Superoxide Dismutases from a Citrus Plant: Presence of Two Iron-containing Isoenzymes in Leaves of Lemon Trees (Citrus limonum L.)

Abstract

Superoxide dismutases (EC 1.15.1.1) in leaves from a Citrus plant (Citrus limonum L.) were characterized for the first time using polyacrylamide gel electrophoresis. The three molecular forms of the enzyme were distinguished from each other by their varying sensitivity to cyanide and H(2)O(2). Leaf extracts from lemon leaves contained at least five electrophoretically distinct SOD isozymes: two Cu,Zn-superoxide dismutases, one Mn-superoxide dismutase and, interestingly, two Fe-containing superoxide dismutases, a type of superoxide dismutase mainly found in procaryotic organisms. The two Fe-SODs were further identified by nutritional experiments. In higher plants, ferric SODs have only been found thus far in three families (Gingkoaceae, Nymphaceae, and Cruciferae) and this is the first report of the presence of two Fe-SODs in a citrus plant, species which are phylogenetically distant from these families. Results obtained may be useful from an evolutionary standpoint and also in mineral nutrition studies using superoxide dismutase isoenzymes as combined markers of functionally active Mn, Fe, Cu, and Zn involved in the plant cell metabolism.