Cell Wall Phenolics Research Articles

The role of cell wall phenolics during the early remodelling of cellulose-deficient maize cells

The habituation of cultured cells to cellulose biosynthesis inhibitors such as dichlobenil (dichlorobenzonitrile, DCB) has proven a valuable tool to elucidate the mechanisms involved in plant cell wall structural plasticity. Our group has demonstrated that maize cells cope with DCB through a modified cell wall in which cellulose is replaced by a more extensive network of highly cross-linked feruloylated arabinoxylans. In order to gain further insight into the contribution of phenolics to the early remodelling of cellulose-deficient cell walls, a comparative HPLC-PAD analysis was carried out of hydroxycinnamates esterified into nascent and cell wall polysaccharides obtained from non-habituated (NH) and habituated to low DCB concentrations (1.5 μM; H) maize suspension-cultured cells.Incipient DCB-habituated cell walls showed significantly higher levels of esterified ferulic acid and p-coumaric acid throughout the culture cycle. In terms of cell wall fortification, ferulic acid is associated to arabinoxylan crosslinking whereas the increase of p-coumaric suggests an early lignification response. As expected, the level of hydroxycinnamates esterified into nascent polysaccharides was also higher in DCB-habituated cells indicating an overexpression of phenylpropanoid pathway. Due to their key role in cell wall strengthening, special attention was paid into the dimerization pattern of ferulic acid. A quantitative comparison of diferulate dehydrodimers (DFAs) between cell lines and cell compartments revealed that an extra dimerization took place in H cells when both nascent and mature cell wall polysaccharides were analysed. In addition, qualitative differences in the ferulic acid coupling pattern were detected in H cells, allowing us to suggest that 8-O-4′-DFA and 8-5′-DFA featured the ferulic acid dimerization when it occurred in the protoplasmic and cell wall fractions respectively. Both qualitative and quantitative differences in the phenolic profile between NH and H cells point to a regioselectivity in the ferulate dehydrodimerization.

Ferulate and lignin cross-links increase in cell walls of wheat grain outer layers during late development

Important biological, nutritional and technological roles are attributed to cell wall polymers from cereal grains. The composition of cell walls in dry wheat grain has been well studied, however less is known about cell wall deposition and modification in the grain outer layers during grain development.In this study, the composition of cell walls in the outer layers of the wheat grain (Triticum aestivum Recital cultivar) was investigated during grain development, with a focus on cell wall phenolics. We discovered that lignification of outer layers begins earlier than previously reported and long before the grain reaches its final size. Cell wall feruloylation increased in development. However, in the late stages, the amount of ferulate releasable by mild alkaline hydrolysis was reduced as well as the yield of lignin-derived thioacidolysis monomers. These reductions indicate that new ferulate-mediated cross-linkages of cell wall polymers appeared as well as new resistant interunit bonds in lignins. The formation of these additional linkages more specifically occurred in the outer pericarp.Our results raised the possibility that stiffening of cell walls occur at late development stages in the outer pericarp and might contribute to the restriction of the grain radial growth.

Release of cell wall phenolic esters during hydrothermal pretreatment of rice husk and rice straw

