A comparison of suberin monomers from the multiseriate exodermis of <Emphasis Type="Italic">Iris germanica</Emphasis> during maturation under differing growth conditions

Iris germanica roots develop a multiseriate exodermis (MEX) in which all mature cells contain suberin lamellae. The location and lipophilic nature of the lamellae contribute to their function in restricting radial water and solute transport. The objective of the current work was to identify and quantify aliphatic suberin monomers, both soluble and insoluble, at specific stages of MEX development and under differing growth conditions, to better understand aliphatic suberin biosynthesis. Roots were grown submerged in hydroponic culture, wherein the maturation of up to three exodermal layers occurred over 21 days. In contrast, when roots were exposed to a humid air gap, MEX maturation was accelerated, occurring within 14 days. The soluble suberin fraction included fatty acids, alkanes, fatty alcohols, and ferulic acid, while the suberin poly(aliphatic) domain (SPAD) included fatty acids, α,ω-dioic acids, ω-OH fatty acids, and ferulic acid. In submerged roots, SPAD deposition increased with each layer, although the composition remained relatively constant, while the composition of soluble components shifted toward increasing alkanes in the innermost layers. Air gap exposure resulted in two significant shifts in suberin composition: nearly double the amount of SPAD monomers across all layers, and almost three times the alkane accumulation in the first layer. The localized and abundant deposition of C18:1 α,ω-dioic and ω-OH fatty acids, along with high accumulation of intercalated alkanes in the first mature exodermal layer of air gap-exposed roots indicate its importance for water retention under drought compared with underlying layers and with entire layers developing under water.     

A feruloyl transferase involved in the biosynthesis of suberin and suberin‐associated wax is required for maturation and sealing properties of potato periderm

Suberin and waxes embedded in the suberin polymer are key compounds in the control of transpiration in the tuber periderm of potato (Solanum tuberosum). Suberin is a cell‐wall biopolymer with aliphatic and aromatic domains. The aliphatic suberin consists of a fatty acid polyester with esterified ferulic acid, which is thought to play an important role in cross‐linking to the aromatic domain. In potato, ferulic acid esters are also the main components of periderm wax. How these ferulate esters contribute to the periderm water barrier remains unknown. Here we report on a potato gene encoding a fatty ω‐hydroxyacid/fatty alcohol hydroxycinnamoyl transferase (FHT), and study its molecular and physiological relevance in the tuber periderm by means of a reverse genetic approach. In FHT RNAi periderm, the suberin and its associated wax contained much smaller amounts of ferulate esters, in agreement with the in vitro ability of the FHT enzyme to conjugate ferulic acid with ω‐hydroxyacid and fatty alcohols. FHT down‐regulation did not affect the typical suberin lamellar ultrastructure but had significant effects on the anatomy, sealing properties and maturation of the periderm. The tuber skin became thicker and russeted, water loss was greatly increased, and maturation was prevented. FHT deficiency also induced accumulation of the hydroxycinnamic acid amides feruloyl and caffeoyl putrescine in the periderm. We discuss these results in relation to the role attributed to ferulates in suberin molecular architecture and periderm impermeability.     

Unraveling ferulate role in suberin and periderm biology by reverse genetics

Plant cell walls are dramatically affected by suberin deposition, becoming an impermeable barrier to water and pathogens. Suberin is a complex layered heteropolymer that comprises both a poly(aliphatic) and a poly(aromatic) lignin-like domain. Current structural models for suberin attribute the crosslinking of aliphatic and aromatic domains within the typical lamellar ultrastructure of the polymer to esterified ferulate. BAHD feruloyl transferases involved in suberin biosynthesis have been recently characterized in Arabidopsis and potato (Solanum tuberosum). In defective mutants, suberin, even lacks most of the esterified ferulate, but maintains the typical lamellar ultrastructure. However, suberized tissues display increased water permeability, in spite of exhibiting a similar lipid load to wild type. Therefore, the role of ferulate in suberin needs to be reconsidered. Moreover, silencing the feruloyl transferase in potato turns the typical smooth skin of cv. Desirée into a rough scabbed skin distinctive of Russet varieties and impairs the normal skin maturation that confers resistance to skinning. Concomitantly to these changes, the skin of silenced potatoes shows an altered profile of soluble phenolics with the emergence of conjugated polyamines.Key words: BAHD feruloyl acyltransferases, ferulate, periderm, potato tuber skin, suberin, suberized tissues, waxRecently published reverse genetic studies in Arabidopsis and potato identified two orthologous genes that encode a BAHD feruloyl transferase acting on aliphatics and showed that deficiency in these enzymes produces a decrease in suberin-associated ferulic acid. These results, here discussed, signify an important advance in suberin biochemistry and ultrastructure, providing a valuable new insight into the organization of the suberized tissues and their role in the control of water vapour loss.     

