PJB-2016-300
DYNAMICS OF SUGAR-METABOLIC ENZYMES AND SUGARS ACCUMULATION DURING WATERMELON (CITRULLUS LANATUS) FRUIT DEVELOPMENT
HUIJUN ZHANG1* AND YU GE2
Abstract
We analyzed sugar accumulation and the activities of sugar-metabolic enzymes in ripening fruits of three cultivars of watermelon; a high-sugar type “w2”, a low-sugar type (“w1”), and their hybrid. In “w2”, the glucose and fructose contents were higher than the sucrose content in the earlier stage of fruit development, and fruit growth was accompanied by increases in glucose, fructose, and sucrose contents. The sucrose content increased substantially after 20 days after anthesis (DAA) and it was the main soluble sugar in mature fruit (sucrose:hexoses ratio, 0.71). In “W1”, the fructose and glucose contents were significantly higher than the sucrose content in mature fruit (sucrose:hexoses ratio, 0.25). Comparing the two parent cultivars, sucrose was the most important factor affecting the total sugar content in mature fruit, although glucose and fructose also contributed to total sugar contents. The fructose and glucose contents in the fruit of F1 were mid-way between those of their parents, while the sucrose content was closer to that of “W1” (sucrose:hexoses ratio in F1, 0.26). In the early stage of fruit development of “W2”, the activities of acid invertase and neutral invertase were higher than those of sucrose synthase and sucrose phosphate synthase. After 20 DAA, the acid invertase and neutral invertase activities decreased and those of sucrose synthase and sucrose phosphate synthase increased, leading to increased sucrose content. In “W1”, the activities of acid invertase and neutral invertase were higher than those of sucrose synthase and sucrose phosphate synthase at the early stage. The sucrose synthase and sucrose phosphate synthase activities were lower in “W1” than in “W2” at the later stages of fruit development. The patterns of sugar accumulation and sugar-metabolic enzyme activities during fruit development in F1 were similar to those in “W1”.
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