## 2 Results and Discussion
### Effect of TDZ on Grape Terpene Synthase (TPS) Activity  
To characterize the functional role of TDZ in relation to the activity of plant terpene synthases (TPSs), we compared the total TPS enzyme activity of treated and control berries during various stages of development on 12 July, 28 July and 28 August in 2018 and 2019 by using the plant terpene synthase (TPS) ELISA Kit. TPS concentrations were determined using the formula y = 0.0026x + 0.1466, where x represents the TPS activity, and y indicates the absorbance of the sample solution (Figure S3). As shown in Figure 2, our results revealed that in the pre-veraison (12 July) and veraison (28 July) stages, the application of TDZ resulted in a significant decrease in TPS activity. During the harvest stage, TPS activity in treated and control berries was nearly equivalent. The activity of TPS was found to increase in accordance with the progression of berry development. Terpene synthases are the type of enzymes that regulate terpen biosynthesis, using the initial substrates (GPP, FPP and GGPP) build of the simple C5-unit isopentenyl pyrophosphate and its isomer dimethylallyl pyrophosphate (DMAPP), which play an important role in terpene metabolism [35]. Over the course of the past three decades, there has been extensive characterization and classification of TPS enzymes which have divided them into seven subfamilies: TPS-a, TPS-b, TPS-c, TPS-d TPS-e/f, TPS-g and TPS-h [36]. Thus, it is highly likely that different types of TPS enzymes catalyzed the observed mixtures of monoterpene volatiles that were released by the grape berries in our study. The majority of the functionally characterized TPSs are multiproduct enzymes and the specific functions of the TPS families have been described in multiple papers [36; 37]. Under our experimental conditions, TPS activity during the harvest stage of berry development did not exhibit an obvious difference between the TDZ treatment and control (Figure 2). These observations help to support the hypothesis that the TDZ activity may affect the development of berry aroma development in the early stages--especially during the pre-veraison and veraison stages. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Bound Terpene Compounds (ng/gFW)** & \multicolumn{2}{c}{**Shing Muscat 2018**} & \multicolumn{2}{c}{**Shing Muscat 2019**} \\ \hline \hline
**Monoterpenes Compound** & **CK** & **TDZ** & **CK** & **TDZ** \\ \hline \hline Linalool & \(32.23\pm 1.54\)a & \(8.42\pm 0.87\)b & \(137.74\pm 9.75\)a & \(47.64\pm 5.52\)b \\ Hotrienol & \(47.31\pm 4.24\)a & \(11.3\pm 1.89\)b & \(72.42\pm 6.16\)a & \(24.71\pm 2.72\)b \\ \(\alpha\)-Terpineol & \(23.45\pm 3.21\)a & \(6.15\pm 0.52\)b & \(42.56\pm 5.12\)a & \(2.76\pm 0.81\)b \\ \(\alpha\)-Citral & \(20.23\pm 1.86\)a & \(4.64\pm 0.39\)b & \(34.17\pm 2.92\)a & \(2.95\pm 0.31\)b \\ Citronellol & \(9.34\pm 0.65\)a & \(5.3\pm 0.43\)b & \(9.55\pm 0.71\)a & \(5.58\pm 0.37\)b \\ Neral & \(45.02\pm 7.01\)a & \(13.57\pm 1.67\)b & \(107.86\pm 10.55\)a & \(16.8\pm 1.96\)b \\ Geraniol & \(130.13\pm 10.14\)a & \(5.53\pm 0.11\)b & \(218.12\pm 18.06\)a & \(16.62\pm 1.12\)b \\ Geranic acid & \(277.4\pm 14.21\)a & \(48.39\pm 4.06\)b & \(333.32\pm 24.42\)a & \(76.57\pm 9.23\)b \\ Citronellal & \(25.52\pm 1.66\)a & \(23.42\pm 2.78\)a & \(64.35\pm 4.78\)a & \(32.81\pm 2.59\)b \\ \(\beta\)-Myroene & \(10.23\pm 1.08\)a & \(3.12\pm 0.22\)b & \(12.32\pm 0.24\)a & \(1.72\pm 0.12\)b \\ p-limonene & \(74.34\pm 5.62\)a & \(12.72\pm 1.04\)b & \(122.41\pm 9.97\)a & \(17.41\pm 1.32\)b \\ Myrtenol & \(10.43\pm 0.76\)a & \(2.3\pm 0.16\)b & \(8.89\pm 0.71\)a & \(1.02\pm 0.12\)b \\ (\(E\))-furanoid linalool & \(342.42\pm 32.06\)a & \(82.42\pm 7.02\)b & \(245.65\pm 19.32\)a & \(57.27\pm 4.76\)b \\ (Z)-furanoid linalool & \(341.18\pm 23.22\)a & \(112.26\pm 9.25\)b & \(303.42\pm 19.87\)a & \(84.42\pm 7.68\)b \\ Total & \(1389.23\) & \(339.54\) & \(1712.78\) & \(388.28\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Bound monoterpenes compounds in berries treated with TDZ or CK and sampled at harvest.