Abstract:

Objective: Quercus palustris is mainly propagated by seeds, but its seeds are sensitive to dehydration, belonging to recalcitrant seeds. Consequently, water loss is an influential factor affecting its seed storage and transportation. This study aims to explore the dynamic movement pattern of water during the water loss process in Q. palustris seeds, in order to provide a theoretical basis for safe transportation and storage of Q. palustris seeds. Method: In this study, the seed water content was reduced by the natural drying method. Magnetic Resonance Imaging (MRI) technology was utilized to analyze the movement path of water in seeds during dehydration and combined with Signal-to-Noise ratio (SNR) to quantitatively analyze the water loss in each part of seeds during the water loss process. Result: 1) The results of high-field MRI and SNR analysis showed that the water content in the radicle region and central part of cotyledons of fresh Q. palustris seeds was higher, while the water content in peripheral parts of cotyledons was relatively lower. The SNR of different tissues, cotyledons and seed coats were different. 2) When the water content of seeds decreased to 30.0%, water content in the radicle region dropped significantly, with the water loss rate of the radicle being the fastest. Meanwhile, the water loss rate of cotyledon periphery also decreased, while the water of cotyledon center did not change significantly, and its water loss rate was the slowest. Additionally, the water loss rate in different parts of seed coat was also different. When the water content continued to drop to 25.0%, the germination percentage of seeds decreased significantly. At this time, the water in radicle region was almost invisible, with a large part of cotyledon below the radicle beginning to turn dark. As the SNR of radicle region fell sharply again, the SNR of three seed coat parts was reduced to a very low level, among which, the SNR of seed chalaza decreased the most, and the chalaza shrank due to water loss. When water content was reduced to 10.0%, the cotyledon shrank obviously, with only a small amount of water remaining in the central part of cotyledon and a small part below it. Conclusion: The important water storage sites of Q. palustris seeds are the radicle region and the cotyledon center. During the water loss process, the water loss rate of radicle is the fastest, while the water loss rate of the cotyledon center is the slowest. The water loss in radicle is a critical factor causing seed quality to decline.

Key words: Quercus palustris seeds, recalcitrant seeds, desiccation, magnetic resonance imaging (MRI), water movement