Abstract
We investigated metabolism of DC using spinach chloroplasts and thylakoid membranes. We detected enzyme activity of the reduction of MG by NADPH in stroma of chloroplasts. In this reaction, NADP+ as Hill oxidant was produced by the reduction of DC. To detoxify DC continuously, NADPH must be regenerated. We hypothesized that DC functioned as Hill oxidant. To verify our hypothesis, we added DC to intact spinach chloroplasts. The addition of DC to chloroplasts induced photochemical quenching of Chl fluorescence. The production of Hill oxidant should accompany with O2-evolution in PS2. But DC induced O2-uptake and H2O2 accumulated. We, furthermore added DC to the illuminated thylakoid membranes and investigated dependence of the DC-dependent O2-uptake rate (Vo2) on DC concentration, temperature and light intensity. Maximum Vo2 reached 210 μmol O2/mg Chl/h. An optimum temperature for Vo2 was 40oC and Vo2 did not saturate against light intensity. DC-dependent uptake of O2 was inhibited by DCMU and DBMIB. These results showed that DC photoreduced at PS1donated electorons to O2 producing H2O2.
