## 3 Results and Discussion
### Effect of BTH Treatment on the Activities of Key Enzymes of LOX Pathway  
LOX activity reflects the grape maturity and degradation of membrane lipids. LOX activity increased and then decreased during grape ripening, with the greatest increase observed during veraison. The LOX activity of BTH-treated and CK grapes increased by 50.32% and 62.03%, respectively, at end-veraison (week 11) compared with mid-veraison (week 9). BTH-treated and CK grapes reached their peaks at end-veraison (week 11) and the mid-ripening stage (week 13), respectively (Figure 3A). [PERSON] et al. [54] found that LOX activity was closely related to the external environment. They also observed variations in the distribution of specific proteins in grape skin at different stages of ripening. During veraison, there is an overexpression of stress and defense-related proteins, which is consistent with the increase in LOX activity. The peak of LOX activity in grapes treated with BTH was advanced. This could be attributed to the enhanced stress and disease resistance of grapevines due to BTH treatment, which activates the response mechanism against diseases. Figure 3: LOX (**A**), HPL (**B**), ADH (**C**), and AAT (**D**) activities of BTH-treated (BTH) and control (CK) Cabernet Gernischt grapes. Data are expressed as means (\(n=3\)). Error bars represent standard deviation. Different uppercase letters indicate significant differences between BTH and CK (\(p<0.05\)), while different lowercase letters indicate significant differences within CK or BTH between different weeks of post-flowering (\(p<0.05\)). HPL catalyzes the cleavage of lipohydroperoxides to C6 or C9 aldehydes and is a member of the _CYP74_ gene family within the cytochrome P450 protein family. The activity of HPL increased and then decreased during grape ripening. It reached its peak at end-veraison (week 11) and decreased during ripening (week 15) to a level comparable to mid-veraison grapes (week 9) during grape ripening, which is in agreement with the findings of [PERSON] et al. [55]. The HPL activity of CK and BTH-treated grapes increased by 116.32% and 73.71% from mid-veraison to end-veraison, respectively. The HPL activity of BTH-treated grapes was significantly reduced by 15.80% compared to the CK at end-veraison (week 11) (Figure 3B). Reports have shown that, in the potato [56], _Arabidopsis_[57], and tomato [58], plant HPL activity is specific to tissue development. In particular, HPL expression is higher in fruits at the softening stage than in other periods and higher in flowers than in other organs. Jasmonic acid (JA) and its derivatives are produced via the allene oxide synthase (AOS) branch of the LOX pathway. The initial precursor for JA synthesis is linolenic acid, which enters the cytoplasm and is oxidized by LOX to 13-hydroperoxy-octadecatrienoic acid. This compound is subsequently catalyzed to 12-oxophyllenoic acid through the action of AOS and allene oxide cyclase. 12-oxophyllenoic acid is converted into JA through the action of 12-oxo-phytodienoic acid reductase and three rounds of \(\beta\)-oxidation. Notably, HPL and AOS exhibit antagonistic behavior due to their membership in the same cytochrome P450 family in plant skin cells. Thus, BTH treatment in grapes results in a decrease in HPL activity due to the overactivation of the JA-generating AOS branch. ADH is a zinc-containing enzyme in plants that reduces C6 aldehydes to their corresponding C6 alcohols, with the assistance of the nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate. ADH activity is related to the plant response to environmental stimuli and cultivation practices. In this study, the activity of ADH showed an initial increase, followed by a decrease, reaching its highest level at end-veraison (week 11) in BTH-treated grapes and at mid-ripening (week 13) in CK grapes. The activity of ADH in BTH-treated grapes was significantly higher by 46.44% and 13.48% compared with the CK at the mid-veraison and end-veraison, respectively (Figure 3C).