Abscisic acid effect on the alteration of the photosynthetic processes induced by thermal stress in Dracocephalum Moldavica L

Abstract Dracocephalum moldavica L. is a heat-sensitive medicinal plant whose productivity may be compromised by temperature stress. This study aimed to evaluate how different growth temperatures (15, 25, and 35 °C) and concentrations of exogenous abscisic acid (ABA; 0, 5, 10, 20, and 40 µM) influence the photosynthetic performance and antioxidant response of D. moldavica . Plants grown at 25 °C without ABA application showed the highest total chlorophyll content and photosynthetic rates, while growth at 35 °C combined with 40 µM ABA led to severe declines in both traits. ABA application consistently reduced stomatal conductance across all temperatures. Lipid peroxidation, measured as malondialdehyde (MDA) content, increased with both temperature and ABA concentration. Although ABA stimulated the activity of antioxidant enzymes, particularly CAT, POD, and APX, this response was insufficient to counteract heat-induced oxidative damage. Overall, our findings indicate that exogenous ABA does not enhance thermotolerance in D. moldavica and may even exacerbate physiological stress at high concentrations. These results highlight the need for further research into more effective strategies, including combined treatments, to improve the heat stress resilience of this species.