Melatonin reduces oxidative stress and promotes drought tolerance in young Coffea arabica L. plants

Water deficit severely compromises the homeostatic balance of plants and suggests a redox imbalance in cells. Melatonin is described as a promoter of stress tolerance in plants that induces the expression of stress-related genes, reduces lipid peroxidation and increases the antioxidant system. To analyze the influence of exogenous melatonin on the promotion of tolerance to water deficit, we applied concentrations of 300 mu M and 500 mu M to Coffea arabica L seedlings. Here, we show that the intensity of the short-term responses to melatonin may vary according to the concentration of melatonin. We also report that lower concentrations of melatonin (300 mu M) promote an increase in the root system and the protection of the photosynthetic apparatus, allowing greater gas exchange, greater carboxylation efficiency and higher chlorophyll contents. Moreover, melatonin improved the activity of the enzymatic and nonenzymatic antioxidant systems and reduced lipid peroxidation. In addition, we demonstrated that higher concentrations (500 mu M) caused negative effects on stress tolerance, thus demonstrating a toxic level. Overall, these results demonstrated that melatonin mediates the signaling for water deficit responses by acting as an inductor of tolerance, most likely enhanced by increased carboxylation efficiency and antioxidant systems. This study provides evidence that exogenous melatonin protects coffee against water deficit.