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

Cellulosic, hemicellulosic and pectinaceous mucilages produced by certain angiosperms as adaptation in myxodiaspory are investigated in the past for seed dispersal. The present understanding of zoochory and telechory are based on mucilage amount, state of hydration and to a limited extent, role of mucilage microstructure studied using adhesion and friction. Pectinaceous mucilages have less adhesion and supports dispersal by zoochory. However, in the case of cellulosic mucilages, the role played by the cellulosic fibrils in seed dispersal is not clear, especially, since they have a negative correlation with endozoochory. Using fresh cellulosic seed mucilages from, sweet basil (Ocimum basilicum) and chia (Salvia hispanica) we investigate the role of microstructure of the mucilage in two key behaviours: anchoring and adhesion properties of the seeds through rheology. We report a special large deformation mechanism triggered through strain stiffening operational in these cellulosic mucilages. In many biopolymers semi-flexible polymer chains and other aligning elements contribute to the strain stiffening. However, the strain stiffening and strong wet adhesion observed in these mucilages have a significant role from the cellulosic components. This behaviour is more pronounced in basil seeds and presents a plausible structure-property mechanism for anti-telechory favoured by plant species found in arid habitats.