Antibiotic potential of plant growth promoting rhizobacteria (PGPR) against Sclerotium rolfsii

High performance liquid chromatographic (HPLC) analysis of culture filtrates of plant growth promoting rhizobacteria (PGPR) and medium of inhibitory zone of interaction of Sclerotium rolfsii with PGPR, viz. Pseudomonas aeruginosa, Pseudomonas fluorescens 4, Pseudomonas fluorescens 4 (new) and Pseudomonas sp. varied from sample to sample. In all the culture filtrates of PGPRs, P. aeruginosa had nine phenolic acids in which ferulic acid (14.52 μg/ml) was maximum followed by other phenolic acids. However, the culture filtrates of P. fluorescens 4 had six phenolic acids with maximum ferulic acid (20.54 μg/ml) followed by indole acetic acid (IAA), caffeic, salicylic, o-coumeric acid and cinnamic acids. However, P. fluorescens 4 culture filtrate had seven phenolic acids in which salicylic acid was maximum (18.03 μg) followed by IAA, caffeic, vanillic, ferulic, o-coumeric and cinnamic acids. Pseudomonas sp. also showed eight phenolic acids where caffeic acid (2.75 μg) was maximum followed by trace amounts of ferulic, salicylic, IAA, vanillic, cinnamic, o-coumeric and tannic acids. The analysis of antibiosis zone of PGPRs showed fairly rich phenolic acids. A total of nine phenolic acids were detected in which caffeic acid was maximum (29.14 μg/g) followed by gallic (17.64 μg/g) and vanillic (3.52 μg/g) acids but others were in traces. In P. aeruginosa, antibiosis zone had seven phenolic acids where IAA was maximum (3.48 μg/g) followed by o-coumeric acid (2.08 μg/g), others were in traces. The medium of antibiosis zone of P. fluorescens 4 and P. fluorescens 4 new had eight phenolic acids in which IAA was maximum with other phenolic acids in traces.     

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.     

Clone-specific responses in leaf phenolics of willows exposed to enhanced UVB radiation and drought stress

The effects of enhanced UVB radiation and drought stress on willow secondary phenolics were studied using the leaves of 8‐week‐old micropropagated plantlets from interspecific hybrids (Salix myrsinites L. ×S. myrsinifolia Salisb.) and pure species (S. myrsinifolia). The plantlets were subjected for 4 weeks to two levels of UVB radiation (ambient, enhanced) and two levels of watering (well‐watered, drought‐stressed) according to a 2 × 2 factorial design. Enhanced UVB radiation increased the total concentration of flavonoids and phenolic acids in all plantlets, while the total concentration of salicylates remained unaffected. Drought stress reduced the total concentration of salicylates and phenolic acids in S. myrsinifolia plantlets, while in hybrids only phenolic acids were affected. The response of phenolic acids to enhanced UVB in drought‐stressed plantlets was different from that in well‐watered ones, indicating that drought stress limited the accumulation of phenolic acids under enhanced UVB radiation. Flavonoids increased in response to enhanced UVB radiation in drought‐stressed plantlets, although drought caused serious physiological stress on growth. There were significant differences between hybrid and S. myrsinifolia plantlets with respect to the composition of phenolics and between families and clones with respect to their concentration. In addition, the response of salicylates, flavonoids and phenolic acids to enhanced UVB and drought stress was clone‐specific, which may indicate that climatic changes will alter the genetic composition of northern forests.     

