Short term applications of low and high temperature stresses to roots for high quality spinach (Spinacia oleracea L.)

Low temperature stress to roots causes a depression in root water absorption, and the resulting water deficit can induce the plant adaptive functions such as osmoregulation and antioxidation. Therefore, plant responses to the root low temperature stress can be expected to produce high quality vegetables with the higher concentrations of the healthful substances such as sugars and antioxidants and with the lower concentrations of the harmful substances such as NO3 - and oxalic acid. Two weeks treatment with the root low temperature stress of 10°C produced high quality spinach with the higher concentrations of sugar, ascorbic acid and Fe, and with the lower concentrations of NO3-and oxalic acid, whereas the longer stress treatment resulted in extremely depressed plant growth. Therefore the short term application of the low temperature stress combined with the short term pre-treatment with the high temperature of 30°C was examined, when the high temperature pre-treatment enhanced favorable effects of the short term low temperature stress. During ten days before the harvest, the high temperature pre-treatment of 30°C was applied for one day or three days, and following the high temperature pre-treatment, the low temperature stress of 10°C was applied for four days or seven days. The three days high temperature pretreatment followed by the seven days low temperature stress brought the highest quality with a slight depression in growth. This suggests that the short-term application of the low temperature stress to roots after the short-term high temperature pretreatment is applicable for value-added leafy vegetables.