Chromium mediated damaging effects on growth, nitrogen metabolism and chlorophyll synthesis in tomato can be alleviated by foliar application of melatonin and jasmonic acid priming

Efficiency of methyl-jasmonate (5 mu M Me-J) priming and the foliar application of melatonin (100 mu M ML) in assuaging the deleterious effects of chromium (Cr) toxicity on growth, nitrogen metabolism, chlorophyll syn-thesis and photosynthesis in tomato were studied. Chromium toxicity reduced growth, chlorophyll synthesis and photosynthesis significantly, however Me-J and ML significantly enhanced the parameters. Decline in the in-termediates of chlorophyll biosynthesis pathway i.e., glutamate 1-semialdehyde, delta-amino levulinic acid, Mg-prototoporphyrin IX, prototoporphyrin IX and protochlorophyllide due to Cr was alleviated to considerable levels due to Me-J and ML treatment. Toxicity of Cr was evident as increased production of superoxide and hydrogen peroxide, and activity of lipoxygenase and protease while as Me-J and ML treatment alleviated the oxidative damage by causing significant decline in these parameters. Priming with Me-J and foliar application of ML alleviated the Cr toxicity induced decline in the activities of nitrogen metabolising enzymes. Treatment of Me-J and ML up-regulated the antioxidant system functioning, increased the content of secondary metabolites and activity of phenylalanine ammonia lyase. Accumulation of osmolytes increased due to Me-J and ML under normal as well as Cr toxicity conditions. Treatment of Me-J and ML increased the gamma-glutamyl kinase activity with significant reduction in proline oxidase.