芦苇腐解土中酚酸类化感物质的水分响应特性研究

芦苇和虉草均具有较强的去污能力,常作为湿地植物配置于同一人工湿地进行污水处理。芦苇作为一种强化感植物对虉草具有较强的化感作用,在自然湿地和人工湿地中均会出现芦苇代替虉草的现象,且这一现象的发生与土壤含水量存在一定联系,此外,芦苇腐解土对虉草的化感抑制效应与腐解土中总酚酸的量密切相关。为了研究芦苇腐解土中主要酚酸类物质的水分响应特性,筛选出其中对水分响应较为明显的酚酸物质种类,该研究采用高效液相色谱法,通过芦苇枯落物腐解土的制备,对不同水分环境下芦苇腐解土中酚酸类物质进行了分离和鉴定。结果表明:芦苇腐解土中可分离出没食子酸、香豆酸、香草酸、丁香酸、对香豆酸、阿魏酸、水杨酸和苯甲酸等8种酚酸类物质,其中香豆酸、苯甲酸和阿魏酸等3种酚酸类物质含量较高。分离出的8种酚酸类物质的含量与腐解土的相对含水量均呈显著线性负相关关系,即随着腐解土相对含水量的上升,酚酸类物质的含量均呈现下降趋势,且各种酚酸类物质对水分的响应趋势均可用线性方程较好地拟合。其中,香豆酸、没食子酸和阿魏酸对芦苇腐解土的水分响应最为明显。因此,可将香豆酸、没食子酸和阿魏酸作为主要调控目标,通过调控湿地土壤中水分含量,削弱芦苇对虉草的化感抑制效应,从而维持人工湿地中虉草芦苇群落的长期稳定共存。     

Mosquito larvicidal efficacy of phenolic acids of seaweed Chaetomorpha antennina (Bory) Kuetz. against Aedes aegypti

Mosquito larvicidal and repellent activities of phenolic acids of Chaetomorpha antennina (Bory) Kuetz. against the third instar larvae of Aedes aegypti were investigated. The larval mortality was observed after 24 h exposure. Results of mosquito larvicidal tests revealed that insoluble bound phenolic acids and soluble conjugated phenolic acid fractions of C. antennina had an excellent inhibitory effect against A. aegypti and its LC₅₀ values were 23.4 and 44.6 μg ml⁻¹, respectively. The repellency assay of insoluble bound phenolic acids and soluble conjugated phenolic acid fractions of C. antennina, at 10 μg cm⁻² concentration gave 100% protection up to 120 min. The results indicate that phenolic acids of C. antennina have a wide spectrum of larvicidal and repellent activities against Aedes aegypti.     

Fractional changes in phenolic acids composition in root nodules of Arachis hypogaea L.

Phenolic acids are active antimicrobial compounds and root signaling molecules that play important roles in plant defense responses. They are generally present in plants as glycosides or esters. A range of soluble and bound phenolic acids were detected in roots and root nodules of Arachis hypogaea L., among which five were identified by high performance liquid chromatography (HPLC) coupled with UV–Vis diode array detector (DAD), viz., p-coumaric acid (p-com), p-hydroxybenzaldehyde (HBAld), p-hydroxybenzoic acid (HBA), caffeic acid (CA) and protocatechuic acid (PA). Para-coumaric acid was constitutively present in all fractions whereas HBA was present in the soluble form only in young nodules. CA and PA were mostly present in the wall bound fraction. The root nodules contain higher concentration of phenolic acids than non-nodulated roots and presence of peroxidase and polyphenol oxidase indicate the metabolism of phenolic acids in roots and root nodules. These results indicate that phenolic acids (p-com and CA) in bound-glycosidic or ester forms were major components in cell wall fortification which provide protection to the root nodule from pathogen attack.     

Genetic diversity in morphological characters and phenolic acids content resulting from an interspecific cross between eggplant,Solanum melongena,and its wild ancestor (S. incanum)

