Molecular mechanisms underlying microplastics-induced inhibition of lateral root development in tomato (Solanum...

Microplastics (MPs) pollution poses significant threats to terrestrial plants, however the molecular mechanisms underlying their phytotoxicity, particularly regarding root developmental plasticity remain poorly understood. Here, we investigated the effects of polyethylene terephthalate (PET) microplastics on tomato (Solanum lycopersicum L.) seedlings grown in organic substrate, exposed to PET-MPs at concentrations of 0.1 %, 0.15 %, and 0.2 % (w/w) for 21 and 28 days. The results demonstrated a significant reduction in root length, surface area, root tips, bifurcation points, root intersections, and root volume after 3 weeks of PET-MPs exposure. These findings indicate a substantial inhibition of lateral root development. Additionally, PET-MPs significantly suppressed aboveground biomass, reduced leaf chlorophyll content, and impaired photosynthesis and transpiration. As PET-MPs concentrations increased from 0.1 % to 0.15 % and 0.2 %, ROS accumulation in roots intensified, with higher levels of O₂^•- and H₂O₂ in the root tips. Moreover, the 0.2 % PET-MPs treatment further reduced the activities of superoxide dismutase (SOD) and catalase (CAT), exacerbating oxidative damage. Hormone profiling revealed decreased levels of auxin and abscisic acid (ABA). RNA-seq analysis identified early stress-responsive genes, with notable enrichment in auxin and ABA signaling pathways. Notably, 13 out of 15 auxin pathway-related genes were upregulated, including SlIAA27, an Aux/IAA transcription factor known to repress lateral root initiation. This inhibition of lateral root development likely restricts water and nutrient uptake, further hindering plant growth. These findings provide novel insights into the molecular toxicity mechanisms of MPs on plant roots and highlight potential molecular targets for improving plants tolerance to MPs pollution.