BackgroundRice husk and rice straw represent promising sources of biomass for production of renewable fuels and chemicals. For efficient utilisation, lignocellulosic components must first be pretreated to enable efficient enzymatic saccharification and subsequent fermentation. Existing pretreatments create breakdown products such as sugar-derived furans, and lignin-derived phenolics that inhibit enzymes and fermenting organisms. Alkali pretreatments have also been shown to release significant levels of simple, free phenolics such as ferulic acid that are normally esterified to cell wall polysaccharides in the intact plant. These phenolics have recently been found to have considerable inhibitory properties. The aim of this research has been to establish the extent to which such free phenolic acids are also released during hydrothermal pretreatment of rice straw (RS) and rice husk (RH).ResultsRS and RH were subjected to hydrothermal pretreatments over a wide range of severities (1.57–5.45). FTIR analysis showed that the pretreatments hydrolysed and solubilised hemicellulosic moieties, leading to an enrichment of lignin and crystalline cellulose in the insoluble residue. The residues also lost the capacity for UV autofluorescence at pH 7 or pH 10, indicating the breakdown or release of cell wall phenolics. Saponification of raw RS and RH enabled identification and quantification of substantial levels of simple phenolics including ferulic acid (tFA), coumaric acid (pCA) and several diferulic acids (DiFAs) including 8-O-4′-DiFA, 8,5′-DiFA and 5,5′-DiFA. RH had higher levels of pCA and lower levels of tFA and DiFAs compared with RS. Assessment of the pretreatment liquors revealed that pretreatment-liberated phenolics present were not free but remained as phenolic esters (at mM concentrations) that could be readily freed by saponification. Many were lost, presumably through degradation, at the higher severities.ConclusionDifferences in lignin, tFA, DiFAs and pCA between RS and RH reflect differences in cell wall physiology, and probably contribute to the higher recalcitrance of RH compared with RS. Hydrothermal pretreatments, unlike alkali pretreatments, release cinnamic acid components as esters. The potential for pretreatment-liberated phenolic esters to be inhibitory to fermenting microorganisms is not known. However, the present study shows that they are found at concentrations that could be significantly inhibitory if released as free forms by enzyme activity.

Structural modification of hemicelluloses and lignin based on the biorefinery process with white-rot fungal

On the concept of biorefinery, hemicellulosic and lignin fractions were isolated from white-rot fungal Trametes velutina D10149 biodegraded poplar, and the structural modification was elucidated in detail according to the different incubation duration. Transversal-section Raman images showed that the fiber secondary walls were preferentially degraded, whereas the compound middle lamellae, including the cell corner regions, were mainly intact after 16 weeks incubation. More importantly, lignin and carbohydrates were simultaneously removed within the fiber secondary wall. From wet chemistry analysis, the yields and structural properties for both hemicellulosic and lignin fractions were not significantly altered. The synergistic effect of ligninolytic system finally obviously appeared after 16 weeks incubation, evidenced by the remarkable decrement of hemicellulose and lignin molecular weights. Additionally, the preferential degradation of S units in lignin biomacromolecule was further confirmed by composition analysis of cell wall phenolics and the integration of 2D NMR correlations in the aromatic region.

Variation in the chemical composition of wheat straw: the role of tissue ratio and composition.

BackgroundWheat straw is an attractive substrate for second generation ethanol production because it will complement and augment wheat production rather than competing with food production. However, like other sources of lignocellulosic biomass, even from a single species, it is heterogeneous in nature due to the different tissues and cell types, and this has implications for saccharification efficiency. The aim of this study has been to use Fourier transform infrared (FTIR) spectroscopy and Partial least squares (PLS) modelling to rapidly screen wheat cultivars for the levels of component tissues, the carbohydrate composition and lignin content, and the levels of simple cross-linking phenolics such as ferulic and diferulic acids.ResultsFTIR spectroscopy and PLS modelling was used to analyze the tissue and chemical composition of wheat straw biomass. Predictive models were developed to evaluate the variability in the concentrations of the cell wall sugars, cell wall phenolics and acid-insoluble lignin. Models for the main sugars, phenolics and lignin were validated and then used to evaluate the variation in total biomass composition across 90 cultivars of wheat grown over two seasons.ConclusionsWhilst carbohydrate and lignin components varied across the varieties, this mainly reflected differences in the ratios of the component tissues rather than differences in the composition of those tissues. Further analysis indicated that on a mol% basis, relative levels of sugars within the tissues varied to only a small degree. There were no clear associations between simple phenolics and tissues. The results provide a basis for improving biomass quality for biofuels production through selection of cultivars with appropriate tissue ratios.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0121-y) contains supplementary material, which is available to authorized users.

