Purification and Characterization of an Acidic Beta-1,3-Glucanase from Cucumber and its Relationship to Systemic Disease Resistance Induced by Colletotrichum lagenarium and Tobacco Necrosis Virus. Cheng Ji. Department of Plant Pathology, University of Kentucky, Lexington, KY 40546 U.S.A. Joseph Kuc. Department of Plant Pathology, University of Kentucky, Lexington, KY 40546 U.S.A. MPMI 8:899-905. Accepted 14 July 1995. Copyright 1995 The American Phytopathological Society.

An acidic Beta-l,3-glucanase was detected in cucumber leaves inoculated with either Colletolrichum lagenarium or tobacco necrosis virus (TNV) as well as in the leaves above those inoculated with the pathogens. The enzyme is extracellular and migrates in native polyacrylamidc gel elec-trophoresis (PAGE) together with a Class III chitinase, a bifunctional chitinase/Iysozyme. The Beta-1,3-gIucanase was separated by ultra-narrow pH range IEF-PAGE or by SDS-PAGE and was purified to apparent homogeneity. Only one isoform of the enzyme was detected. Its apparent molecular mass is 38 kDa as estimated by SDS-PAGE, its isoelectric point is 3.6 and the specific activity is approximately 26 alpha mol glucose equivalents liberated from lami-narin min-1 mg-1 protein. Partial amino acid (five peptide fragments with a total of 65 amino acids) sequencing of the Beta-1,3-glucanase revealed similarities of 49% to 72% to sequences of published Beta-1,3-gIucanases from tobacco, tomato, soybean, barley, and rice plants. A time course study indicated that the increase of the Beta-1,3-glucanase activity was associated with induced resistance against C. lagenarium. The implications of these results to coordinate defense responses in plant-microbe interactions are discussed.