Multi-site modulation of flux during monolignol formation in loblolly pine (Pinus taeda).
Loblolly pine (Pinus taeda L.) cell suspension cultures secrete monolignols when placed in 8% sucrose/20 mM KI solution, and these were used to identify phenylpropanoid pathway flux-modulating steps. When cells were provided with increasing amounts of either phenylalanine (Phe) or cinnamic acid, cellular concentrations of immediate downstream products (cinnamic and p-coumaric acids, respectively) increased, whereas caffeic and ferulic acid pool sizes were essentially unaffected. Increasing Phe concentrations resulted in increased amounts of p-coumaryl alcohol relative to coniferyl alcohol. However, exogenously supplied cinnamic, p-coumaric, caffeic, and ferulic acids resulted only in increases in their intercellular concentrations, but not that of downstream cinnamyl aldehydes and monolignols. Supplying p-coumaryl and coniferyl aldehydes up to 40, 000-320,000-fold above the detection limits resulted in rapid, quantitative conversion into the monolignols. Only at nonphysiological concentrations was transient accumulation of intracellular aldehydes observed. These results indicate that cinnamic and p-coumaric acid hydroxylations assume important regulatory positions in phenylpropanoid metabolism, whereas cinnamyl aldehyde reduction does not serve as a control point.
Anterola
A M
AM
Institute of Biological Chemistry, Washington State University, Pullman, 99164-6340, USA.
van Rensburg
H
H
van Heerden
P S
PS
Davin
L B
LB
Lewis
N G
NG
D000447:Aldehydes / Q000008:administration & dosage; D002109:Caffeic Acids / Q000378:metabolism; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D002934:Cinnamates / Q000008:administration & dosage / Q000378:metabolism; D003373:Coumaric Acids / Q000378:metabolism; D005960:Glucosides / Q000378:metabolism; D007700:Kinetics; D008031:Lignin / Q000096:biosynthesis*; D010649:Phenylalanine / Q000008:administration & dosage / Q000378:metabolism; D041603:Pinus taeda
D000447:Aldehydes; D002109:Caffeic Acids; D002934:Cinnamates; D003373:Coumaric Acids; D005960:Glucosides; C029010:cinnamic acid; D010649:Phenylalanine; D008031:Lignin; C004999:ferulic acid; C040048:caffeic acid