Wound healing response and xylem differentiation in tobacco plants over-expressing a fungal endopolygalacturonase is mediated by copper amine oxidase activity

In this work, we have investigated the involvement of copper amine oxidase (CuAO; EC 1.4.3.21) in wound healing and xylem differentiation of Nicotiana tabacum plants over-expressing a fungal endopolygalacturonase (PG plants), which show constitutively activated defence responses. In petioles and stems of PG plants, we found higher CuAO activity and lower polyamine (PA) levels, particularly putrescine (Put), with respect to wild-type (WT) plants. Upon wounding, a more intense autofluorescence of cell wall phenolics was observed in correspondence of wound surface, extending to epidermis and cortical parenchima only in PG plants. This response was mostly dependent on CuAO activity, as suggested by the reversion of autofluorescence upon supply of 2-bromoethylamine (2-BrEt), a CuAO specific inhibitor. Moreover, in unwounded plants, histochemical analysis revealed a tissue-specific expression of the enzyme in the vascular cambium and neighboring derivative cells of both petioles and stems of PG plants, whereas the corresponding WT tissues appeared unstained or faintly stained. A higher histochemical CuAO activity was also observed in xylem cells of PG plants as compared to WT xylem tissues suggesting a peculiar role of CuAO activity in xylem differentiation in PG plants. Indeed, roots of PG plants exhibited early xylem differentiation, a phenotype consistent with both the higher CuAO and the lower Put levels observed and supported by the 2-BrEt-mediated reversion of early root xylem differentiation and H2O2 accumulation. These results strongly support the relevance of PA-catabolism derived H2O2 in defence responses, such as those signaled by a compromised status of cell wall pectin integrity.

Variation in the chemical composition of wheat straw: the role of tissue ratio and composition

BackgroundWheat straw is an attractive substrate for second generation ethanol production because it will complement and augment wheat production rather than competing with food production. However, like other sources of lignocellulosic biomass, even from a single species, it is heterogeneous in nature due to the different tissues and cell types, and this has implications for saccharification efficiency. The aim of this study has been to use Fourier transform infrared (FTIR) spectroscopy and Partial least squares (PLS) modelling to rapidly screen wheat cultivars for the levels of component tissues, the carbohydrate composition and lignin content, and the levels of simple cross-linking phenolics such as ferulic and diferulic acids.ResultsFTIR spectroscopy and PLS modelling was used to analyze the tissue and chemical composition of wheat straw biomass. Predictive models were developed to evaluate the variability in the concentrations of the cell wall sugars, cell wall phenolics and acid-insoluble lignin. Models for the main sugars, phenolics and lignin were validated and then used to evaluate the variation in total biomass composition across 90 cultivars of wheat grown over two seasons.ConclusionsWhilst carbohydrate and lignin components varied across the varieties, this mainly reflected differences in the ratios of the component tissues rather than differences in the composition of those tissues. Further analysis indicated that on a mol% basis, relative levels of sugars within the tissues varied to only a small degree. There were no clear associations between simple phenolics and tissues. The results provide a basis for improving biomass quality for biofuels production through selection of cultivars with appropriate tissue ratios.

An UPLC-MS/MS Method for the Simultaneous Identification and Quantitation of Cell Wall Phenolics in Brassica napus Seeds

The seed residues left after pressing of rapeseed oil are rich in proteins and could be used for human nutrition and animal feeding. These press cakes contain, however, antinutritives, with fiber being the most abundant one. The analysis of fiber phenolic component (localized to seed coat cell walls) is, therefore, important in breeding and food quality control. However, correct structure and content assignments of cell wall-bound phenolics are challenging due to their low stability during sample preparation. Here, a novel LC-MS/MS-based method for the simultaneous identification and quantitation of 66 cell wall-bound phenolics and their derivatives is described. The method was internally standardized, corrected for degradation effects during sample preparation, and cross-validated with a well-established UV-based procedure. This approach was successfully applied to the analysis of cell wall phenolic patterns in different B. napus cultivars and proved to be suitable for marker compound search as well as assay development.