Effects of NO 3 deficiency and NaCl stress on suberin deposition in rhizo- and hypodermal (RHCW) and endodermal cell walls (ECW) of castor bean (Ricinus communis L.) roots

Castor bean (Ricinus communis L.) plants were hydroponically cultivated to achieve NO₃ deficiency (N starvation), salt stress (addition of 100 mM NaCl), or normal conditions. Endodermal (ECW) and rhizodermal and hypodermal cell walls (RHCW) were isolated enzymatically from roots, and suberin monomers were released by transesterification after solvent extraction. Aromatic and aliphatic suberin monomers were identified and quantified by gas chromatography and mass spectrometry. Between 90 and 95% of the released suberin monomers were linear, long-chain, aliphatic compounds (alcohols, acids, diacids, ω-hydroxy acids and 2-hydroxy acids) with an average chain length of 19 C-atoms. The remainder was an aromatic suberin fraction mainly composed of coumaric and ferulic acid. Suberin amounts were significantly increased in ECW and RHCW in the presence of NaCl. In contrast, N starvation led to significantly reduced levels of suberization in ECW and RHCW. It is concluded that R. communis plants reinforce their apoplastic transport barriers in roots in adaptation to NaCl stress in order to minimize NaCl uptake. Under conditions of N starvation the opposite occurs and plants reduce the suberization of their apoplastic transport barriers to facilitate nutrient uptake form the soil.     

Bioavailability of hydroxycinnamates: a brief review of in vivo and in vitro studies

Hydroxycinnamates including p-coumaric acid, caffeic acid, ferulic acid, sinapic acid, and their esterified/etherified conjugates such as chlorogenic acids are abundant in cereals, coffee, fruit and vegetables. Studies have shown their potential in the prevention of chronic diseases such as cardiovascular disease and cancer. The impact of these dietary hydroxycinnamates on health depends on their bioavailability. In this article, in vivo and in vitro studies pertaining to bioavailability of hydroxycinnamates are reviewed and discussed. The chemical structures, existing forms, and/or doses of hydroxycinnamates may affect their metabolic fate. Limited studies suggest that the relative bioavailability of hydroxycinnamates may be in the following order: chlorogenic acid < rosmarinic acid < caffeic acid < ferulic acid < p-coumaric acid. Bound hydroxycinnamates generally have lower bioavailability than their monomer counterparts. Further pharmacokinetic and phamacodynamic studies are required to characterize the metabolism of hydroxycinnamates and their potential health impact in humans.     

The Arabidopsis cytochrome P450 CYP86A1 encodes a fatty acid omega-hydroxylase involved in suberin monomer biosynthesis

The lipophilic biopolyester suberin forms important boundaries to protect the plant from its surrounding environment or to separate different tissues within the plant. In roots, suberin can be found in the cell walls of the endodermis and the hypodermis or periderm. Apoplastic barriers composed of suberin accomplish the challenge to restrict water and nutrient loss and prevent the invasion of pathogens. Despite the physiological importance of suberin and the knowledge of the suberin composition of many plants, very little is known about its biosynthesis and the genes involved. Here, a detailed analysis of the Arabidopsis aliphatic suberin in roots at different developmental stages is presented. This study demonstrates some variability in suberin amount and composition along the root axis and indicates the importance of omega-hydroxylation for suberin biosynthesis. Using reverse genetics, the cytochrome P450 fatty acid omega-hydroxylase CYP86A1 (At5g58860) has been identified as a key enzyme for aliphatic root suberin biosynthesis in Arabidopsis. The corresponding horst mutants show a substantial reduction in omega-hydroxyacids with a chain length 相似文献   

Apoplastic polyesters in Arabidopsis surface tissues--a typical suberin and a particular cutin

