Two cultivars of peanut (Arachis hypogaea L.) which were designated as resistant (Florispan) and sensitive (Gazipasa) according to their growth retardation under drought stress conditions were compared for their oxidative damage and antioxidant responses. Sixteen days-old peanut seedlings were subjected to PEG-6000 solutions of two different osmotic potentials; -0.4 and -0.8 MPa, and various growth parameters, photosystem II activity, changes in malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ) and proline levels, activities of ascorbate peroxidase (APX), catalase (CAT), peroxidase (POX) and gluthatione reductase (GR) enzymes were determined. Both cultivars exhibited water deficit at -0.8 MPa osmotic potential of PEG-6000 and H 2 O 2 levels significantly increased during exposure to -0.4 MPa osmotic potential. However, H 2 O 2 levels were under control in both cultivars at exposure to -0.8 MPa osmotic potential. Significant proline accumulation was observed in the tissues of cv. Florispan at -0.8 MPa osmotic potential, whereas proline accumulation did not appear to be an essential part of the protection mechanism against drought in cv. Gazipasa. No significant variation in chlorophyll fluorescence values were detected in neither of the cultivars. Enzyme activity measurements revealed that Gazipasa copes well with lesser magnitudes of drought stress by increasing the activity of mainly APX, and during harsh stress conditions, only APX maintains its activity in the tissues. In cultivar Florispan, GR activity appears to take role in lesser magnitudes of drought stress, whereas CAT and APX activities appear to be very crucial antioxidative defenses during intense stress conditions. The results indicate that, the level of proline and activities of the enzymes CAT and APX are important mechanisms for the maintenance of drought tolerance in peanut plants.
In this study, the effects of long-term NaCl treatment were investigated in two cultivars of peanut designated as drought-resistant and drought-sensitive. Growth parameters, changes in the concentrations of MDA, H2O2 and proline, and the activities of antioxidant enzymes were determined under salinity stress. Growth parameters indicated the superiority of cv. Florispan to cv. Gazipa?a under milder salinity stress treatment. However, comparative analysis of the two cultivars showed that MDA, H2O2, ion leakage levels and photosystem II activities were not significantly different, except for the proline activity, which increased only in Florispan leaf tissues under 100 mM salt treatment. Among the processes that govern the tolerance in peanut tissues, proline level and the activity of glutathione reductase (GR) appeared to be only components that play an important part in salt stress protection.
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