Journal Article

The <i>Arabidopsis-accelerated cell death</i> Gene <i>ACD1</i> is Involved in Oxygenation of Pheophorbide <i>a</i>: Inhibition of the Pheophorbide <i>a</i> Oxygenase Activity does not Lead to the “Stay-Green” Phenotype in <i>Arabidopsis</i>

Ryouichi Tanaka, Masumi Hirashima, Soichirou Satoh and Ayumi Tanaka

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 44, issue 12, pages 1266-1274
Published in print December 2003 | ISSN: 0032-0781
Published online December 2003 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcg172
The Arabidopsis-accelerated cell death Gene ACD1 is Involved in Oxygenation of Pheophorbide a: Inhibition of the Pheophorbide a Oxygenase Activity does not Lead to the “Stay-Green” Phenotype in Arabidopsis

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Oxygenation of pheophorbide a is a key step in chlorophyll breakdown. Several biochemical studies have implicated that this step was catalyzed by an iron-containing and ferredoxin-dependent monooxygenase, pheophorbide a oxygenase (PaO). It has been proposed that inhibition of its activity arrests the chlorophyll breakdown and leads to the “stay-green” phenotype. We searched the Arabidopsis genome for a possible PaO-encoding gene and hypothesized that it has homology to known iron-containing Rieske-type monooxygenase sequences. We identified three such open reading frames, Tic55, ACD1 and ACD1-like. We produced transgenic Arabidopsis plants which expressed antisense RNA as a method to inhibit the expression of these genes. The appearance of these antisense plants were indistinguishable from that of the wild type under illumination. However, after they were kept under darkness for 5 d and again illuminated, the leaves of the antisense ACD1 plants (AsACD1) were bleached. Leaves of AsACD1 accumulated 387 nmol (g FW)–1 pheophorbide a which corresponded to 60% of chlorophyll a degraded. The rate of decrease in chlorophyll a was not influenced in senesced AsACD1 leaves. These results demonstrated that ACD1 is involved in PaO activity, and its inhibition led to photooxidative destruction of the cell instead of the “stay-green” phenotype.

Keywords: Keywords: Accelerated cell death 1 — Arabidopsis — Chlorophyll — Pheophorbide a oxygenase — Photosynthesis — Senescence.; Abbreviations: Chl, chlorophyll; CMO, choline monooxygenase; CAO, chlorophyllide a oxygenase; PaO, pheophorbide a oxygenase; RCC, red chlorophyll catabolite; FCC, fluorescent chlorophyll catabolite; pFCC, primary fluorescent chlorophyll catabolite.

Journal Article.  5708 words.  Illustrated.

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

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