Cutinized and suberized cell walls form physiological important plant-environment interfaces as they act as barriers limiting water and nutrient loss and protect from radiation and invasion by pathogens. Due to the lack of protocols for the isolation and analysis of cutin and suberin in Arabidopsis, the model plant for molecular biology, mutants and transgenic plants with a defined altered cutin or suberin composition are unavailable, causing that structure and function of these apoplastic barriers are still poorly understood. Transmission electron microscopy (TEM) revealed that Arabidopsis leaf cuticle thickness ranges from only 22 nm in leaf blades to 45 nm on petioles, causing the difficulty in cuticular membrane isolation. We report the use of polysaccharide hydrolases to isolate Arabidopsis cuticular membranes, suitable for depolymerization and subsequent compositional analysis. Although cutin characteristic omega-hydroxy acids (7%) and mid-chain hydroxylated fatty acids (8%) were detected, the discovery of alpha,omega-diacids (40%) and 2-hydroxy acids (14%) as major depolymerization products reveals a so far novel monomer composition in Arabidopsis cutin, but with chemical analogy to root suberin. Histochemical and TEM analysis revealed that suberin depositions were localized to the cell walls in the endodermis of primary roots and the periderm of mature roots of Arabidopsis. Enzyme digested and solvent extracted root cell walls when subjected to suberin depolymerization conditions released omega-hydroxy acids (43%) and alpha,omega-diacids (24%) as major components together with carboxylic acids (9%), alcohols (6%) and 2-hydroxyacids (0.1%). This similarity to suberin of other species indicates that Arabidopsis roots can serve as a model for suberized tissue in general.     

Differential induction of polar and non‐polar metabolism during wound‐induced suberization in potato (Solanum tuberosum L.) tubers

Wound‐induced suberin deposition involves the temporal and spatial coordination of phenolic and fatty acid metabolism. Phenolic metabolism leads to both soluble metabolites that accumulate as defense compounds as well as hydroxycinnamoyl derivatives that form the basis of the poly(phenolic) domain found in suberized tissue. Fatty acid metabolism involves the biosynthesis of very‐long‐chain fatty acids, 1‐alkanols, ω‐hydroxy fatty acids and α,ω‐dioic acids that form a poly(aliphatic) domain, commonly referred to as suberin. Using the abscisic acid (ABA) biosynthesis inhibitor fluridone (FD), we reduced wound‐induced de novo biosynthesis of ABA in potato tubers, and measured the impact on the expression of genes involved in phenolic metabolism (StPAL1, StC4H, StCCR, StTHT), aliphatic metabolism (StCYP86A33, StCYP86B12, StFAR3, StKCS6), metabolism linking phenolics and aliphatics (StFHT) or acyl chains and glycerol (StGPAT5, StGPAT6), and in the delivery of aliphatic monomers to the site of suberization (StABCG1). In FD‐treated tissue, both aliphatic gene expression and accumulation of aliphatic suberin monomers were delayed. Exogenous ABA restored normal aliphatic suberin deposition in FD‐treated tissue, and enhanced aliphatic gene expression and poly(aliphatic) domain deposition when applied alone. By contrast, phenolic metabolism genes were not affected by FD treatment, while FD + ABA and ABA treatments slightly enhanced the accumulation of polar metabolites. These data support a role for ABA in the differential induction of phenolic and aliphatic metabolism during wound‐induced suberization in potato.     

Changing the Dimensions of Suberin Lamellae of Green Cotton Fibers with a Specific Inhibitor of the Endoplasmic Reticulum-Associated Fatty Acid Elongases

The fibers of the green lint mutant of cotton (Gossypium hirsutum L.) contain large amounts of wax and are suberized. More than 96% of the bifunctional aliphatic suberin monomers ([alpha],[omega]-alkanedioic acids and [omega]-hydroxyalkanoic acids) have chain lengths of C22 and C24 in green cotton fiber suberin. In fibers grown in the presence of S-ethyl-N,N-dipropylthiocarbamate (EPTC), a specific inhibitor of the endoplasmic reticulum-associated fatty acid elongases, the aliphatic suberin monomers were shortened to chain lengths of C16 and C18. Whereas the amounts of most suberin monomers were not negatively affected by the inhibitor treatment, the amounts of [alpha],[omega]-alkanedioic acids and of glycerol were reduced by more than 80%. Analysis in the transmission electron microscope showed a reduction in suberin content after EPTC treatment. The suberin layers were discontinuous and consisted of fewer lamellae than in the controls. A small proportion (up to 22%) of the electron-translucent suberin lamellae were thinner after EPTC treatment, probably because of the shortening of the aliphatic suberin monomers. A larger proportion of the electron-translucent lamellae were thicker than the lamellae in the controls. Possible explanations for this observation are discussed.     

