Carbohydrate composition and sucrose-metabolizing enzyme activities of hydroponic tomato fruit with salts added to nutrient solutions

Abstract

To explore the effect of adding different salts to a nutrient solution (NaCl, KCl, CaCl2 or CaSO4·2H2O, the electric conductivity (EC) was controlled at 0.40 S·m-1) on carbohydrate composition and sucrose-metabolizing related enzyme activities of hydroponic tomato fruit during fruit development, the experimental design was totally randomized block, and this experiment cultivated Lycopersicon esculentum 'Fentailang 2' using the nutrient film technique (NFT), and twelve tomato plants were labeled with good growth in every treatment, one tomato fruit with the same size and development degree was selected from the second layers at different growth stages, and content of carbohydrates and sucrose-metabolizing related enzyme activities in four parts of the tomato fruit (peel, pulp, dissepiment, and pectinic) were determined. Significant difference analysis was conducted by least significant difference (LSD). The main results included a total mass fraction of four sugars (sucrose, fructose, glucose, and starch) in each part of the fruit that were relatively high at the color conversion stage and had a slight decline after maturity. Fructose was the main sugar in four parts of the fruit at the stage of color conversion and ripening, and glucose was the main sugar at the green ripening stage. More sucrose (P < 0.05) was accumulated in each part at the color conversion stage, and a large amount (P < 0.05)of sucrose was decomposed at the ripening stage. During fruit ripening, except some treatments sucrose synthase (SS) and sucrose phosphate synthase (SPS) activities rose at the color conversion stage and fell at the ripening stage in the shape of an inverted V. For all treatments, acid invertase (AI) and neutral invertase (NI) activities in each part of ripened fruits were higher than those at the green ripening stage. Overall, adding NaCl or KCl to the nutrient solution could reduce (P < 0.05)the mass fraction of sucrose in the peel, pulp, and dissepiment of ripened fruits; adding different salts to the nutrient solution could inhibit the SS activity of the color conversion stage fruit in varying degrees and increase invertase activities of ripened fruit; adding KCl, CaCl2, or CaSO4·2H2O could increase (P < 0.05)the SPS activity of the color conversion stage fruit; and adding NaCl or KCl could change the original trend of SS activity in some parts of the fruit.