DWARF50 (D50), a rice (Oryza sativa L.) gene encoding inositol polyphosphate 5‐phosphatase, is required for proper development of intercalary meristem

Rice internodes are vital for supporting high-yield panicles, which are controlled by various factors such as cell division, cell elongation and cell wall biosynthesis. Therefore, formation and regulation of the internode cell-producing intercalary meristem (IM) are important for determining the shape of internodes. To understand the regulation of internode development, we analysed a rice dwarf mutant, dwarf 50 (d50). Previously, we reported that parenchyma cells in the elongated internodes of d50 ectopically deposit cell wall phenolics. In this study, we revealed that D50 encodes putative inositol polyphosphate 5-phosphatase (5PTase), which may be involved in phosphoinositide signalling required for many essential cellular functions, such as cytoskeleton organization, endocytosis and vesicular trafficking in eukaryotes. Analysis of the rice genome revealed 20 putative 5PTases including D50. The d50 mutation induced abnormally oriented cell division, irregular deposition of cell wall pectins and thick actin bundles in the parenchyma cells of the IM, resulting in abnormally organized cell files of the internode parenchyma and dwarf phenotype. Our results suggest that the putative 5PTase, encoded by D50, is essential for IM formation, including the direction of cell division, deposition of cell wall pectins and control of actin organization.

Modification of esterified cell wall phenolics increases vulnerability of tall fescue to herbivory by the fall armyworm

Feruloylation of arabinoxylan in grass cell walls leads to cross-linked xylans. Such cross-linking appears to play a role in plant resistance to pathogens and insect herbivores. In this study, we investigated the effect of ferulate cross-linking on resistance to herbivory by fall armyworm (Spodoptera frugiperda) making use of genetically modified tall fescue [Schedonorus arundinaceus (Festuca arundinacea)] expressing a ferulic acid esterase gene. Mature leaves of these plants have significant reduced levels of cell wall ferulates and diferulates but no change in acid detergent lignin. These reduced levels of esterified cell wall ferulates in transgenic plants had a positive effect on all measures of armyworm larval performance examined. More larvae survived (89 vs. 57%) and grew faster (pupated 2.1days sooner) when fed transgenic leaves with reduced levels of cell wall ferulates, than when fed control tall fescue leaves where levels of cell wall ferulates were not altered. Overall, mortality, growth and food utilization were negatively associated with level of esterified cell wall ferulates and diferulates in leaves they were fed. This study is the first to use transgenic plants with modified level of cell wall esterified ferulates to test the role of feruloylation in plant resistance to insects. It is concluded that the accumulation of ferulates and the cross-linking of arabinoxylans via diferulate esters in the leaves of tall fescue underlies the physical barrier to insect herbivory. Reducing ferulate cross-linking in grass cell walls could increase susceptibility of these plants to insect folivores.

Interaction between boron and aluminum and their effects on phenolic metabolism of Linum usitatissimum L. roots

Aluminum toxicity is the most important limiting factor for plant growth and development in acidic soils (pH < 5.5). Inhibition of root growth has been considered as a sensitive marker of aluminum toxicity and the best indicator of boron deficiency as well. On the other hand cell wall phenolics (lignin and phenolic acids) have important roles in the reduction of extensibility of cell wall under stress conditions. Therefore, the interaction between boron and aluminum on phenolic compounds and the activity of the enzymes involved in their biosynthesis were investigated in flax seedlings. The seedlings were grown in Hoagland's solution and were treated with 3 B levels (4.5, 45 and 450 μM of H₃BO₃ at deficient, normal, and excess conditions, respectively) and 3 Al levels (0, 50 and 100 μM of AlCl₃.6H₂O). The results showed that Al treatment did not affect B content of roots (B content of Al-treated and non-treated plants were identical), while B treatment, particularly in higher concentrations, decreased Al content of roots compared with the control plants. In addition, the highest B concentration prevented the inhibitory effect of Al on the root length of plants. High concentrations of B also resulted in the decrease of enzyme activities involved in phenolic compounds (i.e., phenylalanine ammonia-lyase, polyphenol oxidase and peroxidase), decrease of lignin content and wall-bound phenols under Al stress, thereby ameliorating Al toxicity. The results suggest that the requirement of flax plants for B under Al stress conditions is higher than that required for growth in normal conditions without Al.

