Journal Article

Photoinactivation of Ascorbate Peroxidase in Isolated Tobacco Chloroplasts: <i>Galdieria partita</i> APX Maintains the Electron Flux through the Water–Water Cycle in Transplastomic Tobacco Plants

Chikahiro Miyake, Yuki Shinzaki, Minori Nishioka, Sayaka Horiguchi and Ken-Ichi Tomizawa

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 47, issue 2, pages 200-210
Published in print February 2006 | ISSN: 0032-0781
Published online February 2006 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci235
Photoinactivation of Ascorbate Peroxidase in Isolated Tobacco Chloroplasts: Galdieria partita APX Maintains the Electron Flux through the Water–Water Cycle in Transplastomic Tobacco Plants

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  • Biochemistry
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We evaluated the H2O2-scavenging activity of the water–water cycle (WWC) in illuminated intact chloroplasts isolated from tobacco leaves. Illumination under conditions that limited photosynthesis [red light (>640 nm), 250 µmol photons m–2 s–1 in the absence of HCO3 ] caused chloroplasts to take up O2 and accumulate H2O2. Concomitant with the O2 uptake, both ascorbate peroxidase (APX) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) lost their activities. However, superoxide dismutase (SOD), monodehydroascorbate radical reductase (MDAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) activities remained unaffected. The extent to which the photosynthetic linear electron flow decreased was small compared with the decline in APX activity. Therefore, the loss of APX activity lowered the electron flux through the WWC, as evidenced by a decrease in relative electron flux through PSII [Φ(PSII)×PFD]. To verify these interpretations, we created a transplastomic tobacco line in which an H2O2-insensitive APX from the red alga, Galdieria partita, was overproduced in the chloroplasts. In intact transplastomic chloroplasts which were illuminated under conditions that limited photosynthesis, neither O2 uptake nor H2O2 accumulation occurred. Furthermore, the electron flux through the WWC and the activity of GAPDH were maintained. The present work is the first report of APX inactivation by endogenous H2O2 in intact chloroplasts.

Keywords: Active oxygen; Ascorbate peroxidase (APX); Chloroplasts; Hydrogen peroxide –— Transplastomic tobacco; Water–water cycle; Abbreviations; APX, ascorbate peroxidase; Asc, ascorbate; DHA, dehydroascorbate; DHAR, dehydroascorbate reductase; GAPDH, NADP+-glyceraldehyde 3-phosphate dehydrogenase; GR, glutathione reductase; MDA, monodehydroascorbate radical; MDAR, monodehydroascorbate radical reductase; MV, methyl viologen; PCO, photorespiratory carbon oxidation; PFD, photon flux density; Φ(PSII)×PFD, relative electron flux through PSII; WWC, water–water cycle

Journal Article.  8123 words.  Illustrated.

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

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