Abstract：
Lignin provides structural support to plants; however, it reduces their utilization rate. According to our previous studies, selenium (Se) reduces lignin accumulation in alfalfa, but the specific mechanism involved remains unclear. Therefore, at the seedling stage, four root irrigation treatments using 2.5, 50, and 5 μmol/L sodium selenite (S-RI), selenomethionine (SS-RI), Se nanoparticles (SSS-RI), and deionized water (CK-RI) were performed. At the branching stage, four treatments of foliar spraying with the three Se fertilizers described above at a concentration of 0.5 mmol/L (S-FS, SS-FS, and SSS-FS) and deionized water (CK-FS) were administered. The results revealed that all Se treatments chiefly reduced the level of deposition of syringyl (S) lignin in the first internode of alfalfa stems. SS-FS and SSS-FS treatments mainly reduced the deposition of S and guaiacyl (G) lignins in the sixth internode of alfalfa stems, respectively, while S-FS treatment only slightly reduced the deposition of G lignin. S, SS, and SSS-RI treatments reduced the level of deposition of S and G lignins in the sixth internode of alfalfa stems. Se application increased plant height, stem diameter, epidermis (cortex) thickness, primary xylem vessel number (diameter), and pith diameter of alfalfa but decreased primary xylem area and pith parenchyma cell wall thickness of the first internode, and SS(SSS)-FS treatment reduced the mechanical strength of alfalfa stems. Therefore, Se application could decrease lignin accumulation by regulating the organizational structure parameters of alfalfa stems and the deposition pattern of the lignin monomers.
摘要：
木质素为植物提供结构支撑；然而，它降低了他们的利用率。根据我们之前的研究,硒（Se）减少紫花苜蓿的木质素积累，但具体机制尚不清楚.因此,在幼苗阶段，使用2.5、50和5μmol/L亚硒酸钠（S-RI）的四种根部灌溉处理，硒代蛋氨酸（SS-RI），硒纳米粒子（SSS-RI），和去离子水(CK-RI)进行。在分支阶段，用上述三种硒肥料以0.5mmol/L的浓度进行叶面喷施的四种处理（S-FS，SS-FS,和SSS-FS）和去离子水（CK-FS）。结果表明，所有硒处理都主要降低了紫花苜蓿茎第一节间丁香基（S）木质素的沉积水平。SS-FS和SSS-FS处理主要减少了苜蓿茎第六节间的S和愈创酰基（G）木质素的沉积，分别,而S-FS处理仅略微减少了G木质素的沉积。S,SS,SSS-RI处理降低了苜蓿茎第六节间S和G木质素的沉积水平。施硒增加了植物高度，阀杆直径,表皮（皮质）厚度，初生木质部血管数（直径），紫花苜蓿的髓直径，但第一节间的初生木质部面积和髓薄壁组织厚度减小，SS(SSS)-FS处理降低了苜蓿茎的机械强度。因此,施硒可以通过调节紫花苜蓿茎的组织结构参数和木质素单体的沉积模式来减少木质素的积累。
