A water-impermeable testa may act as a barrier to seed imbibition, imposing dormancy. Janská et al. test six pea accessions of contrasting dormancy type for their ability to imbibe. The strophiole is identified as the major site for the water entry into non-dormant seed, while in dormant seeds water uptake is distributed, rather than localized.
The light-line in the seed coat is identified as the major barrier to water penetration in dormant seeds. Its outer border abuts a waxy subcuticular layer, representing the interface between two distinct environments – the waxy subcuticular layer and the cellulose-rich secondary cell wall. The mechanistic basis of dormancy break includes changes in the testa’s lipid layer, along with the mechanical disruption induced by oscillation in temperature and by a decreased moisture content of the embryo.
Janská, A., Pecková, E., Sczepaniak, B., Smýkal, P., & Soukup, A. (2018). The role of the testa during the establishment of physical dormancy in the pea seed. Annals of Botany, 123(5), 815–829. https://doi.org/10.1093/aob/mcy213