UV light selectively coinduces supply pathways from primary metabolism andflavonoid secondary product formation in parsley

The UV light-induced synthesis of UV-protective flavonoids diverts substant ial amounts of substrates from primary metabolism into secondary product fo rmation and thus causes major perturbations of the cellular homeostasis, Re sults from this study show that the mRNAs encoding representative enzymes f rom various supply pathways are coinduced in UV-irradiated parsley cells (P etroselinum crispum) with two mRNAs of flavonoid glycoside biosynthesis, en coding phenylalanine ammonia-lyase and chalcone synthase. Strong induction was observed for mRNAs encoding glucose 6-phosphate dehydrogenase (carbohyd rate metabolism, providing substrates for the shikimate pathway), 3-deoxyar abinoheptulosonate 7-phosphate synthase (shikimate pathway, yielding phenyl alanine), and acyl-CoA oxidase (fatty acid degradation, yielding acetyl-CoA ), and moderate induction for an mRNA encoding S-adenosyl-homocysteine hydr olase (activated methyl cycle, yielding S-adenosyl-methionine for B-ring me thylation). Ten arbitrarily selected mRNAs representing various unrelated m etabolic activities remained unaffected. Comparative analysis of acyl-CoA o xidase and chalcone synthase with respect to mRNA expression modes and gene promoter structure and function revealed close similarities. These results indicate a fine-tuned regulatory network integrating those functionally re lated pathways of primary and secondary metabolism that are specifically re quired for protective adaptation to UV irradiation. Although the response o f parsley cells to UV light is considerably broader than previously assumed , it contrasts greatly with the extensive metabolic reprogramming observed previously in elicitor-treated or fungus-infected cells.