Visualization of formation of lignified cell wall by microautoradiography

银杏和松木甘露聚糖的选择性放射标记是通过在葡聚糖生物合成抑制剂和苯丙氨酸解氨酶抑制剂（即2-脱氧-d -葡萄糖和l -a-氨基氧基-b-苯丙酸）存在的情况下，分别向生长的茎中施用d -甘露糖- [2-3H]来实现的。为了研究甘露聚糖在细胞壁形成过程中的沉积和分布，采用显微放射自显影技术观察了甘露聚糖在分化木质部中的放射性分布。从早期到S3（次生壁内层）形成阶段，放射性长期进入细胞壁。在次生壁外层（S1）形成开始后的阶段，这种合并最为显著。说明甘露聚糖沉积在次生壁形成过程中增强，甘露聚糖主要存在于次生壁中。用放射性标记针叶树和紫丁香苷饲喂木兰树，研究了单酚类糖苷的作用。由于紫丁香苷在木质素组织和生长季节中的浓度较低，因此可能不是木质素的直接前体。显微放射自显影研究显示，即使在非木质化季节，施用紫丁香素也被纳入树皮的皮层。而针叶树素在木质素生长过程中被引入分化的木质部和韧皮部纤维中，表明针叶树素参与了木质素的生物合成。

Selective radio-labeling of mannan in ginkgo and pine was achieved by the administration of D-mannose- [2-3H] in the presence of both glucan biosynthesis inhibitor and phenylalanine ammonia-lyase inhibitor, namely, 2-deoxy-D-glucose and L-a-aminooxy-b-phenylpropionic acid, respectively, to growing stems. To study the deposition and distribution of mannan during cell wall formation, the distribution of the radioactivity in differentiating xylem was visualized by microautoradiography. Radioactivity was incorporated into the cell walls for a long period from early stage to S3 (inner layr of secondary wall) formation stage. The incorporation was most significant at the stage following the start of S1 (outer layr of secondary wall) formation. This result indicates that mannan deposition was enhanced during secondary wall formation and mannan is present mainly in secondary wall.The role of monolignol glucosides was also investigated by the feeding of radiolabeled coniferin and syringin into magnolia tree. It was suggested that syringin was not the direct precursor of lignin because of low concentration in lignifing tissues and grawing seasons. Microautoradiographic studies revealed that administered syringin was incorporated into cortex in the bark even in the non-lignifying season. While, coniferin was incorporated into the differentiating xylem and phloem fiber during the lignifing season, which indicated that coniferin is involved in the lignin biosynthesis.