Substrate Degradation Patterns of Polygalacturonic Acid Lyase fromErwinia carotovoraandBacillus polymyxaand Release of Phytoalexin-eliciting Oligosaccharides from Potato Cell Walls

The patterns of substrate degradation by purified pectate lyase (PGL) (E.C. 4.2.2.2) from Erwinia carotovora and Bacillus polymyxa were compared. Reaction products released by both enzymes from potato cell walls, sodium polypectate and citrus pectin were separated by anion exchange chromatography using a TSK DEAE-5PW column and measured quantitatively. The relative amounts of oligomers released by both enzymes varied, especially the level of unsaturated tetramers. Degradation patterns also varied according to the substrate used and results with citrus pectin suggested that methylation reduced the ability of E. carotovora PGL to release wall fragments. Oligomers released from potato cell walls by E. carotovora PGL were pooled separately and assayed for phytoalexin elicitor activity using the soybean cotyledon bioassay. Fractions containing deca- and undecagalacturonides had the highest elicitor activity when tested at 5.0μg of uronic acid per cotyledon.