Effects of Extreme Root Restriction on the Nutritional and Flavor Quality, and Sucrose Metabolism of Tomato (Solanum lycopersicum L.)

Root restriction is suitable for horticultural soilless cultivation characterized by high efficiency and quality in the case of high density and low node order pinching. However, little research is available on the mechanism of root restriction improving the flavor and nutritional quality of tomatoes. We investigated the effects of Extreme Root Restriction (ERR, 750 mL/plant) on the content of metabolites, activity of enzymes, and gene expression level involving sucrose metabolism in different clusters of two tomato types. The fruit diameter and single fruit weight of common tomato at CIII were reduced by 5.6% and 14% under ERR, as a result, the fruit uniformity throughout the whole plant was improved. The ERR enhanced the accumulation of metabolites in tomato fruits, such as soluble sugars, amino acids, vitamin C, lycopene, and polyphenol, which was caused by ‘concentration effect’ that occurred with a reduction of fruit size. The activities of enzymes (SS, SPS, NI, AI) at CIII and CIV of cherry tomatoes increased by 3–4 folds under ERR. ERR enhanced accumulation of sucrose, glucose, and fructose in tomato fruits not only by modulating activities of metabolizing enzymes but also by inducing the expression of sucrose metabolism genes, including sucrose synthase genes (SS1, SS3–6) in common tomato, fructokinase genes (FKs), hexokinase genes (HKs), and sucrose phosphate synthase genes (SPSs), in cherry tomato. The above results are expected to provide a theoretical basis for root restriction cultivation techniques and practical guidance for high-quality tomato production in industrialized cultivation.