Inhibition of fungal growth by plant chitinases andβ-1,3-glucanases - A morphological study

Plant chitinases and β-1,3-glucanases have been demonstrated to inhibit fungal growth in model experiments, both on agar plates or in liquid media. Here, Trichoderma longibrachiatum was taken as a model to study the morphological changes caused by chitinase and glucanase treatments, using cytochemical techniques in combination with fluorescence and electron microscopy. Chitinase, alone or in the presence of glucanase, arrested growth of the hypha: it affected the extreme tip of the fungus producing a thinning of the wall, a balloon-like swelling and a rupture of the plasma membrane. Chitin and glucans were present in the wall, as shown by lectinand enzyme-binding experiments, but they had a different susceptibility to chitinase and β-1,3-glucanase. Chitin was present at the apex and in the inner parts of the lateral walls; it was more susceptible to chitinase at the tip than in the subapical part. Glucans mostly occurred on the outer layer where they were degraded by glucanase. The latter did not affect the inner hyphal skeleton. It is suggested that the growth inhibition of Trichoderma by hydrolytic enzymes is the consequence of a thinning of the cell wall in the hyphal apex, leading to an imbalance of turgor pressure and wall tension which causes the tip to swell and to burst.