Yan-Hong Li

Protective roles of nitric oxide on germination and antioxidant metabolism in wheat seeds under copper stress

Nitric oxide (NO) is a multifunctional gaseous signal in plant. In the present study, we found that pretreatment with NO could significantly improve wheat seeds germination and alleviate oxidative stress against copper toxicity. With the enhancement of copper stress, the germination percentage of wheat seeds decreased gradually. Pretreatment during wheat seed imbibition with sodium nitroprusside (SNP), an NO donor, could greatly reverse the inhibitory effect of the following copper stress to wheat seeds germination. SNP-pretreated seeds also tended to retain higher amylase activities than that of the control without SNP pretreatment. On the other hand, there was no apparent difference in the activities of esterase in wheat seeds pretreated with or without SNP. Further investigations showed that pretreatment with NO donor dramatically stimulated the activities of superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT, EC 1.11.1.6), decreased the activities of lipoxygenases, sustained a lower level of malondialdehyde, and interfered with hydrogen peroxide (H2O2) excessive accumulation compared with the control, thereby enhancing the antioxidative capacity in wheat seeds under copper stress. In addition, the seed copper contents were not significant different between those pretreated with SNP and the controls, inferring that protective roles of NO was not responsible for preventing Cu uptake.

Hydrogen Sulfide Prolongs Postharvest Shelf Life of Strawberry and Plays an Antioxidative Role in Fruits

Accumulating evidence shows that hydrogen sulfide (H(2)S) plays various physiological roles in plants, such as seed germination, root organogenesis, abiotic stress tolerance, and senescence of cut flowers. However, whether H(2)S participates in the regulation of ripening and senescence in postharvest fruits remains unknown. In the present study, the effect of H(2)S on postharvest shelf life and antioxidant metabolism in strawberry fruits was investigated. Fumigation with H(2)S gas released from the H(2)S donor NaHS prolonged postharvest shelf life of strawberry fruits in a dose-dependent manner. Strawberry fruits fumigated with various concentrations of H(2)S sustained significantly lower rot index, higher fruit firmness, and kept lower respiration intensity and polygalacturonase activities than controls. Further investigation showed that H(2)S treatment maintained higher activities of catalase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase and lower activities of lipoxygenase relative to untreated controls. H(2)S also reduced malondialdehyde, hydrogen peroxide, and superoxide anion to levels below control fruits during storage. Moreover, H(2)S treatment maintained higher contents of reducing sugars, soluble proteins, free amino acid, and endogenous H(2)S in fruits. We interpret these data as indicating that H(2)S plays an antioxidative role in prolonging postharvest shelf life of strawberry fruits.

Effects of exogenous nitric oxide donor on antioxidant metabolism in wheat leaves under aluminum stress

With the enhancement of aluminum stress, the content of chlorophyll in wheat seedlings (Triticum aestivum L.) decreased dramatically. At 0.2 mM AlCl3, the chlorophyll content halved. The aluminum-induced decrease in chlorophyll content could be alleviated by exogenous nitric oxide donor, sodium nitroprusside (SNP) in a dose-dependent manner. Treatment with SNP dramatically promoted the activities of superoxide dismutase, catalase, ascorbate peroxidase and increased the proline content, whereas it decreased hydrogen peroxide and malondialdehyde and maintained the level of soluble protein as compared with water controls. Therefore, NO donor enhanced the antioxidant capacity in wheat seedlings under aluminum stress.

Hydrogen Sulfide Prolongs Postharvest Storage of Fresh-Cut Pears (Pyrus pyrifolia) by Alleviation of Oxidative Damage and Inhibition of Fungal Growth

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.

Hydrogen Sulfide Alleviates Postharvest Senescence of Broccoli by Modulating Antioxidant Defense and Senescence-Related Gene Expression

Accumulating evidence has shown that hydrogen sulfide (H₂S) acts as a signaling regulator in plants. Here we show that H₂S delays the postharvest senescence of broccoli in a dose-dependent manner. H₂S maintains higher levels of metabolites, such as carotenoids, anthocyanin, and ascorbate, and reduces the accumulation of malondialdehyde, H₂O₂, and the superoxide anion. Further investigations showed that H₂S sustained higher activities of guaiacol peroxidase, ascorbate peroxidase, catalase, and glutathione reductase and lower activities of lipoxygenase, polyphenol oxidase, phenylalanine ammonia lyase, and protease than those of water control. Moreover, the expression of the chlorophyll degradation related genes BoSGR, BoCLH2, BoPaO, BoRCCR, as well as cysteine protease BoCP1 and lipoxygenase gene BoLOX1, was down-regulated in postharvest broccoli treated with H₂S. The functions of H₂S on the senescence of other vegetables and fruits suggest its universal role acting as a senescence regulator.

An antifungal role of hydrogen sulfide on the postharvest pathogens Aspergillus niger and Penicillium italicum.

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.

The Hydrogen Sulfide Donor NaHS Delays Programmed Cell Death in Barley Aleurone Layers by Acting as an Antioxidant

H2S is a signaling molecule in plants and animals. Here we investigated the effects of H2S on programmed cell death (PCD) in barley (Hordeum vulgare L.) aleurone layers. The H2S donor NaHS significantly delayed PCD in aleurone layers isolated from imbibed embryoless barley grain. NaHS at 0.25 mM effectively reduced the accumulation of superoxide anion (·O2 −), hydrogen peroxide (H2O2), and malondialdehyde (MDA), promoted the activity of superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), and decreased those of lipoxygenase (LOX) in isolated aleurone layers. Quantitative-PCR showed that NaHS treatment of aleurone tissue led to enhanced transcript levels of the antioxidant genes HvSOD1, HvAPX, HvCAT1, and HvCAT2 and repressed transcript levels of HvLOX (lipoxygenase gene) and of two cysteine protease genes HvEPA and HvCP3-31. NaHS treatment in gibberellic acid- (GA-) treated aleurone layers also delayed the PCD process, reduced the content of ·O2 −, and increased POD activity while decreasing LOX activity. Furthermore, α-amylase secretion in barley aleurone layers was enhanced by NaHS treatment regardless of the presence or absence of GA. These data imply that H2S acted as an antioxidant in delaying PCD and enhances α-amylase secretion regardless of the presence of GA in barley aleurone layers.

Sulfur Dioxide Enhances Endogenous Hydrogen Sulfide Accumulation and Alleviates Oxidative Stress Induced by Aluminum Stress in Germinating Wheat Seeds

Aluminum ions are especially toxic to plants in acidic soils. Here we present evidences that SO2 protects germinating wheat grains against aluminum stress. SO2 donor (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 SO2 donor for 12 h prior to exposure to Al stress for 48 h and the ameliorating effects of SO2 on wheat radicles were studied. SO2 donor pretreatment reduced the content of reactive oxygen species, protected membrane integrity, and reduced Al accumulation in wheat radicles. Gene expression analysis showed that SO2 donor 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 SO2 could increase endogenous H2S accumulation and the antioxidant capability and decrease endogenous Al content in wheat grains to alleviate Al stress.

Stomatal closure in sweet potato leaves induced by sulfur dioxide involves H2S and NO signaling pathways

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.

Hydrogen sulfide alleviates postharvest ripening and senescence of banana by antagonizing the effect of ethylene

[This corrects the article DOI: 10.1371/journal.pone.0180113.].