Changes in amylose, amylopectin and total starch content in jonagold apple fruit during growth and maturation

摘要

Total starch, amylose and amylopectin concentrations were measured in Jonagold apple Malus domestica Borkh. fruit from early June till full maturation in 1995, 1996 and 1997. Ten fruits, selected for their approximate identical size, were picked regularly. After preparation of samples, 200 #mu#l of I2-KI were added and absorbance was measured at 530 for Amylose (AM) and 606 nm for Amylopectin (AP). Total starch, amylose and amylopectin concentrations were calculated using equations derived by Magel (1991). From end of Augustus, starch iodine tests were conducted on the same ten selected fruits. Troughout the season, the diameter of 50 labelled fruits was also regularly measured. Total starch accumulation started seriously in fruitlets only as their mean size reached more than 20 mm. Its concentration reached more than 120 mg/g of dry matter when fruits were 50 mm at mid of July. In young fruitlets, Amylopectin was the most important component; the accumulation of Amylose began later and presented a lower rate. Proportions of AM and AP stayed quite constant (40/60) between august and mid of september. During the two latest maturation weeks, Amylose degraded more quickly than amylopectin. Initiation of total starch accumulation appeared more than 15 days later in 1996 compared with 1997 showing flowering dates influences. Only 3 days separated 1996 and 1997 Starch Index curves, indicating no proportional correspondance between flowering date and maturity date. Regression coefficients between Starch Index and Total starch, Amylose or Amylopectin were all higher than 0.97. Implications for fruit growth as well as for harvest are discussed.