Abstract
Chitosan (a polymer of b-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 mg
ml21. 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 mg ml21
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.