Biopolyester Membranes of Plants: Cutin and Suberin

Arabidopsis thaliana CYP77A4 is the first cytochrome P450 able to catalyze the epoxidation of free fatty acids in plants

An approach based on an in silico analysis predicted that CYP77A4, a cytochrome P450 that so far has no identified function, might be a fatty acid-metabolizing enzyme. CYP77A4 was heterologously expressed in a Saccharomyces cerevisiae strain (WAT11) engineered for cytochrome P450 expression. Lauric acid (C(12:0)) was converted into a mixture of hydroxylauric acids when incubated with microsomes from yeast expressing CYP77A4. A variety of physiological C(18) fatty acids were tested as potential substrates. Oleic acid (cis-Delta(9)C(18:1)) was converted into a mixture of omega-4- to omega-7-hydroxyoleic acids (75%) and 9,10-epoxystearic acid (25%). Linoleic acid (cis,cis-Delta(9),Delta(12)C(18:2)) was exclusively converted into 12,13-epoxyoctadeca-9-enoic acid, which was then converted into diepoxide after epoxidation of the Delta(9) unsaturation. Chiral analysis showed that 9,10-epoxystearic acid was a mixture of 9S/10R and 9R/10S in the ratio 33 : 77, whereas 12,13-epoxyoctadeca-9-enoic acid presented a strong enantiomeric excess in favor of 12S/13R, which represented 90% of the epoxide. Neither stearic acid (C(18:0)) nor linolelaidic acid (trans,trans-Delta(9),Delta(12)C(18:2)) was metabolized, showing that CYP77A4 requires a double bond, in the cis configuration, to metabolize C(18) fatty acids. CYP77A4 was also able to catalyze the in vitro formation of the three mono-epoxides of alpha-linolenic acid (cis,cis,cis-Delta(9),Delta(12),Delta(15)C(18:3)), previously described as antifungal compounds. Epoxides generated by CYP77A4 are further metabolized to the corresponding diols by epoxide hydrolases located in microsomal and cytosolic subcellular fractions from Arabidopsis thaliana. The concerted action of CYP77A4 with epoxide hydrolases and hydroxylases allows the production of compounds involved in plant-pathogen interactions, suggesting a possible role for CYP77A4 in plant defense.

Gene expression and metabolism in tomato fruit surface tissues

The cuticle, covering the surface of all primary plant organs, plays important roles in plant development and protection against the biotic and abiotic environment. In contrast to vegetative organs, very little molecular information has been obtained regarding the surfaces of reproductive organs such as fleshy fruit. To broaden our knowledge related to fruit surface, comparative transcriptome and metabolome analyses were carried out on peel and flesh tissues during tomato (Solanum lycopersicum) fruit development. Out of 574 peel-associated transcripts, 17% were classified as putatively belonging to metabolic pathways generating cuticular components, such as wax, cutin, and phenylpropanoids. Orthologs of the Arabidopsis (Arabidopsis thaliana) SHINE2 and MIXTA-LIKE regulatory factors, activating cutin and wax biosynthesis and fruit epidermal cell differentiation, respectively, were also predominantly expressed in the peel. Ultra-performance liquid chromatography coupled to a quadrupole time-of-flight mass spectrometer and gas chromatography-mass spectrometry using a flame ionization detector identified 100 metabolites that are enriched in the peel tissue during development. These included flavonoids, glycoalkaloids, and amyrin-type pentacyclic triterpenoids as well as polar metabolites associated with cuticle and cell wall metabolism and protection against photooxidative stress. Combined results at both transcript and metabolite levels revealed that the formation of cuticular lipids precedes phenylpropanoid and flavonoid biosynthesis. Expression patterns of reporter genes driven by the upstream region of the wax-associated SlCER6 gene indicated progressive activity of this wax biosynthetic gene in both fruit exocarp and endocarp. Peel-associated genes identified in our study, together with comparative analysis of genes enriched in surface tissues of various other plant species, establish a springboard for future investigations of plant surface biology.

Seed-coat dormancy in Grevillea linearifolia: little change in permeability to an apoplastic tracer after treatment with smoke and heat

BACKGROUND AND AIMS

Seeds of Grevillea linearifolia germinate following fire, and have seed-coat dormancy broken by smoke and heat shock. Smoke breaks seed coat dormancy in Emmenanthe penduliflora by altering the permeability of the seed coat to an internal germination inhibitor, which subsequently escapes. This model was tested for in G. linearifolia by investigating the permeability of the seed coat to diffusion of high-molecular-weight compounds, and whether this changed after exposure to fire cues.

METHODS

Germination response of the seeds to heat shock, smoke or heat + smoke was tested. Penetration of Lucifer Yellow dye into intact seeds was examined after 24 and 48 h of exposure, and penetration of the dye from the inside of the seed coat outwards was examined after 24 h. Histochemical staining with Nile Red and Acridine Orange was used to locate cuticles, suberin and lignin.

KEY RESULTS

Twenty-three per cent of untreated seeds germinated; heat shock and smoke increased germination additively up to approx. 80 % for both cues combined. Lucifer Yellow did not penetrate fully through the seed coat of untreated seeds, whether diffusing inwards or outwards. Three barriers to diffusion were identified. Treatment with heat or smoke slightly increased penetration of the dye, but did not completely remove the barriers. Suberin was identified in secondary walls of exotestal and mesotestal cells, and was absent from primary cell walls. Movement of Lucifer Yellow occurred through the middle lamella and primary cell wall of suberized cells; movement of the dye was impeded where suberin was absent.

CONCLUSIONS

Fire cues did not significantly decrease barriers to diffusion of high-molecular-weight compounds in the seed coat of Grevillea, and must be breaking dormancy by another mechanism.