Solanum incanum, the wild ancestor of eggplant, Solanum melongena, has been considered as a source of variation for high content of phenolic acid conjugates in breeding programmes aimed at improving the functional quality of eggplant. We have evaluated the morphological and phenolic acids content in an interspecific family including S. incanum (P1), S. melongena (P2), their interspecific hybrid (F1), progeny from the selfing of the F1 (F2) and the backcross of the F1 to P2 (BC1P2). Many morphological differences were found between parents, while the F1 was intermediate for most traits. However, F1 plants were taller and pricklier and presented higher fruit flesh browning than any of the parents. F2 and BC1P2 were morphologically highly variable and the results obtained suggest that a rapid recovery of the characteristic combination of S. melongena traits can be achieved in a few backcross generations. Segregation for prickliness was found to be compatible with simple genetic control, prickliness being dominant over non‐prickliness. A total of 16 phenolic acid conjugates were studied, of which chlorogenic acid (5‐O‐(E)‐caffeoylquinic acid) was the most common compound in all samples, averaging 77.8% of all hydroxycinnamic acid derivatives. Contents of total phenolic acid conjugates were much higher in S. incanum than in S. melongena fruit flesh, and no major differences were found in the profile of phenolic acids among parents. The interspecific hybrid (F1) was intermediate between the two parents in phenolic acids content. Non‐segregating generations presented considerable variation in phenolic acids content, but the range of variation was wider in segregating F2 and BC1P2 generations. Additive genetic effects were the most important in explaining the results obtained for the phenolic acids content. A number of BC1P2 plants presented a good combination of phenolic acids content and fruit weight or flesh browning. Overall, the results demonstrate that improvement of functional quality in S. melongena can be obtained using S. incanum as a donor of alleles for high phenolic acids content.     

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%).     

Qualitative analysis and simultaneous quantification of phenolic compounds in the aerial parts of Salvia miltiorrhiza by HPLC-DAD and ESI/MS(n)

Introduction – The increasing demands of roots and rhizomes of Salvia miltiorrhiza almost exhausted the wild Salvia sources in China. However, the content and composition of phenolic acids in the aerial parts of the plant and their potential to be used as a substitute has not been explored. Objective – To evaluate the potential of the aerial parts of Salvia miltiorrhiza as new natural sources of phenolic acids. Methodology – HPLC coupled with diode array detection (DAD) and electrospray ionization multistage mass spectrometry (ESI/MSⁿ) has been used for qualitative and quantitative analysis of phenolic compounds. Results – A total of 38 phenolic compounds were identified or tentatively characterized. A quantitative HPLC‐DAD method allowing the simultaneously quantification of six phenolic acids was optimized and validated for linearity, precision, accuracy, and limits of detection and quantification. Calibration curves showed good linear regression (r² > 0.9991) within test ranges; the recoveries ranged between 95.64 and 101.67% and the RSDs were less than 3.01%. Conclusion – The developed methods have been proved to be effective for the identification and quantification of phenolic acids in S. miltiorrhiza. The results obtained suggest that the aerial parts of the plant could be used as an alternative source of sage phenolics. Copyright © 2010 John Wiley & Sons, Ltd.     

Phenolic acids: Possible agents of modifying N2-fixing symbiosis through rhizobial alteration?

