Investigation of Water Distribution and Mobility Dynamics in Recalcitrant Quercus acutissima Seeds during Desiccation Using Magnetic Resonance Methods

Recalcitrant seed vigor is closely related to seed moisture, so how do the water distribution and status change during seed drying? In this study, we investigated the association between water content (WC) and germination of Quercus acutissima seeds and used nuclear magnetic resonance (NMR) to monitor the water dynamics during seed drying. Results showed that freshly dispersed seeds had 38.8% WC, but drying to 14.8% WC resulted in a complete loss of vigor. Magnetic resonance images (MRI) reveal that the embryonic axis had the highest WC and the fastest rate of water loss, and seeds lost water from the embryonic axis to the apex and from the center to the end of cotyledons during desiccation. According to low-field NMR results, the proportion of free water in fresh seeds was the highest at 55%, followed by bound water at 10% and immobile water at 35%. During drying, the bound water and free water of seeds were lost simultaneously, and free water was lost most when the seeds died. Our results revealed that Q. acutissima seeds are highly sensitive to desiccation and that the water loss sites of the seeds were at the micropyle and scar. During desiccation, the bound water could not be retained, and the water balance in the seeds was broken, eventually leading to seed death.