The Mechanism Of Hydrogen Sulfide-Alleviation Of Senescence And Inhibition Of Enzymatic Browning In Postharvest Daylily

Hydrogen sulfide(H2S),same as nitric oxide(NO)and carbon oxide(CO),is one of gaseous cellular messenger molecules.Recent results indicated that appropriate concentration of H2S play an extremely important role in fruits and vegetables to delay the senescence.However,the molecular mechanisms of regulation senescence and inhibit browning of hydrogen sulfide in postharvest fruits and vegetables are still not very clear.In this research,the effects of the H2S donor sodium hydrosulfide(NaHS)treatments on postharvest aging and browning of daylily were investigated.Our study showed that:1.Hydrogen sulfide alleviates senescence of postharvest daylily flower via increasing antioxidant capacity and maintaining energy status.In this process,the endogenous H2S level is decreased.LCD and DCD,which were identified as main enzymes for produces endogenous H2S in the plant,showed an overall downward trend.These data implied that the close correlation among H2S metabolism and senescence in daylily.Exogenously applied with 4.0 mM NaHS not only increased H2S content determined by spectrophotography and fluorescent analysis,but also maintained good sensory quality,such as delaying the decrease of the total chlorophyll and soluble protein content,inhibiting the degradation of DNA.Further investigation showed that NaHS treatment significantly reduced the content of malondialdehyde(MDA).Staining analysis showed that H2S can effectively alleviate the oxidative damage,reduce reduced hydrogen peroxide(H2O2)and superoxide anion(O2-)in daylily flower.These responses were related to a significant increase in the total representative antioxidant enzymes the activities of antioxidant enzymes,including superoxide dismutase(SOD),ascorbate peroxidase(APX)and catalase(CAT).Isoenzyme showed consistent results with enzyme activity of SOD.During storage time,the respiration rate increased,while NaHS treatment significantly inhibited the increase in daylily.The liquid phase analysis of ATP,ADP,AMP and energy charge,compared with the control group,we found that H2S treatment increased ATP content,decreased ADP and AMP content and maintained a higher energy charge.By contrast,above changes were sensitive to the cotreatment with DL-propargylglycine(PAG),the specific scavenger of H2S.All together,these results suggest a novel role for H2S in the regulation senescence process of daylily.2.H2S might as an antioxidant and inhibits enzymatic browning in daylily flowers.NaHS treatment significantly retarded browning degree of daylily,maintained a higher content of Vc and DPPH radical scavenging,increased the total phenol content and total flavonoids content,reduced browning enzymes such as phenylalanine ammonialyase(PAL),polyphenol oxidase(PPO)and peroxidase(POD)activity.Moreover,we found that H2S synthase inhibitors PAG and scavenger taurine HT can reduce the total phenolic content and improve PPO and POD activity in daylily during storage time.Above inducible responses were blocked significantly when NaHS was applied.Thus,these results suggested that H2S might be antioxidant involved in enzymatic browning in daylily flowers.In summary,this research demonstrated H2S might play important roles in regulated senescence and inhibited enzymatic browning in postharvest daylily flowers during storage time.