Effects of dopamine on reducing salt stress damage in pepper (Capsicum annuum L.) at morphological, physiological, biochemical, and molecular levels

Salt stress is a major environmental challenge that significantly reduces agricultural productivity, particularly in arid and semi-arid regions. Excessive sodium chloride (NaCl) accumulation in soil negatively affects plant growth, physiological functions, and biological processes. Dopamine, a catecholamine neurotransmitter, has emerged as a potential regulator of plant stress responses. This study aimed to investigate the effects of exogenous dopamine on salt stress tolerance in pepper, examining morphological, physiological, biochemical, and molecular responses. Pepper seedlings were subjected to 100 mM NaCl stress and treated with dopamine at concentrations of 50, 100, and 200 μM. Dopamine application, particularly at 100 and 200 μM concentrations, significantly improved plant growth parameters, including height, stem diameter, leaf area, and biomass accumulation. It enhanced photosynthetic efficiency by increasing chlorophyll content, stomatal conductance, and transpiration rate, while reducing oxidative stress markers such as H₂O₂ and MDA. Dopamine also regulated the activity of antioxidant enzymes (SOD, CAT, POD) and maintained ion homeostasis by reducing sodium (Na+) and chloride (Cl−) accumulation and promoting potassium (K+) and calcium (Ca2+) uptake. At the molecular level, dopamine influenced the expression of genes involved in ion transport (AKT1, HKT1, HKT2;2) and photosynthesis (psb). This study demonstrates that dopamine is a promising plant growth regulator that enhances salt tolerance in pepper plants. It achieves this by improving growth, photosynthetic efficiency, antioxidant defence, and ion homeostasis, while modulating key molecular pathways. These findings suggest that dopamine could be utilised as a sustainable strategy to mitigate salt stress and improve crop productivity in saline-affected agricultural regions. Further research is needed to explore its application in other crops and under field conditions.