Polyamines (PAs) are signaling molecules that exhibit promising roles in improving stress tolerance in plants. Limited information is available concerning the effects of the exogenous PAs on medicinal plants including chamomile. This experiment was carried out to study the effects of foliar application of PAs [Putrescine (Put), Spermidine (Spd), and Spermine (Spm)] on physiological and biochemical processes to understand the possible mechanisms concerning the water deficit stress [soil Field Capacity (FC) as control, 80% of FC (FC80), and 60% of FC (FC60)] alleviation in German Chamomile. We found that PAs partially inhibited water deficit-induced stomatal closure and induced antioxidant enzymes to eliminate the increased H2O2. Spd increased stomatal conductance (gs) by 66, 65, and 35% at FC, FC80, and FC60, respectively, compared with the control. The increased gs enhanced leaf net photosynthesis (AN) by 52 and 86% at FC80 and FC60, respectively, compared with the control. The role of PAs in oxidative damage alleviation was approved by the negative correlation of leaf antioxidant activities and Malondialdehyde (MDA) and H2O2 content. According to the results, PAs function as stress-protecting compounds to instigate the antioxidative enzymes to scavenge stressinduced H2O2, improve membrane stability, and enhance water deficit tolerance. Generally, our results suggested that PAs could be potential growth regulators to alleviate mild to severe water deficit stress.

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