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Abstract Detail


Secondary Metabolism

Shadle, Gail L. [1], Chen, Fang [2], Jackson, Lisa A. [2], Dixon, R. A. [2].

Down-regulation of cinnamyl alcohol dehydrogenase and its impacts on lignin and forage quality in alfalfa (Medicago sativa).

There is a negative correlation between lignin content and/or composition and forage digestibility as well as saccharification of cell walls for processing of liquid biofuels. Thus there is a significant interest in plant lines possessing a reduced lignin content and/or altered lignin composition. The three cinnamyl alcohols from which lignin is derived are present in lignin polymers in varying proportions. In dicotyledonous angiosperms, lignin is derived from two main monomer types; syringyl (S) and guiacyl (G) units. S units are dimethoxylated and are derived from sinapyl alcohol. G units are monomethoxylated, and therefore result in more highly condensed lignin; they are derived from coniferyl alcohol. The third, less common monolignol is the H, or p-hydroxyphenyl, unit. The H unit is not methylated and is derived from p-coumaryl alcohol. Monolignol alcohols are formed from the corresponding aldehydes by the action of cinnamyl alcohol dehydrogenase (CAD). Recently, we have systematically down-regulated each of the key enzymes in the lignin biosynthetic pathway in the forage legume Medicago sativa (alfalfa). We here describe the effects of down-regulating CAD, which catalyses the final step in monolignol biosynthesis. Cinnamaldehydes can become incorporated into lignin, or else accumulate as monomers, when conversion to cinnamyl alcohols is blocked, resulting in a red coloration of the xylem. We have observed this phenotypic change in some of our plant lines down-regulated in the CAD gene. Reductions in total biomass, fiber, and acid detergent lignin were observed, as well as an increase in digestibility in CAD down-regulated lines. Lignin content, as analyzed by the acetyl bromide method, was reduced in several lines.


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1 - The Samuel Roberts Noble Foundation, Inc, Plant Biology, 2510 Sam Noble Pkwy, Ardmore, OK, 73401, USA
2 - The Samuel Roberts Noble Foundation, Inc, Plant Biology

Keywords:
lignin
cinnamyl alcohol dehydrogenase
CAD
forage quality
monolignols
Medicago sativa
legume.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P20030
Abstract ID:987


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