Influence of benzothiadiazole on isoprene metabolism and aroma accumulation in Chardonnay grapes (Vitis vinifera L.) during development

Chardonnay is a non-floral grape with economic value and nutritional properties that is widely grown in northwestern China. However, limited research has been conducted on exogenous spraying to regulate volatile compound metabolism (especially isoprene metabolism) in Chardonnay grapes. Benzothiadiazole (BTH) can induce disease resistance and augment the contents of phenolics and volatile compounds in grapes. This study aimed to evaluate the influence of BTH on the accumulation of isoprene aroma, carotenoid levels and the activity profiles of key enzymes. Chardonnay grapevines were treated with 0.37 mM BTH at veraison to investigate the impact on physicochemical parameters, carotenoids, metabolic enzyme activities, and free and bound isoprenoids in developing Chardonnay grapes. The results showed that reducing sugars, and total soluble solids of BTH-treated grapes increased, while the content of titratable acidity, β-carotene, zeaxanthin, β-cryptoxanthin, chlorophyll, and total carotenoids in treated ripe grapes decreased relative to control berries. BTH-treated ripe grapes exhibited elevated levels of bound norisoprenoids and three key enzemy activities (carotenoid cleavage dioxygenase, phytoene synthase, lycopene β-cyclase), with a slight decrease in free norisoprenoids. Free and bound terpenoids profiles were also significantly enhanced by BTH treatment at veraison. Our findings offer novel perspectives into the modulation of isoprene biosynthesis in grape berries when exposed to BTH.