Ultraviolet-B- and Ozone-Induced Biochemical Changes in Antioxidant Enzymes of Arabidopsis thaliana

Abstract

Earlier studies with Arabidopsis thaliana exposed to ultraviolet 6 (UV-6) and ozone (O,) have indicated the differential responses of superoxide dismutase and glutathione reductase. In this study, we have investigated whether A. thaliana genotype Landsberg erecfa and its flavonoid-deficient mutant fransparent testa ( t f 5 ) is capable of metabolizing UV-B-and O,-induced activated oxygen species by invoking similar antioxidant enzymes. UV-6 exposure preferentially enhanced guaiacol-peroxidases, ascorbate peroxidase, and peroxidases specific to coniferyl alcohol and modified the substrate affinity of ascorbate peroxidase. O, exposure enhanced superoxide dismutase, peroxidases, glutathione reductase, and ascorbate peroxidase to a similar degree and modified the substrate affinity of both glutathione reductase and ascorbate peroxidase. Both UV-B and O, exposure enhanced similar Cu,Zn-superoxide dismutase isoforms. New isoforms of peroxidases and ascorbate peroxidase were synthesized in tt5 plants irradiated with UV-B. UV-B radiation, in contrast to O,, enhanced the activated oxygen species by increasing membrane-localized NADPH-oxidase activity and decreasing catalase activities. These results collectively suggest that (a) UV-B exposure preferentially induces peroxidase-related enzymes, whereas O, exposure invokes the enzymes of superoxide dismutase/ ascorbate-glutathione cycle, and (b) in contrast to O,, UV-B exposure generated activated oxygen species by increasing NADPHoxidase activity.

UV-B effects on leaves—Oxidative stress and acclimation in controlled environments

“…UV-B enhanced SOD activity in this study but peroxidase enzymes were unaffected [40]. Thus the ratio of peroxidase activation to SOD activation was < 1, unlike in experiments when leaves were less stressed and peroxidases were preferentially enhanced [29,39].…”

“…According to the original model [43], extremely imbalanced peroxidase : SOD activation ratios in response to a stress condition result in cell damage (gray shaded boxes). Responses to UV-B (blue-framed boxes) are special: experimental data support our hypothesis that peroxidase : SOD activation >1 facilitate acclimation [29,39], and ratios <1 promote oxidative damage [40] as detailed in section 3.…”

“…In addition to examining different species, the two experiments were different in several other conditions and are only mentioned here to illustrate the diversity of outdoor responses. Less diverse results from controlled laboratory experiments suggest that acclimative antioxidant responses to UV-B are directed at H 2 O 2 , preferentially via peroxidases and not catalase activity [29,39], which argues for the photosynthesis derived nature of this ROS. 13 …”

Antioxidant Effect of Caffeic Acid on Oxytetracycline Induced Lipid Peroxidation in Albino Rats

“…For example, phenolic compounds can trap the free radicals directly or scavenge them through a series of coupled reactions with antioxidant enzymes [12]. According to recent research, caffeic acid was a superior antioxidant compared with p-coumaric and ferulic acids, in inhibiting LDL oxidation [13,14] but also quenching radicals [15] and singlet oxygen.…”

Partial purification of superoxide dismutase and peroxidase from ber (Zizyphus mauritiana Lamk.) fruit using anion exchange chromatography

“…Peroxidase was assayed by determining the rate of guaiacol oxidation in the presence of H 2 O 2 at 470 nm (Rao et al, 1996). Reaction mixture (3.0 ml) contained 2.15 ml of 0.1 M Tris HCl buffer (pH 7.0), 0.6 ml of 1% guaiacol, 0.1 ml of enzyme extract and 0.15 ml of 100 mM H 2 O 2 .…”