NMR characterization of lignins in Arabidopsis altered in the activity of ferulate 5-hydroxylase

Nuclear magnetic resonance (NMR) of isolated lignins from an Arabidopsis mu tant deficient in ferulate 5-hydroxylase (F5H) and transgenic plants derive d from the mutant by overexpressing the F5H gene has provided detailed insi ght into the compositional and structural differences between these lignins . Wild-type Arabidopsis has a guaiacyl-rich, syringyl-guaiacyl lignin typic al of other dicots, with prominent beta-aryl ether (beta-O-4), phenylcoumar an (beta-5), resinol (beta-beta), biphenyl/dibenzodioxocin (5-5), and cinna myl alcohol end-group structures. The lignin isolated from the F5H-deficien t fah1-2 mutant contained only traces of syringyl units and consequently en hanced phenylcoumaran and dibenzodioxocin levels. In fah1-2 transgenics in which the F5H gene was overexpressed under the control of the cauliflower m osaic virus 35S promoter, a guaiacyl-rich, syringyl/guaiacyl lignin similar to the wild type was produced. In contrast, the isolated lignin from the f ah1-2 transgenics in which F5H expression was driven by the cinnamate 4-hyd roxylase promoter was almost entirely syringyl in nature. This simple ligni n contained predominantly beta-aryl ether units, mainly with erythro-stereo chemistry, with same resinol structures. No phenylcoumaran or dibenzodioxoc in structures (which require guaiacyl units) were detectable. The overexpre ssion of syringyl units in this transgenic resulted in a lignin with a high er syringyl content than that in any other plant we have seen reported.