Sexual Reproduction in
Flowering Plants
INTRODUCTION
yy Plants are a boon to the whole mankind. They
provide us with food, fruits, medicine fiber,
textile for humans. Thus, these plants need to
reproduce continuously so that the plants can be
maintained on the earth and the balance of the
ecosystem is maintained.
yy Plants reproduce asexually and sexually. The
propagules through which the plants reproduce
are the leaves, roots, stem while the reproductive
organ for sexual reproduction is the flower.
FLOWER-THE REPRODUCTIVE ORGAN OF A
PLANT
yy Flowers have been of great importance to
humans.
yy It has aesthetic, ornamental, social, cultural and
religious values.
yy Flowers are structurally divided into the following
different whorls:
○○ Calyx-group of sepals, usually green in colour.
○○ Corolla-group of petals, brightly coloured
except green.
Sexual Reproduction in Flowering Plants
1.
, ○○ Androecium-male reproductive part of a
flower consisting of the stamen having Gray Matter Alert!!!
filament and anther.
Exceptions: Moringa and
○○ Gynoecium-female reproductive part of a
Wolfia-Each anther lobe has one
flower known as pistil or carpel consisting of
microsporangium
stigma, style and ovary.
Arceuthobium-One
yy There are many structural and hormonal changes
microsporangium per anther.
that take place in the formation of the flower.
yy These changes lead to the modification of the
floral primordium and thus the arrangement of
the different whorls of the flower.
yy Sexual reproduction in flowering plants has been
divided into the following events:
○○ Pre–Fertilisation: Structures and Events
○○ Fertilisation Event
○○ Post–Fertilisation: Structures and Events
PRE–FERTILISATION: STRUCTURES AND EVENTS
STRUCTURE OF STAMEN
yy Stamen consists of two parts-
yy Filament–Sterile part which connects the anther
to the thalamus or petals of the flower.
yy Anther-Fertile part, within which are formed the
pollen grains.
yy Anther is usually bilobed, each lobe has two
theca and thus known as dithecous. Each theca
has two microsporangia (four in total) and thus
a typical angiosperm anther is tetrasporangiate.
yy Each microsporangium develops and become
Sexual Reproduction in Flowering Plants
the pollen sac that produces a large number of
microspores known as pollen grains.
Definition
ANTHER DEVELOPMENT
yy Anther is parenchymatous in nature.
Microsporangium: Structure
yy Hypodermal archesporial cells are differentiated,
formed in the anther of the
one in each angle. Each archesporial cell
flowering plants where the
undergoes a periclinal division to form an
development and maturation of
outer primary parietal cell and inner primary
microspores into pollen grains
sporogenous cell.
take place.
yy The primary parietal cell undergoes divisions to
form 3-5 layered anther wall.
2.
, Wall Layers
Epidermis Previous Year’s Question
yy Outermost wall layer of the anther. It is protective
in function. Product of sexual reproduction
generally generates
Endothecium (1) new genetic combinations
yy The endothecial cells develop a fibrous thickening leading to variations
before the dehiscence of the anther. (2) large biomass
yy It occurs in the form of radial bands on the
(3) longer viability of seeds
tangential wall.
(4) prolonged dormancy
yy This thickening is made-up of a-cellulose with
a little pectin and lignin in some cases. It is
hygroscopic in nature.
Rack Your Brain
yy It helps in the dehiscence of the anther and
dispersal of pollen grains.
Which type of plants do not have
endothecium layers?
Middle layers
yy Middle layers may range from 1-6 or in some
cases, several middle layers are present.
Previous Year’s Question
yy Middle layers degenerate at maturity of the
anther. Which one of the following is
yy They provide nutrition and also help in the surrounded by a callose wall?
formation of pollenkitt. (1) Male gamete (2) Egg
(3) Pollen grain (4) MMC
Sexual Reproduction in Flowering Plants
3.
, Tapetum
yy It is the innermost layer of the anther. Provides Definition
nourishment to developing pollen grains. The
tapetum is of two types: Microsporogenesis: Different
○○ Amoeboid or periplasmodial or invasive: events through which haploid
Tapetal cells break up releasing the microspores are formed in the
protoplast into the pollen chamber. microsporangium.
All such protoplasts now fuse to form
periplasmodium. Microspore mother cells
get surrounded by periplasmodium.
○○ Secretory or glandular or parietal:
Tapetal cells remain throughout the
development of microspores and finally
they degenerate.
Sporogenous Tissue
yy The sporogenous tissue formed from the
archesporial cell divides to form the pollen grain
through a process known as microsporogenesis.
yy The primary sporogenous cells divide by mitosis
to form a mass of sporogenous tissue.
yy The sporogenous tissue divides by mitosis to
form microspore mother cell or pollen mother
cell (PMC).
yy These PMCs undergo meiosis and produce a
tetrad of microspores. Callose gets deposited
over microspores and they are arranged in tetrad
in following ways-
○○ Tetrahedral
○○ Isobilateral
○○ Decussate
○○ Linear
Sexual Reproduction in Flowering Plants
○○ T-Shaped
yy These microspores separate out and produce the
pollen grains.
