Insights into the accumulation and transformation of Ch-SeNPs by Raphanus sativus and Brassica juncea: Effect on essential elements uptake

Selenium (Se) at very low doses has important functions for humans. Unfortunately, the low levels of Se in soils in various regions of the world have implemented the agronomic biofortification of crops by applying Se-enriched fertilizers (mainly based on selenate). Lately, the use of nanofertilizers is growing in interest as their low size reduces the amount of chemicals and minimizes nutrient losses in comparison with conventional bulk fertilizers. However, the knowledge on their fate and environmental impact is still scarce. This study aims to evaluate the biotransformation of chitosan-modified Se nanoparticles (Ch-SeNPs) as well as their effect on the metabolism of essential metals (Fe, Cu, Zn and Mo) when applied to hydroponic cultivation of R. sativus and B. juncea. In house-synthesized Ch-SeNPs were characterized in both synthesis and hydroponic culture media by transmission electron microscopy (TEM), dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA). The composition of one-tenth strength Hoagland's solution did not affect the size, shape and concentration in number of particles per mL of Ch-SeNPs. The plants were grown inside a box at 25 °C during the months of May–July in 2018. After a week of treatment with Ch-SeNPs, plants were harvested and divided into roots and aerial part. The biotransformation of Ch-SeNPs was evaluated through a process of enzymatic hydrolysis and subsequent analysis by HPLC-ICP-MS and HPLC-ESI-MS/MS. The results confirmed the transformation of Ch-SeNPs to seleno-amino acids: Selenomethionine (SeMet), Semethylselenocysteine (SeMetSeCys) and ɣ-glutamyl-Se-MetSeCys. Moreover, Multiple-way analysis of variance (ANOVA) and principal component analysis (PCA) showed that, regardless the plant species, Ch-SeNPs supplementation affected the absorption of Zn.