Applications of salt and drought stress on the antioxidative enzyme activities and malondialdehyde content in callus tissues of pumpkin genotypes

The responses to salt and drought stress of 4 pumpkin varieties (A-24, CU-7, Iskenderun-4, and AB-44) were investigated under in vitro culture conditions. Of the 4 pumpkin varieties, 2 were salt-sensitive and the other 2 were salt-tolerant. Growth inhibition in callus tissues was observed in media that contained 100 mM NaCl or 15% (w/v) of polyethylene glycol (PEG-6000) compared to the control in all of the varieties on the 4th and 8th day of the salt and drought stress. As it is known, the malondialdehyde measurement can show the amount of lipid peroxidation in the cell wall. In this study, the magnitude of cell wall damage (lipid peroxidation) was lower in the tolerant genotypes than in the sensitive ones. On the other hand, the pumpkin genotypes were more affected by salt stress than by drought stress. The amount of lipid peroxidation was higher in the salt-stressed calli than in those that were drought-stressed. Besides the MDA measurements, the antioxidant enzyme (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) activities were also investigated in the callus tissues of 4 pumpkin genotypes under salt and drought stress. The antioxidant enzyme activities showed differences among pumpkin genotypes.