Analysis of irreversible process of cell differntiation in higher plants

百日菊叶肉细胞分化为导管分子的过程中存在一个转折点。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，我试图分离与次生壁形成相关的分子标记。结果，获得了微管蛋白（ZTUB 1 -3）的cDNA。分离到苯丙氨酸解氨酶（ZPAL 1 -4）和壁结合型过氧化物酶（ZPO-C）。ZPO-C的转录本在分化细胞中特异性表达，在木质素沉积前短暂表达，表明该基因是一个很好的不可逆过程的标记。其次，还分离了参与自溶的半胱氨酸蛋白酶的cDNA。该cDNA的转录本也显示出瞬时和特异性表达模式。比较ZPO-C和半胱氨酸蛋白酶基因的上游区域，将为不可逆过程中的基因调控提供新的思路。第三，我尝试分离对应于在分化转折点表达的转录物的cDNA，并成功分离了设计为TED 2 -4的cDNA克隆。以TED 2 -4 cDNA为探针对百日菊进行原位杂交，结果表明TED 3、4和2分别在具有分化为导管分子、木质部细胞和木质部或韧皮部细胞潜能的细胞中表达。

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.