CHILLING STRESS EFFECT ON BIOCHEMICAL CHANGES IN CALLUS TISSUES OF MELON GENOTYPES DIFFERING IN SALT AND DROUGHT TOLERANCE

The effects of chilling stress were studied on 2 salt-and drought-tolerant (CU-159 and CU-196) and 2 sensitive (CU-40 and CU-252) melon genotypes under in vitro culture conditions. A growth inhibition was exposed in the callus tissues compared to the control group in all of the genotypes on day 4 and 8 of the chilling stress. The salt- and drought tolerant genotypes showed less of an increase in lipid peroxidation (MDA), and more of an increase in superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) under chilling stress. The amount of proline, glucose, and fructose increased in the callus tissues during the chilling stress. This increase was stronger in the salt-and drought-tolerant genotypes than in the sensitive ones. These results indicated a certain amount of increase in antioxidative stress enzymes in the callus tissues of 4 melon genotypes under chilling stress. The plants subjected to chilling stress showed that salt- and drought-tolerant melon genotypes were able to tolerate chilling stress, while the salt- and drought-sensitive melon genotypes did not. This may create significant protection mechanisms against reactive oxygen species in tolerant genotypes. Generally, the increase of antioxidant enzyme activity, proline, and carbohydrates are associated with a tolerance to chilling stress.