Hydrogen Sulfide Alleviates Postharvest Ripening And Senescence Of Banana By Antagonizing The Effect Of Ethylene

China is a big country of fruit production and consumption.Due to the fact that postharvest storage and transportation technology is not yet fully mature,fruit undergo the postharvest ripening,aging,rotting deterioration and the annual harvest fruit and vegetable loss rate is as high as 20% or more.Therefore,in-depth fruit ripening mechanism research has significant economic and social significance.Ethylene is a kind of hormones that are important for regulating plant growth and maturation,and its physiological function runs through the whole process of plant growth cycle,especially in climacteric fruit.More and more studies have shown that hydrogen sulfide?H₂S?as a multi-functional plant gaseous signal molecule,involved in regulating stomatal movement,photosynthesis,seed germination,leaf and root organ development,stress resistance and many other physiological processes.Recent studies have found that H₂ S can delay the process of maturation and senescence of various fruits and vegetables,and whether H₂ S can antagonize the ethylene signal to alleviate the senescence process of banana has not been reported.In this paper,the effects of exogenous H₂ S and ethylene on the senescence of postharvest banana were studied by using sodium hydrosulfide?Na HS?and ethephon solution as the donor of H₂ S and ethylene,using immature green banana fruit as experimental material.The results showed that compared with the control group,ethylene treatment could accelerate the process of senescence of green banana,while H₂ S delayed the process.Treated with H₂ S and ethylene,compared with the ethylene treatment group,H₂ S can inhibit ethylene and delay the ripening of banana,so as to extend the storage period after harvest.Treated with H₂ S alone,or with H₂ S and ethylene treatment,H₂ S can maintain the banana skin color,delay fruit browning,softening and yellowing process,inhibited the decomposition of chlorophyll and flavonoid content,delaying the degradation of starch content and the increase of reducing sugar content,increased the content of soluble protein in the flesh,delaying fruit senescence process and maintaining the commodity value of the fruit.The antioxidant metabolism is closely related to the process of ripening and senescence.Therefore,this paper studied the regulation of H₂ S and ethylene signals in the process of postharvest banana fruits in the view of the antioxidant-related metabolic pathway.The results showed that ethylene treatment accelerated the decomposition of antioxidants in banana fruits compared with the control group.Compared with the ethylene treatment group,H₂ S alone or H₂ S plus ethylene could can improve the content of antioxidant substances in banana fruit,such as total phenolics and flavonoids,reduce the production rate of superoxide anion?O₂^-?,inhibited the increase of hydrogen peroxide?H₂O2?and malondialdehyde?MDA?content,improve antioxidant enzyme including ascorbate peroxidase?APX?,guaiacol peroxidase?POD?,superoxide dismutase?SOD?,catalase?CAT?and disease resistance related enzyme phenylalanine ammonia lyase?PAL?activity,enhanced free radical scavenging capacity and inhibiting increase of activity of polyphenol oxidase?PPO?,lipoxygenase?LOX?and polygalacturonase?PG?.Thus the results indicated that H₂ S might increase the antioxidant activity of banana fruit by enhancing the antioxidant activity of banana fruit to delay the maturation and senescence process,thereby extending the post-harvest storage period of green banana.Moreover,we also investigated the effects of H 2S and ethylene signaling from the gene level in antioxidant and disease resistance metabolism,ethylene biosynthesis and signal transduction,fruit softening resistance-related gene expression,and showed that compared with the ethylene treatment group,H 2S and ethylene treatment could up-regulated the expression of antioxidant gene Ma APX and disease resistance gene Ma PAL,down-regulated the expression of Ma ACS1,Ma ACS2,Ma ACO1 and Ma ACO2 genes in ethylene biosynthesis pathway,improve the expression of Ma ETR,Ma ERS1,Ma ERS2 and Ma ERS3 in ethylene signal transduction,inhibition of Ma PL gene expression,and to some extent,affected the expression of ethylene signal transduction genes in Ma EIL1,Ma EIL2,Ma EIL3 and Ma EIL4 in postharvest banana tissue.This indicates that H₂ S signaling may be involved in the regulation of banana antioxidant and disease resistance metabolism,ethylene biosynthesis and signal transduction and physiological regulation of fruit softening,thereby improving the antioxidant capacity of fruit,inhibiting ethylene synthesis,delaying fruit softening and delaying the senescence process of post harvest green banana.In summary,exogenous H₂ S gas signal molecules can inhibit the regulation of ethylene on the ripening and senescence of fruit,maintain the contents of banana fruit nutrients,through in vivo antioxidant metabolism regulation of banana fruit,reducing the accumulation of ROS and cell membrane lipid peroxidation injury,the regulation of ethylene biosynthesis and signal transduction,and involving in the regulation of antioxidant metabolism and softening process in the molecular level,thereby prolonging the storage period of post harvest green banana.