Suberin phenolic materials

The structure of suberin is even less well understood than that of cutin. As indicated earlier, even the composition of the phenolic constituents of this polymer is unknown. The high content of phenolic materials in suberin and the finding that bark lignin usually contains fewer methoxyl groups than the... 

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). 

The advent of modem analytical techniques, particularly combined glc and mass spectrometry, was responsible for the great advances in our knowledge of the chemistry of waxes, cutin, and suberin. However, what is known constitutes only a beginning, as much more remains unknown. Even the monomer composition of the polymeric lipids of only a very limited number of plants has been determined, and hardly anything is known about the chemistry of the numerous internal layers of lipidlike staining materials veuiously designated suberin, cutin, suberin-cutin-like, etc. The phenolic components of suberin and the intermolecular structure of the polymerized lipids are very poorly understood. 

The time course of deposition of aromatic monomers into the phenolic portion of suberin in wound-healing slices of Solanum tuberosum tubers was determined using the amount of / -hydroxybenzaldehyde and vanillin generated by alkaline nitrobenzene oxidation as a measure of aromatic deposition (85). The deposition of such phenolics into the polymer exhibited a lag period of about three days after wounding followed by several days when the deposition of phenolics increased rapidly, and subsequently the process ceased. Exogenous L-[U- C]-phenylalanine and [U- Clcinnamic acid were incorporated into the insoluble polymeric material by wound-healing slices of S. tuberosum (85). Nitrobenzene oxidation of the polymeric material derived from labeled cinnamic acid released labeled /7-hydroxybenzaldehyde and vanillin. The time course of incorporation of phenolics into the suberin polymer correlated with the time course for the deposition of aliphatic monomers into the polymer, the deposition of suberin-associated waxes into the periderm layer and the development of diffusion resistance (Fig. 6.4.12) (86). 

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