Impacts of ambient salinity and copper on brown algae: 2. Interactive effects on phenolic pool and assessment of metal binding capacity of phlorotannin

The aim of this study was to establish in laboratory experiments a quantitative link between phenolic pool (production, composition and exudation) in Ascophyllum nodosum and Fucus vesiculosus and their potential to bind metals. Additionally, the copper binding capacity of purified phlorotannin was investigated. A reduction in salinity decreased total phenolic contents, altered phenolic composition by increasing proportion of cell-wall phenolics, and also increased phenolic exudation of the two seaweed species. After 15 days at a salinity of 5, the inhibition of photosynthesis observed previously for A. nodosum coincided with the high exudation of phenolic compounds into the surrounding water of the seaweed tips which resulted in a significant reduction of phenolic contents. Increased copper concentration also reduced total phenolic contents, changed phenolic composition (increase in proportion and level of cell-wall phenolics), and positively affected phenolic exudation of A. nodosum and F. vesiculosus. A decrease in salinity enhanced the copper toxicity and caused the earlier impact on the physiology of seaweed tips. An involvement of phlorotannins in copper binding is also demonstrated; purified phlorotannins from A. nodosum collected from a site with little anthropogenic activity contained all four metals tested. When placed in copper-enriched water, as for the seaweed material, copper contents of the phenolics increased, zinc and cadmium contents decreased, but no change in chromium content was observed. The use of cell-wall phenolic content as biomarker of copper contamination seems promising but needs further investigation.

Composition of cell wall phenolics and polysaccharides of the potential bioenergy crop -Miscanthus

The composition and concentrations of cell wall polysaccharides and phenolic compounds were analyzed in mature stems of several Miscanthus genotypes, in comparison with switchgrass and reed (Arundo donax), and biomass characteristics were correlated with cell wall saccharification efficiency. The highest cellulose content was found in cell walls of M. sinensis‘Grosse Fontaine’ (55%) and in A. donax (47%) and lowest (about 32%) in M. sinensis‘Adagio’. There was little variation in lignin contents across M. sinensis samples (all about 22–24% of cell wall), however, Miscanthus×giganteus (M × g) cell walls contained about 28% lignin, reed – 23% and switchgrass – 26%. The highest ratios of cellulose/lignin and cellulose/xylan were in M. sinensis‘Grosse Fontaine’ across all samples tested. About the same total content of ester-bound phenolics was found in different Miscanthus genotypes (23–27 μg/mg cell wall), while reed cell walls contained 17 μg/mg cell wall and switchgrass contained a lower amount of ester-bound phenolics, about 15 μg/mg cell wall. Coumaric acid was a major phenolic compound ester-bound to cell walls in plants analyzed and the ratio of coumaric acid/ferulic acid varied from 2.1 to 4.3, with the highest ratio being in M × g samples. Concentration of ether-bound hydroxycinnamic acids varied greatly (about two-three-fold) within Miscanthus genotypes and was also the highest in M × g cell walls, but at a concentration lower than ester-bound hydroxycinnamic acids. We identified four different forms of diferulic acid esters bound to Miscanthus cell walls and their concentration and proportion varied in genotypes analyzed with the 5-5-coupled dimer being the predominant type of diferulate in most samples tested. The contents of lignin and ether-bound phenolics in the cell wall were the major determinants of the biomass degradation caused by enzymatic hydrolysis.

The phenolic profile of maize primary cell wall changes in cellulose-deficient cell cultures

Cultured maize cells habituated to grow in the presence of the cellulose synthesis inhibitor dichlobenil (DCB) have a modified cell wall in which the amounts of cellulose are reduced and the amounts of arabinoxylan increased. This paper examines the contribution of cell wall-esterified hydroxycinnamates to the mechanism of DCB habituation. For this purpose, differences in the phenolic composition of DCB-habituated and non-habituated cell walls, throughout the cell culture cycle and the habituation process were characterized by HPLC. DCB habituation was accompanied by a net enrichment in cell wall phenolics irrespective of the cell culture phase. The amount of monomeric phenolics was 2-fold higher in habituated cell walls. Moreover, habituated cell walls were notably enriched in p-coumaric acid. Dehydrodimers were 5–6-fold enhanced as a result of DCB habituation and the steep increase in 8,5′-diferulic acid in habituated cell walls would suggest that this dehydrodimer plays a role in DCB habituation. In summary, the results obtained indicate that cell wall phenolics increased as a consequence of DCB habituation, and suggest that they would play a role in maintaining the functionality of a cellulose impoverished cell wall.

