Isoenzyme pattern of superoxide dismutase in different varieties of citrus plants

Superoxide dismutases (SOD; EC 1.15.1.1) in leaves from different cultivars of citrus plants were characterized using isoelectric focusing in polyacrylamide gels. The plants studied included Citrus limonum R. (cvs Verna, Fino, and Eureka), C. paradisi Mac (cvs Red Blush and Marsh), C. aurantium L. (cv. Comun), C. sinensis L. Osbeck (cvs Navel, Valencia, and Salustiano), and C. reticulata B. (cv. Satsuma). The three molecular forms of SOD were distinguished from each other by their different sensitivity to cyanide and H₂O₂. In C. limonum leaves, four Cu,Zn-SODs, three Fe-SODs and two Mn-SODs were present. However, in leaves from different varieties of C. sinensis, C. paradisi, C. aurantium and C. reticulata the activity and number of Fe-SOD isoenzymes were lower than in lemon leaves, whereas the number of MN-SOD isozymes was increased. Cu,Zn-SODs did not show significant variations in the different species and cultivars. The identification of Fe-SODs in several species of the plant family Rutaceae extends the small number of higher plants where the presence of these Fe-containing metalloenzymes has been demonstrated. Results obtained may be useful from an evolutionary viewpoint and also in mineral nutrition studies using SOD isozymes as markers of functional metals.