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 the purified beta-1,3-glucanase, the three purified isoforms of chitinase 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 concentration of 250 mu g ml(-1) buffer solution and inhibited the growth of C. lagenarium at a concentration of about 7 mu g ml(-1) agar medium. The latter concentration is equivalent to the concentration in infected cucumber leaves 7 days after inoculation with C. lagenarium and in leaf 2 of induced plants 3 days after challenge with the fungus. Chitinase A and B did not inhibit spore germination or fungal growth at the concentrations tested, whereas chitinase C inhibited spore germination 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 wash fluid (ICF) and concentrated ICF (5x) from control and induced plants did not inhibit fungal growth. However, the crude ICF in the presence of purified beta-1,3-glucanase and chitinase C had antifungal activity. The implications of these results are discussed. (C) 1996 Academic Press Limited.