Cell Wall-Bound Phenolic Acid and Lignin Contents in Date Palm as Related to its Resistance to Fusarium Oxysporum

The root cell walls of the resistant cultivars of the date palm were more resistant to the action of the cell wall-degrading enzymes (CWDE) of Fusarium oxysporum f. sp. albedinis than those of the susceptible cultivars. Date palm roots contain four cell wall-bound phenolics identified as p-hydroxybenzoic acid, p-coumaric acid, ferulic acid and sinapic acid. The contents of p-coumaric acid and ferulic acid in the resistant cultivars (IKL, SLY, BSTN) were about 2 times higher than those in the susceptible cultivars (BFG, JHL, BSK). The contents of p-hydroxybenzoic acid and sinapic acid in the resistant cultivars were 8.4 and 4.5 times, respectively, higher than those in the susceptible cultivars. The lignin contents in roots of the resistant cultivars were 1.8 times higher than those of the susceptible cultivars. The cell wall-bound phenols accumulated particularly in resistant cultivars reduced strongly the mycelial growth and the CWDE production in vitro.     

Structure-function relationships of the antibacterial activity of phenolic acids and their metabolism by lactic acid bacteria

Aims: To determine structure–function relationships of antibacterial phenolic acids and their metabolites produced by lactic acid bacteria (LAB). Methods and Results: Minimum inhibitory concentrations (MICs) of 6 hydroxybenzoic and 6 hydroxycinnamic acids were determined with Lactobacillus plantarum, Lactobacillus hammesii, Escherichia coli and Bacillus subtilis as indicator strains. The antibacterial activity of phenolic acids increased at lower pH. A decreasing number of hydroxyl groups enhanced the activity of hydroxybenzoic acids, but had minor effects on hydroxycinnamic acids. Substitution of hydroxyl groups with methoxy groups increased the activity of hydroxybenzoic, but not of hydroxycinnamic, acid. Metabolism of chlorogenic, caffeic, p‐coumaric, ferulic, protocatechuic or p‐hydroxybenzoic acids by L. plantarum, L. hammesii, Lactobacillus fermentum and Lactobacillus reuteri was analysed by LC‐DAD‐MS. Furthermore, MICs of substrates and metabolites were compared. Decarboxylated and/or reduced metabolites of phenolic acids had a lower activity than the substrates. Strain‐specific metabolism of phenolic acids generally corresponded to resistance. Conclusions: The influence of lipophilicity on the antibacterial activity of hydroxybenzoic acids is stronger than that of hydroxycinnamic acids. Metabolism of phenolic acids by LAB detoxifies phenolic acids. Significance and Impact of the Study: Results allow the targeted selection of plant extracts for food preservation, and selection of starter cultures for fermented products.     

Cell wall alterations in the leaves of fusariosis-resistant and susceptible pineapple cultivars

Fusariosis, caused by the fungus Fusarium subglutinans f. sp. ananas (Syn. F. guttiforme), is one of the main phytosanitary threats to pineapple (Ananas comosus var. comosus). Identification of plant cell responses to pathogens is important in understanding the plant–pathogen relationship and establishing strategies to improve and select resistant cultivars. Studies of the structural properties and phenolic content of cell walls in resistant (Vitoria) and susceptible (Perola) pineapple cultivars, related to resistance to the fungus, were performed. The non-chlorophyll base of physiologically mature leaves was inoculated with a conidia suspension. Analyses were performed post-inoculation by light, atomic force, scanning and transmission electron microscopy, and measurement of cell wall-bound phenolic compounds. Non-inoculated leaves were used as controls to define the constitutive tissue characteristics. Analyses indicated that morphological differences, such as cell wall thickness, cicatrization process and lignification, were related to resistance to the pathogen. Atomic force microscopy indicated a considerable difference in the mechanical properties of the resistant and susceptible cultivars, with more structural integrity, associated with higher levels of cell wall-bound phenolics, found in the resistant cultivar. p-Coumaric and ferulic acids were shown to be the major phenolics bound to the cell walls and were found in higher amounts in the resistant cultivar. Leaves of the resistant cultivar had reduced fungal penetration and a faster and more effective cicatrization response compared to the susceptible cultivar.     

