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ARS Home » Midwest Area » Ames, Iowa » Corn Insects and Crop Genetics Research » Research » Publications at this Location » Publication #68071
Title: SYRINGALDAZINE OXIDASE AND PHENYLALANINE AMMONIA LYASE ACTIVITIES IN RELATION TO LIGNIN DEPOSITION IN LEGUMES

Author
item BIDLACK, JAMES - UNIV CENTRAL OKLAHOMA
item Buxton, Dwayne
item SHIBLES, RICHARD - ISU
item ANDERSON, IRVIN - ISU

Submitted to: Trends in Agricultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cell walls of forage plants consumed by livestock are important because, besides protecting plants from environmental stresses such as drought, and insect and disease attack, they also limit digestibility of forages when consumed by livestock. As a result, about 50% of forage fed to ruminant livestock passes through the animal undigested. This adds to feed cost and results in large amounts of manure that must be disposed. To improve forage digestibility, increased understanding of the synthesis and development of the cell wall is required, including better understanding of the temporal relationship between enzyme activity and cell-wall deposition. This type of information is necessary for targeted manipulation of wall biosynthesis to improve its digestibility without restricting the protection that cell walls provide to plants. Lignin deserves special attention because it provides most of the resistance to digestion. We studied enzymes because they form the lignin precursors in plants. In this study, there was from 2 to 12 days between maximum activities of the first and last enzymes in the lignin pathway. This information will be useful for pinpointing when enzyme activity should be modified to alter lignin synthesis. Scientists studying cell-wall formation and forage quality will be most interested in these results.

Technical Abstract: Temporal relationships of maximum enzyme activity were evaluated in relation to cell wall (CW) and lignin deposition in maturing legume stems. Three forage legumes, alfalfa, birdsfoot trefoil, and red clover, were established in a greenhouse and basal stem regrowth was sampled biweekly for 10 weeks. Tissue was analyzed for phenylalanine ammonia lyase (PAL) and syringaldazine oxidase (SAO) activities as well as CW components including lignin. Cell wall and lignin content increased sigmoidally; PAL activity increased, peaked, and decreased; and SAO activity increased, peaked, and leveled off or decreased as a function of regrowth days. Maximum deposition of lignin followed that of other CW components. Time of maximum PAL activity occurred 8 days before maximum lignin deposition in birdsfoot trefoil and red clover and 3 days after maximum lignin deposition in alfalfa. Time of maximum PAL activity always preceded time of maximum SAO activity. Neither PAL nor SAO activity on a protein basis were correlated with lignin content. However, on a per plant basis, PAL was correlated with lignin content across species (r = 0.60). Syringaldazine oxidase activity was correlated with lignin content in alfalfa (r = 0.88), birdsfoot trefoil (r = 0.97) and red clover (r = 0.97).