Removal of 2,4,6-trichlorophenol from a solution by humic acids repeatedly extracted from a peat soil

Humic acid (HA) is one of the major components of soil organic matter. It strongly affects the sorption behavior of organic and inorganic contaminants in soils. To obtain a better understanding of the interactions of contaminants with HA, a repeated extraction technique has been applied to a peat soil to obtain HA fractions with varying aliphaticity and aromaticity, which were subsequently correlated to the sorption properties of 2,4,6-trichlorophenol (TCP). HA fractions were extracted repeatedly using an alkaline solution and each HA fraction was separated into two portions with an air-drying or re-suspending (denoted as RSHAs) process. Solid-state (13)C NMR and elemental analysis demonstrated that the aromaticity and polarity of HAs decreased with extractions. Kinetic results indicated that air-dried HAs exhibited two-step first order sorption behavior with a rapid stage followed by a slower stage. The slower sorption is attributed to the diffusion of 2,4,6-TCP in the condensed aromatic domains of HAs. Conversely, sorption of 2,4,6-TCP on RSHAs was extremely rapid and could not be fitted with any kinetic model. For air-dried HAs the sorption capacity (K(oc)) was weakly correlated with the chemical compositions of HAs. However, a positive trend between K(oc) and aromaticity was observed for RSHAs. Compared with the results of air-dried HAs with their counterparts of RSHAs, it is therefore concluded that air-drying may alter the structure of HAs through artificially creating a more condensed domain in HAs. The structural alternation may result in an incorrect interpretation of the relationship between sorption capacity and chemical composition of HAs and a misjudgment of the transport behavior of 2,4,6-TCP in soils and sediments.

The hydrophobic coatings of plant surfaces: epicuticular wax crystals and their morphologies, crystallinity and molecular self-assembly

Plant surfaces are the interfaces of the organisms with respect to their environment. In the micro-dimension they show an enormous variety of functional three-dimensional structures. Their materials and structures developed over millions of years by evolutionary processes in which their functionality has been proven and selected by environmental pressures. As a result, nature developed highly functional materials with several amazing properties like superhydrophobicity and superhydrophilicity. These functional structures are built up by a complex biopolymer called cuticle. The cuticle is mainly composed of a three-dimensional network of cutin, and integrated and superimposed lipids called "waxes". Superimposed waxes are also called "epicuticular waxes". Epicuticular waxes often form two- and three-dimensional structures, in dimensions between hundreds of nanometers and some micrometers, which influence the wettability, self-cleaning behaviour and the light reflection at the cuticle interface. This review gives a brief introduction into the functions of the plant epicuticular waxes and summarises the current knowledge about their morphologies, crystal structures, growth by self-assembly and provides an overview about the microscopy and preparation techniques for their analysis.

Cuticular wax biosynthesis in petunia petals: cloning and characterization of an alcohol-acyltransferase that synthesizes wax-esters

The surface of plants is covered by cuticular wax, which contains a mixture of very long-chain fatty acid (VLCFA) derivatives. This wax surface provides a hydrophobic barrier which reduces non-stomatal water loss. One component of the cuticular wax is the alkyl esters, which typically contain a VLCFA esterified to an alcohol of a similar length. As part of an EST project, we recently identified an acyltransferase with 19% sequence identity (amino acid) to a bacterial 'bifunctional' wax-ester synthase/diacylglycerol acyltransferase (WS/DGAT). Northern analysis revealed that this petunia homologue was expressed predominantly within the petals. The cDNA encoding the WS/DGAT homologue was introduced into a yeast strain deficient in triacylglycerol biosynthesis. The expressed protein failed to restore triacylglycerol biosynthesis, indicating that it lacked DGAT activity. However, isoamyl esters of fatty acids were detected, which suggested that the petunia cDNA encoded a wax-synthase. Waxes were extracted from petunia petals and leaves. The petal wax extract was rich in VLCFA esters of methyl, isoamyl, and short-to-medium straight chain alcohols (C4-C12). These low molecular weight wax-esters were not present in leaf wax. In-vitro enzymes assays were performed using the heterologously expressed protein and 14C-labelled substrates. The expressed protein was membrane bound, and displayed a preference for medium chain alcohols and saturated very long-chain acyl-CoAs. In fact, the activity would be sufficient to produce most of the low molecular wax-esters present in petals, with methyl-esters being the exception. This work is the first characterization of a eukaryotic protein from the WS/DGAT family.

A genomic approach to suberin biosynthesis and cork differentiation

Cork (phellem) is a multilayered dead tissue protecting plant mature stems and roots and plant healing tissues from water loss and injuries. Cork cells are made impervious by the deposition of suberin onto cell walls. Although suberin deposition and cork formation are essential for survival of land plants, molecular studies have rarely been conducted on this tissue. Here, we address this question by combining suppression subtractive hybridization together with cDNA microarrays, using as a model the external bark of the cork tree (Quercus suber), from which bottle cork is obtained. A suppression subtractive hybridization library from cork tree bark was prepared containing 236 independent sequences; 69% showed significant homology to database sequences and they corresponded to 135 unique genes. Out of these genes, 43.5% were classified as the main pathways needed for cork biosynthesis. Furthermore, 19% could be related to regulatory functions. To identify genes more specifically required for suberin biosynthesis, cork expressed sequence tags were printed on a microarray and subsequently used to compare cork (phellem) to a non-suberin-producing tissue such as wood (xylem). Based on the results, a list of candidate genes relevant for cork was obtained. This list includes genes for the synthesis, transport, and polymerization of suberin monomers such as components of the fatty acid elongase complexes, ATP-binding cassette transporters, and acyltransferases, among others. Moreover, a number of regulatory genes induced in cork have been identified, including MYB, No-Apical-Meristem, and WRKY transcription factors with putative functions in meristem identity and cork differentiation.

The lipid polyester composition of Arabidopsis thaliana and Brassica napus seeds

Mature seeds of Arabidopsis thaliana and Brassica napus contain a complex mixture of aliphatic monomers derived from the non-extractable lipid polyesters deposited by various seed tissues. Methods of polyester depolymerization of solvent-extracted seeds and analysis of aliphatic monomers were compared. Sodium methoxide-catalyzed depolymerization, followed by GC analysis of the acetylated monomers, was developed for routine quantitative analysis suitable for 0.5g seed samples. In Arabidopsis seeds, the major C16 and C18 monomers identified included omega-hydroxy fatty acids and alpha,omega-dicarboxylic acids derived from palmitate, oleate and linoleate, and 9,10,18-trihydroxyoctadecenoic acid. Among monomers which can collectively be considered likely to be derived from suberin, docosan-1-ol, docosane-1,22-diol, 22-hydroxydocosanoic acid, 24-hydroxytetracosanoic acid, tetracosane-1,24-dioic acid and ferulic acid were the major species. Compared to Arabidopsis, Brassica seeds showed a roughly similar proportion of monomer classes, with the exception that alkan-1ols were 3-fold higher. Also, there were much less C24 aliphatic species and significant amounts of C14-C16 alkan-1ols, including iso- and anteiso-methyl branched compounds. Dissection and analysis of mature Brassica seeds showed that the trihydroxy C18:1 fatty acid was found mainly in the embryo, while ferulate, fatty alcohols and C22 and C24 species were specific to the seed coat plus endosperm.