Role of phenolic acids and enzymes of phenylpropanoid pathway in resistance of chayote fruit (Sechium edule) against infestation by melon fly,Bactrocera cucurbitae

Melon fly is a serious pest of cucurbits all over the world causing huge losses to yield. However, the only exception is the chayote fruit (Sechium edule) that shows resistance to melon fly infestation. Studies on culture of melon fly indicated the absence of plant traits resisting oviposition on chayote fruit. However, the melon fly was unable to complete its life cycle successfully on chayote showing that factors inhibiting larval development in melon fly could be attributed to biochemical constituents. Studies were, therefore, carried out to compare the biochemical responses of chayote, a melon fly resistant species and bitter gourd, a susceptible species to melon fly infestation with regard to the levels of phenolic acids and activities of the enzymes of phenylpropanoid pathway (PPP) leading to synthesis of lignin. The resistant chayote exhibited significantly higher accumulation of lignin associated with higher activities of phenylalanine ammonia‐lyase (PAL), tyrosine ammonia‐lyase (TAL), cinnamyl alcohol dehydrogenase (CAD) and peroxidase (POD). On the contrary, the susceptible bitter gourd recorded lower activities of PAL, CAD and POD and a decreasing trend of TAL during infestation associated with a lower lignin content. The monomer composition of lignin in the resistant chayote showed twofold higher level of guaiacyl (G) and syringyl (S) units compared to susceptible bitter gourd and the G/S ratio during infestation increased in chayote while decreasing in bitter gourd. The levels of PPP intermediates, p‐coumaric acid was higher in chayote while p‐hydroxy benzoic acid, a chemo‐attractant, was higher in bitter gourd. Incorporation of p‐coumaric acid in the larval diet strongly inhibited larval growth even as p‐hydroxy benzoic acid promoted growth confirming the direct role of p‐coumaric acid in conferring resistance to chayote. The level of salicylic acid, a signal molecule involved in induction of defence response, was higher in chayote compared to bitter gourd. Chayote also exhibited higher level of activity of POD in the phloem exudates compared to bitter gourd. The higher concentration of sugars in exudates of chayote might act like signalling molecules causing activation of plant genes, especially of the phenylpropanoid biosynthesis pathway and possibly produce an osmotic effect inducing resistance against the melon fly. Thus, the study revealed that the resistance in chayote to melon fly infestation is a complex, multi‐layered process in which the activities of PPP enzymes generating phenolic intermediates leading to lignin biosynthesis and the composition of exudates appear to play significant roles. Besides, the study also indicated that different forms of lignin might play a role in the resistance of chayote against melon fly infestation.     

Wine phenolic compounds influence the production of volatile phenols by wine-related lactic acid bacteria

Aims: To evaluate the effect of wine phenolic compounds on the production of volatile phenols (4‐vinylphenol [4VP] and 4‐ethylphenol [4EP]) from the metabolism of p‐coumaric acid by lactic acid bacteria (LAB). Methods and Results: Lactobacillus plantarum, Lactobacillus collinoides and Pediococcus pentosaceus were grown in MRS medium supplemented with p‐coumaric acid, in the presence of different phenolic compounds: nonflavonoids (hydroxycinnamic and benzoic acids) and flavonoids (flavonols and flavanols). The inducibility of the enzymes involved in the p‐coumaric acid metabolism was studied in resting cells. The hydroxycinnamic acids tested stimulated the capacity of LAB to synthesize volatile phenols. Growth in the presence of hydroxycinnamic acids, especially caffeic acid, induced the production of 4VP by resting cells. The hydroxybenzoic acids did not significantly affect the behaviour of the studied strains. Some of the flavonoids showed an effect on the production of volatile phenols, although strongly dependent on the bacterial species. Relatively high concentrations (1 g l^?1) of tannins inhibited the synthesis of 4VP by Lact. plantarum. Conclusions: Hydroxycinnamic acids were the main compounds stimulating the production of volatile phenols by LAB. The results suggest that caffeic and ferulic acids induce the synthesis of the cinnamate decarboxylase involved in the metabolism of p‐coumaric acid. On the other hand, tannins exert an inhibitory effect. Significance and Impact of the Study: This study highlights the capacity of LAB to produce volatile phenols and that this activity is markedly influenced by the phenolic composition of the medium.     

