Effects Of Strigolactone On NO,H₂S And Phenylpropane Metabolism In Postharvest Strawberry Fruits

With the improvement of people′s living standard,their demand for fresh fruit is increasing every day.Strawberry fruits are favored by customers because of their rich nutritional value and excellent taste.However,the epidermis of strawberry fruit is thin and juicy,perishable after harvest,and extremely resistant to storage.Therefore,it is urgent to find a healthy and effective treatment method to maintain the postharvest quality of strawberry fruit.Strigolactone is one of the hot spots in the study of phytohormones in recent years.It is widely existed in the root system of various higher plants and is the general name of monoleptic alcohol compound and plays an important role in regulating physiological and biochemical processes of plants.However,the effects of strigolactone on the physiology and biochemistry of postharvest fruits are rarely reported.In this paper,"Tianbao"strawberry was used as experimental material,and different concentrations of exogenous strigolactone(0,0.5,1,2,4μmol·L^-1)were used to treat postharvest strawberry fruits.The effects of exogenous strigolactone on antioxidant system,nitric oxide（NO）synthesis pathway,hydrogen sulfide（H₂S）synthesis pathway and phenylpropane metabolism of postharvest strawberry fruits were discussed,and the optimal concentration of monolauractone treatment was found,which laid a foundation for the application of strigolactone in storage and preservation of postharvest strawberry fruits.（1）The results showed that 1μmol·L^-11 exogenous strigolactone significantly inhibited the activity peaks of peroxidase（POD）and polyphenol oxidase（PPO）in strawberry fruits after harvest,and reduced the degree of fruit browning of strawberry fruits,thus enhanced the ability to clear·DPPH·,·OH,and·O₂^-,compared to other concentrations.At the same time,exogenous strigolactone treatment effectively inhibited the increase of weightlessness rate and respiratory intensity,maintained the water content in the fruit and better maintained the quality of the fruit.Strigolactone treatments improved the activities and substance contents of superoxide dismutase（SOD）,catalase（CAT）and various enzymes in ascorbic acid-glutathione cycle in strawberry fruit anti-oxidation system,including ascorbic acid peroxidase（APX）,glutathione reductase（GR）,dehydroascorbic acid reductase（DHAR）and monodehydroascorbic acid reductase（MDHAR）,and the contents of reduced ascorbic acid（AsA）and reduced glutathione（GSH）.This shows that strigolactone treatment can slow down the oxidative damage of strawberry fruits by improving the defense capability of antioxidant system.（2）The results showed that there were no significant difference in the NR activity and nitrite content between strigolactone treated strawberry fruits and the control.However,the NOS activity and L-arginine content of strigolactone treated strawberry fruits were significantly increased,which increased the endogenous NO content of strawberry fruits.These results suggested that strigolactone regulate the synthesis of NO mainly through the NOS pathway.（3）The results showed that 1μmol·L^-1exogenous strigolactone treatment promoted the cleavage of L-cysteine by activating the activities of L-cysteine demethylase,O-acetylserine thiolyase（OAS-TL）and serine acetyltransferase（SAT）,thus increased the content of endogenous H₂S in strawberry fruits and maintained good fruit quality.（4）The results showed that 1μmol·L^-1exogenous strigolactone effectively increased the activities of phenylalanine ammonia-lyase（PAL）and 4-coumaric acid coenzyme A ligase（4CL）,thus promoting the accumulation of antioxidant substances such as total phenol,flavonoid and lignin content in the harvested strawberry fruits,enhancing the antioxidant capacity of the fruits,prolonging the shelf life of the fruits and maintaining the good quality of the fruits.The above results indicated that 1μmol·L^-1strigolactone treatment is a feasible method to inhibit browning and maintain the quality of strawberry fruits.