Khosh-Khui M, Ashiri F and Saharkhiz MJ
Drought is a major abiotic factor that limits agricultural crop production. Antioxidant activity of some plants may be changed by water stress. In this study, a pot experiment was conducted to assess the effect of drought on the antioxidant activity of thyme (Thymus vulgaris L.). Different irrigation regimes (2, 4, 6, 8 and 10 day intervals) were applied for about 6 months and the antioxidant capacity was evaluated by using two different assays; the FRAP (ferric reducing antioxidant power) and DPPH (2,2-diphenylpicrylhydrazyl) scavenging assays. Although in some other species water stress might increase the antioxidant capacity, but the experimental results showed that long-term drought caused
a reduction in the antioxidant activity and total phenolic content of thyme. While all plants died with 10 day irrigation interval, with 2 (control), 4, 6, and 8 days irrigation intervals, IC50 values of the DPPH assay was 87.82, 105.86, 118.05 and 133.60 μg/ml respectively. A higher value of IC50 showed a lower antioxidant activity, which indicated that severe water stress (8 days) significantly decreased the antioxidant activity of thyme (P≤0.05). FRAP values showed a trend to reduction by increasing the irrigation intervals, but this trend was not significant.