Hydrogen Sulfide Is Involved in Melatonin-Induced Drought Tolerance in Maize (Zea mays “Beiqing340”)

Melatonin and hydrogen sulfide (H₂S) have both been demonstrated to enhance plant drought tolerance. However, the relationship between melatonin and H₂S during the drought resistance response remains unclear. In this study, under drought stress, the synthesis pathways for both melatonin and H₂S in maize seedlings were activated. The application of exogenous melatonin enhanced the expression of key genes, namely LCD and DCD, which are involved in H₂S synthesis, thereby promoting the accumulation of H₂S. Conversely, the application of NaHS did not significantly influence the expression of genes related to melatonin synthesis or the levels of endogenous melatonin. Melatonin enhanced drought tolerance in maize through the H₂S signaling pathway, as evidenced by a 124.1% increase in the photosynthetic rate and improved activity of antioxidant enzymes. Specifically, there were increases of 66.5%, 75.6%, and 51.0% in the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), respectively. Furthermore, there was an elevation in the levels of osmotic regulatory substances and non-enzymatic antioxidants. The application of the H₂S scavenger (HT) significantly inhibited the drought tolerance effects mediated by melatonin, whereas the melatonin synthesis inhibitor (p-CPA) did not exert a significant impact on the drought resistance induced by H₂S. Overall, our findings suggest that H₂S plays a role in the melatonin-mediated enhancement of drought tolerance in maize, primarily through coordinated modulation of osmotic balance and antioxidant defense systems.