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Antioxidant Response to Salt Stress During Fiber Development in Cotton Ovules
Satyendra N. Rajguru, Stephen W. Banks, Dalton R. Gossett, M. Cran Lucas, Tolvert E. Fowler, Jr., and Eddie P. Millhollon
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Ovules from flowers were removed 2 days post anthesis from greenhouse-grown plants of the salt-tolerant cotton (Gossypium hirsutum L.) cultivar 'Acala 1517-88' and the salt-sensitive cotton cultivars: 'Deltapine 50', 'MAR-LBCBHGDPIS-1-91', and 'Coker 312'. The ovules were grown in culture media amended with either 0 mM (control conditions) or 100 mM (stress conditions) NaCl and analyzed at 24 days post anthesis for differences in ovule fresh weights and antioxidant enzyme activities. Salt treatment reduced ovule fresh weight in all cultivars except Acala 1517-88. Superoxide dismutase activity increased under salt treatment in Acala 1517- 88 and MAR-LBCBHGDPIS-1-91, but not in Coker 312 or Deltapine 50. Catalase activity was constitutively high in Acala 1517-88, and NaCl-induced changes were recorded in MAR-LBCBHGDPIS-1-91 and Coker 312, but not in Deltapine 50. Glutathione reductase activity was constitutively high in Acala 1517-88, increased significantly in MAR-LBCBHGDPIS-1-91 and Coker 312 under NaCl stress, and decreased significantly in Deltapine 50 ovules subjected to a high concentration of NaCl. Under stress conditions, peroxidase activity increased significantly in MAR-LBCBHGDPIS-1-91 and Acala 1517-88 and decreased significantly in Coker 312 and Deltapine 50. High constitutive levels of ascorbate peroxidase activity were observed in Acala 1517-88 and Deltapine 50. The activity of this enzyme increased in MAR-LBCBHGDPIS-1-91 and Coker 312 ovules subjected to NaCl stress. Glutathione-S-transferase activity significantly increased in all the cultivars treated with NaCl. These findings indicate that ovules from the more salt-tolerant cultivar did not exhibit a reduction in growth when subjected to NaCl stress and furthermore suggest this variation may be partially due to the varietal differences in the activities of the antioxidant enzymes.