De novo biosynthesis of defense root exudates in response to Fusarium attack in barley

Summary *Despite recent advances in elucidation of natural products in root exudates, there are significant gaps in our understanding of the ecological significance of products in the rhizosphere. *Here, we investigated the potential of barley (Hordeum vulgare) to secrete defense root exudates when challenged by the soilborne pathogen Fusarium graminearum. *Liquid chromatography with photodiode array detection (LC-DAD) was used to profile induced small-molecular-weight exudates. Thus, t-cinnamic, p-coumaric, ferulic, syringic and vanillic acids were assigned to plant metabolism and were induced within 2 d after Fusarium inoculation. Biological tests demonstrated the ability of those induced root exudates to inhibit the germination of F. graminearum macroconidia. In vivo labeling experiments with (13)CO(2) revealed that the secreted t-cinnamic acid was synthesized de novo within 2 d of fungal infection. Simultaneously to its root exudation, t-cinnamic acid was accumulated in the roots. Microscopic analysis showed that nonlignin cell wall phenolics were induced not only in necrosed zones but in all root tissues. *Results suggest that barley plants under attack respond by de novo biosynthesis and secretion of compounds with antimicrobial functions that may mediate natural disease resistance.

Metabolic effects of glyphosate change the capacity of maize culture to regenerate plants

Since the presence of glyphosate in maize tissue cultures of proprietary line L2 was very detrimental to plant regeneration, we determined metabolic changes associated with the glyphosate effects on plant regeneration in maize cultures. The polar fraction composition and soluble and cell-wall-bound phenolics were analyzed in the regenerable (R) and non-regenerable (NR) calluses of maize line L2. The tissues with high regeneration capacity had low sugar and 4-aminobutyric acid (GABA) concentrations and increased concentrations of most amino acids, polyamines and indole-3-butenol in the soluble polar fraction and higher ferulic acid/coumaric acid and ferulic acid/diferulic acid ratios and higher levels of the predominant G (guaiacyl) units in the cell wall fraction compared with NR calluses as was found before with H99 and HiII maize R and NR tissues, indicating an association of these metabolites with the capacity of maize cultured tissue to regenerate plants. We also found that di-coumaroyl spermidine and coumaroyl-feruoyl spermidine are present in the soluble fraction of L2 R tissues and are practically absent in NR tissues. However, we did not see such differences in HiII and H99 samples, which indicate that these are genotypic features not related to the capacity to regenerate plants in maize tissue cultures. Glyphosate treatment caused the accumulation of shikimic and quinic acids (not detected in untreated samples) in R and NR calluses (with higher levels found in R tissues) and also decreased the FA/diFA ratio in cell wall phenolics, polyamine and amino acid levels, and increased sugar concentrations in the R L2 tissues, indicating a metabolic shift of R callus to NR tissues.

Changes in Phenolic Concentrations during Recurrent Selection for Resistance to the Mediterranean Corn Borer (Sesamia nonagrioides Lef.)

Recurrent selection has been reported as successful for improving maize resistance against corn borers. This study was conducted to determine if phenolics concentration in maize changes during recurrent selection to improve stalk resistance to the Mediterranean corn borer. Three cycles of selection [EPS12(S)C0, ESP12(S)C2, and EPS12(S)C3] from the maize synthetic population EPS12 and test crosses to inbred lines A639, B93, and EP42 were field grown and artificially infested with Mediterranean corn borer larvae, and the pith tissues were sampled for biochemical analyses. Two major simple phenolic acids [p-coumaric (p-CA) and trans-ferulic (E-FA) acids] were identified in free and cell-wall fractions, whereas four isomers of diferulic acid (DFA) (8-5'l, 5-5', 8-o-4', and 8-5' benzofuran form) were present in the cell-wall bound fraction. The selection cycles EPS12(S)C0 and EPS12(S)C3 showed less damage and higher cell wall phenolics concentrations than the cycle EPS12(S)C2. In addition, higher concentrations of total DFAs were associated with shorter tunnel length and lower numbers of larvae per stem. The current study shows new and concrete evidence that the cell-wall bound phenolics could have a determinative role in the resistance to the Mediterranean corn borer, although future development of recurrent and divergent selection cycles will clarify this point.

