VIEW ARTICLE

Biochemistry and Physiology

Polygalacturonase Inhibition in Rind of Valencia Orange Infected with Diplodia natalensis. Charles R. Barmore, Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, 700 Experiment Station Road, Lake Alfred 33850; Tuong K. Nguyen, Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, 700 Experiment Station Road, Lake Alfred 33850. Phytopathology 75:446-449. Accepted for publication 22 October 1984. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-446.

A protein that inhibited polygalacturonase (PG) secreted by Diplodia natalensis was isolated from extracts of noninfected and infected cultivar Valencia orange rind. The inhibitor had a molecular weight (determined by gel filtration) near 54,000 daltons and was inactivated by heat and protease. In vivo and in vitro inhibition of PG involved the formation under acidic conditions of an inhibitor-PG (INH-PG) complex with a molecular weight of about 95,000. The INH-PG complex was dissociated at pH 8.0 which restored PG activity when assayed for optimum activity at pH 5.0. Results of reaction kinetics studies of the inhibitor indicated that the mode of PG inhibition was competitive.