Activities of Cu‐containing proteins in Cu‐depleted pea leaves

Abstract

The effect of Cu deficiency on Cu‐containing enzymes and on their activities was studied with two subsequent generations of Cu‐deficient pea plants (Pisum sativum L., cv. Progress) grown in low Cu2+ media. Cu deficiency caused growth inhibition and a decrease in photosynthesis as well as in the activities of 3 Cu‐containing enzymes: diamine oxidase (EC 1.4.3.6), ascorbate oxidase (EC 1.10.3.3) and superoxide dismutase (EC 1.15.1.1). Determinations of photosynthetic electron‐transport rates as well as the concentrations of several redox components showed that the target of Cu deprivation in the photosynthetic apparatus is the synthesis of Cu‐containing plastocyanin which is positively correlated to the Cu content of the leaves. Inhibited formation of plastocyanin resulted in low activities of photosynthetic electron transport in photosystem I. Under Cu‐deficient conditions, the activities of diamine oxidase and ascorbate oxidase were inhibited by about 50% in the first and 80% in the second generation of pea plants. Enzyme assays showed an inhibition of the activities of both the plastidic and cytoplasmic Cu/Zn‐containing superoxide dismutases. An observed simultaneous increase of Mn‐superoxide dismutase may be a compensation mechanism to partially maintain the total superoxide‐dismutase activity under Cu‐deficient conditions. This result indicates that the formation of superoxide‐dismutase isoenzymes is interdependent and coordinated.