关键词: 紫荆, 吸胀, 层积, 核磁共振, 水分相态, 营养物质

Abstract:

【Objective】Using low-field nuclear magnetic resonance (NMR) technology, changes in the water phase during the imbibition and stratification of Cercis chinensis seeds were detected nondestructively. Combined with the nutrient content changes during stratification, the role of each water phase was analyzed to reveal the material base and physiological conditions during the germination of C. chinensis seeds. 【Method】After being treated with hot water at 80 ℃, the hardness of C. chinensis seeds was removed and its water absorption curve was calculated by the gravimetric method. Cold stratification was applied to break the physiological dormancy of C. chinensis seeds by random selection. The germination percentage and nutrient content of seeds were determined during different stratification periods. Low-field NMR was employed to investigate the dynamic transitions of the water phase and water content during imbibition and stratification. 【Result】(1)Hot water immersion at 80 ℃ for 5 min followed by 60 days of cold stratification effectively improved the germination rate of C. chinensis seeds. (2)The water absorption curve of C. chinensis seeds exhibited an “S” type variation and from 0 h to 9 h was the rapid water absorption stage. At from 9 h to 24 h, seed water absorption gradually slowed. Ultimately, the seeds entered a balanced water absorption stage after 24 h. (3)NMR spectra revealed that the water mass (x) of C. chinensis seeds and the peak areas of the NMR relaxation spectra (y) exhibited a significant linear relationship, according to the linear regression equation y = 164 604.7 x + 4 962.3, with a correlation coefficient R² = 0.999 6. (4)NMR T₂ relaxation spectra enabled division of the water phases during the imbibition process of C. chinensis seeds into three types: bound water T_2a, free water T_2b, and newly absorbed water T_2c. (5)During the water absorption process from 0 to 3 h, the content of T_2a decreased continuously, whereas T_2b content increased dramatically. After 3 h, T_2c appeared and T_2a disappeared. Only T_2b and T_2c existed in the seeds; both showed an increasing trend, with the peak maximum moving to the right and water mobility being enhanced. Peaks T_2b and T_2c shifted to the right during stratification, with fluctuating changes in peak area and peak ratio, and in general showed a trend towards increased water mobility. (6)During the stratification process of C. chinensis seeds, the starch content continued to decrease, soluble sugar content increased, and soluble protein content showed an increasing trend, followed by a decreasing trend. 【Conclusion】Water mobility is enhanced during the absorption and the stratification of C. chinensis seeds. There are three types of water phases in the imbibition process of C. chinensis seeds: T_2a, T_2b and T_2c. However, only T_2b and T_2c appear during stratification. The changes in the nutrient contents of starch, soluble sugars, and soluble proteins roughly follow the same trend as those in T_2b content. The fluctuations in water in each phase provides a suitable water environment for C. chinensis seed germination, and the changes in T_2b during the stratification process might be closely related to germination.

Key words: Cercis chinensis, imbibition, stratification, low-field nuclear magnetic resonance, water phase, nutritive materials