Effect of drought stress on metabolite adjustments in drought tolerant and sensitive thyme

Drought is one of the most important threats to plants and agriculture; therefore, understanding of the mechanism of drought tolerance is crucial for breeding of drought tolerant plants. Here, we assessed effects of four levels of drought (90%, 55%, 40% and 25% FC) on some physiological criteria and metabolite adjustment of two different drought-responsive thyme plants (Thymus vulgaris as drought sensitive and T. Kotschyanus as drought tolerant species), using ¹H-NMR. Among three physiological parameters and 18 identified metabolites, species × treatment effects were significant (P ≤ 0.01) for leaf temperature, acetic acid, citric acid, fumaric acid, malic acid, succinic acid, fructose, sucrose and serine. RWC, chlorophyll and carotenoids content, glucose, alanine and choline were affected by simple effects of species and treatment. Correlation analysis revealed that there is a different correlation between physiological parameters and metabolites in both species. This analysis also revealed that, by ignoring the correlation between malic acid and succinic acid in T. vulgaris, there was no significant correlation between TCA intermediate in both species. According to results, sugars, amino acid and energy metabolism were affected by drought and, among them, TCA intermediates had more alternation in two studied species so, this cycle and its intermediates probably have more prominent role than other identified metabolites in the induction of drought tolerance.