The combination of hyperspectral imaging, untargeted metabolomics and lipidomics highlights a coordinated stress-related biochemical reprogramming triggered by polyethylene nanoparticles in lettuce.

Polyethylene nanoplastics (NPs) are widely diffused in terrestrial environments, including soil ecosystems, but the stress mechanisms in plants are not well understood. This study aimed to investigate the effects of two increasing concentrations of NPs (20 and 200 mg kg of soil) in lettuce. To this aim, high-throughput hyperspectral imaging was combined with metabolomics, covering both primary (using NMR) and secondary metabolism (using LC-HRMS), along with lipidomics profiling (using ion-mobility-LC-HRMS) and plant performance. Hyperspectral imaging highlighted a reduced plant growth pattern. Several vegetative indexes indicated plant toxicity, with 20 mg kg NPs significantly decreasing lettuce density and vegetation health (as indicated by NDVI and plant senescence reflectance indexes). Consistently, photosynthetic activity also decreased. At the biochemical level, metabolomics and lipidomics pointed out a multi-layered broad biochemical reprogramming of primary and secondary metabolism involving a decrease in sterols, sphingolipids, glycolipids, and glycerophospholipids in response to NPs. The reduction in phosphatidylinositol coincided with an accumulation of diacylglycerols (DAG), suggesting the activation of the phospholipase C lipid signaling pathway. Moreover, nanoplastic treatments down-modulated different biosynthetic pathways, particularly those involved in N-containing compounds and phenylpropanoids. Our mechanistic basis of NPs stress in plants will contribute to a better understanding of their environmental impact.