【目的】应用低场核磁共振技术揭示紫荆(Cercis chinensis)种子吸胀和层积过程中水分相态的变化,再结合层积过程中营养物质含量的变化,分析各相态水分在其中的作用,揭示紫荆种子萌发过程中的物质基础和生理状态。【方法】对80 ℃热水处理解除硬实后的紫荆种子,用称重法确定其吸水曲线。随机选取一部分紫荆种子经低温层积处理解除其生理休眠,测定不同层积阶段紫荆种子的发芽率和营养物质含量,同时采用低场核磁共振技术测定吸胀和层积过程水分相态及含量的动态变化。【结果】①80 ℃热水浸种5 min后再进行60 d低温层积可以有效提高紫荆种子的发芽率。②紫荆种子的吸水曲线呈“ S”形变化,(0,9] h为快速吸水阶段,(9,24] h吸水速率逐渐减慢,24 h后进入平衡吸水期。③核磁共振波谱图表明,紫荆种子水分质量(x)与核磁共振弛豫图谱峰面积(y)呈显著线性关系:y = 164 604.7 x + 4 962.3,决定系数R² = 0.999 6。④根据核磁共振T₂弛豫谱将紫荆种子吸胀过程中水分相态分为束缚水(T_2a)、自由水(T_2b)和刚进入种子的水分(T_2c)3种。⑤紫荆种子吸水0~3 h过程中T_2a含量持续下降,T_2b含量大幅度增加;3 h后出现了T_2c,此后仅存在T_2b和T_2c,两者含量均呈增加趋势,峰顶点右移,水分流动性增强。层积过程中T_2b和T_2c峰顶点向右偏移,峰面积和峰比例波动变化,总的来说向水分流动性增强的趋势发展。⑥紫荆种子层积过程中,淀粉含量持续下降,可溶性糖含量呈上升态势,可溶性蛋白含量呈先上升后下降的变化趋势。【结论】紫荆种子吸水层积过程中,水分的流动性增强。吸胀过程紫荆种子中出现过T_2a、T_2b和T_2c 3种相态的水分,层积过程仅出现过T_2b和T_2c两种水分,且淀粉、可溶性糖和可溶性蛋白等营养物质含量的变化与T_2b含量的变化趋势大体相同。各相态水分的波动变化为紫荆种子萌发提供适宜的水分环境,其中层积过程T_2b的各种变化可能与其萌发密切相关。

【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.