Changes in activities of enzymes involved in flavonoid metabolism during the initiation and suppression of anthocyanin synthesis in carrot suspension cultures regulated by 2,4‐dichlorophenoxyacetic acid

Abstract

When anthocyanin synthesis was induced in cell suspension cultures of carrot (Daucus carota L. cv. Kurodagosun) by transfer to medium lacking 2,4‐dichlorophenoxyacetic acid (2,4‐D), phenylalanine ammonia‐lyase (PAL, EC 4.3.1.5), chalcone synthase (CHS, EC 6.‐.‐.‐), and chalcone‐flavanone isomerase (CHFI, EC 5.5.1.6) activities appeared, reaching maxima 6–7 days after transfer. The maximum specific activity of CHS was much lower than that of PAL or CHFI. In a medium containing 2,4‐D, no anthocyanin was synthesized, PAL and CHFI activities were suppressed and CHS activity could not be detected at all. The activities of PAL and CHS in cells cultured without 2,4‐D for 6 days began to decrease within 3–6 h of 2,4‐D addition. CHS activity was completely repressed 24–36 h after the addition, but CHFI activity was almost unchanged at this time. After culture without 2,4‐D for 6 days, cell suspensions were transferred to fresh media either lacking or containing 2,4‐D. After transfer, PAL increased in both media within 3 h, whereas CHS activity and anthocyanin accumulation were coordinated and both were completely regulated by 2,4‐D. Changes in CHS activity rather than PAL activity correlate with changes in anthocyanin accumulation under various culture conditions.