Effects of storage conditions on the accumulation of ferulic acid derivatives in white asparagus cell walls

AbstractWhite asparagus cell walls have shown to contain important amounts of phenolics, including ferulic acid and its dimers and trimers. It has been suggested that these phenolic compounds are mainly responsible for cross‐linking the different cell wall polymers related to asparagus hardening. During post‐harvest storage, the asparagus texture and the amount of cell wall phenolics increased significantly. In the present work, the effect of post‐harvest storage conditions on the accumulation of ferulic acid and its derivatives has been investigated. Three different storage conditions were used: keeping the spears in aerobic conditions at room temperature (ART) and at 4 °C (A4 °C), and in anaerobic conditions at room temperature (AnRT). A direct relationship between phenol accumulation and increases in texture was observed, and these changes are dependent on temperature and storage atmosphere. An increase in temperature led to a higher amount of cell wall phenolics and the absence of oxygen in the storage atmosphere delayed their accumulation. The evolution of ferulic dimers during the three storage conditions suggests a relevant role of 8‐O‐4′‐diFA and 8,5′‐BAdiFA in white asparagus hardening. Copyright © 2006 Society of Chemical Industry

Biochemical features of maize tissues with different capacities to regenerate plants

Metabolic profiling using GC-MS and LC-MS analyses of soluble metabolites and cell wall bound phenolic compounds from maize calluses of different morphogenic competence revealed a number of biochemical characteristics that distinguish tissues with high plant regeneration ability from tissues that cannot efficiently regenerate plants in vitro. Maize cultures of different ages from H99 (compact type I callus) and HiII (friable type II callus) were divided into two different samples: regenerable (R) and non-regenerable (NR) based on known morphologies. Tissues from both genotypes with high morphogenic potential had higher asparagine and aspartate and indole-3-butenol concentrations, decreased sugar and DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) concentrations, low levels of 4-aminobutyric acid (GABA) and chlorogenic acid and lower levels of feruloyl- and sinapoyl glucosides compared to NR tissues. The ether bound cell wall phenolics of tissues with high regeneration potential had higher levels of the predominant G (guaiacyl) units and lower levels of H (p-hydroxyphenyl) and S (syringyl) units and higher ferulic acid/coumaric acid and ferulic acid/diferulic acid ratios. The same trends were found with the ester-bound phenolics of HiII, however, there were only small differences between the H99 R and NR tissues. Concentrations of the major sugars, organic acids, amino acids and soluble aromatic compounds tended to increase as the time after culture initiation increased. The results show that there are differences in general metabolism, phenolic secondary compounds and cell wall composition between R and NR cell types.

Ripening‐related changes in the cell walls of olive (Olea europaea L.) pulp of two consecutive harvests

AbstractOlive fruits, harvested in two consecutive seasons at green, cherry and black stages, were used to study compositional changes in the cell walls during ripening. Ripening‐related changes in both harvests were characterised mainly by an increase in the solubilisation of pectic and hemicellulosic polysaccharides, an increase in the relative amount of arabinose in pectic polysaccharides and a decrease in the degree of methylesterification of pectic polysaccharides. Further to degrading processes, the data obtained suggest the synthesis of new polysaccharides. The analysis of olive cell wall phenolics showed mainly the presence of p‐coumaric acid, which increased in one harvest, whereas in the other the values did not differ. The samples of the second harvest, although presenting green, cherry and black colours, had less distinct ripening characteristics than those of the previous harvest. Different activity levels of polyphenol oxidase, polygalacturonase and pectin methylesterase might have contributed to the differences observed between the two harvests. The results showed the distinct extension of ripening‐related changes in the cell walls of the two harvests, indicating that the olive colour, although characteristic of the stage of ripening, cannot be strictly used for its evaluation and definition. Copyright © 2006 Society of Chemical Industry