Nitric oxide induced Cd tolerance and phytoremediation potential of B. juncea by the modulation of antioxidant defense system and ROS detoxification.

The present study designed to illustrate correlation between cadmium induced stress and plant growth, photosynthetic pigments, morphological and physiological attributes. To study these parameters 2 weeks old seedling of B. juncea were subjected to 50 µM Cd, 100 µM Cd and 100 µM SNP separately and in combination with SNP. After 96 h, the treated plant were harvested to analyze the cellular homeostasis and metal tolerance mechanism via examining growth, stress parameters, enzymatic and non enzymatic antioxidants and expression level of NR. Higher level of Cd (100 µM) significantly increased accumulation of reactive oxygen species and malonaldehyde content in comparison to 50 µM Cd. Exogenous supplementation of SNP (100 µM) to 50 µM Cd treated plant had an additive effect on plant growth by improving the level of proline, photosynthetic pigments and activities of enzymatic antioxidants which was confirmed by histochemical staining for NADPH-d and NO fluorescence from DAF-DA staining in roots of B. juncea. Applying SNP to 50 µM Cd exposed B. juncea roots enhanced NR activity by 1.36 folds and increased NO production by 1.12 folds than individual Cd treated roots. In addition, semi quantitative RT-PCR study revealed the induction of BjNR was more pronounced in 50 µM Cd treated roots in comparison to 100 µM Cd treated roots. The present finding revealed NO confers increased B. juncea tolerance to Cd stress by stimulation of antioxidants and reestablishment of cellular redox status. Different biochemical analysis showed that plant growth, photosynthetic pigment and antioxidants were positively correlated with NO and it's negatively correlated with oxidative stress biomarkers. Therefore, NO is gaseous signalling molecule with potential role in Cd detoxification mechanism in B. juncea.