Resistance of Photosynthesis to Hydrogen Peroxide in Algae

The effects of H₂O₂ on the photosynthetic fixation of CO₂ andon thiol-modulated enzymes involved in the photosynthetic reductionof carbon in algae were studied in a comparison with those inchloroplasts isolated from spinach leaves. In both systems,H₂O₂-scavenging enzymes were inhibited by addition of 0.1 mMNaN₃ 1 h prior to the addition of H₂O₂. A concentration (10^-4M) of H₂O₂ caused strong inhibition of the CO₂ fixation by intactspinach chloroplasts, as observed by Kaiser [(1976) Biochim.Biophys. Acta 440: 476], but not that by Euglena and Chlamydomonascells. The same results were also obtained with cells of thecyanobacteria Synechococcus PCC 7942 and Synechocystis PCC 6803in the presence of 1 mM hydroxylamine. These results indicatethat algal photosynthesis is rather resistant to H₂O₂. The insusceptibilityto H₂O₂ of thiolmodulated enzymes, namely, fructose-1,6-bisphosphatase,NADP-glyceraldehyde-3-phosphate dehydrogenase, and ribulose-5-phosphatekinase, was also observed in the chloroplasts of Euglena andChlamydomonas and in cyanobacterial cells. It seems likely thatthe resistance of photosynthesis to H₂O₂ is due in part to theinsusceptibility of the algal thiol-modulated enzymes to H₂O₂. (Received April 22, 1995; Accepted June 29, 1995)