Sebnem Kusvuran

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.

Citrulline is an important biochemical indicator in tolerance to saline and drought stresses in melon.

Salt- and drought-induced alterations in citrulline were assessed in 4 local melon genotypes, 2 sensitive (CU-52, CU-94) and 2 tolerant (CU-196, CU-280), grown in vermiculite in a growth chamber. Salt and drought stresses were started using 30-day-old plants, with 250 mM NaCI and 45 mM PEG (−1.0 MPa) and continued for 12 days. After 12 days under salt and drought conditions, the citrulline contents were increased in the tolerant CU 196 to 25.10 μmol gDW−1 and 24.10 μmol gDW−1 for salt and drought stresses, respectively. However, the citrulline contents of the sensitive CU-52 were 11.68 μmol gDW−1 and 11.76 μmol gDW−1 for salt and drought, respectively. The striking alteration was obtained in the citrulline accumulation. The tolerant melons accumulated 2 times more citrulline than the sensitive melons. For assessing or screening melon genotypes in a large number of accessions or breeding lines for their tolerance to salinity and drought during their young plant stage, the amount of citrulline accumulation in response to the given treatments might be considered as a novel biochemical indicator of interest in early selection studies.

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.

The defensive role of silicon in wheat against stress conditions induced by drought, salinity or cadmium

In the crust of earth, silicon (Si) is one of the two major elements. For plant growth and development, importance of Si remains controversial due to the widely differences in ability of plants to take up this element. In this paper, pot experiments were done to study Si roles in improving salt, drought or cadmium (Cd) stress tolerance in wheat. Up to full emergence, all pots were watered at 100% field capacity (FC) every other day with nutrient solution without any treatments. Fifteen days after sowing, pots were divided into four plots, each with 40 pots for no stress (control) and three stress treatments; drought (50% FC), salinity (200 mM NaCl) and cadmium (2 mM Cd). For all plots, Si was applied at four levels (0, 2, 4 and 6 mM). Under no stress condition, Si applications increased Si content and improved growth as a result of reduced electrolyte leakage (EL), malondialdehyde (MDA) and Na+ contents. Under stress conditions, Si supplementation conferred higher growth, gas exchange, tissue water and membranes stabilities, and K+ content, and had limited MDA and Na+ contents and EL compared to those obtained without Si. Compared to those without Si, enzyme (e.g., superoxide dismutase, catalase and peroxidase) activity was improved by Si applications, which were linked with elevated antioxidants and osmoprotectants (e.g., free proline, soluble sugars, ascorbic acid and glutathione) contents, might providing antioxidant defense against abiotic stress in wheat. The level of 4 mM Si was most effective for mitigating the salt and drought stress conditions, while 6 mM Si level was most influentially for alleviating the Cd stress condition. These results suggest that Si is beneficial in remarkably affecting physiological phenomena and improving wheat growth under abiotic 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.

Effects of Different NaCl Doses on Morphological and Physiological Parameters in Mentha piperita L.

Salt stress is one of the most serious limiting factors for crop growth and production. This study was carried out to evaluate the effects of salt stress in four Mentha piperita L. varieties, in greenhouse conditions. The seedlings were irrigated with 1⁄2 Hoagland nutrition solutions. Following 10 d of growth in the pots, the seedlings were subjected to salt stress with different concentrations of NaCl (0, 50 and 100 mM, respectively). Responses of the mint varieties to salt stress were evaluated using some plant growth and physiological parameters, such as plant height, root length, shoot and root fresh and dry weight, and ion concentrations in leaves, such as Na, K, Ca and Cl. Salt stress caused reduction in physiological parameters. However, this reduction was significant at 100 mM NaCl compared to 50 mM NaCl. These two concentrations of NaCl increased Na and Cl contents in leaves. However, K and Ca contents were decreased with salinity. The results showed that Mentha piperita cv. Sewiss and Granada were found more tolerant to salt stress than cv. Marokko and Citaro.