The involvement of photomorphogenic photoreceptors in anthocyanin synthesis was investigated in apple fruits under UV light from 280 to 320 nm (UV-B) and red light (R). Short-term R treatment was ineffective in the induction of anthocyanin synthesis but the involvement of phytochrome was indicated by the results of long-term irradiation (18 h) with R. The inductive effect of 18 h UV-B on anthocyanin synthesis was stimulated synergistically by subsequent irradiation with R for 15 min, and the R, far-red light (FR) photorevesibility of this effect indicated the involvement of phytochrome in this synergism. The effect of UV-B on anthocyanin synthesis was not influenced by subsequent irradiation with FR, suggesting that the effect of UV-B was independent of phytochrome, and that a specific photoreceptor for UV-B was involved. When R was given simultaneously with UV-B (18 h), anthocyanin was synthesized at a much higher rate than it was after sequential irradiation with UV-B and R. Photosynthesis was shown to be involved inthis synergistic increase in the synthesis of anthocyanin, although the involvement of phytochrome in the expression of this response, at least in part, was suggested by a reduction in the rate of anthocyanin synthesis by FR.
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