Light-dependence of cadmium and paraquat effect on catalase in sunflower discs

AZPILLICUETA CE; BENAVIDES MP; GALLEGO SM; TOMARO ML

Pinamar-Argentina

Congreso; X PABMB Congress- XLI Annual Meeting of the Argentinean Society for Biochemistry and Molecular Biology Research; 2005

SAIB

Catalase (CAT, EC 1.11.1.6) is involved in detoxification of H2O2 generated by environmental stresses, as well as by physiological conditions. In sunflower (Helianthus annuus L.), 8 isoforms of CAT, products of 4 different genes, were identified: CATA1 and CATA2 code for matrix CATs, whereas CATA3 and CATA4 code for core CATs. The effect of different oxidative conditions, generated by Cd2+, H2O2 and paraquat (PQ), on CAT transcripts, isoforms and activity were studied. CAT activity decreased 30% respect to control, after 8 h of 300 µM CdCl2 treatment under light conditions and this effect was avoided when 10 mM MnCl2 was supplied with Cd2+ in the incubation medium. Native PAGE staining revealed no differences in CAT isoenzymes. The transcript analysis of CATA3 showed an increase of 2.9 times over the control. In order to compare Cd2+ stress with other oxidative stress conditions, PQ or H2O2 were assayed. PQ increased CATA3 expression 2.2 times (over the control) after 2 h of incubation under light. However, no changes were observed when H2O2.was used. The qualitative pattern of carbonylated proteins showed that Cd2+ increased oxidation of proteins with molecular weight higher than 45 kDa. Cd2+ and PQ induced ROS formation in the chloroplasts, evidenced with 2´,7´-dichlorofluorescein diacetate, and this effect was reverted by ascorbate. Considering the results detailed above, we can conclude that light is necessary for Cd2+ and PQ effect on CATA3 transcript. Neverthless, the decrease observed on CAT activity was due to a an oxidative modification produced by the metal on the CAT protein.