Modulatory role of jasmonic acid on photosynthetic pigments, antioxidants and stress markers of Glycine max L. under nickel stress

Jasmonic acid (JA) is a very young candidate of plant growth regulators which is being explored for various antistress properties. Present study deals with the hypothesis that JA can modulate antioxidant mechanism of higher plants with tight regulation of biomembrane peroxidation, making plants tolerant to toxic Ni2+. 2 mM NiCl2 as a source of Ni2+ appeared as sub lethal dose for the growth of 15 days old Glycine max seedlings. Exogenous application of 1 μM and 1 nM JA prior to NiCl2 exposure, made seedlings of Glycine max more tolerant to Ni2+stress as compared to control untreated seedlings. Regulatory inhibition of MDA and H2O2 production by JA with or without Ni2+ treatment made plants more resistant to Ni2+ stress which may be associated with ameliorative activity of antioxidant enzymes system composed of SOD, POD, CAT and APOX. Ascorbate, a secondary metabolite synthesized from D-glucose act as an antioxidant in plant cells. Many fold enhancements in AsA content of Ni2+ treated seedlings supplemented with different concentrations of JA was observed. Significant improvement in AsA levels by JA with or without Ni2+ stress may involve two aspects, either denovo synthesis level regulation of AsA or recycling of AsA from an oxidized form. Improvement in total protein content showed the uplift modulation of transcriptional machinery by JA which was also maintained under Ni2+ stress. Photosynthetic pigments as total chl, chl a and b showed inhibition in presence of Ni2+ stress which was not found much effective under JA supplementation as compared to control. Present findings revealed that although JA was not helpful for protection of photosynthetic pigments but it modulates the other machinery of plants significantly including various antioxidants positively, while tightly inhibiting stress related processes responsible for lipid peroxidation to make plants tolerant to Ni2+ stress.