Involvement of phytochrome and a blue light photoreceptor in UV-B induced flavonoid synthesis in parsley (Petroselinum hortense Hoffm.) cell suspension cultures.

Flavonoid synthesis in cell suspension cultures of parsley (Petroselinum hortense Hoffm.) occurs only after irradiation with ultraviolet light (UV), mainly from the UV-B (280-320 nm) spectral range. However, it is also controlled by phytochrome. A Pfr/Ptot ratio of approximately 20% is sufficient for a maximum phytochrome response as induced by pulse irradiation. Continuous red and far red light, as well as blue light, given after UV, are more effective than pulse irradiations. The response to blue light is considerably greater than that to red and far red light. Continuous red and blue light treatments can be substituted for by multiple pulses and can thus probably be ascribed to a multible induction effect. Continuous irradiations with red, far red and blue light also increase the UV-induced flavonoid synthesis if given before UV. The data indicate that besides phytochrome a separate blue light photoreceptor is involved in the regulation of the UV-induced flavonoid synthesis. This blue light receptor seems to require the presence of Pfr in order to be fully effective.