Early events induced by chitosan on plant cells

Chitosan (a polymer of p-1,4-glucosamine residues) is a deacetylated derivative of chitin which presents antifungal properties and acts as a potent elicitor of plant resistance against fungal pathogens. Attention was focused in this study on the chitosan-induced early events in the elicitation chain. Thus, it was shown that chitosan triggered in a dose-dependent manner rapid membrane transient depolarization of Mimosa pudica motor cells and, correlatively, a transient rise of pH in the incubation medium of pulvinar tissues. By using plasma membrane vesicles (PMVs), it was specified that a primary site of action of the compound is the plasma membrane H + -ATPase as shown by its inhibitory effect on the proton pumping and the catalytic activity of the enzyme up to 250 |jig m -1 . As a consequence, chitosan treatment modified H + -mediated processes, in particular it inhibited the uptake of the H + -substrate co-transported sucrose and valine, and inhibited the light-induced H + /K + -mediated turgor reaction of motor cells. The present data also allowed the limit of the cytotoxicity of the compound to be established close to a concentration of 100 μg ml -1 at the plasma membrane level. As a consequence, chitosan could be preferably used in plant disease control as a powerful elicitor rather than a direct antifungal agent.