The substitution of far-red for the first six hours of a prolonged irradiation with red light resulted in a large increase in anthocyanin yield, which was greater than the combined yields from far-red and red when the two treatments were given separately. When intermittent far-red irradiation was followed by a single short exposure to red, a considerable amount of anthocyanin was formed, although each treatment given separately had little effect. Four hours continuous far-red alone yielded some anthocyanin and also resulted in a further large increase in the effect of a short red treatment; this terminal red effect was fully reversible by a subsequent brief exposure to far-red. It is concluded that at least two photochemical reactions are involved in the responses to red and far-red, the first leading to the formation of substrate(s) used in the second reaction.
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