24-Epibrassinolide mitigates nickel toxicity in young Eucalyptus urophylla ST Blake plants: nutritional, physiological, biochemical, anatomical and morphological responses

Key message Our research revealed that 24-epibrassinolide alleviated nickel toxicity in young Eucalyptus urophylla plants, inducing benefits on nutritional, physiological, biochemical, anatomical and morphological responses. Context Soil contamination by heavy metals may limit the Eucalyptus production. Disturbances caused by nickel (Ni) toxicity interfere with the absorption of other essential nutrients. 24-Epibrassinolide (EBR) is one form of brassinosteroid (BR) that provides benefits for plant metabolism under Ni toxicity. Aims The aim of this study was to determine whether exogenous EBR can improve ionic homeostasis by evaluating nutrient concentrations, anatomical characteristics and chlorophyll fluorescence in young Eucalyptus urophylla plants subjected to Ni toxicity. Methods The experiment was randomized into four treatments, including two Ni concentrations (0 and 600 mu M Ni) and two 24-epibrassinolide concentrations (0 and 100 nM EBR). Results EBR significantly reduced Ni contents. Plants exposed to Ni2+ and sprayed with steroid had increases in the Ca2+/Ni2+ and Mn2+/Ni2+ ratios in the leaves of 38% and 15%, respectively, compared with the same treatment without EBR. The treatment of Ni2+ toxicity + EBR presented an increase of 42% in effective quantum yield of PSII photochemistry, when compared with plants exposed to Ni without EBR. Ni toxicity induced negative effects on stomatal functionality, but EBR application mitigated these effects. Conclusion Benefits on effective quantum yield of PSII photochemistry after EBR spray can be related to increases in manganese contents. EBR reduced oxidative stress, alleviating the deleterious effects induced by Ni toxicity and inducing positive repercussions on antioxidant enzymes, photosynthetic pigments and biomass.