| The sand culture experiment was conducted with different levels of potassium in nutrient solution applied once at flowering phase / or fruit swelling period of tomato plant growth, in order to investigate their effects on the growth and development of tomato plants, leaves and fruit sugar accumulation and sucrose-metabolizing enzyme activity and fruit quality. There were three treatments: the modified Hoagland nutrient solution with the concentration of K~+ 6mmol/L was applied in control, while the nutrient solution with the concentration of K~+ 9mmol/L in treatment 1(T1) and the nutrient solution with the concentration of K~+ 12mmol/L in treatment 2(T2). The main results are as follows.1. Application of high potassium level promoted the contents of fructose, glucose, total soluble sugar and starch in tomato leaves. On the fifth day after application of high potassium level at flowering phase, fructose content in leaves of T1 and T2 were significantly increased by 21.9% and 16.4% compared with the control respectively. On the seventh day after treatments, compared with the control, the sucrose and total soluble sugars in leaves of T1 were significantly increased by 6.35% and 18.6%, while that of T2 were significantly increased by 21.7% and 21.4% respectively.2. Application of high potassium level increased sugar content in fruit. On the 60th day after application of high potassium level at flowering phase, the fruit fructose and glucose content of T1 were significantly higher than that of the control by 19.9% and 23.9% respectively , while that of T2 were increased significantly by 21.7% and 22.3% respectively. Compared with the control, T1 and T2 fruit total soluble sugar Levels were significantly increased by 19.1% and 18.4%, respectively. On the 25th day after application of high potassium level at fruit swelling period, T2 fruit fructose, glucose and total soluble sugar content were significantly increased by 11.1%, 20.3% and 19.8% compared with control respectively , while fruit total soluble sugar and glucose of T1 was significant increased by 13.6%和14.9% respectively. T1 and T2 fruit sucrose content was significantly 27.2% and 24.2% higher than that of the control, while starch content of T1 and T2 were significantly higher than that of the control by 64.2 % and 38.0% respectively.3. Application of high potassium level promoted the activities of sucrose metabolizing enzyme in tomato leaves and fruits. On the fifth day after application of high potassium level at flowering phase, the Sucrose Phosphate Synthase(SPS) activity in leaves of T1 and T2 was significantly12.9% and 14.4% higher than that of the control respectively. On the seventh day after application of high potassium level at flowering phase, the Acid Invertase (AI) and Neutral Invertase (NI) activity in leaves of T2 were significantly 52.5% and 32.5% higher than that of the control respectively, while the Sucrose Synthase (SS) activity in leaves of T1 and T2 were significantly 30.6% and 12.8% higher than that of the control. On the 60th day after application of high potassium level at flowering phase, AI and NI activities in fruit of T2 were significantly 24.9% and 13.8% higher than that of the control respectively, and the fruit SS activity of T1 and T2 were significantly higher than that of the control by 26.5% and 24.3% respectively. T1 and T2 fruit AI activities were significantly increased by 53.7% and 38.8% compared with control respectively on the 25th day after application of high potassium level at fruit swelling period. The fruit NI activity of T1 was significantly 17.2% higher than that of the control, while the fruit NI activity of T2 was not significant difference with the control. The fruit SPS activities of T1 and T2 were significantly 32.6% and 45.0% higher than that of the control, respectively.4. Application of high potassium level (K~+: 12mmol/L) with interval of 6 days significantly increased the level of tomato yield and quality. Tomato fruit weight and yield per plant were significantly increased by 20.0% and 31.8% compared with the control respectively. The fruit Vc, soluble sugar and organic acid contents were significantly 14.9%, 9.36% and 35.4%higher than that of the control, respectively.
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