Interactive effects of molybdenum and vanadium on the nitrogenase and nitrate reductase activities of aulosira fertilissima

ABSTRACT

The effects of molybdenum and vanadium interactions on the nitrogenase and nitrate reductase enzymatic systems in the cyano-bacterium Aulosira fertilissima were investigated at different time intervals. Addition.of Va to + Mo cultures up to 0.015 ppm increased both dry weight gain and pigment biosynthesis. Beyond this concentration significant inactivation of such enzymes was observed at all growth periods. Nitrogenase and nitrate reductase activities were significantly increased by addition of Va at different levels to the cultures augmented with Mo, a phenomenon that was reversed by increasing Va concentrations. Maximum nitrogenase activity was recorded after 48 hr of incubation, whereas the highest enzymatic potential was maintained after 96 hr incubation period. Nitrogenase and nitrate reductase activities in + Mo cultures were significantly higher than in -Mo cultures. Addition of Va to + Mo Aulosira cultures resulted in a marked elevation in heterocyst frequency particularly after 48 hr incubation