Strigolactone and Methyl Jasmonate-Induced Antioxidant Defense and the Composition Alterations of Different Active Compounds in Dracocephalum kotschyi Boiss Under Drought Stress

Strigolactone (SL) and methyl jasmonate (MeJA) are one of the most important plant hormones that exert biological activity in plant responses to environmental stresses. Considering the undetected role of SL in drought tolerance and essential oil yield of medicinal plants as well as conceivable interaction among MeJA and SL, a factorial experiment was performed as a complete randomized design with three replications. Experimental factors including two irrigation regimes such as irrigation to 80% field capacity (control) and 40% field capacity (drought stress) and spraying treatments include MeJA (0 and 0.5 mM) and SL (0 and 10 mu M) were applied. Treatment of plants with SL and MeJA resulted in higher tolerance to drought stress due to higher fresh and dry weights as well as lower electrolyte leakage, malondialdehyde, H2O2, total phenol content, total antioxidant activity and antioxidant power assay. The most important essential oil constituents of D. kotschyi included geranyl acetate (41.1-48.6%), alpha-pinene (16.2-18.9%), geranial (7.9-10.1%), limonene (5.5-7.0%), neral (3.5-4.1%), methyl geranate (2.3-3.3%) and geraniol (1-2.2%), the least of which was found in non-MeJA- and SL-treated plants under drought and the highest in MeJA- and SL-treated plants under drought stress. Drought tolerance of D. kotschyi became more intense and the amount of essential oil components of water stressed plants was the highest (99.2%) when these plant hormones were used together. These results suggest a cross-link between MeJA and SL in improving drought resistance and optimizing the production of essential oil of D. kotschyi.