Hydrological transport and endosperm weakening mechanisms during dormancy release in Tilia henryana seeds

Seed germination is a pivotal stage in the plant life cycle, with endosperm weakening and radicle elongation serving as crucial prerequisites for successful endospermic seed germination. Tilia henryana seeds exhibit deep dormancy, necessitating a period of 2–3 years to germinate in a natural environment, and the germination rate is extremely low. This study employed morphological and physiological approaches to dynamically analyzing the hydrological mechanism and the endosperm weakening process during the dormancy release of T. henryana seeds. It was found that there was no physiological post-ripening effect of embryos, but there were mechanical and physiological obstacles in endosperm. During the dormancy release process of T. henryana seeds, initial endosperm weakening occurred at the radicle-endosperm interface. In this process, the GA/ABA level is imbalanced along with a continuous decrease in IAA and SA levels. Substantial depletion of storage materials within cells resulted in degradation of endosperm cell contents, forming numerous cavities through which significant amounts of free water entered. As moisture content increased, endosperm hardness gradually decreased to approximately 5 N/0.09 cm². Furthermore, the area and content of lignin and cellulose were reduced by 58.91% and 84.49%, respectively, while the hemicellulose and pectin contents were decreased by 72.11% and 83.50%, in that order. Following treatment, the activity of pectin lyase, propectinase, galacturonase, and cellulase was observed to be 5.81, 8.72, 5.96, and 9.43 times higher, respectively, in comparison to their respective activities before treatment. The physiological changes facilitated the rapid rupture of the endosperm cell wall, leading to a transition in cell morphology from palisade-like to irregular and interlocking, thereby further expediting the weakening and cleavage of the endosperm. Additionally, T. henryana seeds exhibited high carbohydrate composition content throughout their dormancy release process, this extensive utilization of storage substances provided energy for radicle elongation and expansion.