A Study On Green Leaf Volatiles From Oxylipin Pathway Of Cabernet Sauvignon Grapes During Berry Development

Fatty acid-derived volatile compounds mainly comprise C6 and C9 aldehydes,alcohols and esters.The C6 compounds are normally the most abundant volatiles in grape berries,which are classified as’Green Leaf Volatiles’(GLVs)due to their characteristic ’green’ and ’fressh’ odor.The C6 and C9 aldehydes are direct products of oxidative cleavage of linoleic acid and a-linolenic acid through the lipoxygenase-hydroperoxide lyase(LOX-HPL)pathway(or oxylipin pathway).They’re important volatiles for grapes and wines due to high concentrations and relatively lower threshold values.However,the sources of variations of GLVs remain unclear yet.In this study,GC-MS combined with RNA-seq techniques were used to invesntigate the influence of region,training systems,cluster thinning and light condition of berry microclimate on GLVs accumulation in berries and wines.The potential regulation of the observed influence and variations was also discussed.The results will improve the understanding of LOX-HPL pathway and the accumulation of GLVs in grape berry,and therefore provide knowdege for improving wine aromatic quality via viticultural practices.Results from analyzing the differences in GLVs level and transcriptional differences of genes in LOX-HPL pathway displayed that Gaotai berry contained higher level of GLVs and the transcriptional level of AOS branch of LOX pathway in Changli berry was higher.The relative expression level of VvADH2 and JOMTs was significantly correlated with the expression level of hormone-related genes such as VvARFs,PP2C and CKX.The results suggested that the more humid environment of Changli provided with berry a higher possibility of facing pathogenic threat which induces the more active AOS branch rather than HPL branch.And the concentration of GLVs showed significant relationship with meterological data of these two regions,especially diurnal temperature difference.The comparison of GLVs and relative gene expression of M-VSP,F-TT and F-MT training system berries indicated that M-VSP and F-TT increased C6 aldehydes of grape berries and the C6 esters of wines roughly.The differences of GLVs from two-levels of cluster thinning showed that cluster thinning had limited influence on TSS and pH,but decreased the level of hexanal and increased the level of C6 alcohols of harvested grapes.Wines made from treated grapes contained lower 1-hexanol.Leaf removing and moving and bagging changed the light envrionment of grape berry.Results showed that light exposure treatments at veraison increased C6 alcohol levels,decreased the level of C6 aldehydes and the hexyl acetate in wines were also increased.Bunch shading led to different results and the influence was more obvious in a cool vintage.Bunch shading during early developing stages was beneficial for the decrease of GLVs in harvested grapes.But early shading and removing of bags after veraison would increase GLVs of mature berries.By analyzing the transcriptional levels via RNA-seq,it was found that the expression of VvLOXs and gene involved in AOS branch was influenced by treatments,but not VvHPLs.The differences in transcription level were mostly occurred at E-L36 and E-L 37 stages.CRE1-1(cytokinin transduction related)and SAPK7(ABA synthesis related)were found to be significantly correlated with LOX and JMT,respectively.Results suggested that light envrionment modified the transcription of LOX-AOS pathway and hormone-related genes.The accumulation ofGLVs was probably then changed due to the sharing of the same substrate of AOS branch.