VARIATION IN CONCENTRATIONS OF PHLORHIZIN AND PHLORETIN IN APPLE FOLIAGE

It is impossible to determine the potential biological effects of the dihydrochalcone glycoside phloridzin and its hydrolysis product, phlor etin, in the foliage of apple trees, without a clear understanding of variation in their concentrations under field conditions. The data pre sented compare variation in phloridzin and phloretin concentrations am ong three leaf types (fruiting spurs, non-fruiting spurs and terminal shoots) on five apple cultivars (cvs Delicious, Golden Delicious, Stay man, Rome Beauty and Yorking) throughout the growing season. Phloridzi n concentrations decline as the season progresses, with both % dry wei ght of phloridzin in leaf tissue and the rate of seasonal decline vary ing among cultivars. Phloridzin concentrations do not vary among leaf types. Phloretin concentrations vary with cultivar and sampling date, with some variation among leaf types on cvs Delicious and Rome Beauty. That phloretin concentrations vary more than those of phloridzin sugg ests that there is variation at three levels in the activity of the en zyme system that hydrolyses phloridzin and phloretin; within trees, am ong cultivars and with date.