Seed coat morphology inSapium sebiferumin relation to its mechanism of water uptake

SUMMARYWe investigated the main water entry sites during imbibition of Sapium sebiferum seeds, and the relationship between seed coat structure and water uptake. Seed coat structure was observed using a scanning electron microscope (SEM), while dye-tracking and blocking experiments were used to determine the major sites of water entry into S. sebiferum seeds. Water uptake by intact or cracked seeds was also compared. SEM images showed that, from the exterior to the interior, the seed coat of S. sebiferum consisted of three layers: the waxy cuticle, the palisade layer, and the parenchymal layer. The results of water uptake studies revealed that cracked seeds absorbed more water and reached saturation faster than intact seeds. This indicated that the seed coat of S. sebiferum was permeable, but could delay water uptake. The results of the blocking experiments confirmed that S. sebiferum seed could absorb water throughout the entire seed coat, but that the major site of water absorption was the middle part of the seed coat, followed by the micropylar region and the end opposite to the micropyle. This agreed with the results of dye-tracking experiments in which red staining was first observed in the middle part of the endosperm.