ACTIVITIES OF CHALCONE SYNTHASE AND UDPGAL - FLAVONOID-3-O-GLYCOSYLTRANSFERASE IN RELATION TO ANTHOCYANIN SYNTHESIS IN APPLE

The activities of two enzymes, chalcone synthase (CS) and UDPGal:flavo noid-3-o-glycosyltransferase (UFGalT), and their relationships with an thocyanin synthesis in apple peel, were studied in 3 years of experime nts. UFGalT activity was positively correlated with anthocyanin accumu lation during fruit maturation in both 'Delicious' and 'Rails' apples. Ethephon treatment at 110 days after full blossom (DAFB) increased UF GalT activity and also promoted anthocyanin formation. However, relati vely high UFGalT activity was detected in control fruit at 90 DAFB alt hough there was no anthocyanin in fruit peel. Also, when ethephon was applied at 70 DAFB, it induced high UFGalT activity and increased flav onoid accumulation without inducing anthocyanin formation at 90 DAFB. CS activity and flavonoid content were relatively high and constant fr om fruitlet to maturation stage. Fruit bagging suppressed accumulation of flavonoids and anthocyanins, but when the bags were removed at 110 DAFB, flavonoids and anthocyanins significantly increased by 130 DAFB . The data indicate that CS do not play a regulatory role in anthocyan in synthesis in apples exposed to light. UFGalT activity was correlate d with anthocyanin synthesis during fruit maturation but it is not the only regulatory enzyme in this process since this enzyme was also act ive at 90 DAFB when no anthocyanin was present. We conclude that UFGal T probably catalyzes both quercetin glycoside and anthocyanin formatio ns, and anthocyanin formation probably depends on cyanidin presence ra ther than on UFGalT activity. The controlling point in regulating anth ocyanin synthesis is likely to be located at the steps from dihydroque rcetin to the formation of cyanidin.