Hua Zhang

Hydrogen sulfide (H2S) has been recently found to be a gaseous signaling molecule in plants. In this work, we studied the role of H2S in alleviating salinity stress during wheat grain germination (Triticum aestivum L. Yangmai 158). Pretreatment with NaHS, a H2S donor, during wheat grain imbibition, could significantly attenuate the inhibitory effect of salinity stress on wheat germination. NaHS-pretreated grain showed higher amylase and esterase activities than water control. NaHS pretreatment differentially stimulated the activities of catalase (CAT), guaiacol peroxidase (POD) and ascorbate peroxidase (APX), decreased the level of malondialdehyde (MDA) and reduced NaCl-induced changes in plasma membrane integrity in the radicle tips of seedlings compared with water control. We conclude that H2S plays an important role in protecting wheat grain from oxidative damage induced by salinity stress.

Broccoli ( Brassica oleracea var. italica ) is an important vegetable crop rich in vitamins and sulforaphane. However, the floral heads of broccoli experience rapid postharvest senescence. Here we found that hydrogen sulfide (H ₂ S) treatment alleviated dark-promoted senescence in broccoli florets. H ₂ S delayed the symptoms of senescence and maintained higher levels of chlorophyll and Rubisco and lower protease activity compared with water control. Gene expression analysis showed that H ₂ S down-regulated the expression of chlorophyll degradation-related genes BoSGR , BoNYC , BoCLH1 , BoPPH, and BoRCCR . Expression of lipoxygenase gene BoLOX1 and the genes involved in the ethylene synthesis pathway, BoACS2 and BoACS3, were also down-regulated by H ₂ S. The reduced expression level in cysteine protease gene BoCP3 and aspartic protease gene BoLSC807 suggested the role of H ₂ S in alleviating protein degradation during broccoli senescence. H ₂ S up-regulated the expression of sulfur metabolism genes BoSR and BoOASTL, and the antioxidant gene BoCAT . These results show that H ₂ S plays a vital role in alleviating broccoli senescence through a broad regulation on gene expression of reactive oxygen species (ROS) metabolism genes, ethylene synthesis genes, and protease genes.

Aluminum ions are especially toxic to plants in acidic soils. Here we present evidences that SO₂protects germinating wheat grains against aluminum stress. SO₂donor (NaHSO₃/Na₂SO₃) pretreatment at 1.2 mM reduced the accumulation of superoxide anion, hydrogen peroxide, and malondialdehyde, enhanced the activities of guaiacol peroxidase, catalase, and ascorbate peroxidase, and decreased the activity of lipoxygenase in germinating wheat grains exposed to Al stress. We also observed higher accumulation of hydrogen sulfide (H₂S) in SO₂-pretreated grain, suggesting the tight relation between sulfite and sulfide. Wheat grains geminated in water for 36 h were pretreated with or without 1 mM SO₂donor for 12 h prior to exposure to Al stress for 48 h and the ameliorating effects of SO₂on wheat radicles were studied. SO₂donor pretreatment reduced the content of reactive oxygen species, protected membrane integrity, and reduced Al accumulation in wheat radicles. Gene expression analysis showed that SO₂donor pretreatment decreased the expression of Al-responsive genes TaWali1, TaWali2, TaWali3, TaWali5, TaWali6, and TaALMT1 in radicles exposed to Al stress. These results suggested that SO₂could increase endogenous H₂S accumulation and the antioxidant capability and decrease endogenous Al content in wheat grains to alleviate Al stress.

Sulfur dioxide (SO₂) is a well-known and widespread air pollutant but it also acts as signaling molecule in various processes in animals. However, there is limited information on the role of SO₂ in plants except of its toxicity. Here we studied the role of SO₂ on stomatal movements in sweet potato (Ipomoea batatas) leaves. SO₂, generated by Na₂SO₃/NaHSO₃ solutions, was applied on epidermal strips. We found that the SO₂ donor induced stomatal closure in a dose-dependent manner. Rapid increases in endogenous hydrogen sulfide and nitric oxide content levels were observed in leaves after the treatment with the SO₂ donor. The SO₂-induced stomatal closure was reversed by the H₂S scavenger hypotaurine and the NO-specific scavenger cPTIO. Our results indicate that the SO₂-induced stomatal closure was likely mediated by the H₂S and NO signaling pathways.

