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Soybean Phytoalexins: Rates of Synthesis Are Not Regulated by Activation of Initial Enzymes in Flavonoid Biosynthesis. J. E. Partridge, Graduate Research Associate, Department of Plant Pathology, University of California, Riverside, CA 92502, Present address of senior author: Department of Plant Pathology, University of Nebraska, Lincoln, NB 68503; N. T. Keen, Associate Professor, Department of Plant Pathology, University of California, Riverside, CA 92502. Phytopathology 67:50-55. Accepted for publication 6 July 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-50.

Soybean cultivars monogenically resistant or susceptible to Phytophthora megasperma var. sojae both showed activation of phenylalanine ammonia-lyase, chalconeflavonone isomerase (CFI), and peroxidase after wounding or inoculation with the fungus. The similarity of the enzymatic responses in all wounded control and inoculated plants indicated that the activity increases were caused primarily by wounding and have no causal role in determining the rapid production of the pterocarpanoid phytoalexin, glyceollin, that occurs specifically in the resistant, inoculated plants. In agreement with the findings of others, two isozymes of soybean peroxidase both catalyzed the appearance of new products from 2, 4, 4-trihydroxy-chalcone. One peroxidase metabolite was positively identified as 4, 7-dihydroxyflavon-3-ol and the other as a spiro-dienone which has been described by other workers. Isoenzymes of CFI were not found in soybeans.

Additional keywords: phenylalanine ammonia-lyase, chalcone-flavonone isomerase, peroxidase, Phytophthora megasperma var. sojae, glyceollin.