salt-stress-induced changes in ascorbic acid content in tomato fruit on cultivar and cropping season

摘要

Salt stress has been applied recently to improve the quality of tomato fruit. However, there is little research on the changes in ascorbic acid content, an important antioxidant, in salt-stressed fruit. The aims of this study were to elucidate the changes in ascorbic acid (ASA) and dehydroascorbic acid (DHA) contents in fruits of salt-stressed plants, and to determine whether these changes depend on cultivars and the cropping season. Two tomato cultivars (Lycopersicon esculentum Mill): normal fruitedtype cv. House momotaro and cherry type cv. Mini carol, were grown in closed irrigation systems during spring-summer and autumn-winter seasons. Salt stress was applied by adding 25, 50, 75 and 100 mM NaCl to the nutrient solution. Here we show that ASAand DHA contents are not always increased by salt stress, and that the effect depends on the cultivars and the cropping seasons. In addition, in the spring-summer season, ASA content in cherry type cultivar was not related to the glucose content, which is a precursor of ASA. The lipid peroxidation as an indicator of oxidative damage was not changed by salt stress in the spring-summer season. These results suggest that salt-induced changes in ASA and DHA contents may have occurred by the protective mechanisms against oxidative stress, rather than the changes in the ASA precursor, but that these changes are subject to considerable variation depending on the cultivars and the cropping seasons.