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.     

Enhanced Lignin Monomer Production Caused by Cinnamic Acid and Its Hydroxylated Derivatives Inhibits Soybean Root Growth

Cinnamic acid and its hydroxylated derivatives (p-coumaric, caffeic, ferulic and sinapic acids) are known allelochemicals that affect the seed germination and root growth of many plant species. Recent studies have indicated that the reduction of root growth by these allelochemicals is associated with premature cell wall lignification. We hypothesized that an influx of these compounds into the phenylpropanoid pathway increases the lignin monomer content and reduces the root growth. To confirm this hypothesis, we evaluated the effects of cinnamic, p-coumaric, caffeic, ferulic and sinapic acids on soybean root growth, lignin and the composition of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) monomers. To this end, three-day-old seedlings were cultivated in nutrient solution with or without allelochemical (or selective enzymatic inhibitors of the phenylpropanoid pathway) in a growth chamber for 24 h. In general, the results showed that 1) cinnamic, p-coumaric, caffeic and ferulic acids reduced root growth and increased lignin content; 2) cinnamic and p-coumaric acids increased p-hydroxyphenyl (H) monomer content, whereas p-coumaric, caffeic and ferulic acids increased guaiacyl (G) content, and sinapic acid increased sinapyl (S) content; 3) when applied in conjunction with piperonylic acid (PIP, an inhibitor of the cinnamate 4-hydroxylase, C4H), cinnamic acid reduced H, G and S contents; and 4) when applied in conjunction with 3,4-(methylenedioxy)cinnamic acid (MDCA, an inhibitor of the 4-coumarate:CoA ligase, 4CL), p-coumaric acid reduced H, G and S contents, whereas caffeic, ferulic and sinapic acids reduced G and S contents. These results confirm our hypothesis that exogenously applied allelochemicals are channeled into the phenylpropanoid pathway causing excessive production of lignin and its main monomers. By consequence, an enhanced stiffening of the cell wall restricts soybean root growth.     

Production of Substituted Styrene Bioproducts from Lignin and Lignocellulose Using Engineered Pseudomonas putida KT2440

Ferulic acid is a renewable chemical found in lignocellulose from grasses such as wheat straw and sugarcane. Pseudomonas putida is able to liberate and metabolize ferulic acid from plant biomass. Deletion of the hydroxycinnamoyl‐CoA hydratase‐lyase gene (ech) produced a strain of P. putida unable to utilize ferulic and p‐coumaric acid, which is able to accumulate ferulic acid and p‐coumaric acid from wheat straw or sugar cane bagasse. Further engineering of this strain saw the replacement of ech with the phenolic acid decarboxylase padC, which converts p‐coumaric and ferulic acid into 4‐vinylphenol and the flavor agent 4‐vinylguaiacol, respectively. The engineered strain containing padC is able to generate 4‐vinylguaiacol and 4‐vinylphenol from media containing lignocellulose or Green Value Protobind lignin as feedstock, and does not require the addition of an exogenous inducer molecule. Biopolymerization of 4‐vinylguaiacol and 4‐vinylcatechol styrene products is also carried out, using Trametes versicolor laccase, to generate “biopolystyrene” materials on small scale.     

