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Sexual Reproduction in Flowering PlantsPreFertilisation Events
● Several hormonal and structural changes result in the
development of a flower.
● Inflorescences bear the flower buds, and then the flowers.
● Flowers are the reproductive parts of a plant.
● In the flowers, the androecium (male reproductive part) and
the gynoecium (female reproductive part) develop.
Androecium
● The androecium consists of whorls of stamen.
● The stamen consists of the f
ilament
(long and slender
stalk) and
anther
(bilobed structure).
● Filament is attached to the thalamus or to the petal.
● Anther
:
○ A typical anther is bilobed and each lobe is dithecous
(consists of two theca).
○ Theca are separated by a longitudinal groove running
lengthwise.
, ○ The microsporangia are located at the corners, two in
each theca. They further develop to form pollen sacs,
which contain the pollen grains.
● Structure of microsporangium
○ The microsporangium is surrounded by four wall layers
(epidermis, endothecium, middle layers, and tapetum).
○ The outer three layers are protective and help in
dehiscence of anther to release the pollen grains. The
tapetum provides nourishment to the developing pollen
grains.
○ In the young anther, the sporogenous tissue forms the
centre of each microsporangium.
, Microsporogenesis
● It is the process of formation of microspore from PMC (Pollen
Mother Cells).
● As development occurs in the anther, the sporogenous
tissue undergoes meiosis to form microspore tetrad.
● Each cell of sporogenous tissue has capacity to give rise to a
tetrad. Hence, each cell is a potential pollen or PMC.
● As the anther matures, the microspores get detached from
each other and develop into pollen grains.
Pollen grains
● Represent the male gamete and are spherical, having a
twolayered wall:
○ Exine (outer) − Hard layer made of sporopollenin,
which is extremely resistant and can withstand high
temperatures, acidic and alkaline conditions, and
enzymes
○ Intine (inner) − Thin and continuous layer made up of
cellulose and pectin
● Mature pollen grain contains two cells:
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