ANTIFUNGAL ACTIVITY OF CUCUMBER BETA-1,3-GLUCANASE AND CHITINASE

An acidic beta-1,3-glucanase and three isoforms of chitinase (A, B, C) were isolated and purified from cucumber (Cucumis sativus L.) leaves inoculated with a necrogenic fungus, Colletotrichum lagenarium. Tests of antifungal activity to C. lagenarium in vitro were conducted with t he purified beta-1,3-glucanase, the three purified isoforms of chitina se and with intercellular wash fluids (ICF) from cucumber leaves above those inoculated with C. lagenarium or those treated with water. beta -1,3-Glucanase alone significantly inhibited spore germination at a co ncentration of 250 mu g ml(-1) buffer solution and inhibited the growt h of C. lagenarium at a concentration of about 7 mu g ml(-1) agar medi um. The latter concentration is equivalent to the concentration in inf ected cucumber leaves 7 days after inoculation with C. lagenarium and in leaf 2 of induced plants 3 days after challenge with the fungus. Ch itinase A and B did not inhibit spore germination or fungal growth at the concentrations tested, whereas chitinase C inhibited spore germina tion only at 1 mg ml(-1) and inhibited fungal growth at 66 mu g ml(-1) agar medium, the highest concentration tested. beta-1,3-Glucanase in combination with chitinase C inhibited fungal growth synergistically. Lysis of hyphal tips and abnormal growth were observed in the presence of a mixture of beta-1,3-9-glucanase and chitinase C. Intercellular w ash fluid (ICF) and concentrated ICF (5x) from control and induced pla nts did not inhibit fungal growth. However, the crude ICF in the prese nce of purified beta-1,3-glucanase and chitinase C had antifungal acti vity. The implications of these results are discussed. (C) 1996 Academ ic Press Limited.