Do nanoparticles delivered to roots affect plant secondary metabolism? A comprehensive analysis in float seedling cultures of Hypericum perforatum L.

Since nanoparticles (NPs), either released from household wastes or applied directly to plants as agrochemicals, can accumulate in the rhizosphere, it is imperative to understand how plant secondary metabolism is affected when the roots of an intact plant are exposed to NPs. Here, the effects of Pd, Au, ZnO and Fe2O3 NPs on secondary metabolism were comprehensively investigated by analyzing 41 major secondary metabolites using ultra-performance liquid chromatography coupled with photodiode array, fluorescence detector and high-resolution mass spectrometry (UPLC-PDA-FLR-HRMS) in Hypericum perforatum L float seedlings. The results showed that exposure of H. perforatum roots to Pd, Au, ZnO and Fe2O3 NPs rapidly led to fluctuations in the levels of secondary metabolites. Although these fluctuations did not correlate with NP type, concentration and duration of treatment, a total of 22 compounds were significantly altered by the NPs tested. In particular, 1 ppm Au increased the content of quercetin 3-(2″-acetylgalactoside) by 5.02-fold, cadensin G by 2.15-fold and leutoskyrin by 2.58-fold after 24 h, 25 ppm Pd NPs led to a 2.1-fold increase in miquelianin after 6 h, 50 ppm Fe2O3 increased furohyperforin (3.09-fold), while miquelianin decreased 5.22-fold after 24 h and 50 ppm ZnO led to a 2.13-fold increase in hypericin after 48 h. These results emphasise the need to understand the intricate interplay between nanomaterials and plant secondary metabolism in order to enable safer and efficient applications of NPs not only in agriculture but also with regard to environmental pollution by NPs.