Effect of Oxygen on Photosynthetic14CO2Fixation inChroomonassp. (Cryptophyta) II. Effects of Inhibitors, Uncouplers and an Artificial Electron Mediator on the Inhibition of14CO2Fixation by Anaerobiosis

摘要

In“air-grown”Chroomonassp. cells, low concentrations of DCMU (less than 0.1μm) could prevent the inhibition of14CO2fixation by anaerobiosis under light-saturating conditions (more than 40 W.m−2), with phenazine methosulfate showing a similar effect. Antimycin A, carbonyl cyanidem-chlorophenylhydrazone (CCCP), andN,N′-dicyclohexylcarbodiimide strongly inhibited anaerobic photosynthesis at concentrations which did not significantly inhibit the rate under 2O2at high light intensity (200 W.m−2), although 0.2μmCCCP stimulated the rate under 2O2to some extent. On the other hand, KCN inhibited the rate much more strongly under 2O2than N2, although it inhibited the rate very strongly at concentrations above 5μM both under N2and 2O2. These results suggest that the inhibition of photosynthetic14CO2fixation by anaerobiosis in this alga result from ATP deficiency caused by over-reduction of electron carriers of the cyclic electron flow and that oxygen can prevent the over-reduction. Cyclic electron flow seems to be necessary to provide additional ATP for CO2reduction under anaerobic conditions, although it seems to be less necessary under aerobi