EFFECT OF GIBBERELLIC-ACID ON PHOTOSYNTHETIC ELECTRON-TRANSPORT REACTIONS AND NITROGENASE ACTIVITY IN ANABAENA-CYLINDRICA

Various concentrations of gibberellic acid (GA) were tested for their effects on photosynthetic reactions and dinitrogen-fixation (acetylene reduction) in Anabaena cylindrica. The optimum concentration of GA fo r growth and oxygen evolution was 10(-4) M, and NADP photoreduction wa s also enhanced. A pronounced effect was evident on the photosystem It -Hill reaction, while the effect on the photosystem I-Mehler reaction was much less. A concentration of 10(-6) M GA exerted some inhibition on growth and photosynthetic reactions, while 10(-2) and 10(-3) M conc entrations led to complete lysis. The optimum concentration of GA for maximum nitrogenase activity was 10(-5) MI which also increased hetero cyst differentiation.