CHANGES IN THE AMOUNTS OF THE NAD-DEPENDENT SORBITOL DEHYDROGENASE AND ITS INVOLVEMENT IN THE DEVELOPMENT OF APPLE FRUIT

Seasonal changes in the amounts of the NAD-dependent sorbitol dehydrog enase (NAD-SDH) (enzyme code, 1.1.1.14) protein in developing apple (M alus pumila Mill var. domestica Schneid) fruit were determined by immu noblotting analysis, The amounts of the enzyme protein were very low i n young fruit and rose as fruit matured, Tile weak correlation between enzyme protein and NAD-SDH activity and also the changes in NAD-SDH s pecific activity suggested that there could be posttranslational modif ication to the pre-existing enzyme or isoenzyme(s) of NAD-SDH, The cha nges in the amounts of NAD-SDH protein did not show the same pattern a s those in relative growth rate, which is used to express sink activit y, especially in young fruit, The role of NAD-SDH on sink activity in apple fruit, therefore, could not be explained simply by the amount an d activity of the enzyme. In young fruit, it seems that enzymes other than NAD-SDH would be more directly related with fruit growth.