Light-induced Synthesis of Anthocyanin in Carrot Cells in Suspension

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Abstract
Time-courses of light-induced activities of enzymes relating to anthocyanin formation were studied. Phenylalanine ammonia-lyase (PAL), 4-cumarate CoA ligase (4CL) and cinnamate-4-hydroxylase (C4H) (group 1 enzymes) and chalcone synthase (CHS) and chalcone-flavanone isomerase (CHFI) (group 2 enzymes), were studied in carrot suspension cells which were irradiated 5 d after transfer to a 2,4-dichlorophenoxyacetic acid (2,4-D)-free medium in the dark. Time-courses of group 1 enzymes showed two peaks (fast and slow) with the slow peak increasing almost parallel to anthocyanin accumulation. Time-courses of group 2 enzymes showed one peak corresponding to the slow peak of group 1. From the inhibitor experiment, the fast peak also corresponded to the activity of the newly synthesized enzyme. From the initial phase of the time-courses, enzymes belonging to group 1 always induced more rapidly than those of group 2, and their induction was co-operative. However, once anthocyanin synthesis was induced by light, neither addition of 2,4-D nor transfer to darkness could prohibit anthocyanin synthesis completely. Addition of 2,4-D in the dark completely suppressed anthocyanin synthesis within 1 d and the activity of CHS also disappeared within 1 d. These results are explained by a previous hypothesis (Takeda, 1988) that 2,4-D induces the state change of cells.