Commentary on the use of nutrient-coated quantum dots as a means of tracking nutrient uptake by and movement within plants

This paper focuses on the use of quantum dots in plant biology as indicators of organic N and inorganic P uptake by, and distribution within, plants, including those with mycorrhizal symbionts. Quantum dots used in this way are fluorescent 2-15 nm diameter CdSe/ZnS semiconductors coated with organic N compounds or with apatite (solid calcium phosphate). While control experiments showed no uptake of the uncoated but otherwise identical quantum dots, experiments by other investigators showed uptake and movement within the plant of some of the other engineered nanoparticles that have been tested. The most likely mechanism of entry of quantum dots is endocytosis, contrasting with the movement of free dissolved amino acids and inorganic phosphate through integral plasma membrane transporters. Further work is needed comparing the results from quantum dot experiments with otherwise identical experiments using ¹⁵N labelling of amino acids and ³²P and/or ³³P labelling of inorganic phosphate not associated with quantum dots to test the validity of this use of quantum dots. A comparison is also needed of the toxicity of CdSe-based quantum dots with that of radioactive P isotopes.