<p>Phenolic compounds are a diverse group of important plant secondary metabolites with antioxidant capacity. Their synthesis can be induced by environmental factors and they help plants to cope with abiotic stress. Treatment of barley with plasma-treated water as a foliar spray resulted in long-lasting changes in the content phenolic compounds in both leaves and roots. The content of phenylalanine and tyrosine was increased, and long-lasting changes in the content of coumaric acid were observed in the leaf. The total chlorophyll content was increased and the ratio of chlorophyll a to b was decreased, while the zeaxanthin content was increased. Luteolin content was increased at all growth stages and shifts in isovitexin and saponarin levels were observed. Mild oxidative stress due to PTW could be a way to prime barley against future abiotic stress factors.</p>