Cysteine Alleviates the Toxicity of Cadmium Telluride Quantum Dots (CdTe QDs) by Modulating the Antioxidant System and Root Metabolic Pathways in Rice

Cadmium telluride quantum dots (CdTe QDs) have been increasing in the environment because of their large application in solar panels and biological industries. However, the potential role and bioaccumulation behavior of CdTe QDs in plants are unknown. Herein, the toxicity of CdTe QDs on the growth and the underlying mechanisms were explored in rice. Compared with the control, chlorophyll, anthocyanin, and net photosynthetic rate (P_n) of seedlings decreased by 44.6%, 53.7%, and 71.2% under 4.8 mg L^-1 CdTe QDs exposure, respectively. However, O₂˙- and H₂O₂ content in the roots significantly increased by 2.2- and 30.8-fold under 4.8 mg L^-1 CdTe QDs exposure relative to the control, respectively. Te and Cd content in the leaves and roots increased incrementally with CdTe QDs exposure. Fourier transform infrared spectrometer (FTIR) analysis showed that toxic Cd of CdTe QDs mainly bound with the functional group (-OH) on the cell surface in rice. Furthermore, the analysis of untargeted metabolomics indicated that CdTe QDs exposure greatly distorted the glycolysis pathway, the amino acid metabolism, and the tricarboxylic acid cycle (TCA cycle). Further experiments confirmed that the activities of GSH, GPX, MDHAR, APX, and DHAR were dramatically upregulated by 5.7%, 18.7%, 32.1%, 20.8%, and 17.3% in the presence of 5 mM cysteine (Cys) compared with the sole CdTe QDs exposure, respectively. Therefore, we proposed that cysteine metabolism plays a key role in mitigating CdTe QDs toxicity. The study also proposes a new understanding regarding the application of Cys in improving crop performance in the CdTe QDs contaminated soil.