Superoxide Dismutases

Abstract

Shoots, roots, and seeds of corn (Zea mays L., cv. Michigan 500), oats (Avena sativa L., cv. Au Sable), and peas (Pisum sativum L., cv. Wando) were analyzed for their superoxide dismutase content using a photochemical assay system consisting of methionine, riboflavin, andpnitro blue tetrazolium. The enzyme is present in the shoots, roots, and seeds of the three species. On a dry weight basis, shoots contain more enzyme than roots. In seeds, the enzyme is present in both the embryo and the storage tissue. Electrophoresis indicated a total of 10 distinct forms of the enzyme. Corn contaned seven of these forms and oats three. Peas contained one of the corn and two of the oat enzymes. Nine of the enzyme activities were eliminated with cyanide treatment suggesting that they may be cupro-zinc enzymes, whereas one was cyanideresistant and may be a manganese enzyme. Some of the leaf superoxide dismotases were found prmarily in mitochondrin or chloroplasts. Peroxidases at high concentrations interfere with the assay. In test tube assays of crude extracts from seedlings, the interference was neglgible. On gels, however, peroxidases may account for two of the 10 superoxide dismutase forms.Superoxide dismutases are metalloproteins catalyzing the dismutation of the superoxide free radical (02--) to molecular oxygen and H202. This enzymic activity was first described by McCord and Fridovich (17) with a cupro-zinc protein (erythrocuprein) from bovine erythrocytes. Similar cupro-zinc proteins with SOD3 activity were subsequently isolated from various eukaryotic sources (8). Manganese-containing proteins with SOD activity were later found in prokaryotes and in mitochondria of eukaryotes (8). Iron proteins from Escherichia coli (10) and algae (15) were recently shown to possess SOD activity.Cupro-zinc SOD has already been isolated from tissues of higher plants: pea seeds (19), spinach leaves (2, 15), and wheat germ (4). Isozymes have also been reported for wheat and spinach cupro-zinc enzyme (4,15). A cyanide-resistant enzyme from wheat germ has been described as manganese-SOD (4). Occurrence of manganese enzyme in spinach chloroplasts has been reported (15), but is not certain (7). There is no report of iron enzyme in higher plants.A comparative study of the SOD distribution in plants has not been conducted thus far. Distribution of the enzyme within the plant and intraspecific differences may be of interest and were the objective of the present study. Embryos and scutella were excised from seeds which had been allowed to imbibe at 25 C for 10 hr and were rinsed three times with distilled H20. Endosperm was obtained from dry corn and oat seeds from which the embryo-bearing end had been removed. Endosperm was drilled from the cut surface by using a size 60 wire bit fitted on a battery operated drill. The hulls of oat seeds were removed, unless the seeds were to be germinated.Preparation of Extracts. The tissues were thoroughly ground with a cold mortar and pestle in an ice bath, until no fibrous residue could be seen. The...

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Alginate oligosaccharides enhanced Triticum aestivum L. tolerance to drought stress

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Induction of Oxidative Stress by Sunflower Phytotoxins in Germinating Mustard Seeds

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