Journal of Plant Process and Function

Thyme is one of the best known genera within Labiatae family, because of its more than 250 species and its antimicrobial and antispasmodic uses. At the present time, demand for thyme products are increasing and hence research demand is increasing. Environmental factors such as drought can affect plant growth and production. Phytohormones take a crucial role in this stress. Indicated T. serpyllum as the most tolerant and T. vulgaris as the most susceptible genotypes to water deficit stress been used. At the end of stress period, shoot dry weight , water content,  water potential and soil moisture were measured. Based upon these traits, tolerant plants known as water saver plants, while, sensitive plants behaved as water spender plants. This experiment was conducted at the University of Birmingham, School of Biosciences in 2013. During the stress, leaf samples were harvested and analyzed through mass spectrometry based metabolomics approach. The results of tolerant plants indicated significant increase in drought-stressed plant rather than control plants as follows: 173% increase in salysilic acid, 133% increase in neoxantin (abscisic acid substrate), 166% of auxin and 180% of gibberellic acid. Nevertheless, sensitive plants showed significant increase in jasmonic acid 132%, salysilic acid 242% and decrease in neoxanthin 62% and gibberellic acid 36%. Auxin had non-significant difference between stressed and control plants of sensitive populations. Increasing of neoxanthin in tolerant plants occurred with water content maintenance and decreased shoot dry weight. This experiment confirmed the key role of abscisic acid and salysilic acid in drought stress tolerance mechanism. Even though, it seems overall response of plant to drought stress is the result of all the phytohormones interaction. Increasing ABA precursor caused growth inhibition in drought tolerant plants, which eventually provided less water usage. Since, sensitive plants didn’t exhibit neoxantin elevation, which seems it is due to being lower than water potential threshold.