Apoplasmic barriers and oxygen transport properties of hypodermal cell walls in roots from four amazonian tree species

The formation of suberized and lignified barriers in the exodermis is suggested to be part of a suite of adaptations to flooded or waterlogged conditions, adjusting transport of solutes and gases in and out of roots. In this study, the composition of apoplasmic barriers in hypodermal cell walls and oxygen profiles in roots and the surrounding medium of four Amazon tree species that are subjected to long-term flooding at their habitat was analyzed. In hypodermal cell walls of the deciduous tree Crateva benthami, suberization is very weak and dominated by monoacids, 2-hydroxy acids, and omega-hydroxycarboxylic acids. This species does not show any morphological adaptations to flooding and overcomes the aquatic period in a dormant state. Hypodermal cells of Tabernaemontana juruana, a tree which is able to maintain its leaf system during the aquatic phase, are characterized by extensively suberized walls, incrusted mainly by the unsaturated C(18) omega-hydroxycarboxylic acid and the alpha,omega-dicarboxylic acid analogon, known as typical suberin markers. Two other evergreen species, Laetia corymbulosa and Salix martiana, contained 3- to 4-fold less aliphatic suberin in the exodermis, but more than 85% of the aromatic moiety of suberin are composed of para-hydroxybenzoic acid, suggesting a function of suberin in pathogen defense. No major differences in the lignin content among the species were observed. Determination of oxygen distribution in the roots and rhizosphere of the four species revealed that radial loss of oxygen can be effectively restricted by the formation of suberized barriers but not by lignification of exodermal cell walls.     

Evidence for Covalently Attached p-Coumaric Acid and Ferulic Acid in Cutins and Suberins

p-Coumaric acid (4-hydroxycinnamic acid) and ferulic acid (4-hydroxy-3-methoxycinnamic acid) have been identified as constituents of cutin. Their reduction products were isolated from a phenolic fraction released from the cutin of the fruits of apple, peach, pear, and two varieties of tomato and apple leaf by treatment with LiAlH(4) or LiAlD(4). They were identified by combined gas chromatography and mass spectrometry. p-Coumaric acid was present in all samples of cutin (0.07-0.53% by weight), whereas only peach and pear cutin contained measurable amounts of ferulic acid (0.007% and 0.035%, respectively). Both p-coumaric acid and ferulic acid were identified to be constituents of the insoluble material recovered after partial hydrolysis (12-42% loss) of cutin in 1 m NaOH at 80 C. A significant part (48%) of the p-coumaric acid contained in tomato cutin was contained in the insoluble material recovered after partial degradation (7.4%) of this cutin with 0.01 m NaOH. These data indicate that these phenolic components are tightly (possibly covalently) bound to cutin. Similar analysis of the phenolic fractions from the suberins of potato, sweet potato, turnip, rutabaga, carrot, and red beet revealed that they contained only ferulic acid (0.05-0.22%). Ferulic acid was identified as a constituent of the insoluble material recovered after partial hydrolysis of potato and beet suberins (34% and 32% loss, respectively) in 1 m NaOH at 80 C. A major part (65%) of the ferulic acid contained in potato suberin was contained in the insoluble material recovered after partial (26.8% loss) degradation of this suberin with 0.01 m NaOH. Ferulic acid appears to be tightly (probably covalently) bound to suberin.     

CYP86B1 Is Required for Very Long Chain ω-Hydroxyacid and α,ω-Dicarboxylic Acid Synthesis in Root and Seed Suberin Polyester

