Saturday, 10 March 2012

MICROSPORANGIUM: Meaning, structure, origin, development, function & signinficance


DEVELOPMENT OF MICROSPORANGIUM


In a huge mass of cells, few cells in the hypodermal region become differentiated, by their large size, radial growth and dense cytoplasm and conspicuous nuclei. They make the archisporium. Generally archisporium consists of 2-3 cell wide plate running along the entire length of the lobe.

The micro sporangial initials (archisporial cells) divide periclinally forming a primary parietal layer and primary sporogenous layer. The cells of the primary parietal layer laying immediately beneath the epidermis divide repeatedly both periclinally and anticlinally giving rise to 3-5 concentric layers forming the wall of the young sporangium.

Cells of the epidermis divide anticlinally only. The cells thus formed become greatly stretched and flattened. Sometimes its cells may be generally lignified or cutinized.
The layer next to the epidermis is the endothecium or fibrous layer. As a rule, by the development of fibrous bands of thickening the endothecium is hygroscopic and is therefore mainly responsible for the dehiscence of the mature anther
.
             NOTE: The cells of the endothecium are thin walled along the line of dehiscence of each anther lobe. The opening through which the pollen grains are discharged from pollen sac is called STROMIUM.
The inner most layer of the wall layer develops into a single layered tapetum. The tapetal layer has dense cytoplasm and conspicuous nuclei. Tapetum makes a nutritive layer for the developing microspores.




FORMATION OF ANTHER LOBES FROM UNDIFFERENTIATED MASS OF CELLS


  In meantime, the primary sporogenous layer cells give rise to microspore mother cell (mmc) or the pollen mother cells. In the beginning mmc remains closely packed but as anther enlarges in size, the pollen sac also increases in size, the mmc also increases in size and becomes spherical in shape and gets loosely arranged. 



MATURED ANTHER





MATURED ANTHER









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