PAL activity in ‘Golden Delicious’ apple peels increased rapidly and reached a peak at 37 DAFB, but then decreased to a very low level (Fig. 5A). Exogenous CA treatment did not affect the trend, butsignificantly stimulated the peak on the 7th day after CA applica-tion. The enzyme activity in the CA treatment was 20% higher than that of the control (P < 0.05). The difference of PAL activity at 37DAFB may be related to russet formation.C4H activity in ‘Golden Delicious’ apple peels also showed asimilar pattern, increased in the first 14 days and then decreased(Fig. 5B). Exogenous CA treatment did not affect the tendency butsignificantly promote the C4H activity in the first 14 days (P < 0.05).The mean of C4H activities of the CA treatment in the first three weeks was 20% higher than that of the control.