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Function of Peroxidase in Resistance of Soybean to Bacterial Pustule¹

Peroxidase activity of soybean [Glycine max (L.) Merr.] plants was determined to investigate its possible role in disease resistance. Activity of the enzyme was determined in mitochondrial and supernatant fractions obtained from roots of the near-isogenic soybean cultivars ‘Clark’ and ‘Clark 63,’ susceptible and resistant, respectively, to bacterial pustule disease caused by Xanthomonas phaseoli var. sojensis. Peroxidase activity in both mitochondrial and supernatant fractions from roots of Clark 63 was greater than in those from Clark. Peroxidase activity was higher in the mitochondrial fraction than in the supernatant fraction from Clark 63.

Peroxidase activity of the mitochondrial fraction from Clark 63 was threefold greater than that of Clark. Peroxidase was partially purified from mitochondria from roots of both cultivars. The peroxidase preparation from Clark 63 had greater bactericidal activity in the presence of hydrogen peroxide than that of Clark. There was a highly significant correlation between peroxidase activity per mg protein in the root preparations and percent survival of bacterial cells. A correlation coefficient of _*0.7112 was obtained when ascorbic acid was present in the bactericidal assay system, and a coefficient of _*0.6141 was obtained when ascorbic acid was omitted from the system.

Key Words: Ascorbic acid • Hydrogen peroxide • Mitochondria • Xanthomonas phaseoli var. sojensis

² Postdoctoral Research Associate, Department of Botany and Plant Pathology, Iowa State University, Ames, IA 50010; and Plant Pathologist, ARS, USDA, and Professor, Department of Botany and Plant Pathology, Iowa State University, respectively.

Received for publication March 20, 1974.