Effects of different concentrations of chitosan bio-stimulant on some physiological and biochemical traits of Andrographis paniculate L.

Chitosan is a nitrogen containing polysaccharide synthesized naturally by deacetylation reaction of chitin, which is confirmed as an efficient bio-stimulant to improve production of secondary metabolites in medicinal plants. In the present study, the effects of chitosan (0, 100, 200, 300, and 400 mg/L) on growth, photosynthetic pigments, secondary metabolites, antioxidant capacity, activity of antioxidant enzymes, quantity and quality of protein, and the expression of HMGS and HMGR genes were examined in Andrographis paniculata L. The results showed that application of chitosan significantly increased the chlorophyll and carotenoids and, as a result, increased plant growth and biomass. Chitosan treatments (300 and 400 mg/L) increased the expression of HMGS and HMGR genes in plant leaves, which was associated with a significant increase in the accumulation of total phenols and flavonoids. Also, chitosan improved the activity of superoxide dismutase and peroxidase enzymes and increased the antioxidant capacity of A. paniculata leaves. Examination of the quantity and quality of proteins showed that the intensity of protein bands with the molecular weight of 60 kD under 300 and 400 mg/L chitosan treatment and also the intensity of protein bands with the molecular weights of 35 and 20 kD under 300 mg/L chitosan treatment increased compared to the other concentrations. Therefore, these results revealed that application of chitosan can increase accumulation of secondary metabolites and the antioxidant capacity in the medicinal plant A. paniculata.