Friday, July 21, 2017

DEVELOPMENT OF ANTHER (Biology)


Sexual Reproduction
In Angisoperms, the main plant body is sporophytic (2n) which is differentiated into root, stem and leaves. Flower
is concerned with sexual reproduction.
Camerarius : discovered that flowers are the reproductive organs associated with the sexuality.
Male Reproductive Structure : It is stamen or microsporophyll.
It consists of filament and anther. The proximal end of the filament is attached to thalamus or pedicel and distal end
is attached to anther lobes. Anther is tetrasporangiate and tetragonal. It is eusporangiate. Longitudinal groove runs
lengthwise separating the theca. Anther consists of two anther lobes (bithecous) or one anther lobe (monothecous).
Development of anther
The young anther is represented by only a group of parenchymatous cells surrounded by epidermis. It soon
becomes four lobed. In each of the four lobes, some of the hypodermal cells begin to act at archesporial initials.
Each archesporial initial divides into an outer primary parietal cell and an inner primary sporogenous cell.
The primary parietal cell divides to form 3-5 wall layers, I. e. Endothecium, middle layers and tapetum. The
primary sporogenous cells divide to produce a mass of sporogenous cells or microsporocytes . The sporogenous
cells undergo a few mitotic divisions simultaneously with the growth of anther. These derivatives function as Microspore mother cells.
Structure of Anther
A mature anther is made of the anther wall and the pollen chamber (microsporangia)
Wall of the anther
The anther wall consists of four layers. These are epidermis, endothecium, middle layers and tapetum.
(i) Epidermis This is the outermost layer. It is only one cell in thickness.
(ii) Endothecium : Inner to epidermis is single layered endothecium. The cells of endothecium are tangentially
elongated and are having fibrous thickenng arising from their inner walls. These fibrous thickenings are
of α-cellulose and help in dehiscence of anther.

(iii) Middle layers : Inner to endothecium are middle layers, which are variable, I. e., 1-4.

 Disintegration of these middle layers usually occurs at maturity.
 They provide nourishment to the pollens on degeneration. Absent in the members of Lemnaceae
and Najadaceae.
iv) Tapetum : This is the innermost layer of the anther wall. The cells are multinucleate.
· These provide nutrition to the developing microspores.

· Tapetum, therefore, secretes both enzymes and hormones.

· Cells of tapetum shows endomitosis and polyteny.

Tapetum cells are of two types

Secretory or glandular The cells of this type of tapetum remain in contact with the anther
wall throughout.
Amoeboid or plasmodial tapetum The cells of this type of tapetum separate from the wall
and move freely is the pollen chamber.

· Tapetum providing nourishment to sporogenous cell, microspore mother cell and pollen grains.

· Takes part in secretion of enzymes, hormones (IAA) and formation of pollenkitt on the
entomophilous pollen grain.
· It forms Ubisch bodies (orbicules) with sporopollenin which help in formation of exine of the pollen
grain.
The pollen chamber
This forms the centre cavity of the anther lobe.The process of microsporogenesis takes in this region.