Plant and Bacterial Chitinases Differ in Antifungal Activity

TLDR

Plant grain chitinases act as endochitinases with lysozyme activity, a characteristic shared with other plant chitinases. The authors isolated chitinases from wheat, barley, maize, and bacterial species Serratia marcescens, Streptomyces griseus, and Pseudomonas stutzeri, and compared their antifungal activity by measuring inhibition of hyphal extension of Trichoderma reesei and Phycomyces blakesleeanus. Grain chitinases inhibited fungal hyphal extension at doses as low as 1 µg, whereas bacterial chitinases showed no activity even at 50 µg, supporting the idea that plant chitinases protect hosts through endochitinase activity while bacterial exochitinases lack antifungal effect.

Abstract

Chitinases were isolated from the grains of wheat, barley and maize, and compared with those obtained from Serratia marcescens, Streptomyces griseus and Pseudomonas stutzeri for antifungal activity and enzyme specificity. The six enzymes were tested for antifungal activity using an assay based upon inhibition of hyphal extension of the fungi Trichoderma reesei and Phycomyces blakesleeanus. Antifungal activity was observed with as little as 1 μg of each of the grain chitinases, whereas none of the bacterial chitinases had any effect on hyphal extension, even at 50 #x03BC;g chitinase per assay. This difference in antifungal activity correlated with the different mechanisms of action of the two classes of enzymes. In common with other plant chitinases, the grain chitinases functioned as endochitinases and contained lysozyme activity. In contrast, the bacterial enzymes were exochitinases and hydrolysed the chromogenic trisaccharide analogue p-nitrophenyl-β-D-N, N′-diacetylchitobiose, which proved to be an excellent substrate for assaying bacterial chitinases. These experiments strengthen the hypothesis that plant chitinases function to protect the host against fungal infections.