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Physiology and Biochemistry

Polygalacturonase from Citrus Fruit Infected with Penicillium italicum. Charles R. Barmore, Plant physiologist, University of Florida, Agricultural Research and Education Center, Lake Alfred 33850; G. Eldon Brown, research scientist III, Florida Department of Citrus, Agricultural Research and Education Center, Lake Alfred 33850. Phytopathology 71:328-331. Accepted for publication 25 July 1980. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-71-328.

An endo-polygalacturonase (E.C. (endo-PG) was isolated and purified from grapefruit (Citrus paradisi) peel infected with Penicillium italicum. The estimated molecular weight of the endo-PG was 36,000 daltons and it had optimum activity at pH 5.0. Citrus pectin and sodium polypectate (NaPP) were degraded by the enzyme, but NaPP was the most readily degraded. The purified enzyme macerated citrus mesocarp in vitro. The microequivalents per gram fresh weight of diffusible free organic acid was 70.0 for decayed peel and 6.7 for healthy peel. Galacturonic acid in the decayed peel averaged 8.6 mg/g fresh weight. Plasmolysis, cell wall swelling, and degradation of the wall at the site of hyphal penetration were associated with invading hyphae. Dissolution of the middle lamella by the endo-PG is a major factor contributing to hyphal penetration.

Additional keywords: pectolytic enzymes, blue mold, tissue maceration, postharvest decay, soft rot.