Reversible inhibition of GS in Tolypothrix tenuis.

L-Methionine DL-Sulphoximine (MSX), a known glutamate analogue of glutamine synthetase (GS) caused inhibition of its activity for a week in the cyanob acterium, Tolypothrix tenuis at 10 mu M concentration. This resulted in a c ontinuous extracellular release of ammonia, accompanied by loss in the prod uction of photosynthetic pigments, diminished photosynthetic rate, low hete rocyst frequency and nitrogen content of cells. The photorespiratory activi ty of the cultures was however, high. The observed changes were reversed on ce the effects of MSX ceased in T. tenuis. This enables its use an efficien t bio-fertilizer for sustained release of ammonia for prolonged periods eve n with a single inoculation of the organism.