Chemical elucidation for the mechanism of the defense reaction of plant cells

在利用植物培养细胞研究生物催化剂的过程中，我们考察了植物细胞对外源底物化学胁迫的防御反应。将各种类异戊二烯作为胁迫化合物添加到几种植物如烟草、洋甘菊、芹菜、大豆和苔的培养细胞中。观察到用香叶醇处理的细胞的细胞核浓缩并断裂，然后基因组DNA以梯状断裂。香叶醇的这种作用具有浓度和时间依赖性。这些观察结果表明，香叶醇具有类似于植物细胞凋亡的细胞死亡活性，而蛋白质和RNA合成抑制剂放线菌酮和放线菌素D则不抑制植物细胞的凋亡。这表明香叶醇诱导的凋亡过程不需要合成新的蛋白质。另一方面，细胞分裂素的加入阻止了香叶醇诱导的细胞DNA片段化。本课题对化学胁迫诱导植物细胞凋亡的机制进行了探讨。

In the course of the studies on the biocatalysts with plant cultured cells, we have examined the defense reaction of plant cells against chemical stress with exogenous substrates. Various isoprenoids as a stress compounds were added to the cultured cells of several plants such as tabacco, chamomile, celery, soybean and liverwort. It was observed that the' nuclei of the cells on treatment with geraniol were condensed and fragmented, and then genomic DNAs were fragmented in a ladder form. Such the effect of geraniol was concentration- and time-dependent. These observations reveal that geraniol has an activity for apoptosis-like cell death of the plant cells.Furthermore, cycloheximide and actinomycin D, inhibitors of protein and RNA syntheses, respectively, did not suppress the apoptosis of the plant cells. This suggests that the apoptotic process induced by geraniol does not require the synthesis of new proteins. On the other hand, addition of cytokinins prevented the geraniol-induced DNA fragmentation in the cells. The mechanism of the plant apoptosis induced by chemical stress was examined and discussed in this project.