Surface coating determines the response of soybean plants to cadmium sulfide quantum dots

Abstract

Quantum dots (QDs) are used in an array of applications from electronic devices to medicine, leading to environmental release and accumulation in landfills and agricultural soils. However, their effects on plants have been least studied among other engineered nanomaterials. In the current study, soybean seedlings were exposed to 50-200 mg/L cadmium sulfide quantum dots (CdS-QDs) to elucidate their bioaccumulation and biological response in comparison to Cd 2+ ions and bulk-CdS. To understand the role of surface coatings on QD stability, uptake, translocation, subcellular localization and cellular response, bare CdS-QDs were capped with ligands varying in polarity and surface charge. Four common ligands, including trioctylphosphine oxide, polyvinylpyrrolidone, mercaptoacetic acid, and glycine were used to synthesize QD-TOPO, QD-PVP, QD-MAA, and QD-GLY, respectively. In aqueous suspension, QD-MAA particles were most stable, maintaining their size at 332 nm with least Cd 2+ dissolution (9%) after 14 d, whereas QD-TOPO formed large aggregates of size 3861 nm with 27% Cd 2+ dissolution. Upon exposure to 100 mg/L bare and coated CdS-QDs in vermiculite for 14 d, soybean roots accumulated Cd, ranging from 568 (QD-MAA) to 1010 (QD-PVP) μg/g tissue dry weight (DW); statistically equivalent to bulk-CdS treatment (639 μg/g DW). In the roots, Cd from CdCl 2 , bulk-CdS, QD-MAA and QD-GLY accumulated primarily in the cell wall (~40-55%) followed by organelles (28-40%), suggesting apoplastic pathway; whereas in QD-TOPO, dissolved Cd 2+ ions accumulated mainly in the membranes. The exception was QD-PVP, which sequestered Cd mainly in the organelles (49%) in roots, potentially via symplastic pathway and translocated to shoots, resulting in reduced leaf biomass. Results suggested that peroxidases play the predominant role in quenching the oxidative stress caused by CdS-QD exposure. At the highest CdS-QD treatment (200 mg/L), root lignification allowed the plants to restrict Cd accumulation, except in QD-PVP, where lignification was reduced by 21% leading to higher Cd content in shoots. Increased amino acid content in the leaves was noted as a stress tolerance mechanism by the plants exposed to 200 mg/L QD treatments. This study highlights the significant influence that surface coating exerts on QDs fate and effects in a planted system.

Proteomic, gene and metabolite characterization reveal the uptake and toxicity mechanisms of cadmium sulfide quantum dots in soybean plants

“…24 In a recent study, we exposed soybean plants to CdS-QDs without any coating or coated with different ligands including a water-soluble polymer (polyvinylpyrrolidone, PVP), a hydrophobic ligand (trioctylphosphine oxide, TOPO), a thiol compound (mercaptoacetic acid, MAA) and an amino acid (glycine, GLY) in vermiculite media. 12 Exposure to CdS-QDs coated with MAA or GLY resulted in Cd accumulation in soybean root cell walls, whereas CdS-QDs coated with TOPO were unstable due to the hydrophobicity of the ligand and released Cd 2+ ions that accumulated in cell membranes. In contrast, PVP coating on the CdS-QDs enabled efficient transport of the particles or Cd 2+ to root organelles and aerial tissues, leading to reduced leaf biomass.…”

“…10,11 However, only a small fraction of Cd 2+ from QDs is dissolved in contrast to soluble Cd-compounds at equimolar Cd concentrations. 12 Hence, the Cd availability from QDs is generally overestimated and the specific mechanism of toxicity of QDs remains unclear. In planktonic bacteria (Pseudomonas aeruginosa), CdSe QDs were found to be more toxic by generating more intracellular reactive oxygen species (ROS) than soluble Cd salts, at equivalent Cd concentrations of 20-125 mg L −1 .…”

Comparative Analysis of Proteins Regulated during Cadmium Sulfide Quantum Dots Response in Arabidopsis thaliana Wild Type and Tolerant Mutants

“…Generally, the influence of exposure duration on Cd-based QDs toxicity is insufficiently understood [ 19 , 20 ]. Only a limited number of studies have analyzed and compared the impacts of CdS QDs and Cd ions on whole organism development, as well as on organ, tissue or cellular structure [ 21 , 22 , 23 , 24 ]. Marmiroli et al [ 14 , 25 ] characterized the transcriptomic and changes associated with exposure to CdS QDs in A. thaliana ; two mutants ( atnp01 and atnp02 ) of Landsberg erecta , collection Soll-Jonson, with Ac/Ds maize transposon insertion, were identified as tolerant to CdS QDs but not to Cd 2+ .…”

Proteomic Analysis Identifies Markers of Exposure to Cadmium Sulphide Quantum Dots (CdS QDs)

“…The proteins most affected by the CdS-QDs are components of mitochondrial respiration complexes III, IV and V. Mitochondria are a significant organelle in QD-induced toxicity [ 67 , 68 ]. It has been shown that CdS QDs damage mitochondrial functionality and reduce respiration activity in yeast [ 24 ], plants [ 22 ], and human cells [ 21 ]. Damage to mitochondrial functions and structure caused by several types of metal-ENMs has been reported in mollusc bivalve and mouse cells [ 69 , 70 ].…”