Selenium modulates dynamics of antioxidative defence expression, photosynthetic attributes and secondary metabolites to mitigate chromium toxicity in Brassica juncea L. plants

The study envisages the stress protective role of selenium (Se) against chromium (Cr) toxicity in Brassica juncea L. Plants were raised in pots with soils containing Cr (0 and 300 μMKg−1) and Se (0, 2, 4 and 6 μMKg−1) in binary combinations and harvested after 30 days of sowing. The harvested plant material was processed for several biochemical and molecular parameters. The observations made on significant results suggested that Se was able to protect the plants by restoring growth, reducing the oxidative damage (low levels of superoxide anions and hydrogen peroxide), and strengthened the enzymatic and non-enzymatic defence systems of B. juncea plants. Quantitative real time PCR studies on gene expression revealed that the expression of genes encoding the antioxidative enzymes (SOD, POD, CAT, GR and GST-1) was enhanced with Se application. Elevated contents of chlorophylls, carotenoids and gas exchange parameters also indicated that Se is instrumental in promoting photosynthetic efficiency, thereby ameliorating Cr toxicity. The expression of genes related to chlorophyll degradation also confirmed the observations. The contents of secondary metabolites (total phenols, flavonoids and anthocyanins) and the relative gene expression of phenylalanine ammonialyase and chalcone synthase, also showed enhanced levels in response to Se. The results thus indicated that Se application improves the overall physio-chemical characteristics of plants and helps them to overcome stress induced by Cr in the soil.