STAMEN -MICROSPOROGENESIS -POLLEN GRAIN
Male reproductive part of a flower is androecium.
individual units of androecium -stamens
stamen consists of long lender stalk called filament anda terminal bilobed anther
typical anther is bilobed dithecousfour sided consists of four microsporangia which become p[olensacs with polen grains
STRUCTURE OF MICROSPORANGIA-
WALL LAYERS-epidermis ,endothecium ,middle layers( funtion -protection and dehiscence of anther) and tapetum(nourishes developing polllen grains)TAPETUM possess dense cytoplam and more than one nucleus .
SPOROGENOUS TISSUES - group of compactly arranged homogenous cells found at the microsporangia each cell capable of giving rise to mocrospore tetrad or pollen grains by meiosis (MICROSPORE MOTHER CELL)
MICROSPOROGENEIS -process of formation of micropores from MICROSPORE MOTHER CELL by MEIOIS
micropores are arranged in a cluster of four cells known as microspore tetrad ,as mature microspores dissociate and gives rise to pollen grains .
POLLEN GRAIN
male gametophyte ,spherical 25 -50 micrometer iin dia with 2 wall layers
EXINE- hard outer layer made upof SPOROPOLLENIN,(preserved in fossils )
GERM PORE -openings present on exine which help in pollen tube germination.
INTINE - inner continuous wall layer mae up of CELULOSE and PECTIN .
a mature pollen contains a large VEGETATIVE CELL an a smmall GENERATIIVE CELL
generative cell floats in the cytoplasm of vegetative cell and produces 2 male gametes .
pollen grains -rich in nutrients
used to increase performance of athlets and race horses(polen tablets)
cause allegies,bronchial afflictions ,respiratory disorders (asthma ,bronchitis)
pollen graiins as to reach on stigma before lose viabiility
wheat and rice -30 minutes .rosacea ,legumiinosae , solanaceae -months
pollen grains artiificially preserve in liquid ntrogen at -196 c
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