Melatonin Attenuates Cadmium-Induced Oxidative Stress in Potato by Remodeling Redox Homeostasis and Activating Multi-Pathway Antioxidant Networks.

Cadmium pollution severely suppresses potato growth, impairs photosynthesis, and disrupts cellular redox balance, threatening crop yield and food safety. Exogenous small-molecule regulators represent low-cost strategies to alleviate heavy-metal phytotoxicity, yet systematic comparisons of N-acetyl-L-cysteine (NAC), L-tryptophan (Trp), and melatonin (MT) on Cd-stressed potatoes remain insufficient. In this study, two rounds of concentration-gradient screening using morphological and physiological assays identified 5 μM of melatonin as the optimal treatment to alleviate cadmium-induced damage in potato seedlings. This concentration significantly restored shoot height, root length, fresh weight, and chlorophyll content. Relative to the Cd-only control, 5 μM of MT reduced MDA and cadmium accumulation by 51.88% and 49.26%, respectively, while increasing proline content by 40.99%. Transcriptomic analysis revealed that MT reversed Cd-induced suppression of photosynthesis and carbon fixation pathways and activated carbohydrate metabolism. Weighted gene co-expression network analysis identified four key modules significantly correlated with Cd tolerance and MT-mediated recovery. Eight hub genes, including StANNAT1 (Ca2+-ROS homeostasis), StNRT1.1 (nitrogen transport), StSWEET10 (carbon allocation), and StHMG1 (MVA pathway), were validated by qPCR, confirming their involvement in Ca2+-ROS signaling, membrane integrity, and photosynthetic recovery. Mechanistically, MT rebalanced cellular redox status, promoted Cd sequestration, optimized carbon-nitrogen distribution, and enhanced antioxidant defense. These findings demonstrate that exogenous MT alleviates Cd toxicity through coordinated regulation of multiple pathways, providing a practical strategy for safe potato cultivation in Cd-contaminated soils and establishing a molecular framework for understanding MT-mediated heavy-metal tolerance in crops.