Abstract: In this study, the optimal concentrations of methyl jasmonate (MeJA) and methyl dihydrojasmonate (MDJA) for Cabernet Gernischt were selected based on basic physicochemical properties of grapes. The key volatile metabolites and key enzyme activities in response to MeJA and MDJA were analyzed by headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and enzyme-linked immunosorbent assay (ELISA), respectively. The effects of pre-harvest MeJA or MDJA treatment on the fruit quality and green leaf volatile components in the lipoxygenase (LOX) metabolic pathway of Cabernet Gernischt were also investigated. The findings revealed that the application of 0.1 mmol/L MeJA or 5 mmol/L MDJA significantly enhanced mass of 100 berries, total sugar content, soluble solids content, pH, total phenol and total anthocyanin contents. Compared with the control group, MeJA increased these indexes by 10.24%, 27.83%, 28.24%, 4.80%, 77.63% and 85.29%, respectively, while MDJA increased them by 9.15%, 24.01%, 24.41%, 8.30%, 69.21% and 71.57%, respectively. Furthermore, MeJA and MDJA reduced titratable acid content by 40.0% and 30.24%, respectively. Accordingly, both MeJA and MDJA significantly improved fruit quality. Moreover, they significantly increased the contents of C6 compounds responsible for the typical aroma of Cabernet Gernischet. Significant correlations were observed between the activity of each key enzyme in the lipoxygenase metabolic pathway and the corresponding metabolites, indicating that the application of MeJA or MDJA at a suitable concentration could positively influence the accumulation of green leaf volatiles in Cabernet Gernischt.

Key words: Cabernet Gernischt; methyl jasmonate; methyl dihydrojasmonate; grape quality; lipoxygenase metabolism