ARABIDOPSIS LINES OVEREXPRESSING THYLAKOIDAL ASCORBATE PEROXIDASE SHOW INCREASED RESISTANCE TO PARAQUAT-INDUCED PHOTOOXIDATIVE STRESS AND TO NITRIC OXIDE-INDUCED CELL DEATH

Ascorbate peroxidases (APX), catalyse the reduction of H2O2 to water by using ascorbic acid as electron donor. To better clarify thylakoidal APX (tAPX) contribute in the ROS scavenging activity, as well as in the fine modulation of ROS for signaling, Arabidopsis lines over- or underexpressing thylakoidal tAPX have been produced. Arabidopsis lines overexpressing tAPX show increased resistance to Paraquat-induced photooxidative stress whereas the lines underexpressing tAPX, in the same conditions, show a higher sensitivity to Pq. However, both the over- and the underexpressing lines show no increased resistance/susceptibility to photoinhibitory treatments (high light or low temperature) nor to treatments with excess Fe/Cu. Interestingly, the nitric oxide-donor SNP inhibits the accumulation of tAPX transcript; moreover, when treated with SNP, the overexpressing lines show reduced symptoms of necrosis whereas the underexpressing lines show enhanced symptoms of necrosis, with respect to controls. These transgenic lines confirm therefore that H2O2 acts in partnership with nitric oxide in causing cell death and highlight the important role of tAPX in the fine modulation of H2O2 for signaling.