C-14 LABELING OF LIGNINS OF NORMAL AND BM3 MAIZES FOR FERMENTATION STUDIES

[U-C-14] phenylalanine (phe) and [(OCH3)-C-14] sinapic acid (sin*) we re infused into the cut ends of normal and bm3 maizes (anthesis stage) under or above the last node or at mid-internode, with or without the leaf, in light or in darkness. Radioactivity was measured in the orga ns, and in phenolic constituents of the cell wall and saponified resid ues of the bases and tops of the apical internode. In both maize genot ype labelled under the node the radioactivity was distributed more eve nly in the organs with sin than with phe*. Infusion above the node an d at mid-internode greatly increased radioactivity in the bases and to ps, respectively. Removal of the leaf only slightly increased the radi oactivity, mainly in the bases, and no clear-cut effect of darkness wa s observed. Phe labelled the phenolic acids and the three lignin unit s, but the syringyl units of bm3 maize were only slightly labelled. Si n specifically labelled the syringyl units, which represented the lea st condensed fraction of lignins. Both the native and labelled lignins were highly alkali soluble. There were differences in lignin biogenes is between the bases and tops, and between normal and bm3 maizes. The newly formed lignins were slightly different from the native lignins b ut had similar types of heterogeneity, with variations in the internod e and between genotypes similar to those in native lignins. Provided d ue allowance is made for the distinguishing characteristics of newly f ormed lignins, the [C-14-lignin] cell walls, which are strongly labell ed on complementary structures, seem suitable model substrates for fer mentation studies.