@ TAL may represent PAL with non-stringent substrate specificity (e.g. the maize PAL has TAL activity; Rosler et al, 1997).

Chalcone = 4,2',4',6'-tetrahydroxychalcone.

In Arabidopsis the order of light-induction of genes PAL1, CHS, CHI and DFR is the same as the order in flavonoid biosynthesis (PAL1 = phenylalanine ammonia-lyase 1; CHS = chalcone synthase (CS), CHI = chalcone isomerase, DFR = dihydroflavonol 4-reductase). These "early" genes appear to be coordinately regulated.

UV and blue light control the expression of flavonoid biosynthesis genes in a range of higher plants. In Arabidopsis both the UV-B and UV-A/blue phototransduction processes regulating the expression of CHS involve calcium, although the elevation of calcium is insufficient on its own to stimulate CHS expression. The UV-A/blue light induction of CHS does not appear to involve calmodulin whereas the UV-B response does. The UV-B and UV-A/blue light signaling pathways of Arabidopsis may be different from the phytochrome signal transduction pathway regulating CHS expression in other species (Christie and Jenkins, 1996). The UV-A/blue inductive pathway may involve the photoreceptor CRY1 (cryptochrome1) (Fuglevand et al, 1996). An anion-channel blocker inhibits anthocyanin accumulation induced by blue light in Arabidopsis, but apparently not by inhibiting induction of CHS, CHI or flavanone-3-hydroxylase proteins (Noh and Spalding, 1998). Plasma membrane redox activity, initiated by photoreception, is proposed to be coupled to the regulation of calcium release from an intracellular store, generating a calcium signal that is required to induce CHS expression in Arabidopsis suspension cultures (Long and Jenkins, 1998).

Christie JM, Jenkins GI 1996 Distinct UV-B and UV-A/blue light signal transduction pathways induce chalcone synthase gene expression in Arabidopsis cells. Plant Cell 8: 1555-1567.

Fuglevand G, Jackson JA, Jenkins GI 1996 UV-B, UV-A, and blue light signal transduction pathways interact synergistically to regulate chalcone synthase gene expression in Arabidopsis. Plant Cell 8: 2347-2357.

Long JC, Jenkins GI 1998 Involvement of plasma membrane redox activity and calcium homeostasis in the UV-B and UV-A/blue light induction of gene expression in Arabidopsis. Plant Cell 10: 2077-2086.

Noh B, Spalding EP 1998 Anion channels and the stimulation of anthocyanin accumulation by blue light in Arabidopsis seedlings. Plant Physiol. 116: 503-509.

Rosler J, Krekel F, Amrhein N, Schmid J 1997 Maize phenylalanine ammonia-lyase has tyrosine ammonia-lyase activity. Plant Physiol. 113: 175-179.