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ARS Home » Midwest Area » St. Paul, Minnesota » Plant Science Research » Research » Publications at this Location » Publication #80499
Title: LIGNIN IMPACT ON FIBER DEGRADATION: INCREASED ENZYMATIC DIGESTIBILITY OF GENETICALLY ENGINEERED TOBACCO (NICOTIANA TABACUM) STEMS REDUCED IN LIGNIN CONTENT

Author
item SEWALT, VINCENT - SAMUEL ROBERTS NOBLE FOUN
item Ni, Weiting
item Jung, Hans Joachim
item DIXON, RICHARD - SAMUEL ROBERTS NOBLE FOUN

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Lignin, a structural polymer in plant cell walls, reduces forage digestibility and the efficiency of paper pulping. Traditional approaches to attribute variation in forage digestibility to changes in lignin content, composition, and/or other structural components have limitations due to many associated changes in chemical constituents and physical structure occurring during plant maturation. Genetically engineered plant with altered lignin biosynthesis could provide a more amenable system to study the relative impact of lignin content and composition on forage digestibility. We tested genetically engineered tobacco plants with reduced lignin contents and altered lignin composition for their digestibility. Our data indicate that the digestibility was improved in the transgenic plants and was highly negatively correlated with the amount of lignin. However, there was no relationship between digestibility and lignin composition. It is clear that lignin concentration is a dominant factor influencing cell wall digestibility. The results show the feasibility of using genetic engineering to reduce the amount of lignin for forage improvement, and provide a basis for new strategies to accomplish such modification. Reducing the amount of lignin in forage plants will result in improved digestibility by rumen animals and more efficient conversion of energy to milk and meat.

Technical Abstract: Cell wall digestibility, lignin content, and lignin composition were analyzed in transgenic tobacco altered in the expression of the phenylpropanoid biosynthetic enzymes caffeic acid 3-O-methyltransferase (COMT) and L-phenylalanine ammonia-lyase (PAL). Reduction of COMT activity by antisense technology resulted in reduced lignin content accompanied by an increased syringyl/guaiacyl monomer ratio, as determined by pyrolysis-GC-MS and measurement of lignin methoxyl content by wet chemistry. These results resemble those obtained by reduction of flux of lignin precursors into the phenylpropanoid pathway by PAL suppression, which results in drastically reduced lignin with sharply increased methoxyl content. Enzymatic digestibility of cell walls from stem internodes was improved in the transgenic lines and was highly negatively correlated with lignin concentration (r=-0.97). Although lignin composition was also affected, lignin concentration was the overriding factor influencing cell wall digestibility. The results provide a basis for new strategies for lignin modification to improve digestibility of forages.