Biochemistry of Suberization: Incorporation of [1-14C]Oleic Acid and [1-14C]Acetate into the Aliphatic Components of Suberin in Potato Tuber Disks (Solanum tuberosum) 1

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Biosynthesis of the aliphatic components of suberin was studied in suberizing potato (Solanum tuberosum) slices with [1-14C]oleic acid and [1-14C]acetate as precursors. In 4-day aged tissue, [1-14C]oleic acid was incorporated into an insoluble residue, which, upon hydrogenolysis (LiA1H4), released the label into chloroform-soluble products. Radio thin layer and gas chromatographic analyses of these products showed that 14C was contained exclusively in octadecenol and octadecene-1, 18-diol. OsO4 treatment and periodate cleavage of the resulting tetraol showed that the labeled diol was octadec-9-ene-1, 18-diol, the product expected from the two major components of suberin, namely 18-hydroxyoleic acid and the corresponding dicarboxylic acid. Aged potato slices also incorporated [1-14C]acetate into an insoluble material. Hydrogenolysis followed by radio chromatographic analyses of the products showed that 14C was contained in alkanols and alkane-α,ω-diols. In the former fraction, a substantial proportion of the label was contained in aliphatic chains longer than C20, which are known to be common constituents of suberin. In the labeled diol fraction, the major component was octadec-9-ene-1,18-diol, with smaller quantities of saturated C16, C18, C20, C22, and C24-α,ω-diols. Soluble lipids derived from [1-14C]acetate in the aged tissue also contained labeled very long acids from C20 to C28, as well as C22 and C24 alcohols, but no labeled ω-hydroxy acids or dicarboxylic acids were detected. Label was also found in n-alkanes isolated from the soluble lipids, and the distribution of label among them was consistent with the composition of n-alkanes found in the wound periderm of this tissue; C21 and C23 were the major components with lesser amounts of C19 and C25. The amount of 14C incorporated into these bifunctional monomers in 0-, 2-, 4-, 6-, and 8-day aged tissue were 0, 1.5, 2.5, 0.8, and 0.3% of the applied [1-14C]oleic acid, respectively. Incorporation of [1-14C]acetate into the insoluble residue was low up to the 3rd day of aging, rapid during the next 4 days of aging, and subsequently the rate decreased. These changes in the rates of incorporation of exogenous oleic acid and acetate reflected the development of diffusion resistance of the tissue surface to water vapor. As the tissue aged, increasing amounts of the [1-14C]acetate were incorporated into longer aliphatic chains of the residue and the soluble lipids, but no changes in the distribution of radioactivity among the α-ω-diols were obvious. The above results demonstrated that aging potato slices constitute a convenient system with which to study the biochemistry of suberization.

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