Chitosan physico–chemical properties modulate defense responses and resistance in tobacco plants against the oomycete Phytophthora nicotianae

Enzymatic defense responses and protection against Phytophthora nicotianae were studied in tobacco plants treated with chitosan of different molecular weights (MW) and degrees of acetylation (DA). The concentration and mode of chitosan application affected enzymatic induction in tobacco leaves. β-1,3-Glucanase (EC 3.2.1.6) activity required 10 times the polymer concentration relative to the oligochitosan mixture to induce the highest activity above control when treated by foliar spray, indicating the influence of molecular weight in this response. PAL (EC 4.3.1.5) and POD (EC 1.11.1.6) activities increased above control as a result of the influence of polymer degree of acetylation when treatments were applied by foliar spray. A higher DA favored PAL activity, whereas a lower DA induced higher POD activity. Using an in vitro bioassay, it was found that the three chitosan compounds caused a reduction of the infection index of P. nicotianae in tobacco plants that was dependent on elicitor concentrations. There was a significant relationship between the reduction of the infection index and an increase in PAL activity when chitosan was applied by foliar spray and by substrate drench to the plant rhizosphere. These results demonstrate the influence of chitosan physico–chemical properties in plant-induced resistance and the relevance of particular responses in plant protection against pathogens.

Changes in soluble protein contents, β-1,3-glucanase, PAL and POD activities in leaves of 25 days old tobacco plants treated with chitosan compounds of different molecular weight, degree of acetylation and concentrations. Treatments were applied by foliar spray (A), soil drench to the plant rhizosphere (B) 72 h before foliar extraction and by soil drench to the substrate at seeding (C).Figure optionsDownload as PowerPoint slideHighlights
► We examined local and systemic enzymatic (β-1,3-glucanase, PAL and POD) responses in tobacco plants induced by chitosans.
► Chitosan molecular weight and degree of acetylation determine enzymatic activities induced in tobacco leaves.
► Chitosans treatments protect tobacco plants against Phytophthora nicotianae infection.
► This tobacco resistance against P. nicotianae seems to be related to β-1,3-glucanase and PAL activities induced by chitosans.