Characterization of Miscanthus cell wall polymers

Efficient utilization of lignocellulosic Miscanthus biomass for the production of biochemicals, such as ethanol, is challenging due to its recalcitrance, which is influenced by the individual plant cell wall polymers and their interactions. Lignocellulosic biomass composition differs depending on several factors, such as plant age, harvest date, organ type, and genotype. Here, four selected Miscanthus genotypes (Miscanthus sinensis, Miscanthus sacchariflorus, Miscanthus × giganteus, Miscanthus sinensis × Miscanthus sacchariflorus hybrid) were grown and harvested, separated into stems and leaves, and characterized for their non‐starch polysaccharide composition and structures, lignin contents and structures, and hydroxycinnamate profiles (monomers and ferulic acid dehydrodimers). Polysaccharides of all genotypes are mainly composed of cellulose and low‐substituted arabinoxylans. Ratios of hemicelluloses to cellulose were comparable, with the exception of Miscanthus sinensis that showed a higher hemicellulose/cellulose ratio. Lignin contents of Miscanthus stems were higher than those of Miscanthus leaves. Considering the same organs, the four genotypes did not differ in their Klason lignin contents, but Miscanthus × giganteus showed the highest acetylbromide soluble lignin content. Lignin polymers isolated from stems varied in their S/G ratios and linkage type distributions across genotypes. p‐Coumaric acid was the most abundant ester‐bound hydroxycinnamte monomer in all samples. Ferulic acid dehydrodimers were analyzed as cell wall cross‐links, with 8‐5‐coupled diferulic acid being the main dimer, followed by 8‐O‐4‐, and 5‐5‐diferulic acid. Contents of p‐coumaric acid, ferulic acid, and ferulic acid dimers varied depending on genotype and organ type. The largest amount of cell wall cross‐links was analyzed for Miscanthus sinensis.     

The phenylpropanoid pathway affects apple fruit resistance to Botrytis cinerea

Apple fruits are rich in phenolic compounds that may enhance resistance to grey mould disease caused by Botrytis cinerea. Using Malus domestica Borkh. cultivars Fuji and Qinguan, we analysed the contents of total phenols, total flavonoids, eight individual phenolic compounds, H₂O₂ and O₂^.? as well as the activities of key enzymes in the phenylpropanoid pathway in the flesh of control and B. cinerea‐inoculated fruits. Chlorogenic acid contents increased for a short period in the less susceptible cultivar Qinguan fruits, but decreased in the disease‐susceptible Fuji fruits. Additionally, ferulic acid production was induced in both cultivars in response to B. cinerea. Furthermore, the activities of phenylalanine ammonia lyase, cinnamate 4‐hydroxylase, 4‐coumarate:coenzyme A ligase and cinnamyl alcohol dehydrogenase were differentially induced between the two apple cultivars. Remarkably, the contents of H₂O₂ and O₂^.? as well as the activities of enzymes in phenolic metabolism tested in this study were always higher in Qinguan fruits than in Fuji fruits. Our data imply that phenylpropanoid metabolism is closely associated with apple fruit resistance to grey mould disease. These findings may be useful for characterizing the mechanism(s) underlying plant resistance to B. cinerea, with potential implications for the screening of grey mould disease‐resistant apple varieties in breeding programmes.     

Soluble and wall-bound phenolics and phenolic polymers in Musa acuminata roots exposed to elicitors from Fusarium oxysporum f.sp. cubense

The accumulation of soluble and wall-bound phenolics and phenolic polymers in Musa acuminata roots exposed to cell wall-derived elicitor from the pathogen, Fusarium oxysporum, f.sp. cubense, race four, was investigated. The root tissue from the banana cultivar "Goldfinger" was found to respond strongly and rapidly towards the elicitor through the increased synthesis of phenolic compounds. Following elicitation, the conjugated and non-conjugated phenolic metabolites in the induced root tissue were extracted and quantified. Induced phenolic synthesis was rapid and reached near maximum values after 16 h. High-performance liquid chromatography revealed both compositional and quantitative differences between induced phenolics (p-coumaric, ferulic, and sinapic acids) and those constitutively present (p-coumaric- and ferulic acid). In addition, vanillic acid was found in the ester-bound fraction and protocatechuic acid in the cell-wall bound fraction of elicited tissue. The deposition and accumulation kinetics of polymerized phenolic monomers as lignin and lignin-like polymers was quantified over a time period of 0-36 h and found to reach maximum values after 24 h. Ionization difference UV spectra of lignin indicated compositional differences in the newly synthesized lignin fraction and correlated with increased concentrations of ferulic acid and sinapic acids esters. The results show that the increased flux through the phenylpropanoid pathway resulted in the synthesis of cinnamic acid and benzoic acid derivatives that were esterified and incorporated into the cell wall fraction as part of the anti-microbial defenses activated in the root tissue.     

Phenolic acid content in potato peel determines natural infection of common scab caused by <Emphasis Type="Italic">Streptomyces</Emphasis> spp.

