Red drop in the quantum yield of fluorescence of sonicated algae.

The change of the quantum yield of fluorescence, Phi, with the frequency of exciting light, was investigated in Chlorella, Anacystis, and Porphyridium suspensions, and in sonicates from these cells prepared under aerobic and anaerobic conditions. In case of Chlorella, sonicates were made in acid and in alkaline media (pH 4.65 and 7.80). In the alkaline medium, a drop of Phi towards the longer waves was found to begin at 1.466 x 10(4) cm(-1) (682 nm) in sonicates, and in suspension. In the acid medium, the drop began at 1.471 x 10(4) cm(-1) (680 nm), 1.418 x 10(4) cm(-1) (705 nm), and 1.389 x 10(4) cm(-1) (720 nm) in suspension, anaerobic sonicate, and aerobic sonicate, respectively. The results indicate that the cause of the change in the red drop is preferential destruction of a long-wave component of chlorophyll a (such as Chl a 693). The amount of this component remaining after sonication is larger in alkaline than in acid sonicates. With Anacystis and Porphyridium, only alkaline suspensions (pH 7.80) could be used for sonication, because in acid medium, the phycobilin-chlorophyll complex is rapidly broken and phycobilin extracted from the cell. In Anacystis, the red drop begins at 1.562 x 10(4) cm(-1) (640 nm) and 1.538 x 10(4) cm(-1) (650 nm) in suspension and sonicate, respectively; in Porphyridium, it starts at 1.550 x 10(4) cm(-1) (645 nm) in both cases. These results suggest that sonication in alkaline medium (pH 7.80) destroys some Chl a 693 in Anacystis, but not in Porphyridium.