4.
Flowering Plants
INTRODUCTION
yy Plants are a boon to the whole mankind. They
provide us with food, fruits, medicine fiber,
textile for humans. Thus, these plants need to
reproduce continuously so that the plants can be
maintained on the earth and the balance of the
ecosystem is maintained.
yy Plants reproduce asexually and sexually. The
propagules through which the plants reproduce
are the leaves, roots, stem while the reproductive
organ for sexual reproduction is the flower.
FLOWER-THE REPRODUCTIVE ORGAN OF A
PLANT
yy Flowers have been of great importance to
humans.
yy It has aesthetic, ornamental, social, cultural and
religious values.
yy Flowers are structurally divided into the following
different whorls:
○○ Calyx-group of sepals, usually green in colour.
○○ Corolla-group of petals, brightly coloured
except green.
Sexual Reproduction in Flowering Plants
1.
, ○○ Androecium-male reproductive part of a
flower consisting of the stamen having Gray Matter Alert!!!
filament and anther.
Exceptions: Moringa and
○○ Gynoecium-female reproductive part of a
Wolfia-Each anther lobe has one
flower known as pistil or carpel consisting of
microsporangium
stigma, style and ovary.
Arceuthobium-One
yy There are many structural and hormonal changes
microsporangium per anther.
that take place in the formation of the flower.
yy These changes lead to the modification of the
floral primordium and thus the arrangement of
the different whorls of the flower.
yy Sexual reproduction in flowering plants has been
divided into the following events:
○○ Pre–Fertilisation: Structures and Events
○○ Fertilisation Event
○○ Post–Fertilisation: Structures and Events
PRE–FERTILISATION: STRUCTURES AND EVENTS
STRUCTURE OF STAMEN
yy Stamen consists of two parts-
yy Filament–Sterile part which connects the anther
to the thalamus or petals of the flower.
yy Anther-Fertile part, within which are formed the
pollen grains.
yy Anther is usually bilobed, each lobe has two
theca and thus known as dithecous. Each theca
has two microsporangia (four in total) and thus
a typical angiosperm anther is tetrasporangiate.
yy Each microsporangium develops and become
Sexual Reproduction in Flowering Plants
the pollen sac that produces a large number of
microspores known as pollen grains.
Definition
ANTHER DEVELOPMENT
yy Anther is parenchymatous in nature.
Microsporangium: Structure
yy Hypodermal archesporial cells are differentiated,
formed in the anther of the
one in each angle. Each archesporial cell
flowering plants where the
undergoes a periclinal division to form an
development and maturation of
outer primary parietal cell and inner primary
microspores into pollen grains
sporogenous cell.
take place.
yy The primary parietal cell undergoes divisions to
form 3-5 layered anther wall.
2.
, Wall Layers
Epidermis Previous Year’s Question
yy Outermost wall layer of the anther. It is protective
in function. Product of sexual reproduction
generally generates
Endothecium (1) new genetic combinations
yy The endothecial cells develop a fibrous thickening leading to variations
before the dehiscence of the anther. (2) large biomass
yy It occurs in the form of radial bands on the
(3) longer viability of seeds
tangential wall.
(4) prolonged dormancy
yy This thickening is made-up of a-cellulose with
a little pectin and lignin in some cases. It is
hygroscopic in nature.
Rack Your Brain
yy It helps in the dehiscence of the anther and
dispersal of pollen grains.
Which type of plants do not have
endothecium layers?
Middle layers
yy Middle layers may range from 1-6 or in some
cases, several middle layers are present.
Previous Year’s Question
yy Middle layers degenerate at maturity of the
anther. Which one of the following is
yy They provide nutrition and also help in the surrounded by a callose wall?
formation of pollenkitt. (1) Male gamete (2) Egg
(3) Pollen grain (4) MMC
Sexual Reproduction in Flowering Plants
3.
, Tapetum
yy It is the innermost layer of the anther. Provides Definition
nourishment to developing pollen grains. The
tapetum is of two types: Microsporogenesis: Different
○○ Amoeboid or periplasmodial or invasive: events through which haploid
Tapetal cells break up releasing the microspores are formed in the
protoplast into the pollen chamber. microsporangium.
All such protoplasts now fuse to form
periplasmodium. Microspore mother cells
get surrounded by periplasmodium.
○○ Secretory or glandular or parietal:
Tapetal cells remain throughout the
development of microspores and finally
they degenerate.
Sporogenous Tissue
yy The sporogenous tissue formed from the
archesporial cell divides to form the pollen grain
through a process known as microsporogenesis.
yy The primary sporogenous cells divide by mitosis
to form a mass of sporogenous tissue.
yy The sporogenous tissue divides by mitosis to
form microspore mother cell or pollen mother
cell (PMC).
yy These PMCs undergo meiosis and produce a
tetrad of microspores. Callose gets deposited
over microspores and they are arranged in tetrad
in following ways-
○○ Tetrahedral
○○ Isobilateral
○○ Decussate
○○ Linear
Sexual Reproduction in Flowering Plants
○○ T-Shaped
yy These microspores separate out and produce the
pollen grains.
4.
