Loss of catalase 2 activity affects the ascorbate metabolism in Arabidopsis upon heavy metal stress

Abstract

Three genes — Cat1 , Cat2 and Cat3 coding for three isoforms of catalase (CAT) are present in the Arabidopsis thaliana genome. Two of these isoforms (CAT2, CAT3) are expressed in leaves, splitting hydrogen peroxide, which is generated in peroxisomes by photorespiration. The protective function of CAT upon excessive illumination (light stress) is well document-ed, but it remains still unclear what is the role of CAT 2 isoform in the maintenance of cellular redox balance upon oxidative stress caused by other stressors, e.g., high concentrations of heavy metal ions. Accordingly, we investigate the effect of copper and cadmium chlorides on the content of low molecular weight antioxidants — ascorbate/dehydroascorbate (Asc/DHA) in A. thaliana wild type and the knockout mutant line cat2 , which lacks the CAT2 isoform. Obtained data indicate that in the cat2 knockout line metabolic alterations occur, which compensate for the decrease in CAT activity. These alterations are, at least par-tially, represented by activation of Asc/DHA metabolism. Although no hydrogen peroxide is generated in peroxisomes in the dark, these compensatory mechanisms remain active for several hours (metabolic «inertia»), leading to a transient shift of the redox balance towards reduction. An increase in the Cu 2+ ions content in the leaf tissues leads to the oxidation of Asc to DHA and to the enhancement of lipid peroxidation, which induces a protective response aimed at stabilizing the Asc+DHA pool. Comparing to the Cu 2+ ions, increase in the concentration of Cd 2+ ions causes much smaller changes in the Asc and DHA content. Taking together our data show that CAT is not directly involved in plant protection upon accumulation of HM ions in leaves. However, the lack of CAT2 activity results in limitation of cell damage due to the activation of Asc/DHA metabolisms.