SUGAR CONTENT, COMPARTMENTATION, AND EFFLUX IN STRAWBERRY TISSUE

Using the compartmental analysis method, the distribution of sucrose, glucose, and fructose and their efflux from the free space, cytoplasm, and vacuole were determined in Nyoho strawberries (Fragaria x ananassa Duch.) picked 25 or 35 days after pollination (DAP). At both stages, >70 % of total sugar accumulated in the vacuole. Concentration of sugar in the free space increased from 167 mm in fruit at 25 DAP to 217 mm at 35 DAP, whereas that within the cell (cytoplasm + vacuole) increased from 233 to 352 mm. Permeability of the plasma membrane to sucrose, glucose, and fructose was higher than that of the tonoplast and, except for that of fructose, the permeability of the plasma membrane to sugars increased with fruit maturation. ABA at 10(-5) m compared to 10(-4) m restricted the release of all sugars from fruit discs and was due mainly to reduced efflux across the plasma membrane rather than the tonoplast. Thus ABA may stimulate the accumulation of sugars in fruit flesh by restricting their efflux. Chemical name used: abscisic acid (ABA).