Suberin-enriched materials

Recent work using the atmospheric dioxane extraction of cork has proved extremely difficult, yielding only small amounts of a lignin- enriched material (7). This was explained by the presence of suberin, a complex structure of phenolic and aliphatic domains and the interaction with lignin. Further work using a saponified cork stressed these arguments (8). 

Solid-state 13C NMR was employed to characterize intact samples of cutin and suberin biopolyesters. Although a considerable degree of structural heterogeneity was observed for both materials, it was possible nonetheless to resolve and assign many NMR peaks, even when the polyesters were accompanied by waxes or cell walls. Quantitative estimates for the various aliphatic, aromatic, and carbonyl carbon types indicated that cutin was primarily aliphatic in composition, whereas suberin had more aromatic and olefinic moieties. Additional analysis should be facilitated by the biosynthetic incorporation of selectively 13C-enriched precursors (26,27). 

The surface layers of plants are covered in cutin or suberin (Section 2.11). Both of these polymeric structures are lipid-derived. Furthermore, the lipid nature of the surface covering is enriched by the presence of wax (Section 2.10), especially in the cuticle. There are two problems which should be borne in mind when considering the structural determination of these compounds. Firstly, cutin and suberin are polymers whose extraction from tissues and analysis thereafter pose all the problems usually associated with such materials. Secondly, wax, cutin and suberin have variable compositions depending on environmental and developmental conditions and, especially, on the nature of the tissue being analysed. 

A fraction analogous to BjOrkman lignin (39) was obtained when a portion of finely-powdered suberin polymer from the periderm of 5. tuberosum was solubilized with dioxane. This soluble fraction, however, was not enriched in either aromatic or aliphatic components over the insoluble residue (unpublished results). Other procedures from lignin chemistry - including refluxing in HCl/dioxane or HCl/dimethylformamide, and dioxane treatment at 160 C and high pressure (268, 396) - resulted in 20 o to 50% solubilization of the suberin preparation, but with each method the insoluble material contained the majority... 

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