Involvement of calcium in the NaCl-induced up-regulation of antioxidant enzyme activity in cotton callus

摘要

Numerous investigations have shown that elevated levels of NaCl induce an increase in the activities of several antioxidant enzymes in cotton callus. The signal transduction pathway responsible for this increase is currently under investigation in our laboratory. A series of experiments was carried out to determine if calcium is involved in the NaCl induced up-regulation of antioxidant enzymes in sail-tolerant callus derived from the cotton cultivar Coker 312. The activities of four antioxidant enzymes, was measured in callus exposed to three calcium channel blockers, (Lanthanum Chloride, ruthenium red and TMB-8), and one calcium ionophore (A23187). Following a 2 hour pre-treatment with one of the Ca~(2+) channel blockers or A23187, antioxidant enzyme activity was measured over an 8-hour (ruthenium red and lanthanum chloride) or 2-hour (TMB-8 and A23187) periods in the absence (control) or presence of 250mM NaCl (salt stressed). The three calcium channel blockers, abolished the NaCl induced increases in the activities of glutathione reductase, catalase, peroxidase and ascorbate peroxidase. However, the Ca~(2+) ionophore, A23187 induced an increase in the activities of glutathione reductase, peroxidase and ascorbate peroxidase but not catalase. In addition, an increase in the activity of all four enzymes was observed in the callus under NaCl stress in the presence of TMB-S and A23187. With control callus, the TMB-8 and A23187 combination induced an up-regulation of peroxidase, glutathione reductase and ascorbate peroxidase activites but no up-regulation of catalase was observed under these conditions. The results of these experiments supports the hypothesis that calcium is most likely involved as a secondary messenger in the NaCl-induced signaltransduction pathway.