Photodynamic Action of Hypericin on Cyanobacteria, Synechocystis and Synechoccus (Anacystis nidulans)

Hypericin, Cyanobacteria, Photosynthesis, Photodynamic Action The photodynamic action of hypericin on photosynthesis and respiration were monitored in Synechocystis sp PCC 6803 and Synechoccus ATCC 6311 (Anacystis nidulans). An oxygen electrode was used to measure net oxygen evolution or consumption. The amount of hyperi­ cin required to inhibit photosynthesis was quantitively determined. Photosynthesis was com­ pletely inhibited in Synechocystis when the molar ratio of chlorophyll/hypericin was about 70:1. Higher concentrations of hypericin did not stop the uptake of oxygen, but rather stim­ ulated the process in the light. Hypericin was readily washed out of the cells forming no permanent associations in the bacterial cell. Hypericin inhibited electron transfer and conse­ quently oxygen production by PSII particles. For half maximum inhibition of oxygen evolu­ tion, with PSII membrane particles, the molar ratio of chlorophyll/hypericin was about 10:1.