The objective of this study was to determine the effects of foliar application of polyamines (PAs) on antioxidant defence and essential oil production of valerian (Valeriana officinalis L.) grown under different drought stress treatments (100, 70, 50 and 30% available water content). This study was carried out using pots in greenhouse condition. Drought–stressed valerian seedlings were sprayed with 1 mM concentration of each putrescine (Put), spermidine (Spd) and spermine (Spm). The results showed that drought stress significantly affected most biochemical characteristics of valerian plants. Characteristics including leaf relative water content, chlorophyll a and b contents were decreased, while carotenoids and electrolyte leakage were increased with the increase of water stress. In this research, defensive characteristics comprising proline content, soluble sugars, catalase, and ascorbate peroxidase were increased followed by drought stress to ameliorate the adverse effect of it. Results revealed that foliar application of Spd and Spm provoked the antioxidant enzymes activity as well as proline accumulation in valerian which alleviate the membrane damages. Consequently, Spd and Spm increased photosynthetic pigments which act as energy supply for plant growth and production. Here, putrescine had detrimental effects on CAT activity and Chl a content. Albeit, PAs presented remarkable effects under moderate drought stress condition but it showed reverse trends in severe drought stress condition. In terms of quantity and quality yield, drought stress reduced root growth but increased the concentration of essential oils. PAs are able to alleviate water deficit-induced diminish root growth. These results suggest that in moderate drought stress, growers can use PAs to increase productivity valerian.
