Springer Online Journal Archives 1860-2000
Summary Experiments on the relationship between nitrogen fixation and photosynthesis in intact Anabaena cylindrica are reported. 1. Uncouplers of the photosynthetic electron transport inhibit CO2-fixation as well as nitrogen fixation, as measured by the reduction of acetylene to ethylene. These experiments indicate the energy requirement for nitrogen fixation in vivo. 2. Similar to the photosynthetic CO2-fixation, also nitrogen fixation is inhibited by DSPD1 and DBMIB, suggesting that ferredoxin is the reductant for nitrogen fixation in the whole cells. 3. In far red light (above 695 nm), the photosynthetic CO2-fixation is completely inhibited by DCMU, whereas acetylene reduction is scarcely affected. These results suggest that the direct role of photosynthesis in nitrogen fixation is restricted to supply the energy by cyclic photophosphorylation at least under some experimental conditions. The reductant for the nitrogen fixation in Anabaena, ferredoxin in all probability, is likely to be reduced in a dark reaction and independently from the photosynthetic electron transport. — Some controversial results on the hypothesis, that nitrogenase in blue-green algae is located in the heterocysts, are discussed.
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