Change of AOX1a Expression, Encoding Mitochondrial Alternative Oxidase, Influence on the Frost-Resistance of Arabidopsis Plants

The resistance of Arabidopsis thaliana (L.) Heynh (Columbia ecotype) plants: Col-0 line (wild type), AS-12 line (plants transformed with the construct carrying the AOX1a gene under control of the CAMV 35S promoter in the antisense orientation) and line XX-2 (plants transformed with the AOX1a gene construct in the sense orientation) (Umbach et al., 2005), to action of subzero temperature has been studied. It is shown that change of the AOX1a expression is accompanied by change of the AOX contribution in respiration and increase of the base frost-resistance of Arabidopsis plants. In the leaves of plants with overexpression of АОХ1а was reduced activity of total superoxide dismutase (SOD), but was increased activity of guaiacol peroxidase and was less content of hydrogen peroxide. It was found that cold hardening during 7 days at 5°C increases the resistance of plants to the subsequent action of subzero temperature regardless of АОХ1а expression degree. The hardening lead to activation of respiration, increase of the contribution of AOX in the respiration, a significant increase of the water-soluble carbohydrates content and increase of the activity SOD and total guaiacol peroxidases in leaves of all lines the plants. In hardened plants of Arabidopsis wild type and AOX1a transformants were detected differences in the contents of individual types of reactive oxygen species and the activity of antioxidant enzymes. The trend to decrease of hydrogen peroxide content in lines with altered expression of AOX1a was observed, but content of superoxide anion radical (SAR) was significantly lower in the AS-12 line compared with the Col-0 and XX-2 plants after hardening. The low content of SAR in leaves of AS-12 line was partly caused by increase of activity total SOD. Thus, we have identified differences in the basic frost-resistance of Arabidopsis plants with altered AOX1a expression, but significant differences in frost-resistance of hardened plants of wild-type and lines with altered AOX1a expression was not found. It was concluded that the frost-resistance of plants depends on the activity of AOX, but the decrease of its activity can be compensated by the activation of other protective systems including antioxidant enzymes.