Sebnem Ellialtioglu

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

Summary 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.

Antioxidative enzyme activity, lipid peroxidation, and proline accumulation in the callus tissues of salt and drought tolerant and sensitive pumpkin genotypes under chilling stress

In this study, the effects of chilling stress were studied on 2 salt- and drought-tolerant and 2 sensitive pumpkin genotypes in callus culture. Growth inhibition occurred in the callus tissues when exposed to 4°C for 8 days. The tolerant genotypes showed lower increase in lipid peroxidation and a greater increase in superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase than the tolerant genotypes under stress conditions. The proline, glucose, and fructose contents continued to increase with progression in the chilling in the pumpkin genotypes. However, this increase was more significant in the tolerant genotypes than in the sensitive ones. These results indicate that chilling stress leads to the production of reactive oxygen radicals, resulting in increased lipid peroxidation and oxidative stress in pumpkin genotypes. The increase of antioxidant enzyme activities is associated with a tolerance to chilling stress.

Antioxidant Enzyme Activities and Abiotic Stress Tolerance Relationship in Vegetable Crops

Climatic changes can cause serious reductions in yield and crop quality. Under the threat of climatic changes, one of the precautions to cope is selection and development of resist‐ ant vegetable genotypes to abiotic stresses. Several physiological and biochemical reac‐ tions and different tolerance levels can occur according to plant species. When plants are subjected to environmental stresses such as salinity, drought, temperature extremes, her‐ bicide treatment and mineral deficiency, the balance between the production of reactive oxygen species (ROS) and the quenching activity of antioxidants is upset, often resulting in oxidative damage. Since activated oxygen species can disrupt normal metabolism through oxidative damage to lipids, protein and nucleic acids, plants possess a number of antioxidant enzymes that protect them from these cytotoxic effects. To control the level of ROS and to protect cells under stress conditions, plant tissues contain several enzymes for scavenging ROS. The high levels of antioxidative enzyme activities were determined in the tolerant genotypes of tomatoes, eggplant, peppers, cucumbers, melons, squash, beans, okra, etc. to several abiotic stress factors. Both the whole plant and in vitro callus culture experiments gave similar results. Antioxidant enzymes can be useful for screen‐ ing to determine the tolerant and sensitive plant genotypes against abiotic stresses.