banks in crop breeding programmes. Pollen grains of some plants (e.g. Parthenium or carrot grass) are allergic for some people. It leads to chronic respiratory disorders - asthma, bronchitis, etc. € a 
