Abstract
Plants act as a crucial interface between humans and their environment. The wide use of nanoparticles (NPs) has raised great concerns about their potential impacts on crop health and food safety, leading to an emerging research theme about the interaction between plants and NPs. However, up to this day even the basic issues concerning the eventual fate and characteristics of NPs after internalization are not clearly delineated due to the lack of a well-established technique for the quantitative analysis of NPs in plant tissues. We endeavored to combine a quantitative approach for NP analysis in plant tissues with TEM to localize the NPs. After using an enzymatic digestion to release the NPs from plant matrices, single particle-inductively coupled plasma-mass spectrometry (SP-ICP-MS) is employed to determine the size distribution of silver nanoparticles (Ag NPs) in tissues of the model plant Arabidopsis thaliana after exposure to 10 nm Ag NPs. Our results show that Macerozyme R-10 treatment can release Ag NPs from Arabidopsis plants without changing the size of Ag NPs. The characteristics of Ag NPs obtained by SP-ICP-MS in both roots and shoots are in agreement with our transmission electron micrographs, demonstrating that the combination of an enzymatic digestion procedure with SP-ICP-MS is a powerful technique for quantitative determination of NPs in plant tissues. Our data reveal that Ag NPs tend to accumulate predominantly in the apoplast of root tissues whereby a minor portion is transported to shoot tissues. Furthermore, the fact that the measured size distribution of Ag NPs in plant tissue is centered at around 20.70 nm, which is larger than the initial 12.84 nm NP diameter, strongly implies that many internalized Ag NPs do not exist as intact individual particles anymore but are aggregated and/or biotransformed in the plant instead.
Highlights
The increasing use of nano-enabled products in our society inevitably leads to more release of engineered nanoparticles (NPs) into the environment
To investigate the effect of Macerozyme R-10 on Ag NPs during plant tissue digestion, Ag NPs were treated with Macerozyme R10 and analyzed using SP-ICP-MS
The most frequent (>97% of the total counts) size detected had a measured diameter of approximately 12.84 nm, slightly larger than the 10 nm NP size the manufacturer had described. This slight increase in size could be explained by the innate size of the Ag NP tested, because there was no significant difference in particle size distribution between enzyme-treated and non-treated: the number of counted NPs that were detected at 12.84 nm diameter did not differ significantly (Figure 1)
Summary
The increasing use of nano-enabled products in our society inevitably leads to more release of engineered nanoparticles (NPs) into the environment. In the agriculture sector for instance, silver nanoparticles (Ag NPs) are often incorporated into nano-agrochemicals, nano-biosensors, and used for nano-agri-food production (Sekhon, 2014). Studies on the interaction of NPs with plants focusing on the phytotoxicity and accumulation precede the actual quantification of NPs in plant tissues, of which the latter is of vital importance for environmental and food risk assessment. The primary challenge to study nanomaterials in plants lies in the detection of internalized NPs within plant tissue matrices and the measurement of their specific characteristics, such as particle size, number, size distribution, and concentration. Impurities or natural occurring plant composites could overwhelm the unique signatures of NPs or, in the situation where only a small portion of the tissues is being analyzed, the outcome may not be representative for the whole plant (Kole et al, 2013; Dan et al, 2015; Ostrowski et al, 2015)
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