Insights into water absorption pathways and structural barriers of Ormosia henryi prain revealed by multimodal imaging techniques

Abstract

The hard seed coat of Ormosia henryi Prain imposes a critical constraint on seed germination. While extensive research has been conducted on the propagation of this tree species, there exists a paucity of studies elucidating the mechanistic basis of physical dormancy in O. henryi seeds. Here we integrated scanning electron microscopy (SEM), dye-tracking assays, magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) spectroscopy to delineate the structural impediments to water absorption and the subsequent pathways of water transport within the seed. SEM analysis revealed a complex seed coat architecture that effectively precludes water entry. Dye-tracking experiments demonstrated that the hilar region constitutes the initial site of dye penetration. MRI further demonstrated that water imbibition commences at a fissure within the hilar region, subsequently migrating towards the micropyle, where it accumulates and facilitates the internal opening of the micropyle. Two dominant water migration routes were identified: one rapid movement along vascular bundles and another traversing the interstitial space between the seed coat and cotyledon. Water mobility was continuously enhanced and transformed in the process of seed swelling absorption provide preliminary preparation for seed germination. This study provides the first comprehensive characterization of early-stage water absorption in O. henryi, offering critical insights for large-scale seedling cultivation.