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Jun Tang, Kang-Di Hu, Lan-Ying Hu, Yan-Hong Li, Yong-Sheng Liu and Hua Zhang

Hydrogen sulfide (H2S) 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 H2S in the regulation of senescence and fungal decay in fresh-cut sweetpotato (Ipomoea batatas L., cv. Xushu 18) roots. H2S 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, H2S fumigation maintained higher levels of reducing sugar in sweetpotato fresh-cut root. H2S 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 H2S treatment maintained a lower level of lipoxygenase (LOX) activity compared with water control. Consistently, the accumulation of malondialdehyde (MDA) was reduced in H2S-treated groups. Three fungal pathogens, Rhizopus nigricans, Mucor rouxianus, and Geotrichum candidum, were isolated from sweetpotato tissue infected with black rot or soft rot. H2S 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, H2S fumigation greatly reduced the percentage of fungal infection. In conclusion, these data suggest that H2S 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.

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Ji-Lian Zheng, Lan-Ying Hu, Kang-Di Hu, Jun Wu, Feng Yang and Hua Zhang

Hydrogen sulfide (H2S) has been identified as a multifunctional signaling molecule in plants. Here, we show that H2S delayed postharvest senescence of fresh-cut apples (Malus ×pumila) in a dose-dependent manner. Exogenous H2S application maintained significantly higher levels of ascorbic acid, flavonoids, total phenolics, reducing sugars and soluble proteins, and lower levels of free amino acids in apple slices compared with controls. Further investigations showed that H2S significantly reduced the accumulation of superoxide radicals, hydrogen peroxide (H2O2) and malondialdehyde (MDA). Apple fruits fumigated with H2S contained significantly higher activities of ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), guaiacol peroxidase (POD) and superoxide dismutase (SOD), and lower activities of lipoxygenase (LOX), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and protease relative to controls. H2S also upregulated MdDHAR expression and downregulated the expression of MdLOX2, MdPG1, MdPPO, MdACO1, MdERS1, and MdETR1 in postharvest apple tissue. The present study indicates that H2S was involved in delaying postharvest senescence of apples by acting as an antioxidant and by regulating senescence-related gene expression.

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Ting-Ting Li, Zhi-Rong Li, Kang-Di Hu, Lan-Ying Hu, Xiao-Yan Chen, Yan-Hong Li, Ying Yang, Feng Yang and Hua Zhang

Kiwifruit (Actinidia deliciosa) is a typical climacteric fruit, and its ripening is closely associated with ethylene. In this study, we present evidence that H2S alleviated ethylene-induced ripening and senescence of kiwifruit. Kiwifruit were fumigated with ethylene released from 0.4 g·L−1 ethephon solution or H2S with 1 mm sodium hydrosulfide (NaHS) as the donor or in combination. Fumigation with ethylene was found to accelerate kiwifruit ripening and H2S treatment effectively alleviated ethylene-induced fruit softening in parallel with attenuated activity of polygalacturonase (PG) and amylase. Ethylene + H2S treatment also maintained higher levels of ascorbic acid, titratable acid, starch, soluble protein, and reducing sugar compared with ethylene group, whereas suppressed the increase in chlorophyll and carotenoid. Kiwifruit ripening and senescence under ethylene treatment was accompanied by elevation in reactive oxygen species (ROS) levels, including H2O2 and superoxide anion and malondialdehyde (MDA), but combined treatment of ethylene plus H2S alleviated oxidative stress in fruit. Furthermore, the activities of antioxidative enzymes catalase (CAT) and ascorbate peroxidase (APX) were increased by ethylene + H2S treatment in comparison with ethylene alone, whereas the activities of lipoxygenase (LOX) and polyphenol oxidase (PPO) were attenuated by H2S treatment. Further investigations showed that H2S repressed the expression of ethylene synthesis-related genes AdSAM, AdACS1, AdACS2, AdACO2, and AdACO3 and cysteine protease genes, such as AdCP1 and AdCP3. Taken together, our findings suggest that H2S alleviates kiwifruit ripening and senescence by antagonizing the effect of ethylene through reduction of oxidative stress and inhibition of ethylene synthesis pathway.

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Shuai-Ping Gao, Kang-Di Hu, Lan-Ying Hu, Yan-Hong Li, Yi Han, Hui-Li Wang, Kai Lv, Yong-Sheng Liu and Hua Zhang

Hydrogen sulfide (H2S) was recently recognized as an endogenous gaseous molecule involved in seed germination, root organogenesis, abiotic stress tolerance, guard cell movement, and delay of senescence in plants. In the present study, we show that H2S participates in the regulation of postharvest ripening and senescence in fresh-cut kiwifruit, Actinidia deliciosa. Fumigation of fresh-cut kiwifruit with the H2S donor sodium hydrosulfide (NaHS) solution prolonged kiwifruit storage time and alleviated senescence and tissue softening in a dose-dependent manner at an optimal concentration of 1.0 mmol·L−1 NaHS. H2S treatment maintained higher levels of reducing sugars, soluble proteins, free amino acids, ascorbate, and chlorophyll and lowered carotenoid levels. H2S treatment also significantly decreased the contents of malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide anion (O2 ) during fruit storage compared with water controls. Furthermore, the activities of guaiacol peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) were increased by H2S treatment, whereas the activity of lipoxygenase (LOX) was decreased compared with untreated controls. Taken together, these results suggest that H2S is involved in prolonging postharvest shelf life and plays an antioxidative role in fresh-cut kiwifruit.

