Pretreatment with 24-Epibrassinolide Synergistically Protects Root Structures and Chloroplastic Pigments and Upregulates Antioxidant Enzymes and Biomass in Na+-Stressed Tomato Plants

Salt stress reduces plant growth by negatively interfering with the division rate and cellular expansion, limiting the growth and development of the roots, stems, and leaves. 24-Epibrassinolide (EBR) is a molecule extracted from plant tissues and is a plant growth regulator with a high capacity to modulate tolerance to abiotic stresses. The objective of this study was to verify the possible improvements promoted by pretreatment with EBR in salt-stressed tomato plants, evaluating the variables related to root anatomy, photosynthetic pigments, antioxidant system, and biomass accumulation. The experiment comprised four treatments: two salt conditions (0 and 150 mM NaCl, described as Na+ (−) and Na+ ( +), respectively) and two concentrations of 24-epibrassinolide (0 and 100 nM EBR, described as EBR (−) and EBR ( +), respectively). EBR modulated the protection and vascularization of root structures, as demonstrated by the increases in epidermis thickness (12%) and metaxilem diameter (119%), respectively. This steroid relieved oxidative damage, which was clearly linked to elevated activities of superoxide ascorbate peroxidase (24%) and guaiacol peroxidase (31%). EBR also benefited photosynthetic pigments, reducing the degradation of chlorophylls. In addition, pretreatment with EBR favoured a higher biomass, which was due to positive effects on leaf and root tissues, including better performance of photosynthetic machinery.