Location: Healthy Processed Foods ResearchTitle: Is it a biological response or chemical process? Chemical and transcriptional regulation experiments probe the cause for the increased accumulation of chlorogenic acid (CGA) in carrot root slices exposed to UV-B light
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/22/2016
Publication Date: 4/2/2017
Citation: Bartley, G.E., Avena Bustillos, R.D., Du, W., Hidalgo, M., Cain, B.R., Breksa Iii, A.P. 2017. Is it a biological response or chemical process? Chemical and transcriptional regulation experiments probe the cause for the increased accumulation of chlorogenic acid (CGA) in carrot root slices exposed to UV-B light. [abstract].
Technical Abstract: We recently demonstrated that wounded carrot roots subjected to a brief UV-B light treatment accumulate large quantities of chlorogenic acid (CGA) in the treated tissues. Chlorogenic acid is an intermediate in the phenylpropanoid pathway and a potent anti-oxidant. Chemical analysis and real-time PCR were used to investigate whether the accumulation was a biological response or chemical process. For real-time PCR (RT-PCR) experiments, we analyzed the expression of a number of the structural genes in the core phenylpropanoid pathway (PAL: phenylalanine ammonia-lyase, C4H: trans-cinnamate 4-monooxygenase, 4CL: 4-coumarate: CoA ligase, HCT: hydroxycinnamoyl-CoA: shikimate/quinate hydroxycinnamoyltransferase, HQT: hydroxycinnamoyl CoA quinate transferase, and C3H: 4-coumarate3-hydroxylase CHS: Chalcone synthase, CHI: Chalcone isomerase) and the proposed regulators of these genes. Chemical analysis consisted of HPLC determinations of chlorogenic, caffeic, coumaric, and ferulic acids. Both analyses were conducted over a six-day period following treatment. The response in wounded plus UV-B treated carrots (treated) was compared to wounded carrots (untreated). The rate of chlorogenic acid accumulation was linear in the treated samples over the study period and by day six, the average chlorogenic acid concentration in the treated carrots was approximately six times greater than the concentration found in untreated samples and 55 times greater than the concentration at day zero. UV-B treatment also simulated the accumulation of caffeic, coumaric, and ferulic acids. RT-PCR experiments revealed that UV-B treatment first induces regulator genes DcHY5, DcMYB3-2 and DcMYB5 followed by induction of DcMYB1 and the downstream phenylpropanoid biosynthetic genes DcPAL1-4, DcC4H, DcC4L, DcHCT, DcHQT1-1, DcC3H1 and DcCHS2. Our results suggest that the enhanced biosynthesis and accumulation of chlorogenic acid resulting from UV-B treatment is a biological response.