01} Reproduction in lower & higher plants part 3 ~ Microsporogenesis.

01 Reproduction in Lower and Higher Plants - part 03 - Microsporogenesis


Microsporogenesis : 
  • Each microspore mother cell divides meiotically to form tetrad of haploid microspores (pollen grains). 
Structure of microspore : 
  • Typical pollen grain is a non-motile, haploid, unicellular body with single nucleus.
  • It is surrounded by a two layered wall called sporoderm. 
  • The outer layer exine is thick and made up of complex, non-biodegradable, substance called sporopollenin. 
  • It may be smooth or with a sculptured pattern (characteristic of the species).
  • It is resistant to chemicals. At some places exine is very thin showing thin areas known as germ-pores. 
  • These are meant for the growth of emerging pollen tube during germination of pollen grain. 
  • The inner wall layer, intine consists of cellulose and pectin.
Always Remember : · 
  • Pollen viability (viability is the functional ablity of pollen grain to germinate to develop male gametophyte) depends upon environmental conditions of temperature and humidity. 
  • It is 30 minutes in rice and wheat. 
  • But in some members of family Solanaceae, Rosaceae, Leguminosae, it lasts even for months.
Development of male gametophyte : 

  • Pollen grain marks the begining of male gametophyte. 
  • It undergoes first mitotic division to produce bigger, naked vegetative cell and small, thin walled generative cell. 
  • The generative cell floats in the cytoplasm of vegetative cell.
  • The second mitotic divisionis concerned with generative cell only and gives rise to two non-motile male gametes. 
  • The mitotic division of generative cell takes place either in pollen grain or in the pollen tube. 
  • The pollen grains are shed from the anther, at this two- celled stagein most of the angiosperms
  • Female reproductive whorl of flower is gynoecium (Pistil). 
  • Individual member of gynoecium is called carpel (megasporophyll). 
  • A flower with many, free carpels is called apocarpous (e.g. Michelia). 
  • A syncarpous flower is one that has many carpels fused together (e.g. Brinjal). 
  • Typical carpel has three parts viz, - 
  1. Ovary
  2. Style and 
  3. Stigma. 
  • The number of ovules in the ovary varies e.g. paddy, wheat and mango are uniovulate whereas tomato and lady's finger are multiovulate.




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