**Co-Application of 24-Epibrassinolide and Titanium Oxide Nanoparticles Promotes** *Pleioblastus pygmaeus* **Plant Tolerance to Cu and Cd Toxicity by Increasing Antioxidant Activity and Photosynthetic Capacity and Reducing Heavy Metal Accumulation and Translocation**

**Abolghassem Emamverdian 1,2,\*, Yulong Ding 1,2, James Barker 3, Guohua Liu 1,2,\*, Mirza Hasanuzzaman 4,\*, Yang Li 5, Muthusamy Ramakrishnan 1,2 and Farzad Mokhberdoran <sup>1</sup>**


**Abstract:** The integrated application of nanoparticles and phytohormones was explored in this study as a potentially eco-friendly remediation strategy to mitigate heavy metal toxicity in a bamboo species (*Pleioblastus pygmaeus*) by utilizing titanium oxide nanoparticles (TiO2-NPs) and 24-epibrassinolide (EBL). Hence, an in vitro experiment was performed to evaluate the role of 100 μM TiO2 NPs and 10−<sup>8</sup> M 24-epibrassinolide individually and in combination under 100 μM Cu and Cd in a completely randomized design using four replicates. Whereas 100 μM of Cu and Cd reduced antioxidant activity, photosynthetic capacity, plant tolerance, and ultimately plant growth, the co-application of 100 μM TiO2 NPs and 10−<sup>8</sup> M EBL+ heavy metals (Cu and Cd) resulted in a significant increase in plant antioxidant activity (85%), nonenzymatic antioxidant activities (47%), photosynthetic pigments (43%), fluorescence parameters (68%), plant growth (39%), and plant tolerance (41%) and a significant reduction in the contents of malondialdehyde (45%), hydrogen peroxide (36%), superoxide radical (62%), and soluble protein (28%), as well as the percentage of electrolyte leakage (49%), relative to the control. Moreover, heavy metal accumulation and translocation were reduced by TiO2 NPs and EBL individually and in combination, which could improve bamboo plant tolerance.

**Keywords:** toxic metals/metalloid; nanoparticles; phytohormones; phytoremediation; reactive oxygen species
