Induction of Anthocyanin Accumulation by Cytokinins in Arabidopsis thaliana

Arabidopsis thaliana plants treated with exogenous cytokinins accumulate anthocyanin pigments. We have characterized this response because it is potentially useful as a genetic marker for cytokinin responsiveness. Levels of mRNAs for four genes of the anthocyanin biosynthesis pathway, phenylalanine ammonia lyase 1 (PAL1), chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR) were shown to increase coordinately in response to benzyladenine (BA). However, nuclear run-on transcription experiments suggested that although CHS and DFR are controlled by BA at the transcriptional level, PAL1 and CHI are controlled by BA posttranscriptionally. CHS mRNA levels increased within 2 h of BA spray application, and peaked by 3 h. Levels of PAL1 mRNA did not increase within 6 h of BA spray. We also showed that PAL1, CHS, CHI, and DFR mRNA levels fluctuate during a 24-h period and appear to be controlled by a circadian clock. The relation between cytokinin regulation and light regulation of CHS gene transcription is discussed.