## 2 Results and Discussion
### Grape Volatile Arromas of Grapes and Their Glycosylated Precursors
#### 2.3.3. Norisoprenoids and Carotenoids  
The norisoprenoids present in grapes contribute to the floral and fruity aromas of wines [23]. In this study, seven norisoprenoids were identified (Text 6). The study revealed that Marselan grapes exhibited a larger variety and total content of norisoprenoids, with the maximum content of \(\beta\)-damascenone nearly twice as high as that in Cabernet Sauvignon grapes. This finding is consistent with the previous study where Marselan wines had strong floral and fruity aromas [28; 29]. Carotenoids, which serve as direct precursors for these aromas in grape berries, are converted to norisoprenoids by carotenoid cleavage dioxygenenses (CCDs) [1]. A total of six carotenoids were identified, with Marselan grapes exhibiting elevated levels of \(\beta\)-carotene, xanthophyll, violaxanthin, and neoxanthin in comparison to Cabernet Sauvignon grapes (Text 6). The total carotenoid content in Marselan grapes was approximately 1.5 times higher than that in Cabernet Sauvignon grapes from the same vintage. The elevated concentration of carotenoids in Marselan grapes may be a contributing factor to its superior norisoprenoid content.  
The LR treatment had a significant impact on the norisoprenoid concentrations in Cabernet Sauvignon berries, resulting in a decreased levels of the majority of norisoprenoids. Notably, \(\beta\)-damascenone was particularly affected, constituting only 12-15% of the control in LR1 for both years. Furthermore, the concentration of \(\beta\)-damascenone exhibited a declining trend with earlier leaf removal. It can be postulated that an extended exposure of the berry's surface may be unfavorable for the accumulation of norisoprenoids, in agreement with the results pf prior research [15]. Violaxanthin and neoxanthin, respectively, are speculated to be precursors of vitispirane and \(\beta\)-damascenone [30; 31]. Violaxanthin is a crucial component of the xanthophyll cycle and plays a significant role in plant photoprotection. In response to excessive light, violaxanthin is transformed into zeaxanthin via antheraaxanthin by violaxanthin de-epoxidase (VDE). Conversely, under low-light conditions, zeaxanthin is converted into antheravanthin and violaxanthin by the activity of zeaxanthin epoxidase (ZEP) [32]. In both years of our study on Cabernet Sauvignon grapes, lower levels of violaxanthin were observed in the LR treatment, and the proportion of violaxanthin within the xanthophyll cycle was also lower in the LR1 and LR2 treatments. However, there were no significant differences in comparison to the control (Table 6). A similar trend was observed for neoxanthin, which is a downstream metabolite of violaxanthin. Therefore, we hypothesize that the reduction in vitispirane and \(\beta\)-damascenone following LR treatments may be associated with the decrease in their precursors, violaxanthin and antheravanthin. This pattern was not observed in Marselan berries, in which LR1 solely reduced the level of glycosylated \(\beta\)-damascenone. Furthermore, the LR treatment had no effect on either total norisoprenoids or carotenoids, in contrast to the results observed in Cabernet Sauvignon grapes during the same year (Text 6).