| Green leaf volatiles(GLVs),with the aroma of green leaves,refer to the short chain of aldehydes and alcohols,produced from the unsaturated fatty acids by LOX,HPL and other enzymes.The GLVs are high in grape berries and have low thresholds.On the one hand,GLVs can provide the fresh aromafor grapes and wines;on the other hand,they are considered as an immature flavor.Therefore,the study on the related genes,enzyme activities and their products content in GLVs metabolic pathway is important for regulating GLVs in grape berries and wines.Based on the previous studies of our research group,the effects of hormone treatment,leaf removal and UV filter on the GLVs were studied in this experiment,in order to provide a theoretical basis for regulation of GLVs in grape berries and wines.The experiment was conducted in Lilan winery,Yinchuan,Ningxia,and three field treatments were desighed.(1)Hormone treatment: at the beginning of verasion,0.1 mmol of abscisic acid(ABA),jasmonic acid(MeJA),salicylic acid(SA)and melatonin(MT)were sprayed on the grape berries.(2)Leaf removal: after verasion,remove all the leaves below the second leave above the berries.(3)UV filter: the berries were covered by different UV filters(PE,PETG and PC).The contents of sugar,acid and phenolic compounds,the enzyme activities of LOX and HPL,the relative expression of VvLOX2 and VvHPL1,and the contents of the main volatile components and C6 substances in the ripe berries were analyzed.The main research resultswere as follows:1.Four hormone treatments raised the sugar content of berries,but decreased the total acid content.The contents of total phenolics,total anthocyanins,total flavonoids and flavan-3-alcohols in MeJA-treated berries were higher than those in other treatments at the ripening stage,followed by MT treatment.Hormone treatments reducedhe contents of unsaturated fatty acids(mainly linoleic acid and linolenic acid)in the berries,and the activities of LOX and HPL were lower than those of the control group.The changes of the enzyme activity increased first and then decreased.The relative expressions of VvLOX2 and VvHPL1 reached the maximum value in 12 weeks after anthesis.The relative expression of VvLOX2(4.98)in MT group was significantly higher than that in other treatment groups andthe control in 12 weeks after anthesis.The relative expression of VvHPL1(4.08)in the control was significantly higher than other treatment groups in 12 weeks after anthesis.Compared with the control,ABA and MeJA increased the content of GLVs and MT reduced the content of GLVs in grape berries.SA had no significant effects on GLVs.2.The treatment of leaf removal increased the content of sugar and acid in the berry,but had no significant effect on the pH value.The contents of total phenolics and total flavonoids decreased by 2.15mg/g and 0.56mg/g,respectively.Leaf removal promoted the accumulation of total anthocyanins,and significantly reduced the contents of linoleic acid and linolenic acid by 0.53mg/g and 0.83mg/g,respectively.Compared with the control,leaf removal had no effects on the activities of LOX and HPL,but their enzyme activities were lower than those of the control.At the beginning of the verasion,the expressions of VvLOX2 and VvHPL1 after leave removal were higher than thosein the control,but lower in late period of the verasion.Leaf removal significantly increased the content of amino acid derivatives and decreaced the content of GLVs in the berry.3.UV filter treatment improved the sugar content in the berry.PETG had a great effect on total phenol content;PC had a significant effect on total flavonoids and total tannin;PE had no significant effect on phenolic compounds.UV filters decreased fatty acids contents and the ratio of unsaturated fatty acids,and the decrease degree was related with UV radiation.PE,PETG and PC filtered 30% UV,30% UV-A and 70% UV-B and 90% UV.UV filter treatment did not significantly change the enzymeactivities.The activities of LOX,9-HPL and13-HPL increased first and then decreased in the developmentprocess.The expression levels of VvLOX2 and VvHPL1 reached high levelsin 12 weeks after anthesis,and their expression levelswere higher than thosein the control at the maturation stage.UV filters significantly increased the contents of amino acid derivatives and reduced the GLVs contents in grape berries.4.The correlation analysis of fatty acids,enzyme activity,gene expression and characteristic aroma showed that the fatty acid metabolic pathway was important for accumulating the volatile components in the grape berries.LOX and 13-HPL played key roles in the formation of C6 compounds in the GLV metabolic pathway.9-HPL and the accumulation of unsaturated fatty acids in the development process showed the similar trend,but they did not show the significant correlation. |
PDF Full Text Request