Determination of anti-oxidant activities in some melon (Cucumis melo L.) varieties and cultivars under salt stress

The response of the antioxidant system to salt stress was studied in leaves of seedlings of four Turkish melon (Cucumis melo L.) varieties 'Besni', 'Yuva', 'Midyat' and 'Semame' and three melon cultivars 'Ananas', 'Galia C8' and 'Galia F1'. The anti-oxidant capability of plants was determined by measuring ascorbate peroxidase (APX) and glutathione reductase (GR) activities together with levels of the anti-oxidant, ascorbic acid (AA). Salt treatment increased APX activities in stress-tolerant 'Galia C8' and 'Galia F1' and in moderately tolerant 'Besni', 'Midyat' and 'Semame'. These increases were greater in salt-tolerant cultivars. On the other hand, salt treatment did not cause a significant increase in APX activity in the salt-sensitive cvs. 'Yuva' and Ananas'. GR activity increased in all varieties and cultivars grown under saline conditions compared to control plants. Increases in GR activities were higher in salt-tolerant and moderately-tolerant varieties than in salt-sensitive ones. Likewise, AA contents increased with salt treatment in all varieties and cultivars except the salt-sensitive 'Ananas'. The data indicate that melon seedlings respond to salt-induced oxidative stress by increasing both their enzymatic and non-enzymatic anti-oxidant defense systems. These increases were most clear in the salt-tolerant cultivars.