Thylakoid-Bound Ascorbate Peroxidase Mutant Exhibits Impaired Electron Transport and Photosynthetic Activity

Abstract

In chloroplasts, stromal and thylakoid-bound ascorbate peroxidases (tAPX) play a major role in the removal of H 2 O 2 produced during photosynthesis. Here, we report that hexaploid wheat (Triticum aestivum) expresses three homeologous tAPX genes (TaAPX-6A, TaAPX-6B, and TaAPX-6D) mapping on group-6 chromosomes. The tAPX activity of a mutant line lacking TaAPX-6B was 40% lower than that of the wild type. When grown at highlight intensity photosystem II electron transfer, photosynthetic activity and biomass accumulation were significantly reduced in this mutant, suggesting that tAPX activity is essential for photosynthesis. Despite the reduced tAPX activity, mutant plants did not exhibit oxidative damage probably due to the reduced photochemical activity. This might be the result of a compensating mechanism to prevent oxidative damage having as a consequence a decrease in growth of the tAPX mutant plants.

Cytosolic Ascorbate Peroxidase 1 Is a Central Component of the Reactive Oxygen Gene Network of Arabidopsis

“…Henzler and Steudle, 2000). The extent of cross-compartment protection, however, might be limited because at least in tobacco (Nicotiana tabacum) and wheat (Triticum aestivum) a deficiency in thylakoid-bound APX was shown to have adverse effects on plant growth and photosynthetic performance Danna et al, 2003). These findings suggest that cytosolic APX1 might not be able to protect the chloroplast against H 2 O 2 produced at the surface of the thylakoid membrane (see also Rizhsky et al, 2003 for the effect of disrupting the water-water cycle in Arabidopsis).…”

The role of antioxidant enzymes in photoprotection

“…Consequently, photoprotection of chloroplast constituents should depend on the efficiency of ROS removal by antioxidants. Indeed, the addition of antioxidants in vitro decreases the extent of photoinactivation (Bare´nyi and Krause 1985;Richter et al 1990;Tschiersch and Ohmann 1993;Tjus et al 2001), and the lack of antioxidant enzymes is associated with a higher sensitivity to light treatment (Danna et al 2003). These findings taken together with the observation that the response to many environmental stresses, particularly chilling, includes up-regulation of antioxidant systems have led plant geneticists to attempt to improve the stress tolerance of some crop species by transforming plants with genes for chloroplast-targeted antioxidant enzymes (for reviews see Foyer et al 1994;Allen 1995).…”

The ascorbate peroxidase regulated by H2O2 and ethylene is involved in cotton fiber cell elongation by modulating ROS homeostasis

“…3,10,11 Chloroplastic APXs protect the photosynthetic apparatus against oxidation while microsomal APXs are involved in detoxifying H 2 O 2 produced by fatty acid b-oxidation, especially during seed germination and photorespiration. 12,13 In addition to peroxisomal APX, peroxisomal membrane-bound monodehydroascorbate reductase 4 was important for scavenging H 2 O 2 molecules that escaped the peroxisomes. 14 Although many APX isozymes have been identified from many higher plants, their functions in regulation of plant growth and development remain elusive.…”