Visualization of sucrose distribution biosynthesized in vitro from external [1-¹³C]sorbitol in apple (Malus domestica) fruit utilizing MALDI-TOF MSI

To clarify the cause of graded distribution of sucrose in apple fruit flesh, a quarter cut of young apple fruit was cultured for 72 h on agar-solidified MS medium supplemented with 0.5 M [1-¹³C]sorbitol, with the longitudinal or horizontal cut face being attached with the medium, and distribution of ¹³C-labelled sucrose in a specimen obtained by slicing the fruit along with the cut face was visualized utilizing MALDI-TOF MSI. Heat map images on the distribution of the peaks of sorbitol containing ¹³C-atom indicated that external [1-¹³C]sorbitol had penetrated evenly into the tissue. In addition, the fact that a graded increase in the content of sucrose containing ¹³C-atom in a molecule was confirmed from the center to the outer areas of the fruit, indicates that sucrose biosynthetic ability might be higher at the cortex side of the receptacle than at the pith side in the fruit flesh.