Compensation for lack of a cytosolic ascorbate peroxidase in an Arabidopsis mutant by activation of multiple antioxidative systems

Abstract

Plants have various systems for scavenging active oxygen species. Ascorbate peroxidase (APX), a component of one of these systems, is involved in scavenging hydrogen peroxide. We isolated and characterized an Arabidopsis thaliana mutant deficient in a gene ( APX1) for cytosolic APX. In this mutant ( apx1), expression of APX1 was not detected at either the mRNA or protein level, and APX activity in a soluble plant extract was about one-third that in wild-type plants, suggesting that apx1 plants completely lack APX1. This mutant grew similar to wild-type plants under normal conditions. In the mutant, the ratio of reduced to oxidized forms of ascorbate was slightly higher than in the wild-type, but the amount of hydrogen peroxide was similar in both lines under normal growth conditions. The activity of catalase and the level of high-intensity-light-induced expression of APX2, the other isozyme of cytosolic APX, were higher in apx1 than in wild-type plants. Low-temperature-induced accumulation of anthocyanin in apx1 plants was also higher than in wild-type plants. These results indicate that the loss of APX1 in this mutant was compensated for by augmentation of other antioxidative systems.