Effect of hydrogen adaptation on fluorescence in normal and manganese-deficient algae.

1. Steady-state fluorescence of normal cells of Ankistrodesmus braunii is about 40% higher under hydrogen-adapted as compared to aerobic conditions. 2. By contrast, fluorescence of manganese-deficient A. braunii, which aerobically is twice as strong as that of normal cells, decreases in the course of adaptation to a considerably lower level which is about as high as that of normal algae adapted to hydrogen. 3. The effects of DCMU on fluorescence of aerobic and anaerobic cells of A. braunii are similar to those brought about by manganese deficiency. 4. In Chlorella fusca (=pyrenoidosa), which develops a very high level of hydrogenase activity, fluorescence of normal cells is about equal under H2-adapted and under aerobic conditions. According to the current concept of the relation between fluorescence intensity and photosynthetic electron transport, these results seem to indicate that, in addition to system I, system II of photosynthesis is at least partly active in H2-adapted and photoreducing algae.