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Zhi-Rong Li, Kang-Di Hu, Fen-Qin Zhang, Shi-Ping Li, Lan-Ying Hu, Yan-Hong Li, Song-Hua Wang and Hua Zhang

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 (H2S) treatment alleviated dark-promoted senescence in broccoli florets. H2S 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 H2S 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 H2S. The reduced expression level in cysteine protease gene BoCP3 and aspartic protease gene BoLSC807 suggested the role of H2S in alleviating protein degradation during broccoli senescence. H2S up-regulated the expression of sulfur metabolism genes BoSR and BoOASTL, and the antioxidant gene BoCAT. These results show that H2S 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.

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Chen Chen, Meng-Ke Zhang, Kang-Di Hu, Ke-Ke Sun, Yan-Hong Li, Lan-Ying Hu, Xiao-Yan Chen, Ying Yang, Feng Yang, Jun Tang, He-Ping Liu and Hua Zhang

Aspergillus niger is a common pathogenic fungus causing postharvest rot of fruit and vegetable, whereas the knowledge on virulence factors is very limited. Superoxide dismutase [SOD (EC 1.15.1.10)] is an important metal enzyme in fungal defense against oxidative damage. Thus, we try to study whether Cu/Zn-SOD is a virulence factor in A. niger. Cu/Zn-SOD encoding gene sodC was deleted in A. niger [MA70.15 (wild type)] by homologous recombination. The deletion of sodC led to decreased SOD activity in A. niger, suggesting that sodC did contribute to full enzyme activity. ΔsodC strain showed normal mycelia growth and sporulation compared with wild type. However, sodC deletion markedly increased the cell’s sensitivity to intracellular superoxide anion generator menadione. Besides, spore germination under menadione and H2O2 stresses were significantly retarded in ΔsodC mutant compared with wild type. Further results showed that sodC deletion induced higher superoxide anion production and higher content of H2O2 and malondialdehyde (MDA) compared with wild type, supporting the role of SOD in metabolism of reactive oxygen species (ROS). Furthermore, ΔsodC mutant had a reduced virulence on chinese white pear (Pyrus bretschneideri) as lesion development by ΔsodC was significantly less than wild type. The determination of superoxide anion, H2O2, and MDA in A. niger-infected pear showed that chinese white pear infected with ΔsodC accumulated less superoxide anion, H2O2, and MDA compared with that of wild type A. niger, implying that ΔsodC induced an attenuated response in chinese white pear during fruit–pathogen interaction. Our results indicate that sodC gene contributes to the full virulence of A. niger during infection on fruit. Aspergillus niger is one of the most common species found in fungal communities. It is an important fermentation industrial strain and is also known to cause the most severe symptoms in fruit during long-term storage (Pel et al., 2007). Meanwhile, plants activate their signaling pathways to trigger defense responses to limit pathogen expansion. One of the earliest host responses after pathogen attack is oxidative burst, during which large quantities of ROS are generated by different host enzyme systems, such as glucose oxidase (Govrin and Levine, 2000). ROS such as singlet oxygen, superoxide anion, hydroxyl (OH), and H2O2 are released to hinder the advance of pathogens (Gara et al., 2003). ROS can react with and damage cellular molecules, such as DNA, protein, and lipids, which will limit fungal propagation in the host plant (Apel and Hirt, 2004).

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Kang-Di Hu, Xiao-Yue Zhang, Sha-Sha Wang, Jun Tang, Feng Yang, Zhong-Qin Huang, Jing-Yu Deng, Si-Yuan Liu, Shang-Jun Zhao, Lan-Ying Hu, Gai-Fang Yao and Hua Zhang

Hydrogen sulfide (H2S) has been proven to be a multifunctional signaling molecule in plants. In this study, we attempted to explore the effects of H2S on the climacteric fruit tomato during postharvest storage. H2S fumigation for 1 d was found to delay the peel color transition from green to red and decreased fruit firmness induced by ethylene. Further investigation showed that H2S fumigation downregulated the activities and gene expressions of cell wall–degrading enzymes pectin lyase (PL), polygalacturonase (PG), and cellulase. Furthermore, H2S fumigation downregulated the expression of ethylene biosynthesis genes SlACS2 and SlACS3. Ethylene treatment for 1 d was found to induce the expression of SlACO1, SlACO3, and SlACO4 genes, whereas the increase was significantly inhibited by H2S combined with ethylene. Furthermore, H2S decreased the transcript accumulation of ethylene receptor genes SlETR5 and SlETR6 and ethylene transcription factors SlCRF2 and SlERF2. The correlation analysis suggested that the fruit firmness was negatively correlated with ethylene biosynthesis and signaling pathway. The current study showed that exogenous H2S could inhibit the synthesis of endogenous ethylene and regulate ethylene signal transduction, thereby delaying fruit softening and the ripening process of tomato fruit during postharvest storage.