Application of Temperature Stress to Root Zone of Spinach II. Effect of the High Temperature Pre-Treatment on Quality

Abstract

Roots of spinach plants (Spinacia oleracea L.) were exposed to temperature of 10°C, 15°C and 30°C to induce the effect of the moderate stress with low and high root temperatures, respectively. The excessive growth depression and the consumption of electric energy for the root zone cooling are the main consideration to apply moderately low temperature to roots of spinach for induction of adaptive functions of osmoregulation and antioxidation, where enrichment of healthful substances and reduction of harmful substances were expected. Spinach plants were grown in the soil-less culture system, where the temperature of the nutrient solution in the root zone was set in the four different temperature regimes during two weeks before the harvest (i.e. two weeks 20°C with no temperature stresses (20°C), two weeks 10°C with the moderate low temperature stress (10°C), the first week 30°C and the second week 15°C (30°C/15°C), and the first week 30°C and the second week 10°C (30°C/10°C). Absorption depression in roots and adaptive functions of osmoregulation and antioxidation were induced by the combination of the one week treatment with a moderately high root temperature of 30°C and the one week treatment with a moderately low root temperature of 10°C (30°C/10°C), while the two weeks treatment with a moderately low root temperature of 10°C induced no significant adaptive functions of osmoregulation and antioxidation. The treatment of 30°C/10°C only enabled to produce value-added spinach shoots with high content of healthful substances such as sugars, Fe²⁺, ASA and SOD and with low content of harmful substances such as NO₃⁻ and oxalic acid.