Production of high quality vegetable by applying low temperature stress to roots

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 high quality vegetables enriched in sugars and antioxidants, etc. However, there are difficulties in stable control of the stress treatment because of seasonal and daily changes in weather condition. A hydroponic system which can control the root zone temperature was newly developed, and low temperature stress treatment was applied only to roots for production of high quality vegetables. Spinach plants (Spinacia oleracea L.) were grown in the newly developed system, where the root zone temperature was controlled at a normal temperature of 20°C. Two weeks before the harvesting, the low temperature stress treatment with a root zone temperature of 5°C was applied for only one week. By the one week application of low temperature stress to roots, sugars, ascorbic acid and Fe²⁺ were significantly enriched in leaves. Furthermore, concentrations of NO₃^- and oxalic axid, which are harmful for human health, were extremely decreased. From these results, it was verified that the one week low temperature stress treatment only to roots is applicable for high quality vegetable production.