Common scab of potato caused by the actinomycete Streptomyces scabies is a common pathogen in almost all the potato growing areas of the world. Twenty cultivars of potato were screened in naturally scab infested farmers fields at two locations Tikari and Bachhawan, Varanasi, in two successive crop seasons (2006–2007 and 2007–2008). Among the cultivars, five cultivars were recorded to be least susceptible and the others ranged from medium susceptible to very highly susceptible. Most of the cultivars showed a stable resistance reaction in both the years. Qualitative as well as quantitative estimation of phenolic acids present in peels of the potato cultivars showed their possible role in protection of the potato cultivars against common scab. All the red skinned potato cultivars that were least susceptible to common scab infection were usually found to be rich in phenolic acid contents in their peels. This showed a positive correlation between cultivar resistance to common scab and phenolic acid content in the peel.     

Ferulic acid: a key component in grass lignocellulose recalcitrance to hydrolysis

In the near future, grasses must provide most of the biomass for the production of renewable fuels. However, grass cell walls are characterized by a large quantity of hydroxycinnamic acids such as ferulic and p‐coumaric acids, which are thought to reduce the biomass saccharification. Ferulic acid (FA) binds to lignin, polysaccharides and structural proteins of grass cell walls cross‐linking these components. A controlled reduction of FA level or of FA cross‐linkages in plants of industrial interest can improve the production of cellulosic ethanol. Here, we review the biosynthesis and roles of FA in cell wall architecture and in grass biomass recalcitrance to enzyme hydrolysis.     

The activity of antioxidative enzymes,contents of H<Subscript>2</Subscript>O<Subscript>2</Subscript> and of ascorbate in tomato leaves of cultivars more or less sensitive to infection with <Emphasis Type="Italic">Botrytis cinerea</Emphasis>

The aim of the present studies was to compare H₂O₂ and ascorbate contents as well as peroxidase (PO) and catalase (CAT) activities in leaves of less susceptible cultivar Perkoz and more susceptible Corindo after B. cinerea infection. Increase in H₂O₂ contents in both Perkoz and Corindo cytosol was observed, however, it appeared earlier in the less susceptible cultivar. The increase in PO activity in the cytosol fraction was observed 48 hours after infection in both cultivars but it was greater in the less susceptible Perkoz. No significant differences between the tested cultivars were observed in ascorbate peroxidase (APX) activity and in reduced and oxidated ascorbate contents. PO activity was thoroughly analyzed in the apoplast fraction. It was measured with syringaldazine (S), tetramethylbenzidine (TMB) and ferulic acid (FA)—substrates characteristic of isoenzymes involved in lignification and stiffening of a cell wall. Increase in PO activity with these substrates was observed earlier in cultivar Perkoz than in cultivar Corindo. Similarly, increase in PO activity with NADH appeared significantly earlier in cultivar Perkoz. Apoplastic PO was separated with DEAE Sepharose and two fractions binding and non-binding were obtained. Binding PO fraction was significantly more active especially with S, TMB and NADH after B. cinerea infection. The increase in the enzyme activity was mostly observed in cultivar Perkoz. Binding PO was separated by electrophoresis on acrylamide gel and revealed six enzymatic forms from which three were much more active after infection in cultivar Perkoz. The obtained results suggest that cell wall strengthening mediated by apoplast PO is a key factor responsible for different resistance of tomato cultivars Perkoz and Corindo to B. cinerea infection.     

Role of phytohormones in organogenic ability of elm multiplicated shoots

The study presents the comparative analyses of endogenous contents of auxin (IAA), cytokinins (CKs), polyamines (PAs), and phenolic acids (PhAs) in apical and basal parts of elm multiplicated shoots with regard to the organogenic potential. The shoot-forming capacity was higher in the apical part than in the basal part. However, the timing of root formation was in the apical type of explant significantly delayed (compared with the organogenic potential of basal part). Significantly higher contents of free bases, ribosides and ribotides of isopentenyl adenine, zeatin and dihydrozeatin that were found in the apical segments, might be considered as the most important factor affecting in vitro shoot formation. The content of endogenous free IAA was approximately three times higher in the basal shoot parts than in the apical parts. The amounts of putrescine and spermidine were higher in the apical part which generally contains less differentiated tissues than the basal part of shoot. The predominant PhA in both types of explants was caffeic acid, and concentrations of other PhAs decreased in the following order: p-coumaric, ferulic, sinapic, vanillic, chlorogenic, p-hydroxybenzoic and gallic acids. The contents of all determined PhAs in their free forms and higher contents of glycoside-bound p-coumaric, ferulic and sinapic acids, precursors for lignin biosynthesis, were found in the basal parts.     

