The Relationship Between Ethylene Synthesis Induction Oxidation Reduction Potential And Related Enzyme Activities In 'Gongcheng' Persimmon(Diospyros Kaki L.)

As a featuring characteristic fruit of China,persimmon(Diospyros kaki)has a wide international market,while the postharvest problems retard its industry development.Regulation of ethylene is meaningful to prolonging the fruit storage period,but the mechanism of induction of ethylene synthesis in fruit is still unknown.In this study,using the cultivar 'Gongcheng' persimmon from Guangxi Province as experimental material,and the model plant tomato as control,the mechanism of induction of ethylene biosynthesis was explored in fruit.The fruits of preharvest and postharvest storage period were applied with different treatments,and ethylene production rate,the oxidation-reduction potential(ORP),fruit firmness,ACS activity,ACO activity,antioxidant enzyme activities as well as other physiological indicators of fruit were determined,in order to explore the relationship between persimmon fruit ethylene synthesis switch and ORP and related enzymes,so as to reveal the ethylene synthesis mechanism.The results show that:1.Mechanism of induction of ethylene biosynthesis in tomato fruit.String harvest was conducted comparing to the common single fruit harvest.Ethylene production of string-harvest tomato was significantly lower than that of the control during the whole storage period.Among them,The ethylene production rate in string-harvest tomato with Rootstock No.l in Area I decreased rapidly to the minimum(0.35 nl g-1h-1)on 5d after harvest,significantly lower than its control(1.36 nl·g-1h-1),and other string-harvest tomatoes in different areas with different root-stocks reduced to their minimum on 15d after harvest.Also,the content of natural antioxidants such as carotenoid,lycopene and ascorbic acid in string-harvest tomatoes increased significantly in the early storage period.Additionally,the string-harvest treatment also inhibited the post-harvest accumulation of soluble sugar and degradation of titratable acid to a certain extent.Therefore,the string of harvesting retained the supply of material from the plant to the fruit,so that the postharvest fruit is close to the state of the maternal plant.This dynamic material flow is a negative regulation on the biosynthesis of ethylene and leads to an increase in antioxidant substances in the fruit,a reduction in oxidative damage,and delaying fruit softening and senescence.2.The mechanism of induction of ethylene biosynthesis in preharvest persimmon fruit.In persimmon young fruit stage,after preserving or picking leaves of fruit,bearing shoots yield of ethylene of the leaf removal treatment group reached the maximum value(4.67 nl· g-1h-1)on the 4d after treatment,and the maximum value of ORP and ACS reached the maximum value at 2d after treatment,which was significantly higher than that in leaves reserved treatment group and CK.The content of endogenous AsA of the leaf removal treatment group decreased rapidly after treatment and decreased to the lowest(6.19 mg· g-1)at 2d.At the beginning after the treatment,the activity of APX,GR,SOD,CAT and the content of soluble sugar,carotenoid of the leaf removal treatment group were higher than those of other treatments.Therefore,the leaf removal treatment on the young fruit period can induce the biosynthesis of ethylene in fruit.Before the start of ethylene,The redox equilibrium in persimmon fruits gradually increased to the oxidation direction(the ORP value rises),The enzymes of antioxidant system and active oxygen scavenging system were also active.3.The mechanism of induction of ethylene biosynthesis in post-harvest persimmon fruit during storage.Mature persimmon fruit was taken as the experimental material.The difference between the treatment of ethephon and the combination of ethephon and AsA was studied.By analyzing the relationship between ethylene synthesis and ORP and related enzyme activities during persimmon fruit storage,results showed that the ORP value of ethephon treated fruit peaked at the 8th day after storage(13.68mv·g-1),and then the ethylene production reached the maximum(1.0649 n· g-1h-1)at the next day,which is significantly higher than the fruit of CK,water treatment and AsA treatment.Before the ethylene synthesis starts,the activities of ACS,APX and GR in the fruits treated with AsA were lower than those in the ethephon treatment group after treatment within6d,the same situation also appeared in SOD and CAT activity of ASA treated fruit on 4d after treatment.In addition,throughout the storage period,the content of soluble sugar and carotenoid in AsA treated fruits was lower than that in the ethephon treatment group,but the hardness was higher than that in the ethephon treatment group.Therefore,the ethephon-stimulated fruit treated with AsA can promote the increase of endogenous AsA content,Which inhibited the enzyme activity of the antioxidant system and the active oxygen scavenging system in the middle and late storage,and reduced the redox balance(ORP)of the fruit,and finally inhibited the biosynthesis of ethylene.In summary,we propose the hypothesis of ethylene initiation mechanism,which is,when external stimuli or ripening produce oxidative stress,the enzyme actives of the antioxidant system and oxygen scavenging system are gradually enhanced to protect against ROS in the fruit.When the free radical scavenging rate is lower than the production rate,the redox state(ORP)in the fruit is in the direction of oxidation enhancement.When the ORP reaches a certain threshold,ACO is activated,starting with ethylene biosynthesis,and then the fruit firmness is decreased rapidly after ripening.