Tarbiat Modares University Journal of Agricultural Science and Technology 1680-7073 27 1 2025 01 01 Alleviation of Drought Stress in German Chamomile (Matricaria chamomilla L.) in Response to Suppressive Oxidative Stress and Water Deficit-Induced Stomatal Closure by Exogenous Polyamines 127 143 17006 10.22034/JAST.27.1.127 EN Mohammad Javad Ahmadi-Lahijani Department of Agrotechnology, Faculty of Agriculture, Ferdowsi University of Mashhad, Islamic Republic of Iran. Jafar Nabati Department of Agrotechnology, Faculty of Agriculture, Ferdowsi University of Mashhad, Islamic Republic of Iran. Saeed Moori Plant Breeding Department, Nuclear Agriculture Research School, Nuclear Science and Technology Research Institute (NSTRI), Tehran, Islamic Republic of Iran. Mohammad Kafi Department of Agrotechnology, Faculty of Agriculture, Ferdowsi University of Mashhad, Islamic Republic of Iran. 0000-0002-0933-1346 Journal Article <span>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 (FC<sub>80</sub>), and 60% of FC (FC<sub>60</sub>)] alleviation in German Chamomile. We found that PAs partially inhibited water deficit-induced stomatal closure and induced antioxidant enzymes to eliminate the increased H<sub>2</sub>O<sub>2</sub>. Spd increased stomatal conductance (g<sub>s</sub>) by 66, 65, and 35% at FC, FC<sub>80</sub>, and FC<sub>60</sub>, respectively, compared with the control. The increased g<sub>s</sub> enhanced leaf net photosynthesis (A<sub>N</sub>) by 52 and 86% at FC<sub>80</sub> and FC<sub>60</sub>, 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 H<sub>2</sub>O<sub>2</sub> content. According to the results, PAs function as stress-protecting compounds to instigate the antioxidative enzymes to scavenge stress-induced H<sub>2</sub>O<sub>2</sub>, 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. </span> Chlorophyll fluorescence Enzymatic antioxidant Hydrogen peroxide Gas exchange variables Non-photochemical quenching https://jast.modares.ac.ir/article_17006_7fb15019103809d7311d26d2e8bb47ed.pdf