How mucilage helps seeds from being washed away? A mechanical interpretation of myxodiaspory using rheology

Abstract

AbstractMyxodiaspory is an adaptation by seeds/achenes of certain angiosperms, where a gelatinous polysaccharide (mucilage) is exuded when hydrated. The polysaccharide composition of seed mucilage includes pectin, cellulose, hemicellulose and starch. The mucilage plays multiple roles in seed physiology including seed hydration, protection and anchorage. In nature, seeds encounter various forces due to different environmental factors. Studies have shown that the mucilage envelope found around certain seeds supports in withstanding these forces by anchoring them to the substrate. What could be the mechanistic basis that triggers the resistive behaviour of mucilage against dislodgement still remains unclear. Rheology, a widely used technique to understand the mechanical response of soft viscoelastic materials is used in the present investigation. The characteristic large amplitude oscillatory shear (LAOS) response of biopolymers can be associated with the corresponding changes in the microstructure during deformation. Herein, we investigate thein vitromechanical response of two model seed mucilages: freshly collected mucilage of sweet basil (Ocimum basilicum) and chia (Salvia hispanica) seeds under shear deformations using LAOS. Tack experiments conducted on mucilage along with rheology suggest that the strain stiffening response of seed mucilage is crucial in resisting the forces during water flow leading to seed anchorage. Unlike pectin gels, mucilages show resistance to large scale deformations through strain stiffening at different length scales. This arises from the hierarchical microstructure of mucilage consisting of hemicellulose, cellulose fibrils and fibrillary bundles (CF and CFB) in addition to the crosslinked pectin matrix. Present investigation also paves way to a novel methodology using rheological techniques to study plant mucilage physiology.