Growth inhibition in lettuce callus exposed to particulate matter: Cellular injury linked to intracellular accumulation

Particulate matter (PM) pollution poses significant but understudied risks to plant cellular health. This study demonstrates that exposure of lettuce (Lactuca sativa) protoplast–callus systems to standardized diesel exhaust particles at environmentally relevant concentrations results in marked intracellular PM accumulation, severe cytostructural damage, and disruption of chloroplast integrity. PM exposure triggered concentration-dependent oxidative stress, evidenced by increased hydrogen peroxide and compromised antioxidant capacity, leading to reduced chlorophyll and sugar contents and impaired photosynthesis. Importantly, we found an auxin-cytokinin interplay indicating hormonal imbalance, accompanied by the upregulation of shoot differentiation genes ARF5 and AIL6PLT3 as a compensatory response to cell damage. These results indicate that PM toxicity in plant cells is driven by intracellular accumulation, oxidative damage, metabolic disruption, and altered hormone homeostasis, ultimately inhibiting early plant growth. Our findings underscore the value of protoplast-based assays for rapidly elucidating phytotoxic mechanisms, and suggest these biomarkers can improve predictions of environmental PM impacts on crops and ecosystems.