Melatonin-mediated redox balance, nutrient acquisition, and endogenous hormone levels confer vanadium stress resilience in pea

Vanadium (V) toxicity impairs pea plants' secondary metabolites, nutrient acquisition, and photosynthesis. • V toxicity increases oxidative stress biomarkers in rice plants. • Melatonin (MT) mitigates V toxicity and promotes growth. • MT improves nutrient acquisition and antioxidant activity in rice leaves under V stress. • MT regulates phytohormone-related genes, enhancing rice biomass and growth. Vanadium (V) stress is a potential challenge for sustainable crop production and healthy plant growth. The potential of melatonin (MT) in V stress mitigation has remained unexplored in the pea plant. In the present study, we investigated the role of exogenous melatonin (MT1; 45 µM, MT2; 75 µM) application in diminishing the adverse effect of V exposure (100 µM) in pea seedlings. Our results showed that V stress negatively affected the germination, biomass, photosynthetic attributes, secondary metabolites, and nutrient acquisition, as well as increased oxidative stress. Moreover, V stress has altered the expression of phytohormone-related genes via enhanced uptake of V. Conversely, the supplementation of MT significantly reversed the negative effect of V stress. Furthermore, MT2+V treatment decreased the malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ) content and improved the photosynthetic attributes, rate of respiration, total phenol, and flavonoid content. Besides, MT2+V enhanced the antioxidant defense system activities, as well as the nutrient content (K, Mg, and Zn) while decreasing the V uptake. The MT2+V treatment also modulated the expression levels of phytohormone-related genes in pea seedlings, with LOX1, LOX2, ACS3 , and JAR1 being upregulated, while OPR1 and NCED 2 were downregulated, which might enhance the plant defense against overproduction of reactive oxygen species (ROS). In conclusion, the present study provided the key insights about the possible role of the MT in the modulation of V stress in pea plants, as well as its use as a priming agent in the alleviation of heavy metal stresses in crop plants.