Plant and Cell Physiology Advance Access originally published online on December 7, 2005
Plant and Cell Physiology 2006 47(2):200-210; doi:10.1093/pcp/pci235
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Photoinactivation of Ascorbate Peroxidase in Isolated Tobacco Chloroplasts: Galdieria partita APX Maintains the Electron Flux through the WaterWater Cycle in Transplastomic Tobacco Plants
Research Institute of Innovative Technology for the Earth (RITE), 9-2 Kizugawadai, Kizu-cho, Soraku-gun, Kyoto, 619-0292 Japan
* Corresponding author: E-mail, cmiyake{at}rite.or.jp; Fax, +81-774-75-2320.
We evaluated the H2O2-scavenging activity of the waterwater cycle (WWC) in illuminated intact chloroplasts isolated from tobacco leaves. Illumination under conditions that limited photosynthesis [red light (>640 nm), 250 µmol photons m2 s1 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 [
(PSII)xPFD]. 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.
(Received August 29, 2005; Accepted November 25, 2005)
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