Enzymatic synthesis of structured phenolic lipids by incorporation of selected phenolic acids into triolein

The synthesis of structured phenolic lipids by lipase-catalyzed transesterification of selected phenolic acids, including p-hydroxyphenyl acetic, p-coumaric, sinapic, ferulic and 3,4-dihydroxybenzoic acids, with triolein was investigated. The highest enzymatic activity (248?nmol esterified phenolic acid/g solid enzyme/min) and bioconversion (62%) was obtained for the transesterification of p-hydroxyphenyl acetic acid with triolein. In addition, the transesterification of p-coumaric with triolein resulted in a higher enzymatic activity (87?nmol esterified phenolic acid/g solid enzyme/min) and bioconversion (46%) than those obtained for the transesterfication of ferulic and sinapic acids. The results also showed that using p-hydroxyphenyl acetic, p-coumaric and ferulic acids as substrate, the maximum bioconversion of phenolic monoacylglycerols was close to that of phenolic diacylglycerols. Although p-coumaric acid had very low radical scavenging activity (2%) compared to that of ferulic acid (62%), the p-coumaroylated lipids demonstrated a higher scavenging potency (16%) than that of the feruloylated one (10%).     

Effects of Ascorbate on the Oxidation of Derivatives of Hydroxycinnamic Acid and the Mechanism of Oxidation of Sinapic Acid by Cell Wall-Bound Peroxidases

A cell wall fraction isolated from epicotyls of Vigna angularis,which contained both ionically and covalently bound peroxidases,rapidly oxidized p-coumaric, caffeic and ferulic acids and slowlyoxidized sinapic acid. The oxidation of sinapic acid was greatlyenhanced in the presence of p-coumaric, caffeic or ferulic acid.Ascorbate (20 µM) inhibited the oxidation of ferulic acidby about 70% and completely inhibited the oxidation of p-coumaricand ferulic acids. The cell wall fraction was capable of bindingferulic and sinapic acids but not caffeic acid. p-Coumaric acidbound only slightly to cell walls. The oxidation of p-coumaricand ferulic acids by KCl-washed cell walls was inhibited byabout 60% and 10%, respectively, by 20 µM ascorbate, butthe oxidation of caffeic acid was completely inhibited by ascorbateat less than 20 µM. The oxidation of derivatives of hydroxycinnamicacid by peroxidases released from cell walls by washing with1 M KCl was completely inhibited by ascorbate. These resultssuggest that the inhibition by ascorbate depends on the substituentgroup of the phenyl ring of the derivatives of hydroxycinnamicacid when the oxidation reaction is catalyzed by cell wall-boundperoxidases and that the oxidation of sinapic acid is mediatedby phenoxyl radicals of derivatives of hydroxycinnamic acidother than sinapic acid. (Received December 2, 1993; Accepted March 3, 1994)     

Differential induction of phenylalanine ammonia-lyase activity in date palm roots in response to inoculation with Fusarium oxysporum f. sp. albedinis and to elicitation with fungal wall elicitor

The inoculation of the roots of resistant (BSTN) and susceptible (JHL) cultivars of date palm seedlings byFusarium oxysporum f. sp.albedinis (Foa) induces an increase in activity of phenylalanine ammonia-lyase (E.C. 4. 3. 1. 5., PAL). The post-infectional response in the PAL activity in the resistant cultivar roots was faster and higher than that in the susceptible cultivar. However, the elicitation of the seedlings by the hyphal wall preparation (HWP) ofFoa induces an identical PAL response in the resistant and the susceptible cultivars. The elicitor activity of HWP was dose-dependent, the optimal concentration which induces a maximum PAL activity was 10 mg of mycelium per mL. The elicitor present in the HWP was thermostable since its elicitor activity was maintained after heat treatment (121 °C for 45 min). The treatment of the HWP with protease (Pronase E) does not have an effect on the HWP elicitor activity. However, the treatment of the HWP with sodium periodate inhibits its elicitor activity. This data suggests that the HWP elicitor is a carbohydrate compound. In addition, the HWP elicitor is non-specific since it induces identical responses of the PAL activity in two cultivars showing different behaviors to the pathogen. The absence of specificity of HWP elicitors and the differential response of the PAL activity to the infection byFoa and to the elicitation by the HWP are discussed. An explanation of the general interactions between plant and parasite is proposed.     

