Introduction to Sexual Reproduction in Flowering Plants, Flower, Structure of Flower, Male Reproductive Part of Flower (Stamens), Development of Anther walls, Anther Walls, Microsporangium (Pollen Sac)

1. Sexual Reproduction in
Flowering Plants
Part - I
Presented by:
ShashankTripathi

2. What are flowering plants??
• Flowering plants are a type of vascular plants that produces flowers in order
to reproduce.
• Flowering plants are the largest grouping under the division Angiosperms
within the plant kingdom (Kingdom Plantae or Viridiplantae) in terms of the
numbers of described species.
• Approximately 260,000 species of flowering plant have been named so far,
constituting nearly 90% of all known species of plants
• Flowering plants produce seeds within a fruit.

3. Flower:
• The reproductive structure of angiosperms, characteristically having either
specialized male or female organs or both male and female organs, such as
stamens and a pistil, enclosed in an outer envelope of petals and sepals.
• Flowers are morphological and embryological wonders and the sites of sexual
reproduction (NCERT).
• The flower is generally defined as a highly specialized reproductive shoot,
comparable to leaves- bearing shoot.
• The sepals and petals may be regarded as modified leaves.
• Stamens and carpels also show some resemblance to leaves in position,
arrangement, internal structure and development.
• Flowers of eudicots are organized into four concentric whorls of organs
(sepals, petals, stamens, and carpels) that arise sequentially from the floral
meristem

4. Structure of a typical flower:
Parts of Flower
Accessory Parts
Calyx
Corolla
Nectar Glands
Reproductive
Parts
Androecium
Gynoecium
Reproductive Parts: Which are
directly involved in reproduction
and perform the Sexual events.
Accessory Parts: Which are
involved in the facilitating the
processes of reproductive parts.
Calyx: The group of Sepals
Corolla: The groups of petals
Androecium: Group of Stamens (Male
reproductive part)
Gynoecium: The group of Pistils or
Carpels (Female reproductive parts)
If a flower is bisexual or monoecious androecium &
Gynoecium will be found in the same body but if its
Dioecious i.e., Unisexual Flower either be Staminate or
Pistillate.

5. Accessory Parts of a typical flower
Pedicel or Peduncle: It is the stem to
which a flower is attached with the plant body.
Receptacles: The receptacle or torus is the
thickened part of a stem (pedicel) from which
the flower organs grow.
Petals: Petals are modified leaves that
surround the reproductive parts of flowers.
These are the units of Corolla and mostly
colorful whorls.
Sepals: These are leaf like and the outermost
green whorl of a flower. A group
of sepals enclose a developing bud and are
mostly green in color.

6. Reproductive Parts of Flower:
Stamens: The stamen (plural
stamina or stamens) is the pollen-
producing reproductive organ of a
flower. Collectively
the stamens form the androecium.
Carpels or Pistils: Carpels are
the basic units of the gynoecium and
may be free (distinct) or fused
(connate).
The term pistil is used in a similar
manner to carpel – in some
situations the terms are equivalent
in meaning but not in others.
Pistil
Stamens

7. Male reproductive part of Flower: The Stamens
• A Stamen has two parts-
Filament: The filament is a long
and slender stalk-like structure that
attaches to the base of the flower and
supports the anther
• Proximal end of the filament is
connected with the receptacle or
Petal, while the distal end with
anther.
Anther: This is the knob like part
of the stamen where pollen is
produced. It can be consider as the
spore case of the flower.

8. How does an Anther look like??
• Each anther consists of two lobes (anther lobes) i.e., bilobed, with each lobe
having two theca, i.e., they are dithecous.
• Each lobe of anther is connected by a connective which can be clearly seen
on the dorsal side as an extension of the filament.
• Each anther lobe, again, has two pollen sacs or pollen chambers placed
longitudinally.
• There are longitudinal grooves or sutures along the ventral face of the
anther demarcating the pollen chambers.
• Each pollen chamber represents a microsporangium and contains
innumerable microspores or pollens.
• Therefore, commonly, a stamen is a microsporophyll bearing four
microsporangia, i.e., the anther is tetrasporangiate.

9. Structure of Microsporangium
In a transvers section, a typical
microsporangium appears near circular
in outline.
It is generally surrounded by four wall
layers of anther:
• The epidermis;
• Endothecium;
• Middle layers; and
• Tapetum;

10. Development of Anther:

11. Development of Anther:

12. Wall Layers of Anther
• Epidermis: It is the outer most protecting layer of anther madeup of Flattened cells.
• Endothecium: This is a single layer of radially elongated cells. These cells have band of
callose.
• Middle layers: There are 3-4 layers of thin walled cells, called middle layers. Generally, at
maturity these cells get crushed, but if persistent contain starch for the nutrition of
microspores.
• Tapetum: This is innermost layer containing single layer of cells having dense cytoplasm
and prominent nuclei. They surrounds the sporogenous tissues, and provide nutrition to
developing microspores. They secretes enzymes, IAA and food materials.
• On the basis of mode of function tapetum can be :
o Amoeboid: If cell wall rupture and protoplasmic strands are formed to provide nutrition to the
microspores. Or,
o Secretory: If the cells do not rupture and remain intact and nutritional substance secretes from
the cells.

13. Thank you!