Analysis of irreversible process of cell differntiation in higher plants

百日叶肉细胞向管状细胞分化的过程中有一个转折点。此时，细胞进入不可逆的分化过程。我在这里研究了不可逆过程的生物化学和分子生物学。首先，我试图分离与二次壁形成相关的分子标记。因此，微管蛋白的cdna （ZTUB1-3）。分离到苯丙氨酸解氨酶（ZPAL1-4）和一个壁结合过氧化物酶（ZPO-C）同型。ZPO-C对应的转录本在分化细胞中特异性表达，并在木质素沉积前短暂表达，表明该基因是不可逆过程的良好标记。其次，分离出参与自溶的半胱氨酸蛋白酶cDNA。该cDNA的转录本也表现出短暂的特异性表达模式。ZPO-C和半胱氨酸蛋白酶基因上游区域的比较将为不可逆过程中的基因调控提供新的思路。第三，我尝试分离出在分化转捩点表达的转录本对应的cDNA，并成功分离出设计为TED2-4的cDNA克隆。以TED2-4 cdna为探针的Zinnia幼苗原位杂交发现，TED3、ted4和ted2分别在具有向管状细胞、木质部细胞和木质部或韧皮部细胞分化的细胞中表达。

There is a turning point in the process of differentiation of Zinnia mesophyll cells into tracheary elements. At the point, cells enter the irreversible process of differentiation. I here studied the irreversible process biochemically and molecular biologically. First, I tried to isolate molecular markers associated with the secondary wall formation. As a result, cDNAs for tubulin (ZTUB1-3). phenylalanine ammonia-lyase(ZPAL1-4) and an isotype ofwall-bound peroxidases(ZPO-C) were isolated. Transcripts corresponding to ZPO-C were found to be expressed specifically in differentiating cells and transiently just before lignin deposition, indicating that this gene was a good marker of irreversible process. Second, a cDNA for cysteine protease which was involved in autolysis was also isolated. The transcripts for this cDNA also showed a transient and specific expression pattern. The comparison of upstream regions of ZPO-C and cycteine protease genes will cast a new light on gene regulation in the irreversible process. Third, I tried isolate cDNAs corresponding to transcripts that were expressed at the turing point of differentiation and succeeded in the isolation of such cDNA clones designed as TED2-4. In situ hybridization of Zinnia seedings with TED2-4 cDNAs as probes revealed that TED3, 4 and 2 were expressed in cells that had a potency to differentiate to tracheary elements, xylem cells, and xylem or phloem cells, respectively.