# The Influence of UV on the Production of Free Trepenes in _Vitis vinifera_ cv. [PERSON]
## 1 Introduction  
Terpenes are secondary metabolites naturally produced by plants, and can be classified as monoterpenes, sesquiterpenes, diterpenes, triterpenes and carotenes, based on the isoprene structure [1]. Terpenes and their oxygenated derivatives, terpenids, present in wine mostly originate from grape. Up to now, there are approximately 200 terpen and terpenids reported in grapes and wine [2, 3]. Terpenes present either as glycosidic precursors or as unbound free volatiles in grapes, where bound terpen are more abundant, especially toward harvest [4]. Bound terpen from grape can be hydrolysed to release free terpen during the winemaking process [3]. Terpenes, especially free terpen, are responsible for attracting insect pollinators and acting as plant defence [5], and importantly contribute to the distinctive flavours and aroma of grapes and wine [6]. Moreover, many terpen, such as D-limonene, \(\beta\)-caryophyllene and carnosol, have been reported to have anticancer, antioxidant and antimicrobial properties [7, 8, 9], which may enhance the health benefits of consumers. The biosynthesis of terpen in grapes varies at different grapevine phenological stages. [PERSON] and [PERSON] [10] reported continuous reduction of monoterpenes and sesquiterpenes from fruit-set to harvest in Riesling and Cabernet Sauvignon grapes. On the contrary, [PERSON] et al. [11] reported themaximum concentration of sesquiterpenes at harvest in Baga grapes. This finding was consistent with our previous study, where rotundone accumulation sped up toward the end of the ripening period [12]. Furthermore, the total amount of monoterenes and C\({}_{13}\)-norisoprenoids in Fernao-Pires grapes peaked at 20 days after veraison and declined until harvest [13]. Terpenes biosynthesis could be influenced by environmental factors, such as temperature, rainfall and solar exposure, and these factors normally interact with each other in field conditions. Solar ultraviolet radiation (UV), such as UV-A (wavelength 315-400 nm) and UV-B (280-315 nm), is a type of solar energy reaching the Earth's surface [14]. UV-B radiation could activate the plant defence system and promote the biosynthesis of secondary metabolites such as terpenes and phenolics [15; 16; 17], while UV-A and visible light (400-700 nm) may interact synergistically to promote the production of UV-B absorbing compounds thus enhancing plant resistance to UV-B [14]. [PERSON] et al. [18] reported that the concentration of linalool in grape was increased by 60% under sunlight exposure, while [PERSON] et al. [19] suggested that UV-B radiation could induce the production of monoterenes to protect grape tissues from UV-B itself. In agreement with this finding, [PERSON] et al. [20] confirmed through molecular study that shaded berries contained fewer linalool. On the other hand, [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [16] suggested that sunlight and UV exposure led to increases of nerol, geraniol and citronello, while [PERSON] and [PERSON] [21] suggested that solar radiation could promote the biosynthesis of norisoprenoids through the elevated production of carotenoids. Research studies on peach have reported that UV radiation could alter the concentration of sesquiterpenes by modifying the transcript levels of relevant terpene synthase [22]. The accumulation of terpenes in grapes could be influenced by environmental factors at different grapevine phenological stages. So far, there is limited research on the impacts of UV on the production of free terpen, especially sesquiterpenes in grapes, at different grapevine phenological stages. This study aimed to investigate the influences of UV attenuation at different phenological stages of grape ripening on the free terpen produced in grapes.