The ultrastructure of the mature wheat grain tissue in its native state, as observed using atomic force microscopy

This study presents a novel application of atomic force microscopy (AFM) for characterising the ultrastructure of dry (15 % moisture) native and mature wheat grains ( Triticum aestivum L. ). A key contribution is the standardisation of a meticulous sample preparation protocol that minimises artefacts. This protocol involves dry-cutting the grains using a device that enables precise surface smoothing via ultramicrotomy, ensuring perfect alignment for AFM scanning without the need for resin-embedding. The research provides a comprehensive histological description ranging from the outer pericarp to the starchy endosperm. The outer layers (pericarp, seed coat, and nucellar epidermis) appear as compact, continuous structures in the dry state, with stronger inter-layer adhesion. The study also discovered a previously undescribed left-handed helical twist in the tube cells of the inner pericarp, a feature that is hypothesised to be lost in conventional resin-embedding techniques. AFM is demonstrated to be a powerful tool for revealing intricate, hydration-dependent ultrastructural adaptations in plant tissues. • A new AFM protocol has revealed the ultrastructure of wheat grains in their native state. • The tube cells layer exhibits an undescribed left-handed helical twist. • Aleurone cell inclusions are hybrid nanocomposites of minerals, proteins, and lipids. • The outer layers have a compact, dense, continuous structure that is firmly adhered. • The seed coat is characterised as a thin layer tightly adhered to the tube cells.