Application of Temperature Stress to Roots of Spinach I. Effect of the Low Temperature Stress on Quality

In the soil-less culture, root zone environment can be easily modified to create stress conditions such as low and high temperatures, drought and high salinity by applying physical and chemical properties of water. Low temperature stress to plant body can induce adaptive functions in plant such as osmoregulation and antioxidation, which are expected to result in production of value-added vegetables enriched in sugars and antioxidants, etc. In this study, production of value-added vegetables was examined by applying low temperature stress only to roots in a soil-less culture. Spinach plants (Spinacia oleracea L. cv. Orai) were grown in a soil-less culture, where the root zone temperature was controlled at a normal temperature of 20°C. Two weeks before the harvest, the low temperature stress treatment with a root zone temperature of 5°C was applied for only one week. This low temperature stress to roots induced plant adaptive functions of osmoregulation and antioxidation, and healthful substances for human health such as sugars, ascorbic acid and Fe were significantly enriched in edible shoots. Furthermore, concentrations of nitrates and oxalic acid in shoots, which are harmful substances, were extremely decreased with depression in water and nutrient absorption by roots. These suggest that the only one week treatment with low temperature stress only to roots is applicable for production of value-added leafy vegetables.