Production of value-added vegetables by applying environmental stresses to roots in soil-less culture

Abstract

In the root zone of the soil-less culture, stress conditions such as low temperature, drought and high salinity can be easily introduced and controlled by applying physical and chemical characteristics of water. These stress conditions in the root zone cause depres-sions in root absorption and leaf photosynthesis and resultantly bring osmotic stress and oxidative stress in the plant body. The osmotic stress and the oxidative stress can induce the respective plant adaptive functions of osmotic adjustment and antioxidation. These plant functions can be expected to bring high quality and value-added vegetables enriched with sugars, functional amino acids, antioxidants etc., if the induced stresses are not so serious that the stress damages are not fatal without the extreme depression in growth. In this paper, two examples of the short term stress application only to roots for production of value-added vegetables are demonstrated. By the one week application of low temperature (5℃) stress only to roots of spinach plants (Spinacia oleracea L.), sugars, ascorbic acid and Fe2+ were significantly enriched in leaves. Furthermore, concentrations of harmful substances of NO3- and oxalic acid were extremely decreased. The two weeks salt stress treatment to roots of tomato plants (Lycopersicon esculentum Mill.) by applying the Muroto deep seawater at the stage of rapid fruit growth induced the osmotic adjustment and the antioxidation, which brought high quality tomatoes enriched with sugar, minerals, functional amino acids and good flavour without occurrence of extremely small-sized fruits and blossom-end rot. These verify that the short term stress application only to roots in the soil-less culture is reliable for production of high quality and value-added vegetables.