A PECTIN LYASE INHIBITOR PROTEIN FROM CELL-WALLS OF SUGAR-BEET

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 pl 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.