24-Epibrassinolide: a molecule with multiple benefits against heavy metal toxicity in plants.

Abstract

Several pollutants have been released into the atmosphere through numerous human activities, among these are heavy metals (HMs), which are the main threats to the environment due to their potentially cytotoxic, genotoxic and mutagenic characteristics. Among of HM, Ni and Pb are elements that can cause phytotoxicity, affecting the physiological performance and biomass accumulation. To overcome these negative interferences, brassinosteroids (BRs) emerge as plant growth regulators that perform a variety of physiological functions such as growth, and that also confer resistance to plants against various biotic and abiotic stresses, being 24- epibrassnolide (EBR) one of the most biologically active. In these contexts, the aim of this study was to verify whether the exogenous application of EBR can alleviate the damage provoked by heavy metals induced stress, precisely by Ni and Pb, in tomato plants, evaluating the biochemical, physiological, anatomical, and nutritional responses. Thus, two experiments were planned and executed, the first analyzed the EBR action on deleterious effects of excess Ni (experiment I), and the second evaluated the role of this steroid in mitigating the Pb toxicity (experiment II). The two experiments were randomized with four treatments each, the first with two concentrations of nickel (0 and 400 µM Ni, described as - Ni and + Ni, respectively), and the second also with two concentrations of lead (0 and 200 µM Pb, described as - Pb and + Pb, respectively), two levels of EBR were used in both experiments (0 and 100 nM EBR, described as - EBR and + EBR, respectively). Regarding experiment I, the results showed that EBR alleviated Ni stress through upregulating the antioxidant system, with increments of 44%, 27%, 46% and 35% in SOD, CAT, APX and POX, respectively, assisting to protect photosynthetic machinery and stimulating the accumulation of biomass. While for experiment II, the results demonstrate the interferences caused by Pb stress in tomato plants, however the exogenous application of EBR also mitigated the negatives effects, confirmed by the improvement in root anatomy with increases of 23%, 24% and 20% in RET, RDT and RMD, respectively, consequently promoting gains of 95%, 115% and 92% in leaf, root and total biomass, respectively. Therefore, this research demonstrated that EBR alleviated the damage provoked by Ni and Pb stress in tomato plants.