Structure-function relationships of the plant cuticle and cuticular waxes - a smart material?

The cuticle is the main interface between plants and their environment. It covers the epidermis of all aerial primary parts of plant organs as a continuous extracellular matrix. This hydrophobic natural composite consists mainly of the biopolymer, cutin, and cuticular lipids collectively called waxes, with a high degree of variability in composition and structure. The cuticle and cuticular waxes exhibit a multitude of functions that enable plant life in many different terrestrial habitats and play important roles in interfacial interactions. This review highlights structure-function relationships that are the subjects of current research activities. The surface waxes often form complex crystalline microstructures that originate from self-assembly processes. The concepts and results of the analysis of model structures and the influence of template effects are critically discussed. Recent investigations of surface waxes by electron and X-ray diffraction revealed that these could be assigned to three crystal symmetry classes, while the background layer is not amorphous, but has an orthorhombic order. In addition, advantages of the characterisation of formation of model wax types on a molecular scale are presented. Epicuticular wax crystals may cause extreme water repellency and, in addition, a striking self-cleaning property. The principles of wetting and up-to-date concepts of the transfer of plant surface properties to biomimetic technical applications are reviewed. Finally, biomechanical studies have demonstrated that the cuticle is a mechanically important structure, whose properties are dynamically modified by the plant in response to internal and external stimuli. Thus, the cuticle combines many aspects attributed to smart materials.

Structural characterization of lignin from leaf sheaths of "dwarf cavendish" banana plant

Dioxane lignin (DL) isolated from leaf sheaths of banana plant (Musa acuminata Colla var. cavendish) and in situ lignin were submitted to a comprehensive structural characterization employing spectroscopic (UV, FTIR, solid state 13C CP-MAS NMR, liquid state 13C and 1H NMR) and chemical degradation techniques (permanganate and nitrobenzene oxidation). Results obtained showed that banana plant leaf sheath lignin is of HGS type with a molar proportion of p-hydroxyphenyl (H)/guaiacyl (G)/syringyl (S) units of 12:25:63. Most of the H units in DL are terminal phenolic coumarates linked to other lignin substructures by benzyl and Cgamma-ester bonds in contrast to ferulates that are mainly ether linked to bulk lignin. It is proposed that banana plant leaf sheath lignin is chemically bonded to suberin-like components of cell tissues by ester linkages via essentially hydroxycinnamic acid residues. beta-O-4 structures (0.31/C6), the most abundant in DL, comprise mainly S units, whereas a significant proportion of G units is bonded by beta-5, 5-5', and 4-O-5' linkages contributing to ca. 80% of condensed structures in DL.

The differential effects of herbivory by first and fourth instars of Trichoplusia ni (Lepidoptera: Noctuidae) on photosynthesis in Arabidopsis thaliana

The effect of different feeding behaviours of 1st and 4th instar Trichoplusia ni on photosynthesis of Arabidopsis thaliana var. Columbia was characterized using spatially resolved measurements of fluorescence and leaf temperature, as well as leaf gas exchange,. First instars made small holes with a large perimeter-to-area ratio and avoided veins, while 4th instars made large holes with a low perimeter-to-area ratio and consumed veins. Herbivory by 1st instars reduced photosynthesis more strongly in the remaining leaf tissue than that by 4th instars. Photosystem II operating efficiency (PhiPSII) was correlated with the rate of CO2 exchange, and reductions in PhiPSII in areas around the missing tissues contributed to a 15.6% reduction in CO2 assimilation on the first day following removal of 1st instars. The corresponding increases in non-photochemical quenching and greater rates of non-stomatal water loss from these regions, as well as the partial reversal of low PhiPSII by increasing the ambient CO2 concentration, suggests that localized water stress and reduced stomatal conductance contributed to the inhibition of photosynthesis. Damage by 1st but not 4th instars reduced the maximum quantum efficiency of photosystem II photochemistry (Fv/Fm) by 4-8%. While herbivory by both 1st and 4th instars increased dark respiration rates, the rates were too low to have contributed to the observed reductions in CO2 exchange. The small holes produced by 1st instars may have isolated patches of tissue from the vascular system thereby contributing to localized water stress. Since neither 1st nor 4th instar herbivory had a detectable effect on the expression of the Rubisco small subunit gene, the observed differences cannot be attributed to changes in expression of this gene. The mode of feeding by different instars of T. ni determined the photosynthetic response to herbivory, which appeared to be mediated by the level of water stress associated with herbivore damage.

Omega Oxygenases: Nonheme-iron enzymes and P450 cytochromes

Enzymes that effect with ease one of the most difficult chemical reactions, hydroxylation of an unfunctionalized alkyl group, are of particular interest because highly reactive intermediates must be produced. A typical example, the hydroxylation of fatty acids in the omega position, is now known to occur widely in nature. The catalysts, which can be called "omega-oxygenases," also insert molecular oxygen into a variety of other substrates at positions removed from activating functional groups, as in steroids, eicosanoids, and numerous drugs and other xenobiotics. Progress in the characterization of bacterial nonheme-iron enzymes, and plant, bacterial, and mammalian P450 cytochromes that catalyze fatty acid omega-oxidation, and evidence for multiple functional oxidants are summarized.

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.

Probing the cell wall heterogeneity of micro-dissected wheat caryopsis using both active and inactive forms of a GH11 xylanase

The external envelope of wheat grain (Triticum aestivum L. cv. Isengrain) is a natural composite whose tissular and cellular heterogeneity constitute a significant barrier for enzymatic cell wall disassembly. To better understand the way in which the cell wall network and tissular organization hamper enzyme penetration, we have devised a strategy based on in situ visualization of an active and an inactive form of a xylanase in whole-wheat bran and in three micro-dissected layers (the outer bran, the inner bran and the aleurone layer). The main aims of this study were to (1) evaluate the role of cuticular layers as obstacles to enzyme diffusion, (2) assess the impact of the cell wall network on xylanase penetration, (3) highlight wall heterogeneity. To conduct this study, we created by in vitro mutagenesis a hydrolytically inactive xylanase that displayed full substrate binding ability, as demonstrated by the calculation of dissociation constants (K(d)) using fluorescence titration. To examine enzyme penetration and action, immunocytochemical localization of the xylanases and of feebly substituted arabinoxylans (AXs) was performed following incubation of the bran layers, or whole bran with active and inactive isoforms of the enzyme for different time periods. The data obtained showed that the micro-dissected layers provided an increased accessible surface for the xylanase and that the enzyme-targeted cell walls were penetrated more quickly than those in intact bran. Examination of immunolabelling of xylanase indicated that the cuticle layers constitute a barrier for enzyme penetration in bran. Moreover, our data indicated that the cell wall network by itself physically restricts enzyme penetration. Inactive xylanase penetration was much lower than that of the active form, whose penetration was facilitated by the concomitant depletion of AXs in enzyme-sensitive cell walls.

