ABSTRACT
Nickel (Ni) excess often generates oxidative stress in chloroplasts, causing redox imbalance, membrane damage and negative impacts on biomass. 24-Epibrassinolide (EBR) is a plant growth regulator of great interest to the scientific community because it is a natural molecule extracted from plants, is biodegradable and environmentally friendly. This study aimed to determine whether EBR can improve ionic homeostasis, antioxidant enzymes, PSII efficiency and biomass by evaluating nutritional, physiological, biochemical and morphological responses of soybean plants subjected to Ni excess. The experiment used four randomized treatments, with two Ni concentrations (0 and 200 µm Ni, described as -Ni2+ and +Ni2+ , respectively) and two concentrations of EBR (0 and 100 nm EBR, described as -EBR and +EBR, respectively). In general, Ni had deleterious effects on chlorophyll fluorescence and gas exchange. In contrast, EBR enhanced the effective quantum yield of PSII photochemistry (15%) and electron transport rate (19%) due to upregulation of SOD, CAT, APX and POX. Exogenous EBR application promoted significant increases in biomass, and these results were explained by improved nutrient content and ionic homeostasis, as demonstrated by increased Ca2+ /Ni2+ , Mg2+ /Ni+2 and Mn2+ /Ni2+ ratios.
