Enzymes involved in flavonoid synthesis in parsley (Petroselinum nortenseHoffm.) cell suspension cultures are induced by light. It has been suggested that the regulation of the enzymes of phenylpropanoid metabolism (group 1) is independent of that of the enzymes of flavonoid synthesis proper (group 2) Hahl-brock, K., Ebel, J., Ortmann, R., Sutter, A., Wellmann, E., Grisebach, H.: Biochim. biophys. Acta (Amst.)244, 7–15 (1971). Phytochrome was demonstrated to be involved in the light effect controlling flavonoid synthesis. Phytochrome is only effective after a preceding irradiation with ultraviolet light (λmax<300 nm) Wellmann, E.: Planta (Berl.)101, 283–286 (1971). — In order to determine whether phytochrome affects phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), a group 1 enzyme, or exerts a general effect of all enzymes of the flavonoid pathway. PAL and two enzymes from group 2, chalcone-flavanone isomerase and UDP-apiose synthetase, were investigated. Under appropriate conditions of irradiation (low UV-dose with subsequent red/far-red pulses) both group 2 enzymes were shown to be controlled by phytochrome to the same extent as PAL. The UV-induced increase in activity of all three enzymes is reduced to about 70 by an irradiation for 10 min with far-red light. This far-red effect is fully reversible by a subsequent irradiation with 10 mith red light. There is no evidence for a rate limiting enzyme (or group of enzymes) involved in flavonoid formation with respect to phytochrome c
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