Influence of nanoscale spatial architecture of seed and root mucilage on its wettability

Abstract

Mucilage secreted by root-tips may alter hydraulic conditions at the root-soil interface and seed coat mucilage increases water availability for seeds. Both significantly affect the water content dynamics of the rhizosphere. Therefore, we examined the nanostructure of different types of dried mucilage (root or seed mucilage and mucilage from different species) and how it affects their wettability. We hypothesized that with increasing roughness wettability of dried mucilage decreases based on the Cassie−Baxter relation due to entrapped air in holes formed in the mucilage layer during drying. In order to visualize the nanostructure of different mucilage species, we dried root mucilage from aeroponically grown seedlings (maize, cress, flax, wheat, barley) and seed mucilage (cress and flax) as thin layers on flat mica surfaces. Spatial structures of the samples were visualized by atomic force microscopy. Variogram analysis was used to analyze the spatially resolved topography data, and the coverage of mucilage was quantified using GeoDict® software. Moreover, by the pore size distribution, the effect of hole-size dispersity on mucilage's wettability was investigated. Our results demonstrate that mucilage of different species have different nanostructures. In contrast to expectations, the wettability of dried mucilage does not follow the Cassie−Baxter relation and does not decrease with increasing roughness. We conclude that wettability of surfaces decreases with increasing mucilage coverage. The lower the coverage the more hydrophilic area of the underlying mineral surface contributes to the overall wettability.