Effect of Boron Deficiency on Photosynthesis and Reductant Sources and Their Relationship with Nitrogenase Activity in Anabaena PCC 7119.

Nitrogenase activity of Anabaena PCC 7119 is inhibited under conditions of boron deficiency. To elucidate the mechanisms of this inhibition, this study examined how the deficiency of boron affected photosynthesis, photosynthetic pigments, the enzymes of the oxidative pentose phosphate pathway, and respiration of Anabaena PCC 7119 cultures. After 24 to 48 hours of boron deficiency, reductions in photosynthetic O(2) evolution and in CO(2) fixation were observed. At the same time, the activities of oxidative pentose phosphate pathway enzymes and respiration increased significantly with boron deficiency. No change was observed in these processes when assays were performed after 4 to 6 hours of deficiency, a time at which nitrogenase activity was severely inhibited. These results suggest that the requirement for boron in N(2) fixation is independent of its effects on photosynthesis and reductant supply.