Soluble sugar and organic acid contents and the occurrence and potential role of phosphoenolpyruvate carboxykinase (PEPCK) (Ribes grossularia L.)

Changes in carbohydrate and organic acid contents, and the occurrence and potential role of phosphoenolpyruvate carboxykinase (PEPCK) were investigated in gooseberry fruit (Ribes grossularia L., cv. White Smith), in 2006, in central Italy.The concentrations of glucose, fructose, and sucrose (mg g-1 FW) were relatively low up to 60 d after full bloom (DAFB), with glucose and fructose levels being higher than that of sucrose. All then increased up to harvest (approx. 110 DAFB), and sucrose became the most abundant soluble sugar. Malate and citrate concentrations (mg g-1 FW) and contents per fruit (mg fruit-1) increased up to 70 - 80 DAFB (malate up to approx. 70 DAFB and citrate up to approx. 80 DAFB) then decreased. The level of PEPCK was determined using both western blotting and enzyme activity measurements. PEPCK increased during fruit ripening and was most abundant when the malate and citrate contents decreased. The results are consistent with PEPCK playing a role in the catabolism of malate and citrate in gooseberry flesh during ripening.