OXIDATIVE STRESS RESPONSES ACCOMPANYING PHOTOINACTIVATION OF CATALASEIN NACL-TREATED RYE LEAVES

When segments of rye leaves (Secale cereale L.) grown at 90 mu mol m(- 2) s(-1) PAR were incubated at a higher photon flux of 400-500 mu mol m(-2) s(-1) PAR in the presence of 0.2-0.6 M NaCl, a preferential loss of catalase activity was induced. The extent of this decline increase d with the concentration of NaCl. In addition, the accumulation of alt ernative antioxidative components, such as ascorbate, glutathione, glu tathione reductase, or peroxidase, was inhibited. The total content of H2O2 was, however, lower in catalase-depleted than in untreated contr ol leaves. The occurrence of strong oxidative stress in NaCl-treated l eaves was indicated by marked declines in the ratios of reduced to oxi dized ascorbate and glutathione and by the degradation of chlorophyll in light. The specific elimination of catalase activity by the inhibit or aminotriazole was also accompanied by a rapid decline in the ratio of reduced to oxidized glutathione but other symptoms of oxidative str ess were much less severe than in the presence of NaCl. However, all s ymptoms of photooxidative damage seen in NaCl-treated leaves were clos ely mimicked by treatment with the translation inhibitor, cycloheximid e, in light. The results suggest that NaCl-induced oxidative damage in light was predominantly mediated by the inhibition of protein synthes is. By this inhibition the resynthesis of catalase, which has a high t urnover in light, was blocked and the leaves were thus depleted of cat alase activity and, in addition, the intensification of alternative an tioxidative systems was also prevented.