Analysis of the signal transduction system involved in cytosolic ascorbate peroxidase induction

Abstract

Ascorbate peroxidase (APX) isoenzymes play a key role in scavenging excess amount of H2O2 generated in cellular organelles and are located in chloroplasts (stromal and thylakoid-membrane), microbody, mitochondria, and cytosol. Recently, we studied the expression of spinach APX isoenzymes in response to several stress conditions (Yoshimura et al., Plant Physiol. 123, 223-233, 2000). The steady-state transcript level of cytosolic APX (cAPX) remarkably increased in response to high-light stress and paraquat treatment. The transcript levels of other APX isoenzymes were not changed in response to any of the stress treatments. To date, several factors have been demonstrated to affect the cAPX expression; however the molecular mechanisms of cAPX gene regulation are not fully understood. Here we studied the signal transduction system which regulates cAPX induction in spinach. The treatment of detached leaves with the photosynthetic electron transport inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, before exposure to high light inhibited the induction of cAPX mRNA. In contrast, cAPX mRNA was induced by the treatment of 2,5-dibromo-6-isopropyl-3-methyl-1,4-benzoquinone under low light. 3-Aminotriazole or paraquat treatments also caused induction of cAPX mRNA. The cellular H2O2 levels were elevated by treatments with 3-aminotriazole or palaquat. The present results support the fact that redox changes in the electron transport through quinone B or plastoquinone and/or cellular H2O2 level can regulate of the cAPX expression in spinach leaves.