Superoxide dismutase activation in response to lime-induced chlorosis

Alterations in superoxide dismutase (SOD) activity were studied on chlorotic grapevines (Vitis vinifera L.) grown under natural conditions on soil containing 30-35% CaCO₃ , and in lupins (Lupinus luteus L.) grown in a greenhouse with addition of 20% CaCO₃ to the soil. In both series of experiments SOD activity in leaves of chlorotic plants was from 20 to 30%, higher. The efficiency and absolute rate of superoxide anion radical formation were found to rise as a result of iron deficiency in the lupin leaves. Increased SOD activity and greater amounts of enzyme isoforms were observed in the leaves of grapevine cultivars resistant to lime-induced chlorosis as compared to less resistant cultivars. The present investigation suggests that initiation of lime-induced chlorosis is determined not only by reduced chlorophyll biosynthesis but also by other consequencies of iron deficiency in tissues, particularly by the high rate of formation of superoxide and other activated oxygen species, causing destructive changes in the photosynthetic apparatus. The increased SOD activity may be regarded as a protective mechanism against the formation of superoxide.