Cloning, Functional Expression, and Characterization of CYP709C1, the First Sub-terminal Hydroxylase of Long Chain Fatty Acid in Plants

We cloned and characterized CYP709C1, a new plant cytochrome P450 belonging to the P450 family, that so far has no identified function except for clustering with a fatty acid metabolizing clade of P450 enzymes. We showed here that CYP709C1 is capable of hydroxylating fatty acids at the omega-1 and omega-2 positions. This work was performed after recoding and heterologous expression of a full-length cDNA isolated from a wheat cDNA library in an engineered yeast strain. Investigation on substrate specificity indicates that CYP709C1 metabolizes different fatty acids varying in their chain length (C12 to C18) and unsaturation. CYP709C1 is the first identified plant cytochrome P450 that can catalyze sub-terminal hydroxylation of C18 fatty acids. cis-9,10-Epoxystearic acid is metabolized with the highest efficiency, i.e. K((m)(app)) of 8 microM and V(max(app)) of 328 nmol/min/nmol P450. This, together with the fact that wheat possesses a microsomal peroxygenase able to synthesize this compound from oleic acid, strongly suggests that it is a physiological substrate. Hydroxylated fatty acids are implicated in plant defense events. We postulated that CYP709C1 could be involved in plant defense by producing such compounds. This receives support from the observation that (i) sub-terminal hydroxylation of 9,10-epoxystearic acid is induced (15-fold after 3 h) in microsomes of wheat seedlings treated with the stress hormone methyl jasmonate and (ii) CYP709C1 is enhanced at the transcriptional level by this treatment. CYP709C1 transcript also accumulated after treatment with a combination of the safener naphthalic acid anhydride and phenobarbital. This indicates a possible detoxifying function for CYP709C1 that we discussed.

Interactions of Humicola insolens cutinase with an anionic surfactant studied by small-angle neutron scattering and isothermal titration calorimetry

The interaction of cutinase from Humicula insolens (HiC) and sodium dodecyl sulfate (SDS) has been investigated by small-angle neutron scattering (SANS) and isothermal titration calorimetry (ITC). The concerted interpretation of structural and thermodynamic information for identical systems proved valuable in attempts to elucidate the complex modes of protein-detergent interaction. Particularly so at the experimental temperature 22 degrees C, where the formation of SDS micelles is athermal (deltaH = 0), and the effects of protein-detergent interactions stand out clearly in the thermograms. It was found that the effect of SDS on cutinase depended strongly on the sample composition. Thus, addition of SDS corresponding to a molar ratio, n(s) = n(SDS)/n(HiC) of about 10, was associated with the formation of HiC/SDS aggregates, which include more than one protein molecule. The SANS results suggested that on the average such adducts contained two HiC, and the ITC traces showed that they form and break down slowly. At slightly higher SDS concentrations (n(s) = 10-25) these "dimers" dissociated, and the protein denatured. The denaturation showed the characteristic positive enthalpy change, but the SDS denatured state of HiC was unusually compact with a radius of gyration close to that of the native conformation. Further titration with SDS was associated with exothermic binding to the denatured protein until the saturation point at about n(s) = 90. At this point, the free monomer concentration was 2.2 mM and the binding number was approximately 40 SDS/HiC. Interestingly, this degree of SDS binding (approximately 0.5 g of SDS/g of HiC) is less than half the amount bound to typical water-soluble proteins.

Unfolding and inactivation of cutinases by AOT and guanidine hydrochloride

We present a comparative analysis of the unfolding and inactivation of three cutinases in the presence of guanidine hydrochloride (GdnHCl) and bis(2-ethylhexyl) sodium sulfosuccinate (AOT). Previous investigations have focused on the cutinase from Fusarium solani pisi (FsC). In addition to FsC, the present study includes the cutinase from Humicola insolens (HiC) and a mutant variant of HiC (muHiC) with increased activity and decreased surfactant sensitivity. Equilibrium and time-resolved denaturation by AOT were studied in aqueous solution and reverse micelles, and were compared with GdnHCl denaturation. The far-UV CD and fluorescence denaturation profiles obtained in the aqueous solutions of the two denaturants coincide for all three cutinases, indicating that unfolding is a co-operative two-state process under these conditions. In reverse micelles, the cutinases unfold with mono-exponential rates, again indicating a two-state process. The free energy of denaturation in water was calculated by linear extrapolation of equilibrium data, yielding very similar values for the three cutinases with averages of -11.6 kcal mol(-1) and -2.6 kcal mol(-1) for GdnHCl and AOT, respectively. Hence, the AOT denatured state (D(AOT)) is less destabilised than the GdnHCl denatured state (D(GdnHCl)), relative to the native state in water. Far-UV CD spectroscopy revealed that D(AOT) retains some secondary structure, while D(GdnHCl) is essentially unstructured. Similarly, fluorescence data suggest that D(AOT) is more compact than D(GdnHCl). Activity measurements reveal that both D(AOT) and D(GdnHCl) are practically inactive (catalytic activity <1% of that of the native enzyme). The fluorescence spectrum of D(AOT) in reverse micelles did not differ significantly from that observed in aqueous AOT. NMR studies of D(AOT) in reverse micelles indicated that the structure is characteristic of a molten globule, consistent with the CD and fluorescence data.

Asymmetric Epoxidation of α-Olefins Having Neighboring Sugar Chiral Templates and Alternating Copolymerization with Dicarboxylic Anhydrides

Sugar-substituted epoxides 5-8 were synthesized by asymmetric epoxidation (in CH(2)Cl(2)/water) of alpha-olefins having neighboring sugars (1-4) by use of an achiral oxidant (MCPBA), in which the sugar moiety acted as a chiral template. The diastereoselectivities depend on the methylene spacer between vinyl group and carbohydrate derivatives. The methylene spacer between sugar and vinyl groups influenced the diastereoselectvity. In the case of epoxidation of 4 at 27 degrees C for 24 h, the diastereoselectivity was the highest (99/1). Copolymerizations of 5-8 with succinic anhydride were attained at 100 degrees C for 72 h to give poly(ethylene succinate) having pendant carbohydrate [poly(SAn-alt-5), M(n) = 1.4 x 10(3); poly(SAn-alt-6), M(n) = 2.2 x10(3); poly(SAn-alt-7), M(n) = 2.9 x 10(3); poly(SAn-alt-8), M(n) = 1.8 x 10(3)]. The methylene spacer between sugar and epoxide has an effect on the reactivity of epoxide in copolymerization as well as the diastereoselectivity. Alternating copolymerization of 7 and glutaric anhydride gave a polyester of M(n) 4.2 x10(3).

