Articles
CELLULAR COMPARTMENTATION AND TRANSPORT INTO TONOPLAST VESICLES OF SUGARS WITH RIPENING OF PEAR FRUIT
The products assimilated in leaves (source tissues) are translocated into fruit (sink tissues), and distributed finally into three parts of free space, cytoplasm and vacuole.
Most assimilated products accumulate in vacuoles as sugars (Yamaki and Ino, 1992). The compartmental analysis method (Macklon and Higinbotham, 1970; Pallaghy and Scott, 1969) is available for this purpose.
Some researchers have applied this method for solute content in the apoplast or vacuole of storage tissue (Damon et al., 1988; Hsu et al., 1984; Kowallick et al., 1980; Saftner et al., 1983).
It is considered that the active transport of sugar across the tonoplast functions actively to deposit much sugar in vacuoles and to reduce sugar in cytoplasm and free spaces, resultantly forming a gradient of sugar concentration between the cytoplasm or free spaces and sieve tubes.
Thus, the translocated sugar is supposed to be unloaded easily into fruit tissues to make the fruit sweeter.
With fruit ripening, pear fruit is well known to become sweeter and more juicy.
This may be due to the accumulation of more sugars in the cytoplasm and free spaces because the membrane becomes leaky and permeable to solutes, and also by the break down of starch to soluble sugars.
The present report deals with the alteration of distribution of sugar into vacuoles, cytoplasm and free spaces and of membrane permeability of sugars with pear ripening using a compartmental analysis method, and the transport system of sugars across tonoplast.