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Abstract
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Drought stress affects a vast range of morphological, physiological and biochemical characteristics in plants;
however, exogenous application of osmotically active materials such as polyamines has been regarded as a good
alternative to counter the adverse effects of various environmental stresses on plant functions. The present study
investigates the response of Thymus vulgaris L. plants to different concentrations of putrescine (0, 20 and
40 mg L−1) under well-watered and drought stress conditions in a factorial experiment based on randomized
complete block design with three replications during 2-year field trial. Drought stress significantly impaired the
plant growth and biomass accumulation, and altered leaf water status, photosynthetic pigment contents, hydrogen
peroxide (H2O2) and malondialdehyde (MDA) levels, free proline and soluble protein contents, ROS
scavenging enzymes such as superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), and ascorbate
peroxidase (APX), essential oil content and chemical profiles of the essential oil compared to the respective
control values. However, exogenously applied putrescine (particularly at 20 mg L−1) improved leaf water content,
accumulated dry matter, reduced cell injury indices and up-regulated antioxidant enzyme activities.
Moreover, stressed plants treated with the highest concentration of putrescine increased their essential oil
content by 23.07% compared to non-stressed plants without putrescine application. A total of 14 compounds
predominantly consisted of monoterpenes such as Thymol, Carvacrol, γ-Terpinene and p-Cymene were identified
in the essential oil of the plants in both years. Percentage of the major essential oil constituents substantially
enhanced under drought stress, whereas exogenous application of putrescine further improved the content of
these specific volatile compounds under well-watered and stressed plants compared to the respective control. A
significant negative correlation was observe
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