Differential expression and evolution of the Arabidopsis CYP86A subfamily

Some members of the Arabidopsis (Arabidopsis thaliana) CYP86A and CYP94B cytochrome P450 monooxygenase subfamilies, which share some sequence homology with the animal and fungal fatty acid hydroxylases, have been functionally defined as fatty acid omega-hydroxylases. With these activities, these and other fatty acid hydroxylases have potential roles in the synthesis of cutin, production of signaling molecules, and prevention of accumulation of toxic levels of free fatty acids. The constitutive and stress-inducible patterns of the five Arabidopsis CYP86A subfamily members have been defined in 7-d-old seedlings and 1-month-old plant tissues grown under normal conditions, and 7-d-old seedlings treated with different hormones (indole-3-acetic acid, abscisic acid, gibberellin, methyl jasmonic acid, brassinosteroid, salicylic acid), chemicals (clofibrate, 1-aminocyclopropane-1 carboxylic acid), or environmental stresses (cold, wounding, drought, mannitol, etiolation). Very distinct expression patterns exist for each of these fatty acid hydroxylases under normal growth conditions and in response to environmental and chemical stresses. Analysis of the promoter sequences for each of these genes with their expression patterns has highlighted a number of elements in current databases that potentially correlate with the responses of individual genes.

Wax and suberin development of native and wound periderm of potato (Solanum tuberosum L.) and its relation to peridermal transpiration

Native and wound periderm was isolated enzymatically from potato (Solanum tuberosum L. cv. Desirée) tubers at different time intervals between 0 days up to 4 weeks after harvesting. Wound periderm formation was induced by carefully removing native periderm from freshly harvested tubers before storage. The chemical composition of lipids (waxes) obtained by chloroform extraction, as well as the monomeric composition of native and wound suberin polymer after transesterification by boron trifluoride/methanol, was analyzed using gas chromatography and mass spectrometry. Both types of periderm contained up to 20% extractable lipids. Besides linear long-chain aliphatic wax compounds, alkyl ferulates were detected as significant constituents. In wound periderm they amounted to more than 60% of the total extracts. Within 1 month of storage, suberin amounts in the polymer increased 2-fold in native periderm (180 microg cm(-2)), whereas in wound periderm about 75.0 microg cm(-2) suberin polymer was newly synthesized. Native potato tuber periderm developed a very efficient transport barrier for water with permeances decreasing from 6.4 x 10(-10) m s(-1) to 5.5 x 10(-11) m s(-1) within 1 month of storage. However, the water permeability of wound periderm was on average 100 times higher with permeances decreasing from 4.7 x 10(-8) m s(-1) after 3 days to only 5.4 x 10(-9) m s(-1) after 1 month of storage, although suberin and wax amounts in wound periderm amounted to about 60% of native periderm. From this result it must be concluded that the occurrence of suberin with wax depositions in cell walls does not necessarily allow us to conclude that these cell walls must be nearly perfect barriers to water transport. In addition to the occurrence of the lipophilic biopolymer suberin and associated waxes, the still unknown molecular arrangement and precisely localized deposition of suberin within the cell wall must contribute to the efficiency of suberin as a barrier to water transport.

Retention and translocation of foliar applied 239,240Pu and 241Am, as compared to 137Cs and 85Sr, into bean plants (Phaseolus vulgaris)

Foliar transfer of 241Am, 239,240Pu, 137Cs and 85Sr was evaluated after contamination of bean plants (Phaseolus vulgaris) at the flowering development stage, by soaking their first two trifoliate leaves into contaminated solutions. Initial retentions of 241Am (27%) and 239,240Pu (37%) were higher than those of 137Cs and 85Sr (10-15%). Mean fraction of retained activity redistributed among bean organs was higher for 137Cs (20.3%) than for 239,240Pu (2.2%), 241Am (1%) or 85Sr (0.1%). Mean leaf-to-pod translocation factors (Bq kg(-1) dry weight pod/Bq kg(-1) dry weight contaminated leaves) were 5.0 x 10(-4) for 241Am, 2.7 x 10(-6) for 239,240Pu, 5.4 x 10(-2) for 137Cs and 3.6 x 10(-4) for 85Sr. Caesium was mainly recovered in pods (12.8%). Americium and strontium were uniformly redistributed among leaves, stems and pods. Plutonium showed preferential redistribution in oldest bean organs, leaves and stems, and very little redistribution in forming pods. Results for americium and plutonium were compared to those of strontium and caesium to evaluate the consistency of the attribution of behaviour of strontium to transuranium elements towards foliar transfer, based on translocation factors, as stated in two radioecological models, ECOSYS-87 and ASTRAL.

Biochemical characterization of elongase activity in corn (Zea mays L.) roots

Chemical analysis of 4-day-old corn (Zea mays L.) root cell walls revealed that the lipophilic biopolymer suberin forms an important constituent of rhizodermal and hypodermal cell walls. Identified aliphatic monomers had chain lengths ranging from C16 to C26 and they belonged to 5 substance classes (omega-hydroxycarboxylic acids, 1,omega-dicarboxylic acids, 2-hydroxycarboxylic acids, carboxylic acids and alcohols) by which suberin is characterized. Biochemical experiments proved the occurrence of elongase activities in corn roots. Highest enzymatic activities were found in corn root microsomes, and major products synthesized by root elongases were elongated fatty acids with chain lengths ranging from C20 to C24. Preferred substrates of root elongases were acyl-CoAs of the chain length C18 and C20, whereas monounsaturated acyl-CoAs (C16:1 and C18:1) and acyl-CoAs of lower (C12-C16) and higher chain lengths (C22-C24) were rarely elongated. Elongase activities significantly decreased over the length (40 cm) of 10-day-old corn roots going from the young tip to the older base of the root. Thus, results presented here show the presence and activity of elongases in roots of plants.

