**3. Results**

*3.1. 24-Epibrasinolide and Titanium Oxide Nanoparticles Promote Antioxidant Capacity in Plants under Cu and Cd Toxicity*

The data analysis revealed a significant difference between the various treatments of the co-application of EBL–TiO2 NPs with Cu and Cd (*p* < 0.001). According to the obtained data, TiO2 and EBL individually could increase antioxidant activity under stress conditions. However, the greatest stimulation of antioxidant activity was observed with the combination of TiO2 and EBL. The combination of TiO2 and EBL showed the highest capacity for antioxidant activity stimulation, with a 1.71-fold enhancement of SOD, 1.49-fold increase in POX, 1.76-fold increase in CAT, 1.52-fold increase in APX, 1.73-fold enhancement of GR, and 1.23-fold enhancement of PAL activity in comparison with their control treatments (Figure 1). Conversely, the lowest amount of antioxidant activity was observed with 100 μM Cu and 100 μM Cd, which resulted in 36% and 61% reductions in SOD, 24% and 40% reductions in POX, 39% and 58% reductions in CAT, 50% and 73% reductions in APX, 44% and 59% reductions in GR, and 28% and 36% reductions in PAL activities, respectively, compared with the control treatment. According to these results, we suggest that TiO2 and EBL individually have the potential to reduce Cu and Cd toxicity, but the combination of TiO2 and EBL has a larger impact on the amelioration of heavy metal toxicity.

*3.2. 24-Epibrasinolide and Titanium Oxide Nanoparticles Reduce Malondialdehyde (MDA), Soluble Proteins (SP), Electrolyte Leakage (EL), Hydrogen Peroxide (H2O2), and Superoxide Radicals (O2* •−*)*

Our results showed that the TiO2 NP and EBL concentrations had the ability to reduce ROS compounds and prevent cell membrane injury. The data analyses showed a significant difference in the co-application of TiO2 NPs and EBL based on the concentration of Cu and Cd in the indices of MDA, H2O2, SP, EL, and O2 •− (*p* < 0.001). The most positive effect of the treatments on heavy metals was related to the combination of TiO2–EBL with Cu and TiO2–EBL with Cd, which demonstrated 49% and 42% reductions in MDA content, 38% and 33% reductions in H2O2 content, 38% and 36% reductions in O2 •− content, 26% and 25% reductions in SP content, and 50% and 44% reductions in EL, respectively. Additionally, the levels of TiO2 and EBL individually showed a positive role in the amelioration of oxidative stress, which occurred by restraining ROS production, which in turn resulted in protecting the cell membrane against oxidative free radicals. Conversely, the results showed that 100 μM Cu and 100 μM Cd increased the levels of MDA, H2O2, O2 •−, SP, and EL, with 48% and 60% increases in MDA content, 35% and 49% increases in H2O2, 28% and 41% increases in O2 •−, 25% and 29% increases in SP, and 50% and 63% increases in EL, respectively, compared with their control treatments (Figure 2).

(POX) (**b**), catalase (CAT) (**c**), glutathione reductase (GR) (**d**), ascorbate peroxidase (APX) (**e**), and phenylalanine ammonia-lyase (PAL) (**f**)) in bamboo species (*Pleioblastus pygmaeus*) with 100 μM Cu and 100 μM Cd. In this study, 1-year-old branches of *P. pygmaeus* were used as plant treatments together with 100 μM TiO2 NPs and 10−<sup>8</sup> M 24-epibrassinolide, individually and in combination with 100 μM Cu and 100 μM Cd using four replications. Planting of the treated bamboo was performed in an Air Tech inoculation hood with fluorescent white lamps and ultraviolet light (wavelengths of 10–400 nm) at 15 ◦C and 30 ◦C. The bamboo plants were constantly exposed to excess heavy metals for three weeks. Sampling for the measurement of antioxidant enzyme activity (**a**–**f**) was conducted after three weeks of plant exposure to the co-application of 24-epibrassinolide and titanium oxide nanoparticles under 100 μM Cu and 100 μM Cd. The capital letters (A–C) indicate significant differences between treatments of control (C), titanium (Ti), 24-epibrassinolide (EBL), and 24-epibrassinolide involving individual or combined application of titanium oxide nanoparticles (EBL–TiO2 NPs) under 100 μM Cu and 100 μM Cd (the bars with similar colors), while the lowercase letters (a–c) denote statistically significant differences at each concentration of the co-application of EBL and TiO2 NPs, individually or in combination with 100 μM Cu and 100 μM Cd (the bars with various colors) based on Tukey s test (*p* < 0.05).
