Abscisic acid mediates the chitosan-induced resistance in plant against viral disease

Chitosan (CHT) antiviral activity has been further investigated in the pathosystem Phaseolus vulgaris –tobacco necrosis virus (TNV). CHT application elicited both callose apposition and ABA accumulation in leaf tissues, at 12 and 24 h after treatment, respectively, and induced a high level of resistance against TNV. Besides, treatment with the ABA inhibitor nordihydroguaiaretic acid (NDGA), before CHT application, reduced both callose deposition and plant resistance to the virus, thus indicating the involvement of ABA in these processes. Exogenous application of ABA also induced a significant resistance to TNV, though this resistance was abolished by NDGA pre-treatment. These results, overall, indicate that the rise of ABA synthesis induced by chitosan plays an important role in enhancing callose deposition but the latter has only a partial effect on virus spreading, which must be constraint by other resistance mechanisms.