NO and melatonin interplay augment Cd-tolerance mechanism in eggplants: ROS detoxification and regulation of gene expression.

Global crop productivity is consistently threatened by cadmium (Cd) soil contamination. Crosstalk between nitric oxide (NO) and melatonin (MT) in enhancing crop resilience to heavy metal stress has gained significant attention. Here, we evaluated the joint effect of sodium nitroprusside (SNP; 200 μM as NO donor) and MT (100 μM) on Cd-stressed eggplant (Solanum melongena L.). Cd stress significantly reduced plant growth, biomass yield, leaf pigments, and biochemical properties. Conversely, SNP, MT, and particularly their combined (SNP + MT) application reduced Cd toxicity and enhanced growth and physio-biochemical traits of eggplants. For instance, at 50 mg Cd kg-1 soil, SNP, MT, and SNP + MT increased root biomass (41.6, 30, and 47%), total chlorophyll (30.7, 26.3, and 46%), soluble protein (20.5, 17.6 and 37%) and RLWC (23, 17.5, and 29%) over their respective control. Furthermore, SNP + MT significantly (p ≤ 0.05) reduced levels of EL, H2O2, proline, and MDA by 54.5, 66, 61 and 70%, respectively, in Cd-stressed eggplants. SNP + MT interplay enhanced antioxidant defense responses in leaf tissues under Cd stress. Besides, SNP and MT upregulated transcript levels of POD, SOD, CAT, and GPX genes in eggplants under Cd stress. SNP and MT applications improved essential nutrient cation homeostasis in Cd-stressed shoot tissues of eggplants. Moreover, SNP + MT lessens metal-induced toxicity by decreasing Cd uptake, translocation (TF) and bioconcentration (BCF) factors. Conclusively, these findings validated the beneficial defensive interaction between SNP and MT in regulating Cd tolerance in eggplants. However, further research is needed to uncover the underlying defensive mechanisms of these synergistic effects.