As for the mechanism of the enhancement of anthocyanin synthesis with UV light, UV irradiation has been reported to increase the phenylalanine ammonia-lyase (PAL) activity
that is involved in phenol synthesis in apple (Farager and Chalmers, 1977). The PAL activ-ity is controlled by phytochrome with a low ratio of red to far-red light (R/FR) suppressing PAL and reducing anthocyanin synthesis (Man-cinelli, 1985). Smart et al. (1988) have shown that R/FR ratio decreases under the canopy of
grape vine and that red light supplementation enhances the accumulation of anthocyanin in the berry skin. The involvement of UV-A-blue (cryptochrome) and UV-B receptors in the gene expression of PAL and chalcone synthase has also been demonstrated in several plant tissues and cells (Fuglevand et al., 1996; Takeda et al., 1997). In peach fruit, it is also likely that the light transduction pathways inducing the gene expression of these enzymes involved in the anthocyanin synthesis are mediated by these receptors. Detailed investigations on the action spectra in the UV region for anthocyanin
synthesis should be conducted to gain better understand the role of light in improving fruit coloration.