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, ranun culus glacialis and Soldanella alpina, both photosystem II (PSII) and the enzyme catalase appeared to be highly resistant to photoinactivati on under natural field conditions, While the D1 protein of PSII and ca talase have a rapid turnover in fight and require continuous new prote in synthesis in non-adapted plants, little apparent photoinactivation of PSII or catalase was induced in the alpine plants by translation in hibitors or at low temperature, suggesting that turnover of the D1 pro tein and catalase was slow in these leaves. In vitro PSII was rapidly inactivated in light in isolated thylakoids from H. alpina and R. glac ialis. In isolated intact chloroplasts from R. glacialis, photoinactiv ation of PSII mas slower than in thylakoids. Partially purified catala se from X. glacialis and S. alpina was as sensitive to photoinactivati on in vitro as catalases from other sources, Catalase from H. alpina h ad, however, a 10-fold higher stability in light, The levels of xantho phyll cycle carotenoids, of the antioxidants ascorbate and glutathione , and of the activities of catalase, superoxide dismutase and glutathi one reductase were very high in S. alpina intermediate in H. alpina, b ut very low in R. glacialis. However, isolated chloroplasts from all t hree alpine species contained much higher concentrations of ascorbate and glutathione than chloroplasts front lowland plants.