What is Gametophyte?

Aug 09, 2022, 16:45 IST

What is Gametophyte? 

Internal Structure of Anther or Structure of Microsporangium

Pollen sac present in stamen is multilayered structure.

Outermost layer of the wall of pollen sac is called

Stomium is the site of dehiscence.

The next layer of cells arising from inner side is called endothecium and the cells has fibrous thickenings. Endothecium helps in dehiscence of anther and consequent liberation of pollen grains.

Beneath the endothecium are present one to five layers of cells called middle layer. Resolve all Biology Doubts from Physics Wallah

Innermost layer of anther (i.e, below middle layer) is tapetum, which is characterized by either polyploidy or multinucleate cells. Tapetum provides nutrition to the developing pollen grains.

Microsporogenous (or Ararchesporium) tissues are present at centre, which are surrounded by tapetum. Microsporogenous tissue after differentiation produce microspore mother cells or pollen mother cells which undergoes meiosis to form haploid microspores or pollen grains.

The development of microsporangia is eusperangiate

Development of microspore mother cell

1. Certain cells of hypodermis of anther wall, begin to enlarge, becomes denser than the neighbouring cells. These cells are now said to be archesporial initials.
2. Archesporial initials divide periclinally to form primary parietal layer towards outside and primary microsporogenous cells towards the inner side.
3. Primary parietal layer undergo periclinal division to form outer and inner secondary parietal layer
4. Primary parietal layer undergoes periclinal and anticlinal division to form outer layer, endothecium and innermost layer, tapetum. Between these two, middle layer is formed.
5. According to the Davis and Sampson there are four types of anther wall developmen.   
6. Basic type

            Formation of middle layer occurs by outer and inner secondary parietal layer one by each.

1. b) Dicotyledonous type

            Middle layers are contributed only by outer secondary parietal layer.

1. c) Monocotyledonous type

            Here middle layers are contributed by only inner secondary parietal layer.

1. d) Reduced type

            Middle layer is absent.

Different stages of the development of anther:

A) T.S. of young anther; B) Differentiated archesporial cells; C) Differentiated primary parietal cells and primary microsporogenous cells; D) T.S. of young anther showing four microsporangia and vascular bundle; E) Detailed structure of one microsporangium; F) A portion of microsporangium showing details

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