## 4 Discussion
### UV Radiation Changes the Composition of Essential Oil  
Depending on the UV irradiation range, the essential oil concentration and its component composition changed. The content of linalool was higher in plants grown under UV-A and UV-B irradiation, while the eugenol content was higher in the control variant. Additionally, under UV-C radiation, eugenol methyl ester (ME) is additionally synthesized.  
ME is found in a number of plants (over 450 species from 80 families, including the angiosperms and gymnosperms) and plays a role in attracting pollininators. Essential oils containing eugenol are used in food, perfumery and pharmaceutical industries [58]. MEis a naturally occurring genotoxic carcinogenic compound with DNA-binding ability and has a toxicological danger due to its structural similarity with known carcinogenic phenylpropanoids, for example, estragole and safrole [59]. From 2021, any product containing more than 0.01% methyl eugenol must be declared in accordance with the Regulation of the European Parliament and of the Council (16 December 2008) [60].  
The \"Red Ruby\" variety belongs to the basil chemotype rich in ME [61]. Researchers have established a strong dependence of eugenol and ME content on seasonal changes (mainly solar radiation, but also on temperature and relative humidity). Other studies show that sweet basil which was grown in a greenhouse up to the first internodes under natural light, and subsequently moved under artificial light with a PAR 400-700 nm spectrum with additional UV-B irradiation for 18 days (up to six developed leaves and a height of 12-15 cm), had a lower content of methyleugenol [30; 62]. During ontogenesis, the activity of eugenol \(O\)-methyltransferase (EOMT) is constantly decreasing, while the level of eugenol increases. UV-B radiation apparently suppresses the activity of EOMT already in young leaves, which indicates a UV-induced change in the enzymatic defense systems in sweet basil leaves. In our study the UV-A and UV-B irradiation depressed the activity of EOMT and prevented ME synthesis. However, in other research, UV-B irradiation had a positive effect on eugenol, phenylpropanol and ME and decreased the content of linalool in young basil leaves and increased it in adult plants [24].  
The scheme of changes in the component composition of essential oil depending on the impact of ultraviolet radiation of various ranges is shown in Figure 3. An amount of phenylpropanoids responsible for plant protective reaction to aggressive environmental influences, including ultraviolet irradiation, increased only in the variant with the use of additional UV-C irradiation. UV-A and UV-B irradiation in this experiment did not cause a stress increase in phenylpropanoids, rather was stimulating and necessary for optimal growth.  
It is known that additional illumination with UV-B wavelengths increases the aromatic volatile compound level in sweet basil leaves [31; 62]. The essential oil content is much higher in young leaves, and the main aromatic components are a-pinene, p-pinene, 1,8-cineole and linalool [63]. The essential oil content can be increased with UV-B irradiation and at later stages of growing [64]. In contrast, our research showed, that the basil leaf total oil content had no statistically significant differences between variants. It can be explained by different reactions of basil varieties to UV-B radiation impact [65].  
In general, it can be said that exposure to UV-A and UV-B irradiation changes the composition of terpen in \"Red Ruby\" variety sweet basil essential oil towards more complex sesquiterpenes that affect the plant aroma.