Salicylic acid is involved in Arabidopsis defense against Cd-induced oxidative stress

ZAWOZNIK M., AZPILICUETA C. AND BENAVIDES MP

Pinamar, Buenos Aires, Argentina

Congreso; X Congress of the Panamerican Association for Biochemistry and Molecular Biology (PABMB). XLI Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology (SAIB).XX Annual Meeting of the Argentine Society for Neurochemistry (SAN); 2005

SAIB

Salicylic acid (SA) has been identified as an important signaling molecule involved in plant disease resistance and in hardening responses to abiotic stressors. The response of wild type Arabidopsis seedlings (Col) and of a SA-deficient transgenic line (NahG) to Cd exposure (500 mM) was studied. The effect of pretreating NahG plants with SA (100 mM) was also examined. A rapid accumulation of H2O2 was observed by in situ localization with DAB, however no visible symptoms of Cd toxicity could be detected until day 5. Catalase activity was significantly diminished 24 h after Cd treatment in Col plants and in the SA-pretreated NahG line, while in NahG plants, it was significantly increased. MDA content was significantly enhanced in Col plants 60 h after Cd treatment while NahG plants showed MDA levels similar to those of untreated Col plants. By day 5, chlorophyll content of Col and NahG plants amended with SA was significantly reduced. SA-unamended NahG plants retained their chlorophyll levels. Superoxide anion (O2-) rapidly accumulated in detached leaf segments exposed to 500 mM Cd, except in NahG line. The transcript level of AtSOD3 gene was negligible in NahG plants. However, when exposed to Cd, the expression of this gene was rapidly induced in all treatments. Our results indicate that constitutive SA tends to potentiate the Cd-induced oxidative damage by activating the expression of SOD and repressing catalase activity and/or expression. Exogenous SA added to SA-deficient Arabidopsis plants seems to have positive long-term effects by slowly reverting the deleterious effects that Cd exerts on the H2O2-detoxifying system.