Evolution Of Expression Of Hydroperoxide Lyase Gene, Enzyme Activity And Volatile Compounds Of Cabernet Sauvignon (Vitis Vinifera L.)

Green leaf volatiles (GLVs) are short-chain acylic aldehydes, alcohols and estersproduced via a serious of enzymes catalyzing polyunsaturated fatty acids in plants. GLVs canaffect the flavor and aroma of fruits and vegetables, including grapes. The C6and C5GLVsare important precursors of aroma compounds, like volatile thiols in wines. GLVs can beproduced during grape berry development and released after grape wounding in great quantity.Hydroperoxide lyase (HPL) and Alcohol dehydrogenase (ADH) are two kinds of importantenzymes in producing GLVs. This biochemical pathway has been well characterised in otherplants as GLV pathway or LOX-HPL pathway. However, GLV pathway in grape has not wellstudied and characterised. This thesis focused on the study of genes, enzymes and theirvolatile compounds in GLV pathway. HPLs are characterised as CYP74enzyme family, oneof representative is cytochrome P450oxidases superfamily. HPLs catalyse FUFA-hydroperoxides and produce aldehydes and oxoacids. HPLs are classified as13-HPLs,9/13-HPLs or9-HPLs according to the substrate specificity.The research identified two HPL genes, and studied the expression of HPL genes and anADH gene in GLV pathway, the activity of enzymes and their volatile products during berrydevelopment, wounding and methyl jasmonate (MeJA) treatments, in different tissues in2011and2012. The studied genes displayed different expression patterns across different stages ofberry development in grape berries and different tissues, and same expression patterns acrossdifferent period of wounding and methyl jasmonate treatments. VvHPL1and VvHPL2arecharacterised as13-HPLs and9-HPLs, respectively. The analysis of HPL and ADH genes,their enzymes and volatile compounds during different berry development indicated that thegenes, enzymes and their volatile compounds had significant positive correlation, displayingincreasing trend gradually.There were the same variation trend between the expression of VvHPL1and VvHPL2, the activity of13-HPLs and9-HPLs, and the C6and C9aldehydes in grape peels and leaves. Thehighest quantity of expression of VvHPL1, VvHPL2and VvADH2presented in leaves, roots,and tendrils respectively. There were difference between the expression of genes and theactivity of enzymes in flowers, stems and tendrils, but the expression of VvHPL1and theactivity of13-HPLs in leaves and roots displayed the same variation trend. The VvHPL2and9-HPLs displayed high quantity of expression and enzyme activity in flowers, whichdisplaying different variation trends. VvHPL2had high quantity of expression in roots, whichwas different with the low level of9-HPLs in roots. The same negative correlation existed instems, which had low quantity expression of VvHPL2and high9-HPLs activity. Theexpression of VvHPL2, VvADH2and9-HPLs, ADHs activity in tendrils had the samevariation trend. The positive correlation also presented in the expression of VvADH2and highADHs activity in roots, leaves and flowers, as well as the C6alcohols in flowers. However,the positive correlation did not exist in grapes in terms of the expression of VvADH2, ADHsactivity and the content of C6alcohols. The variation of genes expression, enzymes activityand characteristic volatile compounds implied the transfer of transcripts or enzymes betweendifferent tissues.Expression levels of VvHPL and VvADH2, enzymes activity and related volatilecompounds were significantly increased in wounded berry peels compared to the unwoundedberries, the volatile compounds released from wounded berries also increased significantly.There were difference among different studied genes, which means the highest quantity ofexpression of different genes as well as their enzyme activity and related volatile compoundsdisplayed in different wounding periods, but the same variation trend presented in all thestudied genes, their enzyme activity and related volatile compounds. At the same time,wounding induced the volatile compounds released from wounded berries also increasedsignificantly compared to the unwounded berries using the dynamic headspace absorptiontechnique. The kinds and content of volatile compounds released, like terpenes exceeded thatreleased from the entire grapes significantly. The same effect was also found among the grapeberries with MeJA treatment, which induced the expression of HPL and ADH and the activityof HPLs and ADHs increased significantly reaching the highest quantity in1to3h afterMeJA treatment. Various volatile compounds emerged in grape berries after MeJA treatment.Therefore, the same variation trend presented among the content of GLVs, genes expressionand enzymes activity across the MeJA treatment.