Abstract text: When flax seeds are imbibed in water, the outermost cells of the hull release mucilage (FSM). The molecular players involved in FSM biosynthesis are being most actively studied, while data linking mucilage composition to its properties – including changes upon germination loss – remain limited. To add some missing pieces to this puzzle, we investigated mucilage produced by seeds of two contrasting genotypes – oil flax (oFSM) and fiber flax (fFSM) – as well as seeds with different germination ability. The main methods were microscopy, chromatography, light scattering, and rheometry.
We found that oFSM forms a tighter capsule around the seed, and its polysaccharides are contained in larger particles with higher proportions of rhamnogalacturonan I compared to fFSM. At large deformations, such a composition results in higher oFSM shear thinning, while fFSM experiences higher stiffening. Decreased germinability is accompanied by seed coat degradation and an increased release of low molecular weight components, which drastically reduces mucilage aggregation and viscoelasticity. Moreover, our results indicate that native mucilage supramolecular structure is lost during centrifugation, and that rhamnogalacturonan I, previously thought of as arabinoxylan’s less viscous companion, might play a key role in maintaining this structure.

The work was partially supported by the RSF #24-14-00383.