Journal Article

Light-Independent Cell Death Induced by Accumulation of Pheophorbide <i>a</i> in <i>Arabidopsis thaliana</i>

Masumi Hirashima, Ryouichi Tanaka and Ayumi Tanaka

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 50, issue 4, pages 719-729
Published in print April 2009 | ISSN: 0032-0781
Published online March 2009 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcp035
Light-Independent Cell Death Induced by Accumulation of Pheophorbide a in Arabidopsis thaliana

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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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 5 d 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.

Keywords: Arabidopsis; Cell death; Pheophorbide a; Senescence

Journal Article.  6023 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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