Photocontrol of Anthocyanin Synthesis

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Abstract
The spectral sensitivity and the irradiance dependence of anthocyanin synthesis, a high irradiance response, in cabbage (Brassica oleracea, cv. Red Acre) and tomato (Lycopersicon esculentum, cv. Beefsteak) seedlings exposed to continuous irradiation depend on the length of the exposure. In cabbage, blue and red are more effective than far red when the irradiations are shorter than 12 h and less effective than far red when the irradiations are longer than 12 h. The irradiance dependence is negligible under red and becomes evident under blue and far red red only for exposures longer than 12 h. Anthocyanin synthesis under intermittent light treatments, of efficiency comparable to that of continuous treatments, obeys the Bunsen-Roscoe reciprocity law and is a function of the dose (irradiance .times. time), rather than of the irradiance alone. The validity of the reciprocity relationships suggests that only 1 photoreceptor is responsible for the photocontrol of the response in the blue, red and far red spectral regions. The characteristics of the response suggest that the photoreceptor is phytochrome, at least in cabbage.