Stachys schtschegleevii Sosn. is an endemic medicinal plant belonging to the Lamiaceae family and mainly grown in North-western Iran. Drought stress is an important factor in reducing the yield of medicinal herbs. Water-stress tolerance involves subtle changes in cellular biochemistry. It appears to be the result of the accumulation of compatible solutes and of chemical compositions that can be rapidly induced by osmotic stress. For this purpose, the effect of different irrigation regimes (well-watered and irrigation after depletion of 40% and 70% of field capacity (FC)) were studied in S. schtschegleevii. The experiment was conducted in a randomized complete block design in three replications. The results showed that water-deficit had negative effects on shoot dry matter, relative water content, and photosynthetic pigments of the exposed plants. The essential oil (EO) content under water-deficit had an increasing trend. Water-deficit significantly increased total phenol content, proline, H2O2, and malondialdehyde contents. Linalool, β-pinene oxide, α-campholenal and germacrene-D were the major compounds of essential oils (EOs) affected by water-deficit stress. Finally, although water deficiency reduces the shoot dry matter yield of the S. schtschegleevii, the accumulation of EO increased as a plant response to water-deficit stress.
