Effects of environmental stresses and abscisic acid on sorbitol-6-phosphate dehydrogenase expression in rosaceae fruit trees

Sorbitol plays an important role in carbohydrate translocation in Rosaceae fruit trees such as apple, pear, and peach and may also contribute to the stress response as a compatible solute. Leaf disc experiments showed enhanced sorbitol accumulation under salt, osmotic, and low-temperature stresses. Northern blot analysis indicated a higher level of mRNA encoding sorbitol-6-phosphate dehydro-genase (S6PDH), a key enzyme in sorbitol biosynthesis, under stress conditions. Thus, sorbitol accumulation under stress may reflect an increase in sorbitol biosynthesis related to expression of the S6PDH gene. Abscisic acid (ABA) also increased in apple leaves under low-temperature conditions. Further investigation revealed that the addition of ABA enhanced S6PDH expression in apple leaves, indicating that S6PDH is an ABA-inducible gene. These results suggest that ABA-mediated S6PDH plays a role in sorbitol biosynthesis in various stress responses and is involved in photo-synthate translocation.