Breaking the Size Barrier: Surface Roughness Enables Oversized Chromium Colloids to Penetrate Plant Cell Walls

The plant cell wall is conventionally regarded as a physical barrier with a strict size exclusion limit. However, this static paradigm fails to explain the pervasive accumulation of oversized colloidal particles within plant tissues. Although the presence of oversized particles inside plant tissues has been increasingly reported, the underlying mechanism enabling these particles to overcome the physical barrier of the cell wall remains largely unresolved. Using oversized chromium (Cr) colloids and rice as a model system, this study integrated cross-scale characterizations, molecular dynamics simulations, and molecular biological assays to elucidate the interfacial dynamics driving the breakthrough of oversized particles across the apoplastic barrier. Multiscale evidence reveals that this cross-barrier penetration is not a matter of pore-size matching, but rather a dynamic remodeling process driven by physicochemical forces. Specifically, the high microscopic roughness of the colloids dramatically amplifies the interfacial contact area, enabling dense multipoint contact with the cell wall. This tight association subsequently induces a strong, enthalpy-driven interfacial affinity, which forces the intrinsically rigid polysaccharide network to undergo spontaneous adaptive loosening and structural deformation, thereby opening a physical pathway for the entry of oversized particles. Ultimately, this study challenges the traditional size-threshold paradigm of biological barriers. These findings highlight that surface topography is not only a critical determinant for the cross-barrier bioavailability of colloids, but also the underlying trigger for systemic growth-defense metabolic trade-offs in plants.