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

TLDR

Previous work has shown that UV‑B and ozone elicit distinct changes in antioxidant enzymes such as superoxide dismutase and glutathione reductase in Arabidopsis thaliana. This study examined whether the Landsberg erecta genotype and the flavonoid‑deficient tt5 mutant can activate comparable antioxidant enzymes to detoxify UV‑B and ozone‑induced reactive oxygen species. UV‑B exposure mainly up‑regulated peroxidase enzymes and increased NADPH‑oxidase activity while reducing catalase, whereas ozone exposure induced superoxide dismutase, glutathione reductase, and ascorbate peroxidase, with both stresses elevating Cu,Zn‑SOD isoforms and altering enzyme substrate affinities; the tt5 mutant produced novel peroxidase isoforms under UV‑B.

Abstract

Earlier studies with Arabidopsis thaliana exposed to ultraviolet B (UV-B) and ozone (O3) have indicated the differential responses of superoxide dismutase and glutathione reductase. In this study, we have investigated whether A. thaliana genotype Landsberg erecta and its flavonoid-deficient mutant transparent testa (tt5) is capable of metabolizing UV-B- and O3-induced activated oxygen species by invoking similar antioxidant enzymes. UV-B exposure preferentially enhanced guaiacol-peroxidases, ascorbate peroxidase, and peroxidases specific to coniferyl alcohol and modified the substrate affinity of ascorbate peroxidase. O3 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 O3 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 O3, 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 O3 exposure invokes the enzymes of superoxide dismutase/ascorbate-glutathione cycle, and (b) in contrast to O3, UV-B exposure generated activated oxygen species by increasing NADPH-oxidase activity.