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The Relationship of Peroxidase and Ortho-Diphenol Oxidase to Resistance of Sugarbeets to Cercospora Leaf Spot. Gopal S. Rautela, Postdoctoral Fellow, Department of Chemistry, Colorado State University, Fort Collins 80521; Merle G. Payne, Professor, Department of Chemistry, Colorado State University, Fort Collins 80521. Phytopathology 60:238-245. Accepted for publication 2 September 1969. DOI: 10.1094/Phyto-60-238.

The localization and fluctuation of peroxidase and o-diphenol oxidase was related to the mechanism of resistance of sugarbeets (Beta vulgaris). In all four varieties of sugarbeets representing a wide range of resistance, peroxidase was located mainly in the soluble fraction, whereas chloroplasts and mitochondria had only small amounts. On the other hand, o-diphenol oxidase was located mainly in the chloroplasts, but mitochondria also had an appreciable amount. The amount of o-diphenol oxidase associated with the soluble fraction was small. The response to infection was characterized by an immediate increase in the amounts of these enzymes, and this increase was consistently higher in resistant than in susceptible varieties. Toward the advanced stages of the disease, this pattern was reversed, and the increase in the amounts of enzymes was higher in susceptible varieties. The significance of localization and changes in the amounts of these enzymes in the resistance of sugarbeet leaves is discussed.