Reverse genetic characterization of cytosolic acetyl-CoA generation by ATP-citrate lyase in Arabidopsis

Acetyl-CoA provides organisms with the chemical flexibility to biosynthesize a plethora of natural products that constitute much of the structural and functional diversity in nature. Recent studies have characterized a novel ATP-citrate lyase (ACL) in the cytosol of Arabidopsis thaliana. In this study, we report the use of antisense RNA technology to generate a series of Arabidopsis lines with a range of ACL activity. Plants with even moderately reduced ACL activity have a complex, bonsai phenotype, with miniaturized organs, smaller cells, aberrant plastid morphology, reduced cuticular wax deposition, and hyperaccumulation of starch, anthocyanin, and stress-related mRNAs in vegetative tissue. The degree of this phenotype correlates with the level of reduction in ACL activity. These data indicate that ACL is required for normal growth and development and that no other source of acetyl-CoA can compensate for ACL-derived acetyl-CoA. Exogenous malonate, which feeds into the carboxylation pathway of acetyl-CoA metabolism, chemically complements the morphological and chemical alterations associated with reduced ACL expression, indicating that the observed metabolic alterations are related to the carboxylation pathway of cytosolic acetyl-CoA metabolism. The observations that limiting the expression of the cytosolic enzyme ACL reduces the accumulation of cytosolic acetyl-CoA-derived metabolites and that these deficiencies can be alleviated by exogenous malonate indicate that ACL is a nonredundant source of cytosolic acetyl-CoA.

Phenanthrene sorption to sequentially extracted soil humic acids and humins

Humic substances strongly influence the environmental fate of hydrophobic organic chemicals in soils and sediments. In this study, the sorption of phenanthrene by humic acids (HAs) and humins was examined. HAs were obtained from progressively extracting a soil, eight times with 0.1 M Na4P207 and two times with 0.1 M NaOH solution, and then the residue was separated into two humin fractions by their organic carbon contents. The chemical and structural heterogeneity of the HAs and humins were characterized by elemental analysis, ultraviolet-visible spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and solid-state 13C NMR. There were significant chemical and structural differences among the HA fractions and humins; the later extracted HAs had relatively high aliphatic carbons content. All sorption data were fitted to a Freundlich equation, S = K(F)C(N), where S and C are the sorbed and solution-phase concentrations, respectively, and K(F) and N are constants. All of the phenanthrene sorptions were nonlinear, and the nonlinearity decreased with further extractions from 0.90 (first extracted HA) to 0.96 (ninth HA) and was the lowest (0.88) for the higher organic carbon content humin. Phenanthrene sorption coefficient by HAs significantly increased with progressive extractions, being the highest for the humins. For HAs isotherms, a positive trend was observed between the sorption coefficient and the aliphaticity, but a negative relation was shown between the nonlinearity and the aliphaticity and between the sorption capacity and polarity of HAs. Phenanthrene sorption was greatly affected by chemical structure and composition of humic substances, even from a same soil. In addition, polarity of humic substances seems to mainly regulate the magnitude of phenanthrene sorption rather than structure.

Structure, chemical composition, and xylanase degradation of external layers isolated from developing wheat grain

The external layers of wheat grain were investigated during maturation with respect to chemical and structural features and xylanase degradability. Cytochemical changes were observed in the isolated peripheral tissues of the wheat grain at four defined stages following anthesis. Marked chemical changes were highlighted at 11 days after anthesis, for which protein and lipid contents varied weakly. The profile of esterified ferulic acid showed large variation in the maturing peripheral layers of grain in contrast to the deposition of ferulate dimers, p-coumaric and sinapic acids. Lignin was monitored at the latest stages of ripening, which corresponds to the cessation of reserve accumulation in the grain. Arabinoxylans (AX) reached a maximum at 20 days and did not display any significant change in arabinosyl substitution proportion until ripeness. When submitted to xylanase, all outer layers were similarly altered in the proportion of soluble AX except for the peripheral tissues of the 11-day-aged wheat grain that had very little AX. Aleurone and nucellar layers were mostly degraded, whereas pericarp stayed intact at all stages of maturation. This degradation pattern was connected with the preferential immunolocalization of xylanase in aleurone and nucellar layers irrespective of the developmental stages. Further chemical examination of the enzyme-digested peripheral tissues of the grain supports the facts that ferulic ester is not a limiting factor in enzyme efficiency. Arabinose branching, ferulic dimers, and ether-linked monomers that are deposited early in the external layers would have more relevance to the in situ degradability of AX.

Sugars--dominant water-soluble organic compounds in soils and characterization as tracers in atmospheric particulate matter

The presence of saccharides is being reported for aerosols taken in urban, rural, and marine locales. The commonly found primary saccharides are alpha- and beta-glucose, alpha- and beta-fructose, sucrose, and mycose with lesser amounts of other monosaccharides. Saccharide polyols are also found in some airsheds and consist mainly of sorbitol, xylitol, mannitol, erythritol, and glycerol. In temperate climate areas these compounds increase from negligible concentrations in winter aerosols (usually dominated by levoglucosan and related anhydrosaccharides from biomass burning) to a maximum in late spring-summer, followed by a decrease to winter. The composition of the saccharide mixtures suggests soil and associated microbiota as the source. Saccharide analyses of soils confirmed these compositions. Therefore, we propose resuspension of soil (also unpaved road dust) from agricultural activities as a major component of aerosol particles and the saccharides are the source specific tracers. In addition, the saccharides as well as the anhydrosaccharide derivatives from biomass burning are completely water soluble and thus contribute significantly to the total water-soluble mass of aerosols.

The ACR4 receptor-like kinase is required for surface formation of epidermis-related tissues in Arabidopsis thaliana

In higher plants, an outer layer of meristematic cells, the protoderm, forms early in embryogenesis and this layer gives rise to the epidermis in differentiating tissues. We proposed previously that an Arabidopsis thaliana homolog of crinkly4 (ACR4), a gene for a receptor-like protein kinase, would be involved in differentiation and/or maintenance of epidermis-related tissues. In the present study, we isolated loss-of-function acr4 mutants by a reverse genetic approach. Our extensive analyses using the transmission electron microscopy and the toluidine blue test -- a method that has recently been developed for the rapid visualization of defects in the leaf cuticle -- showed that the acr4 mutations significantly affected the differentiation of leaf epidermal cells, suggesting similar roles for ACR4 and CR4 in the differentiation of leaf epidermis. Our acr4 mutants also had various abnormalities related to epidermal differentiation, which included disorganized cell layers in the integument and endothelium of ovules. In addition, the green fluorescent protein fused to ACR4 was localized preferentially on the lateral and basal plasma membranes in the epidermis of the leaf primordia, suggesting a role for ACR4 in epidermal differentiation at cell surfaces that make contact with adjacent cells. Furthermore, the loss-of-function mutations in the ACR4 and ABNORMAL LEAF SHAPE1 (ALE1) genes, which encode a putative subtilisin-like serine protease, synergistically affected the function of the epidermis such that most leaves fused. Thus, ACR4 seems to play an essential role in the differentiation of proper epidermal cells in both vegetative and reproductive tissues.

