Effects Of Exogenous 5-aminolevulinic Acid(5-ALA) On Ripening And Quality Characteristics Of Grape

Grape,as one of the more consumed sectors of fruit tree industry in China,with the rising consumption level of people,the qualities of grape affect consumer purchase intention and market value to some extent.Research has found that many kinds of plant growth regulators can promote Grape Fruit Coloration and improve fruit quality,but food safety problems caused by the large number of applications of plant growth regulators have been high-profile.Therefore,the discovery and rational utilization of green and highly effective plant growth regulators becomes the focus of current research.Studies on5-aminoacetic propionic acid（5-ALA）have shown that it can significantly improve Grape Fruit Coloration and improve quality.Because of its natural,nontoxic,and nonpolluting nature,it has attracted much attention from a wide range of fruit tree workers and has promising application prospects and market development,but few studies have been conducted on the exogenous application of 5-ALA on different grape varieties.Therefore,in this study,16 fresh grape varieties were used as experimental materials,and 5-ALA was applied on the surface of fruit under field conditions to explore the effect of 5-ALA on fruit maturity and quality of different grape varieties.The effects of 5-ALA on Photosynthetic Characteristics of grape leaves and fruit quality were studied by spraying 5-ALA on leaves.The main results are as follows.1.Effects of exogenous 5-ALA on fruit appearance and quality traits in 16 fresh food grape cultivars by exogenous application of 5-ALA,the CIRG values of fruit peels among the pigmented cultivars,except for’Hupei 2’,’Champagne’,increased significantly compared with the control after entering the color transition.Meanwhile,the rate of total anthocyanin content increase was relatively higher in the peel of light colored varieties.After 5-ALA treatment,it improved fruit quality,and the single fruit weight and longitudinal fruit texture were higher than the control,and the trend of soluble sugar content change was similar to the TSS content change.Seven cultivars,’Muscat Bailey A’,’Jumeigui’,’Hupei 2’,’Chaobao’showed that more soluble sugars were rapidly increased in the fruit at the transition stage after treatment than the control,and more soluble sugars were accumulated in the fruit at fruit maturity.5-ALA decreased the acid content more rapidly in fruits from some cultivars such as’Anyunhuanghou’,Muscat Bailey A’,’Hartford’than the control,but did not affect the content of multiple organic acids of fruit flavor at ripening.5-ALA had less effect on the phenolic content of grape peel.The content of volatile aroma compounds after treatment of’Hartford’and’Muscat Angel’decreased compared with both controls,and phenylethanol with sweet rose aroma in’Hartford’increased from 21.8 ng/kg to 35.5 ng/kg after treatment.Cultivars showed different affiliation function values after treatment,with the highest value of’Heimeigui’affiliation function at 0.59 and the lowest value of’Rose dioutat’affiliation function at only 0.35.2.Effect of exogenous 5-ALA treatment of leaves on grape fruit quality and coloration:the levels of endogenous 5-ALA and photosynthetic pigments（chlorophyll a,chlorophyll b,and carotenoids）in the leaves of four different grape cultivars’Hartford’,’Moldova’,’Pinger’,’Zijixin’treated with exogenous 5-ALA were significantly increased compared with the control.At 45 d after treatment,the number of cells in the palisade tissue of leaves increased,arranged orderly,and more chloroplast distributed;the thickness and compactness of the spongy tissue increased significantly.The net photosynthetic rate（PN）,transpiration rate（TR）,and intercellular CO₂ concentration（CI）of the leaves all increased significantly.The fruit’s single grain weight and transverse longitudinal diameter were higher than those of the control.The hardness of’Hartford’,’Moldova’,’Pinger’decreasedrapidly but results in maturity with the control.The changes of soluble sugars,organic acids and total phenolics in the fruit were not significantly different.The fruit peel color CIRG value and anthocyanin content increased faster and showed higher content than the control.After 5-ALA treatment,the expression levels of chlorophyll synthesis related genes（Vv PORa,Vv Fe2,Vv HO3）in leaves of’Moldova’and’Pinger’were significantly increased,and the expression levels of glucose metabolism related genes（Vv SUT3 and Vv SPS）were higher than those of the control.The key photoreceptor genes（Vv CRY1,Vv CRY2,Vv PHY1,Vv PHY2,Vv UVR8）and Vv COP1,Vv RCA in the treatment group were higher than those in the control group,and the peak values appeared in the 4th stage.3.Initial insights into the mechanism by which exogenous 5-ALA affects grape fruit quality and color:the endogenous 5-ALA content in pericarp was significantly higher than that in flesh,and the content of endogenous 5-ALA in the pericarp of dark grape varieties was relatively high,such as’Jumeigui’and’Zijixin’.The total anthocyanins in the pericarp of the four colored cultivars all increased,and the highest values of CHI activity were observed in the’Hupei 2’treatment versus the control at the early stage of fruit transformation versus the stage of fruit expansion,respectively,with no significant differences among the other cultivars.The PAL activity of’hupe2’at the color transition stage was significantly higher than that of the control,but at maturity the activity was not significantly different from that of the control.At the gene expression level,only’Muscat Angel’expressed higher than the control after treatment,and the other cultivars expressed lower levels of glucose metabolism related genes（Vv SUT1,Vv SUT2,Vv SUT3,Vv SPS,Vv AI,Vv NI,Vv SS3）at most of the time.The expression of aroma metabolism related genes Vv QR and Vv EGS in flesh was significantly higher than that of the control only when’Muscat Angel’and’Hupei 2’ripened,’Jumeigui’and’Muscat Angel’and’Hupei 2’fruits,respectively,while Vv ECar was significantly higher than that of the control before ripening.’Muscat Angel’showed a significant upregulation of carotenoid synthesis genes（Vv PSY1,Vv PSY2）in pericarp compared with the control at the fruit expansion stage,while the expression of genes related to chlorophyll synthesis（Vv HO3,Vv Fe2,Vv PORa）and genes related to chlorophyll degradation（Vv CLH1）were significantly decreased in all cultivars after treatment.Before fruit ripening,the expression of key functional genes on the anthocyanin synthesis pathway（Vv CHS,Vv CHI,Vv F3H,Vv DFR,Vv UFGT,Vv LDOX）was significantly higher in the pericarp of three color cultivars,namely’Anyunhuanghou’,’Hupei2’and’Zijixin’.In conclusion,application of 5-ALA on grape leaves increased stomatal tension and increased leaf thickness,which in turn increased the net photosynthetic rate and enhanced the accumulation of photosynthetic products in the leaves.Meanwhile,application of5-ALA onto the fruit surface improved anthocyanin synthesis related genes and enzyme activities,promoted sugar accumulation and organic acid metabolism,improved grape fruit appearance color and intrinsic nutritional quality of fruit.Therefore,5-ALA can act as a plant growth regulator,improve fruit quality,and improve the rate of good quality fruit.