Phenolic acids, low molecular weight phenolics, are precursors of a variety of antimicrobial compounds, root signalling molecules, and phytoalexins that play an important role in plant defence responses. In agro ecosystem, a large amount of litter is turned over during the cropping season, fallow period and land preparation. This releases a flush of phenolic acids, amounts of which exceed very much the quantities released in root exudation. In rhizobial inoculation of legumes, these phenolic acids, depending on the concentration, may affect the persistence of rhizobia in the soil and their symbiotic efficiency, in terms of N₂ fixation. The present study evaluates the effects of different concentrations of four phenolic acids (protocatechuic, p-coumaric, ferulic and vanillic) on population size of four rhizobial strains (Bradyrhizobium elkanii SEMIA 5019, B. japonicum TAL 102 and TAL 620, and Azorhizobium caulinodans ORS 571). Culture media with different concentrations of phenolic acids in the presence or absence of manitol were used to evaluate rhizobial population size on day 6. Rhizobial total proteins were extracted and electrophoresed on polyacrylamide gels. Further, the effects of phenolic acid-affected rhizobia on N₂ fixing capacity were also investigated by inoculating two of those strains to soybean. Phenolic acid-treated B. elkanii SEMIA 5019 and B. japonicum TAL 102 were inoculated to soybean, and plant growth, N accumulation and nodule dry weight were assessed in a pot experiment. The population size of TAL 102 was induced when the culture medium was supplied with different phenolic acids as the sole carbon source. In many cases, the presence of manitol in the medium masked the differential effects of phenolic acids on the rhizobial population size. All four phenolic acids used in our study suppressed the population size of TAL 620. Strain ORS 571 showed low population size at low concentrations followed by a growth recovery at high phenolic acid concentrations. Strain SEMIA 5019 treated with 0.03 mM ferulic acid produced the highest increase in shoot growth of soybean, (ca. 65%). Treating strain SEMIA 5019 with 9 mM protocatechuic acid produced the largest decrease in nodule dry weight (ca. 50%) without any significant changes in shoot N accumulation. P-coumaric acid, even at 0.12 mM, could stimulate the N₂ fixing activity of SEMIA 5019, whereas the same concentration reduced the effectiveness of TAL102 in a soybean-rhizobium symbiosis. Phenolic acid interactions with rhizobia led to biochemical, and hence physiological changes, resulting in an alteration in their symbiotic ability. Different leguminous plants secrete different phenolic compounds other than phenolic acids during root exudation. Further studies should therefore be conducted to evaluate the effects of those compounds on the symbiosis. It is concluded from this study that the effect of phenolic acids is concentration and structure dependant, and strain-specific. The effect will also be pH dependant. Thus, phenolic acids are possible agents for modifying the legume-rhizobial symbiosis.     

Effect of Plant Growth-Promoting Rhizobacteria and Culture Filtrate of <Emphasis Type="Italic">Sclerotium rolfsii</Emphasis> on Phenolic and Salicylic Acid Contents in Chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis>)

Two plant growth-promoting rhizobacteria (PGPR), viz., Pseudomonas fluorescens strain Pf4 and P. aeruginosa strain Pag, protected chickpea (Cicer arietinum) plants from Sclerotium rolfsii infection when applied singly or in combination as seed treatment. Pag gave the best protection to the seedlings, applied either singly (mortality 16%) or in combination with Pf4 (mortality 17%) compared with 44% and 24% mortality in control and Pf4 treatment, respectively. The two PGPR strains induced the synthesis of specific phenolic acids, salicylic acid (SA), as well as total phenolics at different growth stages of chickpea seedlings with varied amount. The maximum amount of total phenolics was recorded in all the aerial parts of 4-week-old plants. Gallic, ferulic, chlorogenic, and cinnamic acids were the major phenolic acids detected in high-performance liquid chromatography (HPLC) analysis. Induction of such phenolic acids in the seedlings was observed up to 6 weeks in comparison with control. Salicylic acid (SA) was induced frequently during the first 3 weeks of growth only. Between the two strains, Pag was more effective in inducing phenolic acid synthesis applied either singly or in combination with strain Pf4 during the entire 6 weeks of growth of chickpea. In the presence of a culture filtrate of S. rolfsii, the two Pseudomonas strains induced more phenolic acids in treated than in non-treated and control plants. The occurrence of salicylic acid was frequent in the first 24 h, but infrequent at 48 and 96 h. Foliar spray of Pseudomonas strains also enhanced the phenolic acid content as well as total phenolics within 24 h of application. Gallic, chlorogenic, and cinnamic acids were consistently discerned in the treated leaves, whereas SA was absent even up to 96 h of application. Resistance in chickpea plants by Pseudomonas strains through induction of phenolic compounds as well as induced systemic resistance via SA-dependent pathway was evident. Received: 1 April 2002 / Accepted: 4 May 2002     

Anti-biofilm potential of phenolic acids: the influence of environmental pH and intrinsic physico-chemical properties

