We report the uptake of MSNs into the roots and their movement to the aerial parts of four plant species and their quantification using fluorescence, TEM and proton-induced x - ray emission (micro - PIXE) elemental analysis. Monodispersed mesoporous silica nanoparticles (MSNs) of optimal size and configuration were synthesized for uptake by plant organs, tissues and cells. These monodispersed nanoparticles have a size of 20 nm with interconnected pores with an approximate diameter of 2.58 nm. There were no negative effects of MSNs on seed germination or when transported to different organs of the four plant species tested in this study. Most importantly, for the first time, a combination of confocal laser scanning microscopy, transmission electron microscopy and proton-induced X-ray emission (micro-PIXE) elemental analysis allowed the location and quantification MSNs in tissues and in cellular and sub-cellular locations. Our results show that MSNs penetrated into the roots via symplastic and apoplastic pathways and then via the conducting tissues of the xylem to the aerial parts of the plants including the stems and leaves. The translocation and widescale distribution of MSNs in plants will enable them to be used as a new delivery means for the transport of different sized biomolecules into plants.

Multiple ectomycorrhizal fungi (EMF) compete to colonise the roots of a host plant, but it is not known whether their success is under plant or fungal control, or a combination of both. We assessed whether plants control EMF colonisation by preferentially allocating more carbon to more beneficial partners in terms of nitrogen supply or if other factors drive competitive success. We combined stable isotope labelling and RNA-sequencing approaches to characterise nutrient exchange between the plant host Eucalyptus grandis and three Pisolithus isolates when growing alone and when competing either indirectly (with a physical barrier) or directly. Overall, we found that nitrogen provision to the plant does not explain the amount of carbon that an isolate receives nor the number of roots that it colonises. Differences in nutrient exchange among isolates were related to differences in expression of key fungal and plant nitrogen and carbon transporter genes. When given a choice of partners, the plant was able to limit colonisation by the least cooperative isolate. This was not explained by a reduction in allocated carbon. Instead, our results suggest that partner choice in EMF could operate through the upregulation of defence-related genes against those fungi providing fewer nutrients.

This study used the radioisotopes (109)Cd and (65)Zn to explore the uptake, retention and organ distribution of these nonessential and essential metals from solution by the freshwater decapod crustacean Macrobrachium australiense. Three treatments consisting of cadmium alone, zinc alone, and a mixture of cadmium and zinc were used to determine the differences in uptake and efflux rates of each metal individually and in the metal mixture over a three-week period, followed by depuration for 2 weeks in metal-free water using live-animal gamma-spectrometry. Following exposure, prawns were cryosectioned and the spatial distribution of radionuclides visualized using autoradiography. Metal uptake and efflux rates were the same in the individual and mixed-metal exposures, and efflux rates were close to zero. The majority of cadmium uptake was localized within the gills and hepatopancreas, while zinc accumulated in the antennal gland at concentrations orders of magnitude greater than in other organs. This suggested that M. australiense may process zinc much faster than cadmium by internally transporting the accumulated zinc to the antennal gland. The combination of uptake studies and autoradiography greatly increases our understanding of how metal transport kinetics and internal processing may influence the toxicity of essential and nonessential metals in the environment.

No abstract

Environmental contextZinc, an essential micronutrient often applied to crops as a fertiliser, can be difficult to analyse in plants due to limitations of conventional techniques. Here, we use radiotracers and a non-destructive imaging technique to visualise how zinc applied as a nanofertiliser moves within wheat plants over time. This is an important step towards developing cost-effective fertilisers to help solve one of the world’s most widespread plant deficiencies. AbstractZinc (Zn) deficiency affects half of the world’s arable soil and one-third of the world’s human population. Application of Zn foliar fertilisers to cereal crops can be an effective way to increase grain Zn content; however, commonly used formulations can scorch the leaf (e.g. soluble Zn salts) or are prohibitively expensive (e.g. chelated Zn, ZnEDTA). Zinc oxide nanoparticles (ZnO-NPs) may offer an efficient and cost-effective alternative, but little is known regarding the mechanisms of Zn uptake and translocation within the plant. Foliar-applied Zn is analytically challenging to detect, locate and quantify, as it is omnipresent. Furthermore, any single analytical technique does not have the detection limit or spatial resolution required. In this study, the uptake and mobility of foliar-applied ZnEDTA, ZnO-NPs and ZnO microparticles (ZnO-MPs) to wheat (Triticum aestivum L.) were investigated using inductively coupled plasma mass spectroscopy (ICP-MS), synchrotron-based X-ray fluorescence microscopy (XFM) and radiotracing techniques using 65Zn-labelled formulations. The three techniques were compared to highlight limitations and advantages of each. We also report, for the first time, a novel time-resolved invivo autoradiography imaging technique that can be used to visualise 65Zn in live plants treated with foliar applications of 65ZnO-NPs and MPs. The images were supplemented by gamma spectroscopy analysis for quantification. The results of this study provide important insights into the analytical challenges faced when investigating foliar-applied Zn nanofertilisers in plants. Potential solutions using nuclear techniques are also discussed, which in turn may ultimately lead to the development of more efficient foliar fertilisers.

Selenium is an important macronutrient with a very narrow margin between essentiality and toxicity. Amphibians are hypothesized to be particularly sensitive due to the potential for metamorphosis-driven mobilization, which could transfer or concentrate contaminant burdens within specific organs. We explored the potential role of tissue degeneration and remodeling during anuran metamorphosis as a mechanism for altering tissue-specific Se burdens. Limnodynastes peronii tadpoles were exposed to dissolved Se (as selenite) for 7 days and depurated until completion of metamorphosis. Bioaccumulation and retention kinetics were assessed in whole tadpoles and excised tissues using gamma spectroscopy, and temporal changes in biodistribution were assessed using autoradiography. Tadpoles retained Se throughout metamorphosis, and partitioned the element predominantly within digestive and excretory tissues, including livers> mesonephros > guts > gallbladder. Importantly, our results demonstrate that Se biodistribution varies significantly throughout development. This is indicative of tissue transference, and particularly in tissues developing de novo after depuration. To the best of our knowledge, this is the first study demonstrating Se transference during metamorphic tissue remodelling. Further research is warranted to explore the fate and metabolism of Se (and other metal and metalloids) during anuran development and the implications of transference for influencing toxicity.

No abstract

The adsorption of radiocesium and radiostrontium onto a range of natural materials has been well quantified, but not for the new media of environmental plastics, which may have enhanced adsorption due to surface-weathering and development of biofilms. Microplastic samples were deployed in freshwater, estuarine and marine conditions, then characterised using infrared spectroscopy to document changes to the plastic surface (vs interior). Synchrotron elemental mapping data revealed surfaces that were well-covered by accumulation of reactive water solutes and sulphur, but, in contrast, had highly discrete coverage of elements such as Fe and Ti, indicating adhered mineral/clay-associated agglomerates that may increase overall adsorption capacity. Plastics that had been deployed for nearly five months adsorbed radionuclides in both freshwater and estuarine conditions with the highest K for cesium (Cs) in freshwater (80 ml g) and lowest for strontium (Sr) in estuarine conditions (5 ml g). The degree of Cs and Sr adsorption onto plastics appears to be approximately 2-3 orders of magnitude lower than for sediment reference values. While lower than for sediments, adsorption occurred on all samples and may indicate a significant radionuclide reservoir, given that plastics are relatively buoyant and mobile in water regimes, and are increasing in global aquatic systems.