Resistance to photoinhibition of photosystem II and catalase and antioxidative protection in high mountain plants

In leaves of three alpine high mountain plants, Homogyne alpina, ranunculus glacialis and Soldanella alpina, both photosystem II (PSII) and the enzyme catalase appeared to be highly resistant to photoinactivation under natural field conditions, While the D1 protein of PSII and catalase have a rapid turnover in fight and require continuous new protein synthesis in non-adapted plants, little apparent photoinactivation of PSII or catalase was induced in the alpine plants by translation inhibitors or at low temperature, suggesting that turnover of the D1 protein and catalase was slow in these leaves. In vitro PSII was rapidly inactivated in light in isolated thylakoids from H. alpina and R. glacialis. In isolated intact chloroplasts from R. glacialis, photoinactivation of PSII mas slower than in thylakoids. Partially purified catalase from X. glacialis and S. alpina was as sensitive to photoinactivation in vitro as catalases from other sources, Catalase from H. alpina had, however, a 10-fold higher stability in light, The levels of xanthophyll cycle carotenoids, of the antioxidants ascorbate and glutathione, and of the activities of catalase, superoxide dismutase and glutathione reductase were very high in S. alpina intermediate in H. alpina, but very low in R. glacialis. However, isolated chloroplasts from all three alpine species contained much higher concentrations of ascorbate and glutathione than chloroplasts front lowland plants.