Signal transduction in the light regulation of the flavonoid biosynthetic pathway in Arabidopsis
The aim of this project was to investigate blue and UV light signal transduction in the induction of the genes encoding the flavonoid biosynthetic enzymes phenylalanine ammonia lyase (PAL) and chalcone synthase (CHS) in Arabidopsis cell culture. First, the induction of the flavonoid biosynthetic pathway was characterised in the cell culture. PAL and CHS transcripts accumulated transiently over a few hours in response to blue/UVA, UVA and UVB light. The transient light induction of PAL and CHS gene expression resembles that found in whole Arabidopsis plants. In addition, flavonol accumulation was demonstrated in response to blue and UVB light, showing that light treatment of the cell culture leads not only to PAL and CHS gene expression but also to activation of the biosynthetic pathway ultimately resulting in the production of flavonoids. Pharmacological inhibitors were used to investigate the role of anion channels in the signal transduction pathways leading to PAL and CHS gene expression. The anion channel inhibitor anthracene-9-carboxylate was found to inhibit the blue/UVA, UVA and UVB light induction of PAL and CHS and had no effect on control gene inductions, suggesting a possible role for anion channel activity in the signal transduction pathways. Attempts were made to measure any light induced changes in extracellular chloride concentration using a chloride selective electrode inserted into the cell culture. No change in chloride concentration was detected. Previous pharmacological studies had suggested a requirement for calcium channels and pumps in the induction of PAL and CHS (e.g. Christie and Jenkins, 1996). To enable direct measurement of light induced changes in cytosolic calcium concentration, aequorin expressing cell cultures were produced. High fluence rate UVA light treatment induced an apparent transient increase in cytosolic calcium concentration in the cell cultures, but this did not appear to relate to PAL and CHS gene expression.