Suberin composition of various plants including Arabidopsis (Arabidopsis thaliana) has shown the presence of very long chain fatty acid derivatives C20 in addition to the C16 and C18 series. Phylogenetic studies and plant genome mining have led to the identification of putative aliphatic hydroxylases belonging to the CYP86B subfamily of cytochrome P450 monooxygenases. In Arabidopsis, this subfamily is represented by CYP86B1 and CYP86B2, which share about 45% identity with CYP86A1, a fatty acid ω-hydroxylase implicated in root suberin monomer synthesis. Here, we show that CYP86B1 is located to the endoplasmic reticulum and is highly expressed in roots. Indeed, CYP86B1 promoter-driven β-glucuronidase expression indicated strong reporter activities at known sites of suberin production such as the endodermis. These observations, together with the fact that proteins of the CYP86B type are widespread among plant species, suggested a role of CYP86B1 in suberin biogenesis. To investigate the involvement of CYP86B1 in suberin biogenesis, we characterized an allelic series of cyp86B1 mutants of which two strong alleles were knockouts and two weak ones were RNA interference-silenced lines. These root aliphatic plant hydroxylase lines had a root and a seed coat aliphatic polyester composition in which C22- and C24-hydroxyacids and α,ω-dicarboxylic acids were strongly reduced. However, these changes did not affect seed coat permeability and ion content in leaves. The presumed precursors, C22 and C24 fatty acids, accumulated in the suberin polyester. These results demonstrate that CYP86B1 is a very long chain fatty acid hydroxylase specifically involved in polyester monomer biosynthesis during the course of plant development.     

Abscisic Acid stimulation of suberization : induction of enzymes and deposition of polymeric components and associated waxes in tissue cultures of potato tuber

Effect of abscisic acid (ABA) on suberization of potato (Solanum tuberosum var. Russet-Burbank) tuber tissue culture was studied by measuring deposition of suberin components and the level of certain key enzymes postulated to be involved in suberization. ABA treatment resulted in a 3-fold increase in the polymeric aliphatic components of suberin and a 4-fold increase in the polymeric aromatic components. Hydrocarbons and fatty alcohols, two components characteristic of waxes associated with potato suberin, increased 9- and 5-fold, respectively, as a result of ABA treatment. Thus, the deposition of the polymeric aliphatics and aromatics as well as waxes, all of which have been postulated to be components of suberized cell walls, was markedly stimulated by ABA. ω-Hydroxy-fatty acid dehydrogenase which showed a rather high initial level of activity increased only 60% due to ABA treatment. Phenylalanine ammonia-lyase activity reached a maximum at a 5-fold level after 4 days in the ABA medium, whereas the control showed only a 3-fold increase. ABA treatment also resulted in a dramatic (7-fold) increase in an isozyme of peroxidase which has been specifically associated with suberization. Thus, ABA appears to induce certain key enzymes which are most probably involved in suberization.     

Continuous synthesis of alkyl ferulate by immobilized Candida antarctica lipase at high temperature

1-Pentyl, 1-hexyl and 1-heptyl ferulates were continuously synthesized at 60–90°C using a reactor system in which a column packed with ferulic acid powders and another column packed with immobilized Candida antarctica lipase particles were connected in series. Conversions greater than 0.9 were achieved for the synthesis of the 1-hexyl and 1-heptyl ferulates at 90°C. The system could be stably operated for the 1-heptyl ferulate synthesis at 90°C for at least two weeks.     

Water and solute permeabilities of Arabidopsis roots in relation to the amount and composition of aliphatic suberin

Although it is implied that suberized apoplastic barriers of roots negatively correlate with water and solute permeabilities, direct transport measurements across roots with altered amounts and compositions of aliphatic suberin are scarce. In the present study, hydroponically grown Arabidopsis wild types (Col8 and Col0) and different suberin mutants with altered amounts and/or compositions (horst, esb1-1, and esb1-2) were used to test this hypothesis. Detailed histochemical studies revealed late development of Casparian bands and suberin lamellae in the horst mutant compared with wild types and esb mutants. Suberin analysis with gas chromatography and mass spectrometry (GC-MS) showed that the horst mutant had ～33% lower amounts of aliphatic monomers than Col8 and Col0. In contrast, enhanced suberin mutants (esb1-1 and esb1-2) had twice the amount of suberin as the wild types. Correlative permeability measurements, which were carried out for the first time with a root pressure probe for Arabidopsis, revealed that the hydraulic conductivity (Lp(r)) and NaCl permeability (P(sr)) of the whole root system of the horst mutant were markedly greater than in the respective wild types. This was reflected by the total amounts of aliphatic suberin determined in the roots. However, increased levels of aliphatic suberin in esb mutants failed to reduce either water or NaCl permeabilities below those of the wild types. It was concluded that the simple view and the conventional assumption that the amount of root suberin negatively correlates with permeability may not always be true. The aliphatic monomer arrangement in the suberin biopolymer and its microstructure also play a role in apoplastic barrier formation.     