Phenolic acids are a particular group of small phenolic compounds which have exhibited some anti-biofilm activity, although the link between their activity and their intrinsic pH is not clear. Therefore, the present work examined the anti-biofilm activity (inhibition of biomass and metabolic activity) of phenolic acids in relation to the environmental pH, as well as other physico-chemical properties. The results indicate that, while Escherichia coli was not inhibited by the phenolic acids, both methicillin resistant Staphylococcus aureus and methicillin resistant Staphylococcus epidermidis were susceptible to the action of all phenolic acids, with the pH playing a relevant role in the activity: a neutral pH favored MRSE inhibition, while acidic conditions favored MRSA inhibition. Some links between molecular polarity and size were associated only with their potential as metabolic inhibitors, with the overall interactions hinting at a membrane-based mechanism for MRSA and a cytoplasmic effect for MRSE.     

Changes in Cell Wall-bound Phenolic Compounds and Lignin in Roots of Date Palm Cultivars Differing in Susceptibility to Fusarium oxysporum f. sp. albedinis

The roots of date palm contain four cell wall‐bound phenolic acids identified as p‐hydroxybenzoic, p‐coumaric, ferulic and sinapic acids. The ferulic acid represents the major phenolic compound since it constitutes 48.2–55.8% of cell wall‐bound phenolic acids. All these phenolic acids were present in the resistant cultivar (BSTN) and the susceptible cultivar (JHL). However, the pre‐infection contents of p‐coumaric, ferulic and sinapic acids were greater in the resistant cultivar than in the susceptible one. For the contents of p‐hydroxybenzoic acid, there was no significant difference between the resistant cultivar and the susceptible cultivar. Similarly, the pre‐infection contents of lignin were approximately equal for both cultivars. Inoculation of the date palm roots by Fusarium oxysporum f. sp. albedinis induced important modifications to the contents of the cell wall‐bound phenolic compounds and lignin, which made it possible to distinguish between resistant and susceptible cultivars. The post‐infection contents of cell wall‐bound phenolic compounds underwent a rapid and intense increase with a maximum accumulation on the tenth day for p‐hydroxybenzoic acid (1.54 μmol/g), p‐coumaric acid (2.77 μmol/g) and ferulic acid (2.64 μmol/g) and on the fifteenth day for sinapic acid (1.85 μmol/g). The maximum contents accumulated in the resistant cultivar were greater than those in the susceptible cultivar, namely, 11 times for p‐hydroxybenzoic acid, 2.6 times for p‐coumaric acid, 1.8 times for ferulic acid and 12.3 times for sinapic acid. In the susceptible cultivar, p‐coumaric acid and ferulic acid contents also increased after inoculation although they did not reach the pre‐infection contents of the resistant cultivar. The contents of p‐hydroxybenzoic acid in the susceptible cultivar roots did not present post‐infection modification and those of sinapic acid decreased instead. The lignin contents increased in both cultivars with a maximum accumulation on the fifteenth day. However, the maximum contents accumulated in the resistant cultivar roots were 1.5 times greater than those of the susceptible cultivar. These results showed clear differences between the resistant BSTN and the susceptible JHL cultivars. The implication of cell wall‐bound phenolic compounds and lignin in the resistance of date palm to F. oxysporum f. sp. albedinis appears to be dependent on the speed and intensity of their accumulation with greater contents in the first stage of infection.     

Plant growth-promoting rhizobacteria-mediated induction of phenolics in pea ( Pisum sativum) after infection with Erysiphe pisi

Qualitative and quantitative estimation of phenolic compounds was done through high performance liquid chromatography (HPLC) in different parts of pea (Pisum sativum) after treatment with two plant growth-promoting rhizobacteria (PGPR), viz., Pseudomonas fluorescens (strain Pf4) and Pseudomonas aeruginosa (referred to here as Pag) and infection by Erysiphe pisi. The phenolic compounds detected were tannic, gallic, ferulic, and cinnamic acids on the basis of their retention time in HPLC. In all the treated plants, synthesis of phenolic compounds was enhanced. The induction of gallic, ferulic, and cinnamic acids was manyfold more than those in the control. Maximum accumulation of phenolic compounds was observed in plants raised from PGPR-treated seeds and infection with E. pisi. Under pathogenic stress, Pag performed better because a relatively higher amount of phenolics was induced compared with plants treated with Pf4. Received: 20 August 2001 / Accepted: 20 September 2001     

