【目的】加拿大紫荆种子具有硬实性,研究解除其硬实性的方法及吸水特性,揭示其种皮结构和吸水的关系可为种子休眠及种子生物学研究提供理论依据。【方法】以不同温度梯度(70~90 ℃)的热水处理加拿大紫荆种子,探究解除其硬实性的最适条件,采用凡士林密封法与苯胺蓝染色法分析种子的吸水特性,同时借助扫描电镜对种皮结构进行观察。【结果】加拿大紫荆种子的吸胀率随温度升高而提高,80 ℃和90 ℃处理均能有效解除种子硬实性,但90 ℃处理的种子生活力显著下降。种子的种脐处有明显的裂缝,热水处理后,裂缝中的胶状物质消失,裂缝更加明显。经观察种皮纵切面发现,大多数部位的种皮由3层结构组成,由外向内分别是角质层、栅栏层和厚壁细胞层。种脐区域除了上述3层结构,还具有明线、反栅栏层和维管束。热水处理后,种孔处的栅栏层和厚壁细胞层分离,形成一个小凸起。凡士林密封实验发现:浸种12 h后,种脐端的吸水量最大,显著高于密封另外2个部位的处理;浸种96 h后,种子中间部位开始缓慢吸水;浸种120 h时,子叶末端仍未吸水。苯胺蓝染色发现:种孔部位的凸起最先着色(2 h),之后种脐的裂缝(3 h)以及维管束通道也被染成蓝色(9 h);随着染色时间的延长,厚壁细胞层与栅栏层的分离区域扩大,角质层和栅栏层着色面积也相应扩大,但厚壁细胞等组织仍未被染色。染色36 h时,整个种皮以及胚乳被染成蓝色。【结论】采用80 ℃热水处理5 min是解除加拿大紫荆种子硬实性的最适条件,可使种子维持较高的生活力;种脐区域是早期吸水的主要部位;种孔是加拿大紫荆种子的最初吸水位点,随后水分沿厚壁细胞层与栅栏层的分离处以及维管束向子叶末端迁移。厚壁细胞等组织对种子的早期吸水有一定的影响。

【Objective】 The hardness of the seed coat seriously hinders water absorption in Cercis canadensis seeds. The structure of the seed coat was studied to determine how to break the hardness and reveal how these seeds uptake water. 【Method】 Seeds were soaked in hot water, then the structure of the seed coat was assessed using scanning electron microscopy (SEM). Seeds of C. canadensis were stained with aniline blue and sealed with Vaseline to determine the relationship between the seed coat and water absorption. 【Result】 Soaking in hot water at various temperatures for 5 min, followed by gradual cooling for 24 h broke the hardness of C. canadensis seeds and improved rate of imbibition. However, seed viability decreased with increasing water temperature. The SEM images of the seed coat revealed some fissures in the hilar region. Soaking in hot water dissolved the wax between the hilum and vascular bundle, and caused the wax in the fissures to disappear. The SEM images of longitudinal sections showed that the seed coat comprised a cuticle, palisade, and sclerenchyma layers. However, unique structures such as light lines, counter-palisade layers, and vascular bundles were found in the hilar region. After being soaked in hot water, sclerenchyma cells and a palisade layer near the micropyle separated and a bulge formed. Blocking various parts of the seeds with Vaseline revealed that the hilar region absorbed water more rapidly than the other blocked regions when soaked in water for 12 h. After soaked in water for 96 h, the middle part of the seed coat began to absorb water. However, the bottom of the cotyledon did not start absorbing water until the seeds were soaked for 120 h. The micropyle was the first to be stained by aniline blue (2 h), followed by the hilum (3 h). Water then entered the seed along the edge of the seed coat, which was the space separating the sclerenchyma cells and the palisade layer (4 h). When soaked in water for 9 h, the vascular bundle was stained blue. 【Conclusion】 Soaking in hot water at 80 ℃ for 5 min was optimal for breaking the hardness of C. canadensis seeds without compromising seed viability. Blocking with Vaseline showed that the hilar region is crucial for water absorption. The results of aniline blue staining further indicated that the micropyle was the initial site of water absorption and that the vascular bundle was an important structure for water movement. Aniline blue staining also showed that sclerenchyma cells could restrict water uptake at the early stage of soaking.