Silicon and Melatonin Mitigate Chromium Stress in Ethiopian Mustard ( Brassica carinata A. Br. cultivar Merawi) by Enhancing Stress Tolerance Mechanisms

Chromium (Cr) stress is a serious threat to global food security as it reduces plant growth, causes oxidative damage, disturbs physiological functions, and affects metabolism. This study explored how applying silicon (Si) and melatonin (MT), alone or together, helps Ethiopian mustard ( Brassica carinata ) cope with Cr toxicity. The results showed that Cr stress (0.5 mM) greatly reduced growth, photosynthetic efficiency, and gas exchange, increased oxidative damage, disturbed water balance, and altered metabolic activity. However, treatment with Si+MT, followed by Si and MT alone, improved plant growth, boosted the accumulation of secondary metabolites and proline, enhanced water relations, gas exchange, photosynthesis, and chlorophyll fluorescence, while lowering ROS levels and maintaining redox balance. Heatmap and Mantel analyses showed strong connections among growth, metabolism, antioxidant activity, and physiological traits. Overall, this study highlights that combined use of Si and MT is an effective and sustainable approach to reduce Cr toxicity and strengthen plant defense mechanisms.