Chromatographic analysis of simple phenols in some species from the genus Salix

Introduction – Salicis Cortex, made from willow bark is a herbal remedy, which is standardised based on the content of salicin, a compound with analgesic and antiphlogistic properties. However, clinical trials suggest that other compounds also present in Salicis Cortex can contribute to the pharmacological effects. Objective – To characterise the composition of phenolic acids in the barks of different species and clones from the genus Salix by use of chromatographic methods—HPTLC and HPLC. Methodology – The phenolic acid composition was analysed by MGD (multiple gradient development)–HPTLC technique. The separation was performed on HPTLC Diol plates with gradient elution using a mixture of chloroform:hexane:ethyl acetate with increasing concentration of ethyl acetate from 10 to 25%. Derivatisation with thymol reagent was employed for the first time for specific detection of phenolic acids containing methoxyl groups. Results – The presence of all phenolic acids previously reported in the genus Salix was confirmed, namely p‐hydroxybenzoic, vanillic, cinnamic, p‐coumaric, ferulic and caffeic acids. Furthermore, pyrocatechol as a constituent of willow bark was revealed. The highest concentration of this compound was observed in the S. purpurea bark (2.25 mg/g). Conclusion – The presence of a relatively high content of pyrocatechol in Salix species may raise doubts about the safe application of this herbal medicine. Copyright © 2010 John Wiley & Sons, Ltd.     

Promotion of phenolic compounds production in Salvia miltiorrhiza hairy roots by six strains of rhizosphere bacteria

Salvia miltiorrhiza Bunge is an important herb for the treatment of cerebrovascular and cardiovascular diseases with bioactive compounds (phenolic acids and tanshinones). Abundant studies showed that tanshinones could be stimulated by biotic and abiotic stresses, but limited information is available on biosynthesis of phenolic acids promoted by biotic stresses. The aim of the present work was to isolate and identify rhizosphere bacteria which stimulated phenolic compound in Salvia miltiorrhiza hairy roots and investigated the internal mechanism, providing a potential means to enhance content of pharmaceuticals in S. miltiorrhiza. The results showed that six bacteria, namely, HYR1, HYR26, SCR22, 14DSR23, DS6, and LNHR13, belonging to the genus Pseudomonas and Pantoea, significantly promoted the growth and content of major phenolic acids, RA and SAB. Bacteria LNHR13 was the most effective one, with the contents of RA and SAB reaching ～2.5‐fold (30.1 mg/g DW) and ～2.3‐fold (48.3 mg/g DW) as those of the control, respectively. Phytohormones and polysaccharides produced by bacteria showed potential responsibility for the growth and biosynthesis of secondary metabolites of S. miltiorrhiza. Meanwhile, we found that the more abundant the types and contents of phytohormones, the stronger their stimulating effect on the content of salvianolic acids.     

Rhizobium-Mediated Induction of Phenolics and Plant Growth Promotion in Rice (Oryza sativa L.)

