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

Abstract

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 micromol 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 [Phi(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.

Efficient regeneration and antioxidative enzyme activities in Brassica rapa var. turnip

“…A UV-visible spectrophotometer (Agilent 8453, CA, USA) was used to determine the absorption of extracts. Superoxide dismutase (SOD; EC 1.15.1.1) was determined by the method of Giannopolitis and Ries (1977), catalase (CAT; EC 1.11.1.6) was determined by the method of Arrigoni et al (1992), peroxidase (POD; EC 1.11.1.7) was determined according to Abeles and Biles (1991), and ascorbate peroxidase (APX; EC 1.11.1.11) was determined by the method of Miyake et al (2006).…”

Theredox imbalancedMutants of Arabidopsis Differentiate Signaling Pathways for Redox Regulation of Chloroplast Antioxidant Enzymes

“…However, the steady-state level of APx activity was elevated during early light stress (Davletova et al, 2005). Since the activity of sAPx and tAPx is highly sensitive to H 2 O 2 (Asada, 2000;Miyake et al, 2006), it implicates expressional induction of chloroplast APx. In the rimb mutants, the redox shift in the Asc pool (Fig.…”

The cDNA Structures and Expression Profile of the Ascorbate Peroxidase Gene Family During Drought Stress in Wild Watermelon

“…APX catalyzes the conversion of H 2 O 2 to water with concomitant oxidation of ascorbate to monodehydroascorbate, thereby playing a pivotal role in the detoxification of ROS under biotic or abiotic stresses (Asada, 2006;Miyake et al, 2006). Extensive research has shown that APX isoenzymes are localized in at least three different subcellular compartments in plant cells, namely, cytosol (cAPX), microbody (mAPX), and chloroplast (Ishikawa & Shigeoka, 2008).…”