Purification and characterization of two basic β-1,3-glucanases induced in Colletotrichum lindemuthianum-infected bean seedlings

Two β-1,3-glucanases which are rapidly induced in the incompatible interaction between bean (cv. Processor) and Colletotrichum, lindemuthianum race β were purified to homogeneity. Characterization of the two enzymes, GE1 and GE2, showed that they both had a basic isolectric point and a similar molecular weight (36,500 for GE1 and 36,000 for GE2), but differed in their pH optimum, thermal stability, and specific activity. GE2 was present in higher amounts but was shown to be less active than GE1 against laminarin and fungal cell walls isolated from race β of the fungus. Both enzymes were specific for β-1,3 linkages and showed a strict endolytic mode of action. Further characterization of GE2 was achieved by amino acid sequence analysis of tryptic peptides; the degree of homology shared with other basic β-1,3-glucanases depended on the plant source. A time-course study showed that GE1 and GE2 were increased during infection. They were also induced by fungal elicitors, thereby indicating that they originate from the host.