Light-Independent Cell Death Induced by Accumulation of Pheophorbide a in Arabidopsis thaliana
Light-Independent Cell Death Induced by Accumulation of Pheophorbide a in Arabidopsis thaliana
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DOI：
10.1093/pcp/pcp035
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发表时间：
2009-04-01
影响因子：
4.9
通讯作者：
Tanaka, Ayumi
中科院分区：
文献类型：
--
作者：
Hirashima, Masumi;Tanaka, Ryouichi;Tanaka, Ayumi
四聚吡咯是众所周知的光敏剂。在植物中，据报道，四吡咯代谢的各种中间分子以光依赖的方式诱导细胞死亡。与这些报道相反，我们发现脱镁叶绿酸a是叶绿素分解代谢的关键中间体，在转基因拟南芥AS-ACD1中，它导致细胞在完全黑暗中死亡。在该植物中，脱镁叶绿酸a加氧酶的mRNA表达被Acd1反义RNA抑制，因此，当叶绿素发生分解时，AS-ACD1积累了过量的脱镁叶绿酸a。我们观察到，当持续的暗期诱导衰老时，AS-ACD1植株的叶片变得脱水。通过测量电解质渗漏，我们估计有50个叶片细胞在5d的黑暗时间内经历了细胞死亡。光镜和电子显微镜观察表明，大量细胞中的细胞结构已经崩溃。用铝箔部分覆盖叶片会导致覆盖区域的不依赖光的细胞死亡，并诱导未覆盖区域的漂白。这些结果表明，脱镁叶绿酸a的积累在黑暗和光照下都会诱导细胞死亡，但在这两种条件下细胞死亡的机制可能不同。我们讨论了光不依赖细胞死亡的可能机制，以及脱镁叶绿酸a参与细胞程序性死亡的信号通路。
Tetrapyrroles are well-known photosensitizers. In plants, various intermediate molecules of tetrapyrrole metabolism have been reported to induce cell death in a light-dependent manner. In contrast to these reports, we found that pheophorbide a, a key intermediate of chlorophyll catabolism, causes cell death in complete darkness in a transgenic Arabidopsis plant, As-ACD1. In this plant, expression of mRNA for pheophorbide a oxygenase was suppressed by expression of Acd1 antisense RNA; thus, As-ACD1 accumulated an excessive amount of pheophorbide a when chlorophyll breakdown occurred. We observed that when senescence was induced by a continuous dark period, leaves of As-ACD1 plants became dehydrated. By measuring electrolyte leakage, we estimated that 50 of the leaf cells underwent cell death within a 5d period of darkness. Light and electron microscopic observations indicated that the cellular structure had collapsed in a large population of cells. Partially covering a leaf with aluminum foil resulted in light-independent cell death in the covered region and induced bleaching in the uncovered regions. These results indicate that accumulation of pheophorbide a induces cell death under both darkness and illumination, but the mechanisms of cell death under these conditions may differ. We discuss the possible mechanism of light-independent cell death and the involvement of pheophorbide a in the signaling pathway for programmed cell death.