Water entry site and movement in permeable Sophora japonica seeds

Seeds of Sophora japonica in Nanjing during the recommended period typically exhibit permeable seed coats. It is imperative to comprehend the water absorption characteristics of the permeable seeds, as water uptake represents a critical step in seed germination. This study employed an integrated approach combining blocking experiments, scanning electron microscopy, staining tests, and magnetic resonance imaging to investigate water entry sites and movement patterns in permeable seeds. Blocking experiments on seeds with both permeable and impermeable seed coat revealed that the lens functions as the water gap. Anatomical observations revealed specialized structural features in S. japonica seeds. The hilum region showed decreased water permeability compared to the lens region (characterized by elongated palisade cells), with the latter serving as the water entry point. Initially (12-28 h), water migrated from the lens to the chalazal region through the space between the seed coat and endosperm. Subsequently (after 28 h), water moved towards the radicle via the vascular bundle connecting the hilum and lens. Following radicle activation, a phase of rapid water absorption was initiated. This regulated water uptake pattern suggests an adaptive strategy ensuring successful germination. These findings enhance our understanding of water absorption characteristics in permeable S. japonica seeds used in forestry production, contributing to improved seed handling practices.