Nitric oxide alters nitrogen metabolism and PIN gene expressions by playing protective role in arsenic challenged Brassica juncea L.

Plants have ability to adapt themselves through altering their growth process. In the present study, we examined exogenous application of nitric oxide (NO) on nitrogen metabolism and auxin (PIN) gene expression, and its possible role in alleviation of arsenic (As) toxicity in Brassica juncea seedlings. Seven days old hydroponically grown B. juncea seedlings were exposed to As ^III (150 μM), Sodium nitroprusside (NO donor, 100 μM), As ^III  + SNP and control (without metal)for 48 h. Experimental results revealed that As ^III stress: enhanced the level of nitrite, NiR activity, NO ₃ ^- and NH ₄ ⁺ content as well as NADH-GOGAT activity; but GDH level decreased; enhanced content of amino acids; upregulated gene expression level of N metabolism and downregulated polar auxin transporter genes (PIN); inhibited plant growth and morphological parameters; increased MDA, H ₂ O _2, cysteine, proline content, enzymatic antioxidants (SOD, CAT, APX; GSH, TT, NPT); and decreased nutrient content. As ^III  + SNP combination reduced the accumulation of As; improved growth; chlorophyll, protein and mineral nutrient content by scavenging ROS generation; maintained amino acids content; downregulated expression of N metabolism genes and upregulated expression of auxin transporter (PIN) genes . Additional biochemical data depicts reduction in the level of nitrogen related enzymatic activities, and other stress related parameters. Overall, this study provides an integrated view that exogenous SNP (NO donor) supplementation alleviated the inhibitory role of As ^III in B. juncea seedlings by altering nutrients, amino acids and auxin redistribution via expression of nitrogen and PIN gene profiling.
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