In this research, the antifungal role of hydrogen sulfide (H₂S) on the postharvest pathogens Aspergillus niger and Penicillium italicum growing on fruits and under culture conditions on defined media was investigated. Our results show that H₂S, released by sodium hydrosulfide (NaHS) effectively reduced the postharvest decay of fruits induced by A. niger and P. italicum. Furthermore, H₂S inhibited spore germination, germ tube elongation, mycelial growth, and produced abnormal mycelial contractions when the fungi were grown on defined media in Petri plates. Further studies showed that H₂S could cause an increase in intracellular reactive oxygen species (ROS) in A. niger. In accordance with this observation we show that enzyme activities and the expression of superoxide dismutase (SOD) and catalase (CAT) genes in A. niger treated with H₂S were lower than those in control. Moreover, H₂S also significantly inhibited the growth of Saccharomyces cerevisiae, Rhizopus oryzae, the human pathogen Candida albicans, and several food-borne bacteria. We also found that short time exposure of H₂S showed a microbicidal role rather than just inhibiting the growth of microbes. Taken together, this study suggests the potential value of H₂S in reducing postharvest loss and food spoilage caused by microbe propagation.

Hydrogen sulfide (H ₂ S) has been shown to be a gaseous molecule in the regulation of many processes in plants such as abiotic stress tolerance, root organogenesis, stomatal movement, and postharvest fruit senescence. We studied the role of H ₂ S in the regulation of senescence and fungal decay in fresh-cut sweetpotato ( Ipomoea batatas L., cv. Xushu 18) roots. H ₂ S donor sodium hydrosulfide (NaHS) alleviated senescence in fresh-cut sweetpotato root tissue in a dose-dependent manner with the optimal concentration of 2.0 mmol·L ⁻¹ NaHS solution. At the optimal concentration of 2.0 mmol·L ⁻¹ NaHS, H ₂ S fumigation maintained higher levels of reducing sugar in sweetpotato fresh-cut root. H ₂ S treatment also significantly increased the activities of guaiacol peroxidase (POD) and decreased those of polyphenol oxidase (PPO) in sweetpotato during storage. Further investigation showed that H ₂ S treatment maintained a lower level of lipoxygenase (LOX) activity compared with water control. Consistently, the accumulation of malondialdehyde (MDA) was reduced in H ₂ S-treated groups. Three fungal pathogens, Rhizopus nigricans , Mucor rouxianus, and Geotrichum candidum , were isolated from sweetpotato tissue infected with black rot or soft rot. H ₂ S fumigation at 1 to 2.5 mmol·L ⁻¹ NaHS resulted in effective inhibition of the three fungi when grown on medium. When the three fungi were inoculated on the surface of sweetpotato slices, H ₂ S fumigation greatly reduced the percentage of fungal infection. In conclusion, these data suggest that H ₂ S effectively alleviated the senescence and decay in sweetpotato slices and might be developed into a novel fungicide for reduction of black rot or soft rot in sweetpotato.

Hydrogen sulfide (H₂S) has proved to be a multifunctional signaling molecule in plants and animals. Here, we investigated the role of H₂S in the decay of fresh-cut pears (Pyrus pyrifolia). H₂S gas released by sodium hydrosulfide (NaHS) prolonged the shelf life of fresh-cut pear slices in a dose-dependent manner. Moreover, H₂S maintained higher levels of reducing sugar and soluble protein in pear slices. H₂S significantly reduced the accumulation of hydrogen peroxide (H₂O₂), superoxide radicals (•O₂⁻) and malondialdehyde (MDA). Further investigation showed that H₂S fumigation up-regulated the activities of antioxidant enzymes ascorbate peroxidase (APX), catalase (CAT), and guaiacol peroxidase (POD), while it down-regulated those of lipoxygenase (LOX), phenylalanine ammonia lyase (PAL) and polyphenol oxidase (PPO). Furthermore, H₂S fumigation effectively inhibited the growth of two fungal pathogens of pear, Aspergillus niger and Penicillium expansum, suggesting that H₂S can be developed as an effective fungicide for postharvest storage. The present study implies that H₂S is involved in prolonging postharvest storage of pears by acting as an antioxidant and fungicide.