Dynamics of phenolic acids and lignin accumulation in metal-treated Matricaria chamomilla roots

Phenylalanine ammonia-lyase (PAL) activity, 11 phenolic acids and lignin accumulation in Matricaria chamomilla roots exposed to low (3 μM) and high (60 and 120 μM) levels of cadmium (Cd) or copper (Cu) for 7 days were investigated. Five derivatives of cinnamic acid (chlorogenic, p-coumaric, caffeic, ferulic and sinapic acids) and six derivatives of benzoic acid (protocatechuic, vanillic, syringic, p-hydroxybenzoic, salicylic acids and protocatechuic aldehyde) were detected. Accumulation of glycoside-bound phenolics (revealed by acid hydrolysis) was enhanced mainly towards the end of the experiment, being more expressive in Cu-treated roots. Interestingly, chlorogenic acid was extremely elevated by the highest Cu dose (21-fold higher than control) suggesting its involvement in antioxidative protection. All compounds, with the exception of chlorogenic acid, were detected in the cell wall bound fraction, but only benzoic acids were found in the ester-bound fraction (revealed by alkaline hydrolysis). Soluble phenolics were present in substantially higher amounts in Cu-treated roots and more Cu was retained there in comparison to Cd. Cu strongly elevated PAL activity (by 5.4- and 12.1-fold in 60 and 120 μM treatment, respectively) and lignin content (by 71 and 148%, respectively) after one day of treatment, indicating formation of a barrier against metal entrance. Cd had slighter effects, supporting its non-redox active properties. Taken together, different forms of phenolic metabolites play an important role in chamomile tolerance to metal excess and participate in active antioxidative protection.     

Carbohydrate, Amino acid, Phenolic and Mineral Nutrient Contents of Pepper Plants in Relation to Age-Related Resistance to Phytophthora capsici

The relationship between age-related resistance of peper plants to Phytophthora capsici and contents of carbohydrates, amino acids, phenolics and mineral nutrients in pepper stems was studied using two pepper cultivars, Hanbyul (susceptible) and Kingkun (resistant). With increasing age of pepper plants, the two cultivars, which differ in their susceptibility to Phytophthora blight, became gradually resistant to the disease. The cultivar Kingkun distinctly showed the age-related resistance to Phytophthora blight at the second branch stage. The weight of dry matter in healthy stems of pepper plants at the second branch stage was twice that at the six leaf stage. The resistant cultivar Kingkun contained lower levels of fructose, glucose and sucrose in stems than the susceptible cultivar Hanbyul at the different developmental stages. No consistent differences between the developmental stages of the plants were recognized with regard to their glucose content. However, the contents of fructose and sucrose in the cultivar Hanbyul greatly increased at the second branch stage. The levels of inositol reduced in both pepper cultivars during plant development. In view of the fact that there were only slight changes in the amount of total amino acids, it seems unlikely that there is a relationship between the amino acid metabolism and the retardation of Phytophthora infection during plant development. The amounts of total phenolic compounds in pepper stems were relatively low at the later growth stages of the plants and also in the resistant cultivar Kingkun. The contents of macroelemental nutrients such as nitrogen, phosphorus, potassium, calcium and magnesium were drastically reduced in pepper stems at the later plant growth stage. No significant differences between the cultivars or the plant growth stages were found in the silicon and microelemental nutrients such as sodium, iron, zinc and manganese. These results suggest that the expression of age-related resistance of pepper plants may be due to the morphological and nutritional changes in tissues of pepper stems during ageing, i.e. the pronounced increase in weight of dry matter, the significant decrease in amounts of mineral nutrients such as nitrogen, phosphorus, potassium, calcium and magnesium, and the tow contents of fructose, glucose and sucrose in the stem tissues.