Qualitative and quantitative estimation of phenolic compounds was done through reverse phase–high performance liquid chromatography (RP-HPLC) from different parts (leaf, stem, and root) of rice plants after inoculation with two rhizobial strains, RRE6 (Rhizobium leguminosarum bv. phaseoli) and ANU 843 (R. leguminosarum bv. trifolii) and infection by Rhizoctonia solani. On the basis of their retention time, the major phenolic acids detected in HPLC analysis were gallic, tannic, ferulic, and cinnamic acids. Furthermore, in all Rhizobium-inoculated rice plants, synthesis of phenolic compounds was more consistently enhanced than in control (uninoculated plants), where the maximum accumulation of phenolic compounds was observed in plants inoculated with RRE6 and infection with R. solani. Under pathogenic stress, RRE6 performed better because a relatively higher amount of phenolics was induced as compared with plants treated with ANU 843. Phenolic acids mediate induced systemic resistance and provide bioprotection to plants during pathogenic stresses. In addition, both rhizobial strains promote growth and productivity of rice plants in greenhouse conditions. This report on Rhizobium-mediated defense responses and growth promotion of nonlegume (such as rice) provides a novel paradigm of symbiotic plant–microbe interaction.     

Time course study on accumulation of cell wall-bound phenolics and activities of defense enzymes in tomato roots in relation to <Emphasis Type="Italic">Fusarium</Emphasis> wilt

Major cell wall-bound phenolic compounds were detected and identified in roots of tomato at different stages of growth. Alkaline hydrolysis of the cell wall material of the root tissues yielded ferulic acid as the major bulk of the phenolic compounds. Other phenolic compounds identified were 4-hydroxybenzoic acid, vanillic acid, 4-hydroxybenzaldehyde, vanillin and 4-coumaric acid. All the six phenolic acids were higher in very early stage of plant growth. Ferulic acid, 4-hydroxybenzoic acid and 4-coumaric acid exhibited a decreasing trend up to 60 days and then the content of these phenolic acids increased somewhat steadily towards the later stage of growth. Total phenolics, phenylalanine ammonia-lyase (PAL) activity and peroxidase (POD) activity were in tandem match with the occurrence pattern of the phenolic acids. Ferulic acid showed highest antifungal activity against tomato wilt pathogen Fusarium oxysporum f. sp. lycopersici. The results of this study may be interpreted to seek an explanation for high susceptibility of tomato plants at flowering stage to Fusarium wilt. It may also be concluded that greater amounts of ferulic acid in combination with other phenolics and higher level of PAL and POD activities after 60 days of growth may have a role in imparting resistance against Fusarium wilt at a late stage of plant growth.     

Stimulation of indoleacetic acid production in a <Emphasis Type="Italic">Rhizobium</Emphasis> isolate of <Emphasis Type="Italic">Vigna mungo</Emphasis> by root nodule phenolic acids

The influence of endogenous root nodules phenolic acids on indoleacetic acid (IAA) production by its symbiont (Rhizobium) was examined. The root nodules contain higher amount of IAA and phenolic acids than non-nodulated roots. Presence of IAA metabolizing enzymes, IAA oxidase, peroxidase, and polyphenol oxidase indicate the metabolism of IAA in the nodules and roots. Three most abundant endogenous root nodule phenolic acids (protocatechuic acid, 4-hydroxybenzaldehyde and p-coumaric acid) have been identified and their effects on IAA production by the symbiont have been studied in l-tryptophan supplemented yeast extract basal medium. Protocatechuic acid (1.5 μg ml⁻¹) showed maximum stimulation (2.15-fold over control) of IAA production in rhizobial culture. These results indicate that the phenolic acids present in the nodule might serve as a stimulator for IAA production by the symbiont (Rhizobium). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

Content of phenolic acids in callus culture of alfalfa (Medicago sativa): The effect of age and biochemical differentiation

Phenolic acids were separated into three fractions and determined by HPLC inMedicago sativa callus culture at the age of two, three and four weeks. The contents of free and especially of predominating ester-bound phenolic acids decreased with callus age to approx. 80 % while the content of phenolic acids nonextractable by methanol increased byca. 90 %. The proportion of benzoic acid derivatives rose from 15 to 21 % within four weeks. The determined difference in the contents of phenolic acids in the upper and lower parts of callus diminished with age. The content of bound forms was higher in the lower part regardless of the callus age. The content of free acids in two weeks old callus was half as high as in the upper part.