MICROSPOROGENESIS & TYPES OF MICTODPORE TETRADS

 

STD-12      UNIT-6  CHA-1

REPRODUCTION IN ORGANISMS 

Microsporogenesis ( Development of Pollen grains )

• Sporogenous tissue fills the whole interior of a microsporangium . 
• Its cells divide with the growth of anther and increase their number. Ultimately they are transformed into microspore or pollen mother cells  ( PMC ) . 
• The latter are diploid , that is , they possess two genomes or sets of chromosomes .
• The microspore mother cells or microsporocytes develop an internal layer of callose ( B - 1 , 3 glucan ) wilich breaks the plasmodesmal connections among them . 
• The separated mother cells round off and undergo meiosis to produce tetrads of haploid microspores or pollen grains . 
• The phenomenon is called microsporogenesis . 

• The pollen grains of a tetrad grow and separate from one another . 

• Usually the arrangement of microspores in a telrad is tetrahedral ( most common type ) or isobilateral . However , decussate , linear and T - shaped tetrads are also found 
• In Aristolochia elegans , all the five type of tetrads have been recorded . Mostly , all the 4 nuclei in a tetrad remain functional to form 4 microspores .

• However , in Cyperaceae , only one functions and therefore , only one microspore instead of 4 is formed by one meiosis . 
• In some cases , all the 4 pollens remain attached forming compound pollen grains e.g. , Juncus , Jatropha , Typha . 

===========================================================

Mail- indiabiologymanishmevada@gmail.com

Subscribe and Follow For more knowledge of Biology

Manish Mevada

M.Sc, M.Phil, B.Ed

THANK YOU.