Melatonina, serotonina e dopamina na mitigação do estresse hídrico em beterraba

Abstract

Modern agriculture faces significant challenges due to the impacts of climate change, especially during extreme weather events. Prolonged droughts have negatively affected crop productivity, leading to morphological and biochemical adaptations that can compromise plant performance. In this context, the use of bioregulators such as melatonin, serotonin, and dopamine emerges as a promising alternative. This potential is based on their roles as antioxidants and plant growth regulators, offering strategies to enhance plant resilience under adverse climatic conditions. This study aimed to evaluate the influence of melatonin, dopamine, and serotonin application on the morphophysiology and postharvest quality of beetroots grown under water deficit conditions. Beet plants were cultivated in pots filled with commercial substrate and subjected to treatments combining two irrigation regimes—well-watered (80% of substrate water-holding capacity) and water deficit (30% of capacity)—and foliar applications of distilled water (control), melatonin and dopamine at 100 mM, and serotonin at 5 mM. Morphological, physiological, and postharvest variables were assessed throughout the experiment. Biomass, morphology, and photosynthetic capacity were reduced by water deficit, and the bioregulators did not mitigate the damage caused by drought for most of the evaluated variables. However, serotonin promoted greater carbon assimilation under drought compared to full irrigation. In drought-stressed plants, dopamine reduced electrolyte leakage compared to untreated plants and increased root sugar content, indicating improved oxidative balance. Water deficit reduced vitamin C content in control roots, whereas no significant differences were observed in bioregulator-treated plants across irrigation conditions. Melatonin showed a stronger effect under well-watered conditions, improving carbon assimilation, photosynthesis, phenolic synthesis, and antioxidant activity, while maintaining soluble solids levels under stress, suggesting an osmoprotective action that reduces the need for osmolyte accumulation. Bioregulator-treated plants preserved skin coloration under drought, enhancing visual quality. These results demonstrate that severe stress greatly affected beet production and quality. Although bioregulators did not reverse most of the effects of water deficit, they influenced plant physiological traits under stress, particularly dopamine and serotonin. Further research is needed to understand how these compounds affect plant physiology under moderate stress and to determine appropriate application concentrations, given their activity at low doses in plants.