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Index >> Nitrogen Fixation Symbiotic Blue-Green Algae >> Nitrogen Fixation and Assimilation

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Nitrogen Fixation by Symbiotic Blue-Green Algae Lichens Stages in Lichen RE Establishment Nitrogen Fixation and Assimilation

Nitrogen Fixation and Assimilation

	Nitrogen Fixation and Assimilation Nitrogen fixation by cyanobacteria in lichen thalli is generally 2-3 times greater than in free-living states as revealed by studies carried out with the cephalodium (structure containing nitrogen fixing blue-green alga) of Peltigera aphthosa and many other lichens. The cyanobiont (also called photobiont) of blue-green alga in cephalodia of P. aphthosa has low levels of glutamine synthetase (GS) and glutamate synthase (GOGAT) activity and hence unable to utilize all the ammonia derived from N2 fixation.
The excess ammonia diffuses out to cyanobiont and is absorbed by the mycobi0ont which incorporates it into glutamate via glutamic dehydrogenase. Since the cyanobiont does not incorporate nitrogen into its own cells, the cells get N starved and this physiological state triggers the development of more heterocysts formation accompanied by the rapid transfer of ammonia out of the cells into the mycobionts can explain the augmented rate of N2 fixation in symbiosis within the lichen thallus when compared to free blue-green alga in culture. The carbon and nitrogen interrelations in the cephalodium of Peltigera aphthosa has been depicted in.
There are various types of interactions in the organisation of the interface between mycobionts and photobionts in the thalli of lichen. Apart from mere juxtaposition of the two symbionts, in many crustose lichens the mycobionts actually penetrates the photobiont cell wall to form haustoria. On the contrary in other lichens the photobiont cell wall to form haustoria. On the contrary in other lichens the mycobionts remains non-invasive except that the cell walls very close to the photobiont are thin and invaginated followed by the cell contents exhibiting aggregation of mitochondria to perform the function of transferring nutrients, especially carbohydrates from photobiont cells.

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Blue Green Algal Association with Bryophytes Blue Green Algal Association with Higher Plants Aazolla Anabaena Asociation Survial of Aazolla Limitations of Aazolla Anabaena Asociation

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