Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/30/2002
Publication Date: 1/31/2003
Citation: MARITA, J.M., VERMERRIS, W., RALPH, J., HATFIELD, R.D. VARIATIONS IN THE CELL WALL COMPOSITION OF MAIZE BROWN MIDRIB MUTANTS. Journal of Agriculture and Food Chemistry. 2003. v. 51. p. 1313-1321. v. 51. pp. 1313-1321. Interpretive Summary: There are four brown midrib (bm) mutants known in maize (Zea mays L.). These mutants, bm1, bm2, bm3 and bm4, are recognized by a reddish-brown color of veins in their leaves and stems. The bm mutants are of interest because of their potentially higher nutritional value as a forage, presumably because of the lower lignin content and more digestible fiber. Lignin itself is a complex polymer that hardens the cell walls of specific plant tissue to provide mechanical strength to the leaves and stems and provides a physical barrier against pests and pathogens. Detailed analysis of the fiber composition of the bm mutants can provide information on the role of specific genes in lignin biosynthesis, and can improve our understanding of how lignins are formed. Different inbred lines can differ substantially in their lignin content and forage quality. Previous studies with the bm1 and bm3 mutations in different genetic backgrounds showed that the overall effect of the mutations was generally the same, but that the extent of the changes varied. Here we report the changes in fiber composition of all four bm mutants (bm1, bm2, bm3, and bm4) and a bm1-bm2 double mutant in the same genetic background (A619). Detailed analyses of the stalks of these mutants revealed structural and compositional changes in their fiber and lignins compared to the control inbred. For example, the bm3 and bm1-bm2 mutants contained less lignin. Specific fiber components in bm1, bm3 and bm1-bm2 were noticeably reduced than in the other mutants. This information regarding changes in fiber compostion and lignin structure/composition allows researchers and breeders insight into which bm mutations might positively impact maize digestibility.As noted, a lower lignin content more digestible fiber maize has a higher nutritional value as a forage for dairy consumption.
Technical Abstract: Most studies published thus far on the four brown midrib (bm) mutants (bm1, bm2, bm3, and bm4) in maize (Zea mays L.) have focused on one or two individual mutants and comparisons between studies have been difficult because of variation in genetic backgrounds, maturity and source of tissue. Detailed analyses of the stalks of the four bm single mutants and a bm1-bm2 double mutant in a common genetic background (inbred A619) revealed structural and compositional changes in their isolated cell walls and lignins compared to the wild-type inbred. 2D-NMR revealed a significant presence of benzodioxane units in the bm3 isolated lignin. 1D 13C NMR revealed increased aldehyde levels in the bm1 and bm1-bm2 mutants compared to the wild-type inbred. The bm3 and bm1-bm2 mutants contained less Klason lignin in the isolated cell walls. The bm1, bm3 and bm1-bm2 mutants contained ~50% less esterified p-coumaric acid with noticeably elevated levels of ferulate in the bm3 mutant. A difference among bm mutants in the solubility of p-coumaric acid-lignin complexes during cellulase enzyme treatment was also discovered suggesting that the bm mutations might also differ in the structural organization of lignin.