Tissue-specific patterns of lignification are disturbed in the brown midrib2 mutant of maize (Zea mays L.)

Despite recent progress, several aspects of lignin biosynthesis, including variation in lignin composition between species and between tissues within a given species, are still poorly understood. The analysis of mutants affec ted in cell wall biosynthesis may help increase the understanding of these processes. We have analyzed the maize brown midrib2 (bm2) mutant, one of th e four bm mutants of maize, using pyrolysis-mass spectrometry (Py-MS) and p yrolysis-gas chromatography-mass spectrometry (Py-GC-MS). Vascular tissues from the leaf blade and leaf sheath from different parts of the plant were investigated and compared to the corresponding samples from a wild-type pla nt of the same genetic background (inbred line A619). Multivariate analysis revealed that the bm2 mutant had reduced amounts of di- and trimeric ligni n derivatives, notably species with mit 272 and mit 330, and that the ratio of guaiacyl residues to polysaccharides was reduced in the bm2 mutant. In addition, differences in cell wall composition between different parts of t he plant (blade versus sheath, young versus old tissue) were much less pron ounced in the bm2 mutant. These changes suggest that the functional Bm2 gen e is important for the establishment of tissue-specific cell wall compositi on.