Hydrogen sulphide (H₂S) is emerging as a potential messenger molecule involved in modulation of physiological processes in animals and plants. In this report, the role of H₂S in modulating photosynthesis of Spinacia oleracea seedlings was investigated. The main results are as follows. (i) NaHS, a donor of H₂S, was found to increase the chlorophyll content in leaves. (ii) Seedlings treated with different concentrations of NaHS for 30 d exhibited a significant increase in seedling growth, soluble protein content, and photosynthesis in a dose-dependent manner, with 100 μM NaHS being the optimal concentration. (iii) The number of grana lamellae stacking into the functional chloroplasts was also markedly increased by treatment with the optimal NaHS concentration. (iv) The light saturation point (Lsp), maximum net photosynthetic rate (Pmax), carboxylation efficiency (CE), and maximal photochemical efficiency of photosystem II (F_v/F_m) reached their maximal values, whereas the light compensation point (Lcp) and dark respiration (Rd) decreased significantly under the optimal NaHS concentration. (v) The activity of ribulose-1,5-bisphosphate carboxylase (RuBISCO) and the protein expression of the RuBISCO large subunit (RuBISCO LSU) were also significantly enhanced by NaHS. (vi) The total thiol content, glutathione and cysteine levels, internal concentration of H₂S, and O-acetylserine(thiol)lyase and L-cysteine desulphydrase activities were increased to some extent, suggesting that NaHS also induced the activity of thiol redox modification. (vii) Further studies using quantitative real-time PCR showed that the gene encoding the RuBISCO large subunit (RBCL), small subunit (RBCS), ferredoxin thioredoxin reductase (FTR), ferredoxin (FRX), thioredoxin m (TRX-m), thioredoxin f (TRX-f), NADP-malate dehydrogenase (NADP-MDH), and O-acetylserine(thiol)lyase (OAS) were up-regulated, but genes encoding serine acetyltransferase (SERAT), glycolate oxidase (GYX), and cytochrome oxidase (CCO) were down-regulated after exposure to the optimal concentration of H₂S. These findings suggest that increases in RuBISCO activity and the function of thiol redox modification may underlie the amelioration of photosynthesis and that H₂S plays an important role in plant photosynthesis regulation by modulating the expression of genes involved in photosynthesis and thiol redox modification.

Various signaling pathways rely on changes in cytosolic calcium ion concentration ([Ca ²⁺ ] _i ). In plants, resting [Ca ²⁺ ] _i oscillates diurnally. We show that in Arabidopsis thaliana , [Ca ²⁺ ] _i oscillations are synchronized to extracellular Ca ²⁺ concentration ([Ca ²⁺ ] _o ) oscillations largely through the Ca ²⁺ -sensing receptor CAS. CAS regulates concentrations of inositol 1,4,5-trisphosphate (IP ₃ ), whichinturndirects release of Ca ²⁺ from internal stores. The oscillating amplitudes of [Ca ²⁺ ] _o and [Ca ²⁺ ] _i are controlled by soil Ca ²⁺ concentrations and transpiration rates. The phase and period of oscillations are likely determined by stomatal conductance. Thus, the internal concentration of Ca ²⁺ in plant cells is constantly being actively revised.

Hydrogen sulfide (H₂S) and nitric oxide (NO) are emerging as messenger molecules involved in the modulation of plant physiological processes. Here, we investigated a signalling network involving H₂S and NO in salt tolerance pathway of barley. NaHS, a donor of H₂S, at a low concentration of either 50 or 100 μM, had significant rescue effects on the 150 mM NaCl-induced inhibition of plant growth and modulated the K⁺/Na⁺ balance by decreasing the net K⁺ efflux and increasing the gene expression of an inward-rectifying potassium channel (HvAKT1) and a high-affinity K⁺ uptake system (HvHAK4). H₂S and NO maintained the lower Na⁺ content in the cytoplast by increasing the amount of PM H⁺-ATPase, the transcriptional levels of PM H⁺-ATPase (HvHA1) and Na⁺/H⁺ antiporter (HvSOS1). H₂S and NO modulated Na⁺ compartmentation into the vacuoles with up-regulation of the transcriptional levels of vacuolar Na⁺/H⁺ antiporter (HvVNHX2) and H⁺-ATPase subunit β (HvVHA-β) and increased in the protein expression of vacuolar Na⁺/H⁺ antiporter (NHE1). H₂S mimicked the effect of sodium nitroprusside (SNP) by increasing NO production, whereas the function was quenched with the addition of NO scavenger. These results indicated that H₂S increased salt tolerance by maintaining ion homeostasis, which were mediated by the NO signal.