SUPEROXIDE RADICALS, SUPEROXIDE DISMUTASES and OXYGEN TOXICITY IN PLANTS

Abstract

In plants, as in other aerobic organisms, 02is a commonly encountered intermediate of oxygen reduction and superoxide dismutases provide a defense against the potential cytotoxicity of this radical. The superoxide dismutases found in plants resemble those encountered in other organisms. Within chloroplasts one finds the CuZn enzyme, while mitochondria contain the Mn enzyme. Nymphaceae, ginkoaceae and cruciferae are unusual among plants, indeed among eukaryotes, in that they contain an iron superoxide dismutase. Bipyridylium herbicides. such as paraquat, exert their effect by diverting electron flow from photosystem I and thus increasing 02production. Paraquat-resistant genotypes of horseweed, tobacco and rye grass were found to contain elevated superoxide dismutase.This enzyme also appears to provide a defense against sulfur dioxide. sunscald and photooxidative death. The evidence supporting these statements and possible explanations are discussed.

Purification and Properties of Glyoxysomal Cuprozinc Superoxide Dismutase from Watermelon Cotyledons (Citrullus vulgaris Schrad)

“…Thus, glyoxysomal Cu,Zn-SOD II appears to be a dimer composed of two equally sized subunits. In its native and subunit mol wt, the glyoxysomal Cu,Zn-SOD II is characteristic ofmost Cu,Zn-SODs (13) and resembles many plant Cu,Zn-SODs that have been characterized thus far (3,9,12,16,17,26). The UV absorption spectrum of purified Cu,Zn-SOD II was characterized by a low absorption at 280 nm (tryptophan absorbance region), and showed a weak absorption maximum at 260 nm and a shoulder at about 220 nm.…”

“…In higher plants, manganese-containing SODs are mainly present in mitochondria (26,29), but also occur in different types of peroxisomes (7,11,28,29). Fe-SODs are localized in chloroplasts (10), but very recently they also have been reported to be present in peroxisomes and mitochondria from Dianthus caryophyllus L. together with a Mn-isozyme (1 1).…”

“…These enzymes play an important role in protecting cells against the indirect deleterious effects of superoxide free radicals ( 13,26). SODs generally occur in three different molecular forms containing Mn, Fe, or Cu plus Zn as prosthetic metals (13), although atypical SODs containing different combinations ofthose metals in their molecules have also been described (2,10,24).…”

“…Fe-SODs are localized in chloroplasts (10), but very recently they also have been reported to be present in peroxisomes and mitochondria from Dianthus caryophyllus L. together with a Mn-isozyme (1 1). Cu,Zn-SODs are localized chiefly in chloroplasts (9,23,26), and also in the cytosol (3,26) and mitochondria (26,28).…”

Intercompartmental differences between cytosol and mitochondria in their respective antioxidative responses and lipid peroxidation levels in acid rain stress

“…Liquidambar formosana. Several SOD forms (MnSOD, FeSOD, CuZnSOD) are known to occur in different plant cell compartments (Rabinowith and Fridovich 1983). While CuZnSOD is found primarily in the cytosol (but also in chloroplasts and mitochondria), MnSOD is located primarily in mitochondria (and peroxisomes) (Gupta et al 1993).…”