No abstract

The enzyme catalase (EC The enzyme catalase from both animal and plant sources is light sensitive (2,4,7,23 we investigated the dynamics of the catalase polypeptide with labeling and chase experiments and immunochemical techniques; for comparison, we investigated the dynamics of the Dl protein in rye leaves exposed to different photon flux densities.The maintenance of proteins depending on rapid tumover will generally be sensitive to all environmental conditions that either overload or hamper the capacity of repair synthesis, as previously described for low temperature (29). Also, other stress conditions known to affect protein synthesis, such as salt (13, 16) or heat shock (28), can be expected to induce specific declines in catalase and possibly in the Dl protein even in only moderate light, simply by preventing repair. Therefore, their influence on catalase and on Dl was investigated. MATERIALS AND METHODS Plant Material and Growing ConditionsExperiments were performed with leaf sections of 6-d-old rye seedlings (Secale cereale L. cv Halo). Seeds were surface sterilized by a 10-min vacuum infiltration and about 30-min soaking in a freshly prepared, filtered solution of 3% (w/v) calcium hypochlorite chloride, thoroughly washed with demineralized H20, and grown at 220C in glass-covered plastic boxes on filter paper (Schleicher & Schull; No. 598

In leaves of three alpine high mountain plants, Homogyne atpina, Ranuncutus gtaciatis and Sotdanetta atpina., both photosystem II (PSIl) and the enzyme catalase appeared to be highly resistant to photoinactivation under natural field conditions. While the Dl protein of PSII and catalase have a rapid turnover in light 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 Dl protein and catalase was slow in these leaves. In vitro PSII was rapidly inactivated in light in isolated thylakoids from H. alpina and R. gtaciatis. In isolated intact chloroplasts from R. gtaciatis., photoinactivation of PSII was slower than in thylakoids. Partially purified catalase from R. gtaciatis and S. alpina was as sensitive to photoinactivation in vitro as catalases from other sources. Catalase from H. atpina had, however, a 10-lbld higher stability in light. The levels of xanthophyll cycle earotenoids, of the antioxidants ascorbate and glutathione, and of the activities of catalase, superoxide dismutase and glutathione reductase were very high in S. atpina, intermediate in H. atpina, but very low in R. gtaciatis. However, isolated chloroplasts from all three alpine species contained much higher concentrations of ascorbate and glutathione than chloroplasts from lowland plants.

Severe photoinactivation of catalase (EC 1.11.1.6) and a decline of variable fluorescence (FJ), indicating photoinhibition of photosynthesis, were observed as rapid and specific symptoms in leaves exposed to a high heat-shock temperature of 40°C as well as in leaves exposed to low chilling temperatures in white light of only moderately high photosynthetic photon flux density of 520 ME m-2 s-'. Other parameters, such as peroxidase (EC 1.11.1.7), glycolate oxidase (EC 1.1.3.1), glutathione reductase (EC 1.6.4.2), or the chlorophyll content, were hardly affected under these conditions. At a compatible temperature of 22°C, the applied light intensity did not induce severe photoinactivations. In darkness, exposures to high or low temperatures did not affect catalase levels. Also, decline of F, in light was not related to temperature sensitivity in darkness. The effective low-temperature ranges inducing photoinactivation of catalase differed significantly for chilling-tolerant and chilling-sensitive plants. In leaves of rye (Secale cereale L.) and pea (Pisum sativum L.), photoinactivation occurred only below 15°C, whereas inactivation occurred at 15°C in cucumber (Cucumis sativus L.) and maize (Zea mays L.). The behavior of F, was similar, but the difference between chilling-sensitive and chillingtolerant plants was less striking. Whereas the catalase polypeptide, although photoinactivated, was not cleaved at 0 to 4°C, the Dl protein of photosystem 11 was greatly degraded during the lowtemperature treatment of rye leaves in light. Rye leaves did not exhibit symptoms of any major general photodamage, even when they were totally depleted of catalase after photoinactivation at 0 to 4°C, and catalase recovered rapidly at normal temperature. In cucumber leaves, the decline of catalase after exposures to bright light at 0 to 4°C was accompanied by bleaching of chlorophyll, and the recovery observed at 25°C was slow and required several days. Similar to the Dl protein of photosystem 11, catalase differs greatly from other proteins by its inactivation and high turnover in light. Inasmuch as catalase and Di protein levels depend on continuous repair synthesis, preferential and rapid declines are generally to be expected in light whenever translation is suppressed by stress actions, such as heat or chilling, and recovery will reflect the repair capacity of the plants.

No abstract