Arabidopsis thaliana deficient in two chloroplast ascorbate peroxidases shows accelerated light-induced necrosis when levels of cellular ascorbate are low

Abstract

Arabidopsis chloroplasts have a multi-layered defense against hydrogen peroxide (H(2)O(2)) that includes a stromal and thylakoid ascorbate peroxidase (sAPX and tAPX). Single and double null mutants in SAPX and TAPX (sapx and tapx) were each crossed with ascorbate deficient vtc2. The single, double and triple mutants did not show visual light stress phenotypes when grown at control or high light intensities (CL and HL; 120 and 1,000 micromol photons m(-2) s(-1)). Upon shift from CL to HL, mesophyll of expanded leaves of the triple mutant bleached within hours, with exclusion of the major vein areas; this contrasts to reported patterns of cell death under ozone treatment and calatase deficiency. tapx-vtc2 and sapx-vtc2, but not tapx-sapx or single mutants, showed limited bleaching. Bleaching and necrosis were accompanied by accumulation of H(2)O(2). Cellular concentrations of alpha-tocopherol, ascorbate and glutathione showed dramatic increase in response to HL in all eight genotypes and the four vtc2 genotypes accumulated more glutathione under CL than the others. Transcript analysis of other ROS responsive genes in vtc2 and the triple mutant showed up to 20-fold induction after transition to HL, generally irrespective of genotype. We conclude that chloroplast APX proteins in Arabidopsis can be effectively compensated by other endogenous H(2)O(2) detoxification systems, but that low cellular ascorbate levels in absence of chloroplast APX activity are detrimental to the cell during excess light.

Stress hardening under long-term cadmium treatment is correlated with the activation of antioxidative defence and iron acquisition of chloroplasts in Populus

“…The trend of the changes in the MDA content was similar to that of Φ NF indicating the involvement of ROS both in the development of membrane damage and in PSII inactivation. According to Giacomelli et al [47], APX and SOD isoforms are of importance in the elimination of ROS in chloroplasts. The rise in the activity of APX was observed in parallel to the decline of lipid peroxidation and the increase of Φ PSII .…”

Overexpression of Arabidopsis Dehydration- Responsive Element-Binding Protein 2C Confers Tolerance to Oxidative Stress

“…1B-1D), we hypothesized that DREB2C may regulate oxidative stress-inducible antioxidant genes. Among antioxidants, APXs play a pivotal role in removing reactive oxygen species by catalyzing the conversion of highly damaging H 2 O 2 into H 2 O (Giacomelli et al, 2007). Hence, we assessed the expression of nine Arabidopsis APX isoforms (Mittler et al, 2004) in DREB2C overexpressors by RT-PCR.…”

Unraveling the Tapestry of Networks Involving Reactive Oxygen Species in Plants

“…These reports strengthen the link between ROS scavenging and metabolism and demonstrate that proper regulation of ROS requires reducing power that can be supplied by photosynthesis, respiration, and/or different carbon utilization pathways. Insight into the cross talk between different ROS and ROS scavenging mechanisms was gained from studies of double or triple mutants that lack key ROS scavenging enzymes in different subcellular locations (Giacomelli et al, 2007;Miller et al, 2007) and exploration of cross talk between distinct ROS such as singlet oxygen and H 2 O 2 (Laloi et al, 2007). These studies not only exposed redundancy of the ROS scavenging network but also suggested that different antioxidant enzymes and different ROS in the same or different compartments mediate signature signals that control chloroplast function and plant response to various environmental stimuli.…”