Ubiquitous biosynthesis of nano selenium in plants

Abstract

Selenium, an essential trace element of the chalcogenide group, is involved in a variety of physiological processes and plays a crucial role in human health. The impact of selenium on the incidence and prognosis of many chronic diseases such as diabetes mellitus type 2 and various cancers is a subject of ongoing scientific discussion. The chemical form of a nutrient not only influences its resorption and kinetics but can also has a strong impact on the physiological effects it causes. Selenium nanoparticles (SeNP) as nutrients were not part of the scientific discourse so far and there is no mention of naturally occurring biosynthesis of SeNP in plants in the relevant literature. <br /> Among higher plants selenium is not considered an essential nutrient. Yet many beneficial effects, such as increased resistance to stressors like drought and cold, are observed. Our aim was to investigate the potential synthesis of SeNP in plants and we hypothesized that it does not only happen as an isolated event but is a widespread phenomenon within the plant kingdom. <br /> To test this hypothesis, a hydroponic system was set up to grow plants under controlled conditions. A tailored procedure for preparing and digesting root and shoot tissues was designed for analysis using a new sp-ICP-MS method, which was developed as a part of this project. The method development included evaluating the most suitable selenium isotope to focus on and fine-tuning of system-specific parameters including ideal conditions for the dynamic reaction cell. <br /> Successfully applying the analytical method on the complex matrix of plant tissue we discovered, for the first time ever, evidence for the natural occurrence of SeNP in plants. A substantial number of nanoparticles were found in the root and shoot tissues of the observed plants. The size distribution showed some variation among the different plant species, as did the particle number, however the size distribution was very narrow for most plants and the main share of particles spans around 40 to 60 nm. <br /> We put a special focus on including a diverse variety of plants from different families and orders of Angiospermae. Remarkably, SeNP were found in every included plant species, providing strong evidence for the ubiquitous occurrence of nanoparticles in plants. The further choice of analytes consisted of a selection of food plants. SeNP were found in all of these additional plants as well. This marks the recognition that SeNP are regular constituents of plant-based food and therefore consumed by almost all humans on a daily basis.