Ag nanoparticles enhancing Phaseolus vulgaris seedling development: understanding nanoparticle migration and chemical transformation across the seed coat†
The increasing number of patents suggests that the use of nanoparticles (NPs) in agriculture will continue to grow in the future. Properties associated with nanosized objects might be desirable, but may pose a threat to the environment since the fate of nanomaterials is poorly understood. Seed treatment is an extensive practice to provide micronutrients and disease protection. This study investigates the effect of Ag2S NPs, Ag0 NPs, and AgNO3 (1, 100, and 1000 mg Ag per L) on the germination of Phaseolus vulgaris seeds and the mechanism of interaction in the seed coat. Ag treatments did not affect the germination rate. On the other hand, the development of seedlings was significantly improved by Ag2S NPs while AgNO3 showed a negative effect compared to the control (water). Silver from different sources was accumulated and biotransformed along the seed coat. Ag from the AgNO3 treatment was found as AgCl and bound to oxygen, and Ag0 NPs underwent oxidative dissolution forming thiolate complexes. On the other hand, Ag2S NPs did not show any detectable chemical changes. Silver distribution and speciation were investigated in the bean testa using μ-XRF and μ-XANES, while the macromolecular composition was assessed by ATR-FTIR. The Ag biotransformation depended on the source. For the FTIR results, it is possible to verify perturbations in the carbohydrate region as well as changes in the protein region. The combination of these results can contribute to building another step in the understanding of how nanoparticles can improve agricultural inputs and benefit food crops.