A cotton (Gossypium hirsutum 1.) control and NaCI-tolerant cell line (cv Coker 312) were grown on media with or without NaCl in the presence or absence of paraquat, buthionine sulfoximine, and oxidized glutathione. On medium with 150 mM NaCl the NaCI-tolerant cell line exhibited no reduction in growth, whereas a 96% reduction was observed in the control lhe. The NaCI-tolerant cell line that was grown on 150 mM NaCl exhibited significantly greater catalase (341 %), peroxidase (31 9%), glutathione reductase (287%), ascorbate peroxidase (450%), y-glutamylcysteine synthetase (224%), and glutathione Stransferase (500%) activities than the intolerant control. The NaCItolerant cell line had a significantly lower dehydroascorbic acid/ascorbic acid ratio. Paraquat reduced growth by 20 and 53.7%, respectively, in the NaCI-tolerant and control cell line. The NaCI-tolerant cell line also showed a slight tolerance to buthionine sulfoximine. In the buthionine sulfoximine experiments reduced glutathione restored growth in both cell lines, whereas oxidized glutathione restored growth only in the NaCI-tolerant cell line. These data indicate that the NaCI-tolerant cell line exhibited a cross-tolerance to a variety of stress variables and had a more active ascorbate-glutathione cycle.When plants are subjected to environmental stress, the balance between the production of reactive O, species and the quenching activity of antioxidants is upset, often resulting in oxidative damage (Harper and Harvey, 1978;

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The role of abscisic acid (ABA) in the signal transduction pathway associated with NaCl-induced up-regulation of antioxidant enzyme activity was examined in a NaCl-tolerant cotton callus cell line treated with NaCl, ABA, paraquat, or H2O2 in the presence and absence or fluridone, an inhibitor of terpene, and therefore, ABA synthesis. Treatment with NaCl resulted in a rapid increase (within 30 minutes) in the ABA levels of the callus tissue, and the NaCl, ABA, and paraquat treatments induced rapid increases in the activities of superoxide dismutase, catalase, peroxidase, and glutathione reductase. Pre-treatment with fluridone significantly suppressed the NaCl-induced increases, but only slightly delayed the increases in tissue subjected to exogenous ABA treatment. This implies that ABA is involved in the signal transduction pathway associated with the NaCl-induced up-regulation of these antioxidant enzymes. Pre-treatment with fluridone had no effect on the paraquat-induced increases, suggesting that these enzymes can also be up-regulated by a pathway other than the one mediated by ABA. Both the NaCl and paraquat treatments produced significant increases in the superoxide levels within the callus, but the increase resulting from the paraquat treatment was significantly higher than the increase resulting from the NaCl treatment. These data suggest that NaCl stress results in the production of reactive oxygen intermediates (ROI) which signals the induction of an ABA-dependent signaling pathway. The production of very high levels of ROI, such as those that occur with paraquat treatment or perhaps during periods of prolonged or extreme stress, may induce an ABA-independent signaling pathway.

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