Effect of water supply on the accumulation levels of phenolic compounds, essential oil properties and antioxidant activity of Thymus vulgaris

Thyme is a widely cultivated medicinal plant adapted to sunny and dry habitats. Essential oil properties of Thymi herba can be quite different, depending both on the growing site and chemotaxon. Among phenolic compounds, rosmarinic acid is the most relevant, however, the importance of phenolic acids and flavonoids is also well documented. In our studies we were aimed at evaluating the effects of water deficit on different thyme taxa ('Varico 3' and essential oil chemotypes of TV17- thymol, TV115- geraniol, TV143- alpha-terpineol), with special respect to its impact on the accumulation levels of active compounds. A pot experiment was conducted among controlled conditions in 2014, where soil water capacity (SWC%) values were kept at 40% (S: stress condition) and 70% (C: control condition), respectively. Three harvest periods were included when vegetative shoots were sampled for detecting the levels of essential oils (EO: mL/100 g DW) and their compounds (GC %), rosmarinic acid (RA: mg/g by HPLC), flavonoids (FL: %, Ph. Hg. 8), total phenolics (TPC: mg/g GSE), and antioxidant capacity (AC: mg/g ASE by FRAP assay). According to our results, the content and composition of active substances were highly affected by water supply, while sampling time and genotype were also influencing factors. In general, higher levels of RA, TPC and AC have been detected under stress conditions. However, negative effects of water deficiency were observed when measuring the amounts of EO and FL. Significant differences were found among taxa involved, concerning drought stress tolerance: the lowest differences between S and C plants were measured at TV 17. During our experiment, increasing levels of RA and TPC were found, while EO content decreased. Among essential oil compounds, percentages of geraniol and thymol were generally higher in C plants, while alpha-terpineol % changed in an opposite direction.

Acknowledgement: Our work has been supported by OTKA Scientific Foundation (No. NN108633).