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Nitrate assimilation and its interplay with Ca2+ ion transport has been studied in Spirulina platensis PCC 7345, an alkaliphilic filamentous cyanobacterium. We have used verapamil, a calcium-channel blocker and sodium orthovanadate, a calcium efflux blocker, to study the effect of nitrate assimilatory setup. Nitrate uptake (NU) increased significantly with verapamil but was inhibited by sodium orthovanadate. Nitrate reductase and nitrite reductase activities were stimulated with verapamil as well as sodium orthovanadate. Glutamine synthetase activity was not significantly altered by both the inhibitors. Our results suggest that the steady state levels of NU, NR and NiR activities are inter linked with Ca2+ influx into the cells from the external medium. |
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