Hydrogen peroxide is involved in hydrogen sulfide-induced carbon assimilation and photoprotection in cucumber seedlings

Hydrogen sulfide (H2S) and Hydrogen peroxide (H2O2) are two crucial gaseous signaling molecules that participate in various physiological processes and abiotic stresses. However, how the synergy of H2S and H2O2 regulates photosynthesis have rarely been studied. This study aimed to reveal the mechanism underlying the interaction between H2S and H2O2 in plants response to photosynthesis. Cucumber (Cucumis sativus L., 'Jinyou 35') seedlings were used as the material and grown in a climate chamber at 26 degrees C/18 degrees C with a 600 mu mol m(-2).s(-1) photon flux density (PFD). Sodium hydrosulfide hydrate (NaHS, an H2S donor), H2O2, and their scavengers or inhibitors were applied as foliar sprayed at the two-leaf seedling stage. The result showed that both NaHS and H2O2 increased the CO2 assimilation, which mainly attributed to an increase in the activity and gene expression of photosynthetic enzymes. NaHS and H2O2 also induced photoprotection for both photosystem II (PSII) and photosystem I (PSI) in cucumber seedlings, by activating the D1 protein repair pathway under chilling stress. Interestingly, 1.0 mM NaHS significantly enhanced the relative gene expression of respiratory burst oxidase homolog (RBOH), which in turn elevated endogenous H2O2 accumulation in cucumber seedlings. However, H2O2 had little effect on gene expression of L-/D-cysteine desulfhydrase (L-/D-CD) and endogenous H2S level. The H2S-induced adaptive response of photosynthesis to chilling stress was suppressed by diphenyleneiodonium (DPI, a H2O2 generation inhibitor) or dimethylthiourea (DMTU, a H2O2 scavenger). These data suggest that NaHS alleviates the negative effects of chilling stress on photosynthesis by improving photosynthetic carbon assimilation, carbon metabolism, and photoprotection for both PSII and PSI in cucumber seedlings. H2O2 may act as a downstream signal in H2S-induced protection of the photosynthetic apparatus in cucumber seedlings under chilling stress.