Composition of alkyl esters in the cuticular wax on inflorescence stems of Arabidopsis thaliana cer mutants

Wax biosynthetic pathways proceed via the elongation of 16:0 acyl-CoA to very long-chain fatty acids (VLCFA), and by further modifications that include reduction to primary alcohols and formation of alkyl esters. We have analyzed the alkyl esters in the stem wax of ten cer mutants of Arabidopsis thaliana together with the corresponding wild types. Alkyl esters with chain lengths between C-38 and C-52 were identified, and the levels of esters ranged from 0.15 mu g cm(-2) in Wassilewskija (WS) to 1.20 mu g cm(-2) in cer2. Esters with even numbers of carbons prevailed, with C-42, C-44 and C-46 favoured in the wild types, a predominance of C-42 in cer2 and cer6 mutants, and a relative shift towards C-46 in cer3 and cer23 mutants. The esters of all mutants and wild types were dominated by 16:0 acyl moieties, whereas the chain lengths of esterified alcohols were between C-20 and C-32. The alkyl chain-length distributions of the wild-type esters had a maximum for C-28 alcohol, similar to the free alcohols accompanying them in the wax mixtures. The esterified alcohols of cer2, cer6 and cer9 had largely increased levels of C-26 alcohol, closely matching the patterns of the corresponding free alcohols and, therefore, differing drastically from the corresponding wild type. In contrast, cer1, cer3, cer10, cer13 and cer22 showed ester alcohol patterns with increased levels of C-30, only partially following the shift in chain lengths of the free alcohols in stem wax. These results provide information on the composition of substrate pools and/or the specificity of the ester synthase involved in wax ester formation. We conclude that alcohol levels at the site of biosynthesis are mainly limiting the ester formation in the Arabidopsis wild-type epidermis.