Synergistic role of melatonin and hydrogen sulfide in modulating secondary metabolites and metal uptake/sequestration in arsenic-stressed tomato plants.

• ML and H 2 S increased the accumulation of anthocyanin and phenolic compounds under as stress. • ML and H 2 S decreased the expression of PT2 and Lsi1 and declined as accumulation under as toxicity. • ML and H 2 S increased the expression of GSH1, PCS , and ABC1 and sequestered as in the roots. • ML and H 2 S strengthened the antioxidant defense system and improved chlorophyll metabolism. The multifunctional roles of melatonin (ML) and hydrogen sulfide (H 2 S) as plant gasotransmitters are well understood. However, their interaction in defensive responses is still unclear. Here, we assessed how the ML-H 2 S interaction impacts tomato plants exposed to arsenic (As, 10 mg/L) toxicity. The results showed that ML and ML+H 2 S treatments alleviated As toxicity by inducing the transcription of ANS, PAL, DFR, CHS , F 3 H, and CHI and an enhanced accumulation of phenolic and anthocyanin compounds. ML and ML+H 2 S led to a drop in the transcription of PT2 and Lsi1 , resulting in reduced As uptake and subsequent movement to the leaves. ML and ML+H 2 S treatments resulted in high GSH1, PCS , and ABC1 transcription. This led to elevated levels of glutathione and phytochelatins, facilitating As sequestration in the roots and protecting root and leaf cells against As. ML and ML+H 2 S treatments enhanced tomato growth under As treatments by optimizing chlorophyll metabolism, increasing internal H 2 S, and amplifying the antioxidant machinery function. In contrast to the sole use of ML treatment, ML+H 2 S exhibited more pronounced positive impacts on As-stressed tomatoes, indicating synergistic/interactive effects between these two substances. On the other hand, the use of hypotaurine, an H 2 S scavenger, demonstrated the inhibition of the beneficial impact of ML and ML+H 2 S treatments in stimulating defensive responses, which highlights the substantial involvement of H 2 S in the signaling pathway activated by ML during As stress. Hence, we can conclude that ML requires the presence of endogenous H 2 S to mitigate the adverse effects of As on tomato seedlings. [Display omitted] [ABSTRACT FROM AUTHOR]