Uptake and transformations of engineered nanomaterials: Critical responses observed in terrestrial plants and the model plant Arabidopsis thaliana

With the applications of engineered nanomaterials (ENMs) continually expanding and production quickly growing, residues of ENMs will end up in the environment at levels that may be harmful to non-target organisms. Many of the tunable properties that have made them desirable, such as type, size, charge, or coating, also contribute to the current difficulties in understanding the fate of ENMs in the environment. This review article focuses on studies that investigate plant-ENM interactions, including techniques used to study these interactions and documented plant responses due to the phytotoxic effects of ENMs. The many variables which can be altered for an experiment, such as type, size, and concentration of ENMs, make it difficult to formulate generalizations about the uptake mechanism involved, or to make an inference on the subcellular localization and distribution of the internalized ENMs in plant tissue. In order to avoid these challenges, studies can utilize a model organism such as Arabidopsis thaliana, and a combination of analytical techniques that can reveal complementary information in order to assess how the different experimental conditions influence the uptake and phytotoxicity of ENMs. This review presents recent studies regarding plant-ENM interactions employing Arabidopsis to demonstrate how the use of this model plant can advance our understanding of plant-ENM interactions and guide additional studies using other plant species. Overarching results suggest that more sensitive tests and consistency in experimental designs are needed to fully assess and understand the phytotoxic effects of ENMs in the environment.

Correlative Microscopy Combining Secondary Ion Mass Spectrometry and Electron Microscopy: Comparison of Intensity-Hue-Saturation and Laplacian Pyramid Methods for Image Fusion

Correlative microscopy combining various imaging modalities offers powerful insights into obtaining a comprehensive understanding of physical, chemical, and biological phenomena. In this article, we investigate two approaches for image fusion in the context of combining the inherently lower-resolution chemical images obtained using secondary ion mass spectrometry (SIMS) with the high-resolution ultrastructural images obtained using electron microscopy (EM). We evaluate the image fusion methods with three different case studies selected to broadly represent the typical samples in life science research: (i) histology (unlabeled tissue), (ii) nanotoxicology, and (iii) metabolism (isotopically labeled tissue). We show that the intensity-hue-saturation fusion method often applied for EM-sharpening can result in serious image artifacts, especially in cases where different contrast mechanisms interplay. Here, we introduce and demonstrate Laplacian pyramid fusion as a powerful and more robust alternative method for image fusion. Both physical and technical aspects of correlative image overlay and image fusion specific to SIMS-based correlative microscopy are discussed in detail alongside the advantages, limitations, and the potential artifacts. Quantitative metrics to evaluate the results of image fusion are also discussed.