Reactive oxygen species formation and cell death in catalase-deficient tobacco leaf disks exposed to cadmium
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The physiological responses of tobacco (Nicotiana tabacum L.) to oxidative stress induced by cadmium were examined with respect to reactive oxygen species (ROS) formation, antioxidant enzymes activities, and cell death appearance in wild-type SR1 and catalase-deficient CAT1AS plants. Leaf disks treated with 100 or 500 µM CdCl2 increased Evans blue staining and leakage of electrolytes in SR1 or CAT1AS plants, more pronouncedly in the transgenic cultivar, but without evidence of lipid peroxidation in any of the cultivars compared to controls. Cadmium significantly reduced the NADPH oxidase-dependent O 2 − formation in a dose dependent manner in SR1 very strongly at 500 µM (to 5% of the activity in the nontreated SR1 leaf disks). In CAT1AS, the NADPH oxidase activity was constitutively reduced at 50% with respect to that of SR1, but the magnitude of the decay was less prominent in this cultivar, reaching an average of 64% of the C at 21 h, for both Cd concentrations. Hydrogen peroxide formation was only slightly increased in SR1 or CAT1AS leaf disks at 21 h of exposure compared to the respective controls. Cd increased superoxide dismutase activity more than six times at 21 h in CAT1AS, but not in SR1 and reduced catalase activity by 59% at 21 h of treatment only in SR1 plants. Despite that catalase expression was constitutively lower in CATAS1 compared to SR1 nontreated leaf disks, 500 µM CdCl2 almost doubled it only in CAT1AS at 21 h. The mechanisms underlying Cd-induced cell death were possibly not related exclusively to ROS formation or detoxification in tobacco SR1 or CAT1AS plants.
KeywordsCell death Heavy metals Hydrogen peroxide Nicotiana tabacum Reactive oxygen species
This work was supported by the University of Buenos Aires (Grant B017). Benavides MP and Groppa MD are researchers from IQUIFIB, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). Rosales EP has a fellowship from CONICET. We thank Dr Frank van Breusegem, Ghent University, Belgium, for providing SR1 and CAT1AS tobacco seeds.
Conflict of interest
The authors of the manuscript declare that they have no conflict of interest with the institution that sponsored the research.
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