Studies in the Physiology of Parasitism

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Abstract
1. Though Sclerotinia fructigena, S. laxa, and Botrytis cinerea cause rotting of apple tissue and death of the protoplasts, little or no pectolytic activity was detectable in extracts of the rotted tissue. 2. Pectic materials were extracted from normal and parasitized apple tissue in three fractions and precipitated as calcium pectate. There was a loss of total, total insoluble, and soluble pectic substances in the invaded tissues. This was most marked with B. cinerea and S. laxa and least with S. fructigena. 3. Pectolytic activity was measured by methods involving (a) maceration of plant tissues, (b) viscosity and reducing group determinations in pectic substrates, (c) increase in acidity of pectin. By these methods it was shown that pectolytic enzymes were produced by all three fungi in synthetic media. With S. fructigena, which was the only fungus studied in detail, replacement of glucose by pectin increased the formation of pectolytic enzymes. 4. When various apple extracts were used as culture media, little or no pectolytic activity was detectable. With all three fungi the presence of apple juice in a culture medium, which by itself was suitable for enzyme formation, resulted in the suppression of pectolytic activity. 5. Oxidized apple juice had a pronounced effect in deactivating certain pectolytic enzymes, an effect which was especially marked with B. cinerea. This points to an interaction between the pectolytic and oxidizing systems and introduces a new line of approach to the study of the biochemical interaction between host and parasite.

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