Acclimation to root chilling increases sugar concentrations in tomato (Solanum lycopersicum L.) fruits

Sugar concentrations in tomato (Solanum lycopersicum L.) fruits increase under water or salt stress. Water stress can be induced by root chilling, but the relationship with fruit sugars has not been reported. To elucidate this relationship, we compared fruit sugar concentrations and other characteristics between tomato plants cultivated at two root temperatures (20 and 12 °C) using a nutrient-film technique during the spring-to-summer season (SS) and during two summer-to-winter seasons (SW) in a greenhouse in Morioka, Japan. The soluble solids, glucose, and fructose concentrations in tomato fruits increased similarly under root chilling at 12 °C without a significant effect on acidity in all experiments. However, the increase was greater in the SW treatment, where water stress was smaller than in the SS treatment based on the vapour-pressure deficit. Root chilling also increased the starch, sucrose, glucose, and fructose concentrations in the leaves. The photosynthetic CO2 exchange rate and stomatal conductance per unit leaf area were not significantly affected by root chilling, despite a marked decrease in leaf area. Root chilling increased fruit dry weight but decreased the dry weight of vegetative organs, especially leaves and roots. The root chilling-induced increase in soluble sugar concentrations was likely caused by sink limitations in the vegetative organs. Water stress did not contribute directly to this result, although it might have contributed to the decreased dry weights of leaves and roots. Root chilling appears to be an effective way to improve tomato fruit quality and avoids the disadvantages of other methods of increasing fruit sugar content.

► Root-chilling acclimation increased glucose and fructose contents in tomato fruits.
► Water stress did not help the root-chilling induced increase in the fruit sugars.
► Root chilling increased the fruit dry yield but decreased the leaf and root dry yields.
► The root-chilling tomato leaves accumulated glucose, fructose and starch.
► Root chilling did not inhibit the tomato photosynthesis.