Induction of a Mehler reaction in chloroplast preparations by flavin mononucleotide: Effects on photosynthesis by intact chloroplasts

Abstract

Addition of flavin mononucleotide (FMN) to spinach chloroplast preparations containing intact chloroplasts was found to result in inhibition of photosynthetic CO 2-dependent oxygen evolution. Since the inhibition could be reversed by catalase, it is attributed primarily to production of H 2O 2 in an FMN-mediated Mehler reaction which occurs in the broken chloroplasts of the preparations. Ascorbate and superoxide dismutase also reversed the inhibition though to a lesser extent. The inhibition was also offset by the presence of ribose-5-phosphate. The complete dependence of these effects on the presence of FMN is consistent with the view that intact chloroplasts do not themselves produce inhibitory concentrations of H 2O 2 under conditions optimal for photosynthetic CO 2-fixation.