24-EPIBRASSINOLIDE ALLEVIATES THE DROUGHT EFFECTS IN YOUNG Carapa guianensis PLANTS, IMPROVING THE HYDRAULIC SAFETY MARGIN, GAS EXCHANGE AND ANTIOXIDANT DEFENCE

Amazon tree; brassinosteroids; peroxidase; photosynthesis; water deficit

Climate change is increasing the frequency of extreme events, such as droughts, causing limitations on growth and productivity in plants. Thus, in view of the deleterious effects generated by water deficit in plant  metabolism, the exogenous application of plant growth regulators, such as 24-epibrassinolide (EBR) appears as a possible solution, because this molecule is organic, eco-friendly and biodegradable. This research is first result in the literature on possible EBR roles on hydraulic safety margin, physiological behavior and metabolism in Carapa guianensis plants exposed to drought. C. guianensis is a tree widely distributed in the tropical forests of the Amazon. The objective of this research is to answer if EBR can improve tolerance to water deficiency in young C. guianensis plants, measuring hydraulic traits, nutritional, biochemical and physiological responses and biomass. The experiment was randomized with four treatments, including two water conditions (control and water deficit) and two concentrations of brassinosteroids (0 and 100 nM EBR). This steroid increased the values of water potential and the hydraulic safety margin. Positive results were found in gas exchange, in which EBR increased CO2 fixation and stimulated stomatal performance. Additionally, this plant growth regulator stimulated antioxidant defense (superoxide dismutase, catalase, ascorbate peroxidase and peroxidase). Therefore, our results prove that pre-treatment with EBR improved drought tolerance in young C. guianensis plants.