Phellogen Regeneration in Injured Peach Tree Bark

Injury to peach bark phellogen leads to the generation of newtissues and the re-establishment of meristematic continuity.Two types of tissue changes after wounding were identified andquantified in bark of seven peach clones: (1) cell wall modifications(lignification and suberization) of tissues present at the timeof wounding, and (2) generation of the new phellogen and itsderivatives. Tissue responses were quantified with a microscopephotometer using selective histochemistry and autofluorescenceto detect lignin and suberin deposition over time. Suberin continuitywas re-established via suberin deposition in a layer of cells,present at the time of wounding, approximately 800 µminternal to the wound surface. Phellogen continuity was re-establishedimmediately internal to and abutting the suberized tissue. Thenew phellogen gave rise to suberized phellem which, in its outwardexpansion, crushed the suberized boundary zone tissue formedearlier. All injured peach clones produced the same sequenceof tissue changes, although timing and degree of response variedwith clone and time of year. Differentiation, impervious tissue, lignin, Prunus persica (L.) Batsch, suberin, wounding     

Expression, characterization and structural modelling of a feruloyl esterase from the thermophilic fungus Myceliophthora thermophila

A ferulic acid esterase (FAE) from the thermophilic fungus Myceliophthora thermophila (synonym Sporotrichum thermophile), belonging to the carbohydrate esterase family 1 (CE-1), was functionally expressed in methylotrophic yeast Pichia pastoris. The putative FAE from the genomic DNA was successfully cloned in P. pastoris X-33 to confirm that the enzyme exhibits FAE activity. The recombinant FAE was purified to its homogeneity (39 kDa) and subsequently characterized using a series of model substrates including methyl esters of hydroxycinnamates, alkyl ferulates and monoferuloylated 4-nitrophenyl glycosides. The substrate specificity profiling reveals that the enzyme shows a preference for the hydrolysis of methyl caffeate and p-coumarate and a strong preference for the hydrolysis of n-butyl and iso-butyl ferulate. The enzyme was active on substrates containing ferulic acid ester linked to the C-5 and C-2 linkages of arabinofuranose, whilst it was found capable of de-esterifying acetylated glucuronoxylans. Ferulic acid (FA) was efficiently released from destarched wheat bran when the esterase was incubated together with an M3 xylanase from Trichoderma longibrachiatum (a maximum of 41% total FA released after 1 h incubation). Prediction of the secondary structure of MtFae1a was performed in the PSIPRED server whilst modelling the 3D structure was accomplished by the use of the HH 3D structure prediction server.     

Determination of structure and composition of suberin from the roots of carrot, parsnip, rutabaga, turnip, red beet, and sweet potato by combined gas-liquid chromatography and mass spectrometry

Suberin from the roots of carrots (Daucus carota), parsnip (Pastinaca sativa), rutabaga (Brassica napobrassica), turnip (Brassica rapa), red beet (Beta vulgaris), and sweet potato (Ipomoea batatas) was isolated by a combination of chemical and enzymatic techniques. Finely powdered suberin was depolymerized with 14% BF₃ in methanol, and soluble monomers (20-50% of suberin) were fractionated into phenolic (<10%) and aliphatic (13-35%) fractions. The aliphatic fractions consisted mainly of ω-hydroxyacids (29-43%), dicarboxylic acids (16-27%), fatty acids (4-18%), and fatty alcohols (3-6%). Each fraction was subjected to combined gas-liquid chromatography and mass spectrometry. Among the fatty acids very long chain acids (>C₂₀) were the dominant components in all six plants. In the alcohol fraction C₁₈, C₂₀, C₂₂, and C₂₄ saturated primary alcohols were the major components. C₁₆ and C₁₈ dicarboxylic acids were the major dicarboxylic acids of the suberin of all six plants and in all cases octadec-9-ene-1, 18-dioic acid was the major component except in rutabaga where hexadecane-1, 16-dioic acid was the major dicarboxylic acid. The composition of the ω-hydroxyacid fraction was quite similar to that of the dicarboxylic acids; 18-hydroxy-octadec-9-enoic acid was the major component in all plants except rutabaga, where equal quantities of 16-hydroxyhexadecanoic acid and 18-hydroxyoctadec-9-enoic acid (42% each) were found. Compounds which would be derived from 18-hydroxyoctadec-9-enoic acid and octadec-9-ene-1, 18-dioic acid by epoxidation, and epoxidation followed by hydration of the epoxide, were also detected in most of the suberin samples. The monomer composition of the six plants showed general similarities but quite clear taxonomic differences.