Melatonin and Hydrogen Sulfide Signaling Synergistically Enhance Iron Bioavailability and Stress Resilience in Strawberry Under Iron Deficiency

Abstract

Iron (Fe) deficiency is a critical constraint on global food security, particularly affecting high-value horticultural crops such as strawberries (Fragaria × ananassa). This study examines the roles of melatonin and hydrogen sulfide (H₂S) signaling in mitigating Fe deficiency stress by improving Fe bioavailability and enhancing plant resilience. Strawberry plants were cultivated under Fe-sufficient and Fe-deficient conditions and treated with 100 μM melatonin and 3 mM dl-propargylglycine (PAG), an inhibitor of L-cysteine desulfhydrase (L-DES), which regulates H₂S production. Fe deficiency significantly reduced chlorophyll content and photosynthetic efficiency while elevating oxidative stress markers such as hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and electrolyte leakage (EL). Melatonin application alleviated Fe deficiency effects by enhancing Fe utilization, stimulating L-DES activity, and promoting H₂S production. Melatonin also improved antioxidant defenses by boosting the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), as well as maintaining ascorbate-glutathione (AsA-GSH) redox dynamics. The addition of 3 mM PAG inhibited L-DES activity, resulting in reduced H₂S levels and diminished melatonin-induced benefits, underscoring the essential role of L-DES-mediated H₂S synthesis. Despite the presence of PAG, the co-application of 0.2 mM sodium hydrosulfide (NaHS) and melatonin restored Fe bioavailability, growth, and antioxidant capacity, suggesting a synergistic interaction between melatonin and H₂S. This study highlights the potential of melatonin and H₂S signaling to improve Fe homeostasis and mitigate oxidative stress in Fe-deficient plants. The findings offer strategies to enhance crop resilience and productivity in nutrient-deficient soils, thereby promoting sustainable agriculture and global food security.