BIOLOGICAL VARIABILITY IN LIGNIFICATION OF MAIZE - EXPRESSION OF THE BROWN MIDRIB BM3 MUTATION IN 3 MAIZE CULTIVARS

Cell wall-linked phenolics were investigated in maize internodes locat ed at three positions of the stem (top-middle-bottom). While the ligni n content did not change drastically with position, the amount of cell wall-ester linked p-coumaric acid sharply increased from the top to t he bottom internodes of the stem. Conversely, the saponified ferulic a cid content remained relatively unchanged along the stem. Moreover, th e highest syringyl content of the beta-O-4-lignin structures was found in the basal (most mature) internode. Therefore, enhanced p-coumaric esterification of the cell wall and preferential deposition of syringy l units in the lignin polymer might indicate an extended maturity stag e of the cell wall of maize internodes. The bm3 mutation in the three maize hybrids is expressed by lignin reduction and ester-bound p-couma ric decrease in the mutant lines. Furthermore, all bm3 hybrids synthes ised lignin polymers which were characterised by a very low S/G molar ratio (0.16-0.43). This ratio originates from the substantial reductio n of the syringyl unit content in beta-O-4-lignin structures compared with the normal lignin. The occurrence in the same range of the 5-hydr oxyguaiacyl unit in bm3 lignin from each type of hybrids was noteworth y, demonstrating the high heritability of the bm3 mutation at the mole cular level. The alkaline solubility of lignin was greater for the thr ee mutant lines compared to the normal cultivars. Furthermore, the alk ali-labile fraction of lignin of both normal and mutant lines had a mo nomeric composition which was consistent with the non-condensed struct ures of in-situ lignin.