A new method for rapid visualization of defects in leaf cuticle reveals five intrinsic patterns of surface defects in Arabidopsis

The epidermis of higher plants generates the cuticle layer that covers the outer surface of each plant. The cuticle plays a crucial role in plant development, and some mutants with defective cuticle exhibit morphological abnormalities, such as the fusion of organs. The way in which the cuticle forms and its contribution to morphogenesis are poorly understood. Conventional detection of the cuticle by transmission electron microscopy (TEM) requires laborious procedures, which include fixation, staining with osmium, and preparation of ultra-thin sections. It is also difficult to survey entire surfaces of expanded leaves because of the limited size of specimens that can be examined. Thus, TEM is unsuitable for large-scale screening for mutants with defective cuticle. We describe here a rapid and inexpensive method, designated the toluidine-blue (TB) test, for detection of cuticular defects in whole leaves. We demonstrated the validity of the TB test using mutants of Arabidopsis thaliana, including abnormal leaf shape1 (ale1), fiddlehead (fdh), and five eceriferum (cer) mutants, in which the structure and/or function of the cuticle is abnormal. Genetic screening for mutants using the TB test allowed us to identify seven loci. The cuticle-defective regions of leaves of the mutants revealed five intrinsic patterns of surface defects (classes I through V), suggesting that formation of functional cuticle on leaves involves various spatially regulated factors.

Evidence for cross-linking in tomato cutin using HR-MAS NMR spectroscopy

Cutin is a polyester biopolymer component of plant leaf and fruit cuticles, most often associated with waxes and cuticular polysaccharides, and sometimes with another aliphatic biopolymer called cutan. Insolubility of these cuticular biopolymers has made it difficult to apply traditional analytical techniques for structure determination, because most techniques providing molecular level details require solubility. By using the relatively new technique of one and two-dimensional high-resolution magic angle spinning (HR-MAS) NMR spectroscopy, with added information from solid-state 13C NMR spectroscopy, detailed through-bond connectivities and assignments are made for cutin from Lycopersicon esculentum (tomato) fruit. Based on the data obtained, tomato cutin is found to be predominantly an aliphatic polyester with some olefinic and aromatic moieties, consistent with previous studies that employed various degradative approaches. Aside from esters, there are free primary and secondary alcohol groups, as well as free fatty acids. A significant finding is the presence of alpha-branched fatty acids/esters. Mid-chain hydroxyls appear to be generally unesterified, but esters of mid-chain hydroxyls have been identified. The alpha-branched fatty acids/esters and esters of mid-chain hydroxyls could point towards cross-linking.

Reactive oxygen species production in association with suberization: evidence for an NADPH-dependent oxidase

In response to wounding, potato tubers generate reactive oxygen species (ROS) in association with suberization. Immediately following wounding, an initial burst of ROS occurs, reaching a maximum within 30 to 60 min. In addition to this initial oxidative burst, at least three other massive bursts occur at 42, 63 and 100 h post-wounding. These latter bursts are associated with wound healing and are probably involved in the oxidative cross-linking of suberin poly(phenolics). The source of ROS is likely to be a plasma membrane NADPH-dependent oxidase immunorelated to the human phagocyte plasma membrane oxidase. The initial oxidative burst does not appear to be dependent on new protein synthesis, but the subsequent bursts are associated with an increase in oxidase protein components. Oxidase activity is enhanced in vitro by hydroxycinnamic acids and conjugates associated with the wound healing response in potato.

Soil-to-root transfer and translocation of polycyclic aromatic hydrocarbons by vegetables grown on industrial contaminated soils

Polycyclic aromatic hydrocarbons (PAHs) are possible contaminants in some former industrial sites, representing a potential risk to human health if these sites are converted to residential areas. This work was conducted to determine whether PAHs present in contaminated soils are transferred to edible parts of selected vegetables. Soils were sampled from a former gasworks and a private garden, exhibiting a range of PAH concentrations (4 to 53 to 172 to 1263 and 2526 mg PAHs kg-1 of dry soil), and pot experiments were conducted in a greenhouse with lettuce (Lactuca sativa L. var. Reine de Mai), potato (Solanum tuberosum L. var. Belle de Fontenay), and carrot (Daucus carota L. var. Nantaise). At harvest, above- and below ground biomass were determined and the PAH concentrations in soil were measured. In parallel, plates were placed in the greenhouse to estimate the average PAH-dust deposition. Results showed that the presence of PAHs in soils had no detrimental effect on plant growth. Polycyclic aromatic hydrocarbons were detected in all plants grown in contaminated soils. However, their concentration was low compared with the initial soil concentration, and the bioconcentration factors were low (i.e., ranging from 13.4 x 10(-4) in potato and carrot pulp to 2 x 10(-2) in potato and carrot leaves). Except in peeled potatoes, the PAH concentration in vegetables increased with the PAH concentration in soils. The PAH distribution profiles in plant tissues and in soils suggested that root uptake was the main pathway for high molecular weight PAHs. On the opposite, lower molecular weight PAHs were probably taken up from the atmosphere through the leaves as well as by roots.

ACR4, a putative receptor kinase gene of Arabidopsis thaliana, that is expressed in the outer cell layers of embryos and plants, is involved in proper embryogenesis

The surfaces of higher plants are characterized by epidermis, which usually consists of a single layer of cells. The epidermis is derived from the outer cell layer of the embryo or protoderm, which arises as a result of periclinal cell division. After seed germination, most of the epidermal cells of the aerial parts of plants are derived from the outer cell layer of the shoot apical meristem (the L1 layer). Thus, knowledge of how the protoderm and/or L1 layer is established is fundamental to understanding the morphogenesis of higher plants. Here, we report the isolation of a gene encoding an Arabidopsis homologue (ACR4) of the maize putative receptor kinase CRINKLY4 (CR4), which is involved in epidermal differentiation. The domain organization of the predicted amino acid sequence of ACR4 is essentially identical to that of CR4. ACR4-GFP fusion protein localized to the cell surface when expressed in tobacco cell (BY-2) culture. ACR4 transcripts were detected in all the organs of the Arabidopsis plant. In developing embryos and shoot apices, ACR4 transcripts accumulated in protoderm and epidermis at relatively higher levels than in the inner tissues. Over-expression of antisense ACR4 in Arabidopsis plants resulted in malformation of embryos to varying degrees. These results suggest that ACR4 is, at a minimum, involved in the normal morphogenesis of embryos, most likely through properly differentiating protoderm cells.

