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.

An acidic beta-1,3-glucanase was detected in cucumber leaves inoculated with either Colletotrichum 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 polyacrylamide gel electrophoresis (PAGE) together with a Class III chitinase, a bifunctional chitinase/lysozyme. The beta-1,3-glucanase 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 in 38 kDa as estimated by SDS-PAGE, its isoelectric point is 3.6 and the specific activity is approximately 26 micromol glucose equivalents liberated from laminarin 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-glucanases 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.