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Changes in Protein and Isozyme Content of Apple Fruits Following Infection by Monochaetia mali. Renupad Naik, Graduate Research Assistant, Department of Plant Pathology, University of Illinois, Urbana 61801; Dwight Powell, Professor Emeritus of Plant Pathology, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 63:851-854. Accepted for publication 12 January 1973. DOI: 10.1094/Phyto-63-851.

Proteins and isozyme patterns of five different enzymes formed by Monochaetia mali during fruit rot of 3- and 5-month-old ‘Golden Delicious’ apple fruits, were examined (relative to the enzyme patterns obtained from noninfected fruits and from the culture-grown fungus) by polyacrylamide gel electrophoresis. There were no changes in total protein bands in gels containing the extracts from infected and noninfected fruits regardless of maturity. However, the number of protein bands decreased with fruit maturity irrespective of infection by the fungus. The isozyme study showed that the number of polyphenol oxidase and malate dehydrogenase bands increased in the infected mature fruit but not in the immature fruit. No polyphenol oxidase and peroxidase isozyme bands were detected in the fungal extract. New isozyme bands which were not found either in extracts from healthy mature fruits or from the fungus, were detected with polyphenol oxidase and malate dehydrogenase in inoculated fruits following infection. An additional isozyme band for both glucose-6-phosphate dehydrogenase and acid phosphatase was found in infected fruits.