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Physiology and Biochemistry

A pectin Lyase Inhibitor Protein from Cell Walls of Sugar Beet. W. M. Bugbee,Research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, Northern Crop Science Laboratory, and adjunct professor, Department of Plant Pathology, North Dakota State University, P.O. Box 5677, Fargo 58105-5677; Phytopathology 83:63-68. Accepted for publication 25 August 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/Phyto-83-63.

A protein from sugar beet roots inhibited pectin lyase (PNL) that was isolated from Rhizoctonia solani. The PNL inhibitor protein (PNLIP) was extracted from healthy sugar beet cell walls and partially purified by ammonium sulfate fractionation, cation exchange, and gel permeation chromatography. Electrophoresis in polyacrylamide with sodium dodecyl sulfate showed a single major band of 57.5 kDa. Isoelectric focusing gave a major band at pI 9.9. Kinetic analysis indicated that the inhibition was uncompetitive (coupling). Pectin lyase inhibitory activity was greater in cell wall extracts from rotted and adjacent tissue than in healthy tissue. The inhibitor concentration was higher in a root rot-resistant germplasm than in a susceptible cultivar and was also higher in root than in hypocotyl or crown tissue. The inhibitor protected root disks from PNL damage in a buffered reaction mixture. The inhibitor was equally effective against PNL from Phoma betae but was less effective against PNL from Aspergillus japonicus.