The effect of light-dependent oxygen consumption on nitrogenase activity in Anabaena cylindrica

Abstract

Light-dependent oxygen consumption (LDOC) was observed in isolated heterocysts and in intact and sonicated CO2-fixing Anabaena cylindrica cells. The rate of LDOC in heterocysts was about three times that of CO2-fixing cells. Photosynthetic oxygen production by A. cylindrica became light saturated at 0.3 to 0.5 mW cm−2. LDOC and nitrogenase activity (acetylene reduction) increased with light intensity up to 2.5 mW cm−2 and incubation under air resulted in much larger relative acetylene reduction increases than incubation under N2. Carbonyl cyanide-m-chlorophenyl-hydrazone, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and cyanide did not affect the rate of LDOC in isolated heterocysts or cell-free preparations of CO2-fixing cells. However, all three substances induced LDOC in CO2-fixing cells. Heat treatment (100 °C for 1 min) caused a doubling of LDOC. Depletion of reduced carbon reserves by dark incubation caused a similar decrease in LDOC and dark respiration. The higher rates of LDOC observed in heat-treated materials were removed by catalase, but not by superoxide dismutase. Catalase injection released half of the O2 consumed through LDOC by heated preparations. LDOC increased with temperature up to 85 °C, and increased threefold with pH between pH 10 and 11.5. The possibility that LDOC may act to protect the nitrogenase of the heterocyst from oxygen inactivation is discussed.