Bidirectional association of MT with H₂S improves maize heat resilience through modulation of ROS and methylglyoxal...

Melatonin (MT) and hydrogen sulfide (H₂S) are important signaling molecules, which regulate cellular metabolism and stress resilience. However, a bidirectional association of MT with H₂S in maize heat resilience is unknown. In this study, their interactions and relation with reactive oxygen species (ROS) and methylglyoxal detoxification pathways in maize heat resilience are investigated. The results showed that MT and H₂S treatment alone increased survival rate and tissue vitality, decreased malondialdehyde content and electrolyte leakage in maize seedlings under heat stress, whereas these effects were abolished by their inhibitors and scavengers. Also, MT enhanced L-cysteine desulfhydrase (LCD) and D-cysteine desulfhydrase (DCD) activities and ZmLCD expression, thus increasing endogenous H₂S content; whereas the MT-increased H₂S was separately blocked by hypotaurine (HT), H₂S scavenger, and propargylglycine (PAG), H₂S inhibitor. Similarly, NaHS, H₂S donor, up-regulated N-acetylserotonin methyltransferase (ASMT) and serotonin N-acetyltransferase (SNAT) activities and ZmASMT expression, increased endogenous MT level. Conversely, the NaHS-increased MT was eliminated by 4-chloro-DL- phenylalanine (CPA) and fluoxetine (FLX), MT inhibitors. Additionally, MT and H₂S alone enhanced the activity of ROS and methylglyoxal detoxification systems; whereas the enhanced detoxification system was counteracted by HT, PGA, CPA, and FLX. These data suggest that MT may be bidirectionally associated with H₂S, which in turn modulates ROS and methylglyoxal detoxification pathways to improve maize heat resilience.