ABSTRACT
BACKGROUND: Chitosan is a polycationic polysaccharide derived from chitin that has been recognized as an effective elicitor in the production of secondary metabolites of many medicinal plants. In this study, the effect of abiotic elicitor (chitosan) at various concentrations on rosmarinic acid (RA) and total phenolic accumulation in shoot cultures of lemon balm was investigated. RESULTS: Treatment of shoots by chitosan led to a noticeable induction of phenylalanine ammonia-lyase (PAL), catalase (CAT), guaiacol peroxidase (GPX) and lipoxygenase (LOX) activities. Besides, the expression of PAL1, TAT and RAS genes and accumulation of RA and phenolic compound increased in chitosan-treated lemon balm shoots. Chitosan treatment also increased H2O2 accumulation and the expression of RBOH, an essential gene implicated in ROS production. Also, the up-regulation of the OPR gene by exogenous chitosan was associated with the induction of endogenous JA determined by GC-MASS. CONCLUSION: The present study showed that the induced production of rosmarinic acid by chitosan involves the trigger of defense-related enzymes, up-regulated expression of TAT and RAS genes, and stimulation of JA biosynthesis.