Hydrogen peroxide is required for poly(phenolic) domain formation during wound-induced suberization

The requirement for hydrogen peroxide (H(2)O(2)) during suberization was demonstrated in wound-induced potato tubers by monitoring the extent of phenolic polymerization after the inhibition of H(2)O(2) production using diphenyleneiodonium (DPI). In DPI-treated tissues the extent of phenolic polymerization in suberized tissues, measured using DFRC (Derivatization Followed by Reductive Cleavage) and thioglycolic acid analyses, was greatly reduced relative to untreated controls. Concomitantly, a large quantity of new soluble phenolics accumulated in the DPI-treated tissue some of which were not present in the controls. We suggest that the inhibition of H(2)O(2) production prevented these phenolics from being oxidized by cell wall peroxidases. As a result, these phenolics were left unpolymerized and accumulated in the tissue. Several of the soluble phenolics were identified as hydroxycinnamic acid derivatives. From the data presented, it was concluded that H(2)O(2) is required for the polymerization step in the formation of the poly(phenolic) domain of suberized potato tubers.

A subtilisin-like serine protease is required for epidermal surface formation inArabidopsisembryos and juvenile plants

The surfaces of land plants are covered with a cuticle that is essential for retention of water. Epidermal surfaces of Arabidopsis thaliana embryos and juvenile plants that were homozygous for abnormal leaf shape1 (ale1) mutations were defective, resulting in excessive water loss and organ fusion in young plants. In ale1 embryos, the cuticle was rudimentary and remnants of the endosperm remained attached to developing embryos. Juvenile plants had a similar abnormal cuticle. The ALE1 gene was isolated using a transposon-tagged allele ale1-1. The predicted ALE1 amino acid sequence was homologous to those of subtilisin-like serine proteases. The ALE1 gene was found to be expressed within certain endosperm cells adjacent to the embryo and within the young embryo. Expression was not detected after germination. Our results suggest that the putative protease ALE1 affects the formation of cuticle on embryos and juvenile plants and that an appropriate cuticle is required for separation of the endosperm from the embryo and for prevention of organ fusion.

An oligomer from flaxseed composed of secoisolariciresinoldiglucoside and 3-hydroxy-3-methyl glutaric acid residues

A straight-chain oligomeric structure composed of five secoisolariciresinoldiglucoside (SDG) residues interconnected by four 3-hydroxy-3-methyl glutaric acid (HMGA) residues (molecular weight ca. 4000 Da) was assigned to the main lignan of flaxseed on the basis of nuclear magnetic resonance spectroscopy (NMR).

Degradation of biomacromolecules during high-rate composting of wheat straw-amended feces

Pig (Sus scrofa) feces, separately collected and amended with wheat straw, was composted in a tunnel reactor connected with a cooler. The composting process was monitored for 4 wk and the degradation of organic matter was studied by two chemical extraction methods, 13C cross polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR) and pyrolysis gas chromatography-mass spectrometry (GC-MS). Wet-chemical extraction methods were not adequate to study the degradation of specific organic compounds as the extraction reagents did not give selective separation of hemicellulose, cellulose, proteins, and lignins. A new method was proposed to calculate the contribution of four biomacromolecules (aliphatics, proteins, polysaccharides, and lignin) from the 13C CPMAS NMR spectrum. Pyrolysis GC-MS allowed identification of the composition of the biomacromolecules. The biomacromolecules showed different rates of degradation during composting. High initial degradation rates of aliphatics, hemicellulose, and proteins were observed, where aliphatics were completely degraded and hemicellulose and proteins were partly recalcitrant during the four weeks of composting. The degradation rate of cellulose was much lower and degradation was not completed within the four weeks of composting. Lignin was not degraded during the thermophilic stage of composting but started to degrade slowly during the mesophilic stage. A combination of 13C CPMAS NMR and pyrolysis GC-MS gave good qualitative and semiquantitative assessments of the degradation of biomacromolecules during composting.

The poly(phenolic) domain of potato suberin: a non-lignin cell wall bio-polymer

Suberized plant cell walls have three distinguishing features: (1) tissue specificity, (2) a poly(aliphatic) domain and (3) a unique, "lignin-like" poly(phenolic) domain. With respect to the latter, comparisons have often been made to lignin, but the unique phenolic composition of suberized cells yields a unique polymer better designated as a poly(phenolic) domain. Potato tubers that have been induced to suberize through wounding make an excellent model system with which the chemistry, biochemistry and macromolecular assembly of the suberin poly(phenolic) domain can be monitored. For example, wound healing potato tubers have been used to determine the unique hydroxycinnamic acid nature of its poly(phenolic) domain using specific carbon-13 labeling studies and specific chemical degradation techniques (e.g. thioacidolysis). Furthermore, a suberization-associated anionic peroxidase has been purified from suberizing potato tubers and subsequently shown to oxidize hydroxycinnamic acids (and their derivatives) in preference to monolignols, as well as yield an unique polymer in vitro. We have since extended these studies to begin analyzing the macromolecular assembly process leading to the deposition of this suberized tissue specific domain. To this end we have begun to describe an H(2)O(2)-generating system with NAD(P)H-dependent oxidase-like properties that is temporally associated with the formation of potato suberin poly(phenolics) during suberization. Herein we describe our progress to date.

A large family of class III plant peroxidases

Class III plant peroxidase (POX), a plant-specific oxidoreductase, is one of the many types of peroxidases that are widely distributed in animals, plants and microorganisms. POXs exist as isoenzymes in individual plant species, and each isoenzyme has variable amino acid sequences and shows diverse expression profiles, suggesting their involvement in various physiological processes. Indeed, studies have provided evidence that POXs participate in lignification, suberization, auxin catabolism, wound healing and defense against pathogen infection. Little, however, is known about the signal transduction for inducing expression of the pox genes. Recent studies have provided information on the regulatory mechanisms of wound- and pathogen-induced expression of some pox genes. These studies suggest that pox genes are induced via different signal transduction pathways from those of other known defense-related genes.