4. Discussion
Our results show that maturity/ripening related fruit characteristics were not significantly influenced by the different treatments, while the accumulation of antocyanin and blush was clearly stimulated by ethephon and the onset of anthocyanin accumulation and blush was clearly delayed about2 weeks by ABG (Fig. 1a and b and Table 1). This indicated that anthocyanin formation in apple skin in not just simply a ripening-related phenomenon. Anthocyanin formation is apparently regulated by both the developmental signals (non-ethylene components) and ethylene signaling. We observed that the changes in the potential of fruit to accumulate anthocyanin and blush started at a certain stage of development, about 2-3 weeks before maturity in ass treatments, except for the ABG treatment in which it started about 2 weeks later (Fig. 1a and b). This is an indication that under normal developmental conditions, ethylene signaling in the apple skin ins limiting foranthocyanin accumulation. We postulate that ABG may suppress the expression of the gene(s) related to anthocyanin biosynthesis by inhibiting the accumulation of the trigger. Ethylene. Once the endogenous ethylene reaches a critical level, it will trigger the gene (s) related to anthocyanin biosynthesis. In the ethephon-treated fruit, the transition to fast anthocyanin accumulation occurred at the same time as in untreated fruit (Fig. 1b). Also, ethephon application at mid-season did not induce anthocyanin formation until shortly before maturation (Ju et al., 1995). This suggests that the onset of fruit maturation results in a change in sensitivity and responsiveness of apples to ethylene (Firn, 1986). Our data support the suggestion of Murphey and Dilley (1988) that enhancement of anthocyanin biosynthesis may require only a brief exposure to ethylene that may be insufficient to affect other fruit ripening characteristics.