Colonic metabolism of dietary polyphenols: influence of structure on microbial fermentation products

The metabolism of chlorogenic acid, naringin, and rutin, representative members of three common families of dietary polyphenols, the hydroxycinnamates, the flavanones, and the flavonols, respectively, was studied in an in vitro mixed culture model of the human colonic microflora. Time- and concentration-dependent degradation of all three compounds was observed, which was associated with the following metabolic events after cleavage of the ester or glycosidic bond: reduction of the aliphatic double bond of the resulting hydroxycinnamate caffeic acid residue; dehydroxylation and ring fission of the heterocyclic C-ring of the resulting deglycosylated flavanone, naringenin, and of the deglycosylated flavonol, quercetin (which differed depending on the substitution). The metabolic events, their sequences, and major phenolic end products, as identified by GC-MS or LC-MS/MS, were elucidated from the structural characteristics of the investigated compounds. The major phenolic end products identified were 3-(3-hydroxyphenyl)-propionic acid for chlorogenic acid, 3-(4-hydroxyphenyl)-propionic acid and 3-phenylpropionic acid for naringin, and 3-hydroxyphenylacetic acid and 3-(3-hydroxyphenyl)-propionic acid for rutin. The degree of degradation of the compounds studied was significantly influenced by the substrate concentration as well as individual variations in the composition of the fecal flora. The results support extensive metabolism of dietary polyphenols in the colon, depending on substrate concentration and residence time, with resultant formation of simple phenolics, which can be considered biomarkers of colonic metabolism if subsequently absorbed. It is also apparent that a relatively small number of phenolic degradation products are formed in the colon from the diverse group of natural polyphenols.     

Inhibition of 15-lipoxygenase-catalysed oxygenation of arachidonic acid by substituted benzoic acids

Elevated levels of phospholipases, prostaglandin synthases and lipoxygenases in colonic cells at various stages of malignancy indicate a strong link between dietary lipids and colon cancer. Lipoxygenase-catalysed arachidonic acid metabolism plays a key role in colorectal carcinogenesis and has the potential to be modulated by phenolic compounds. Plant-based foods are rich sources of phenolic compounds and in the human colon they are predominantly available as simple phenolics such as the benzoic acids. Benzoic acids were determined in faecal waters from four volunteers consuming a western-style diet. Structure-activity relationships were established for the lipoxygenase-catalysed oxygenation of arachidonic acid using an oxygen electrode. All compounds studied inhibited this reaction (21-73%; p<0.001) and many of the structural features could be rationalised by computational modelling. No correlation was observed with the ability to act as reductants, supporting the hypothesis that their mode of inhibition may not be by a direct redox effect on the non-haem iron.     

Effect and analysis of phenolic compounds during somatic embryogenesis induction in Feijoa sellowiana Berg

Summary. The effect of phenolic compounds on somatic embryogenesis in Feijoa sellowiana was analysed. The results showed that caffeic acid (140–560 μM) significantly increased somatic embryogenesis induction compared with the control. The presence of phloridzin, even at lower concentrations (11.5 μM), or caffeic acid or phloroglucinol at concentrations greater than 140.0 and 197.5 μM, respectively, inhibited somatic embryo development beyond the globular stage. When somatic embryos were transferred to the germination medium, the highest rates of germination (81.9%) were obtained with embryos induced in the presence of phloroglucinol (79.0 μM). At all concentrations tested, somatic embryos induced in medium containing phloroglucinol germinated at higher rates than those induced in the presence of caffeic acid. Histological and ultrastructural studies showed that somatic embryos were formed in close association with phenolic-rich cells which, in more advanced stages of development, formed a zone isolating the embryo from the maternal tissue. A comparative analysis of total phenolic content indicated that phenolics reached a peak by the third week of culture, independently of the medium used. However, after that period, the amount of phenolic compounds was significantly higher in explants cultured in the presence of phloroglucinol than in those cultured in the control or in caffeic acid-containing medium. Attempts to identify the type of phenolic compounds showed that flavan-3-ols and gallic acid derivatives were mainly produced in phloroglucinol-containing medium, whereas flavanones and dihydroflavonols were also present in medium containing caffeic acid. Flavones were the main phenols detected in the control. The ways in which phenolic compounds may affect somatic embryogenesis are discussed. Correspondence: J. M. Canhoto, Departamento de Botanica, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Cal?ada Martim de Freitas, 3001-455 Coimbra, Portugal.     

Phenolic acids from beer are absorbed and extensively metabolized in humans

In spite of the wide literature describing the biological effects of phenolic compounds, scarce data are available on their absorption from diet. In the present work, we studied the absorption in humans of phenolic acids from beer, a common beverage rich in different phenolic acids with related chemical structures. Beer was analyzed for free and total (free+bound) phenolic acids. Ferulic, caffeic and sinapic acids were present in beer mainly as bound forms, while 4-hydroxyphenylacetic acid and p-coumaric acid were present mainly as free forms. Vanillic acid was present equally in the free and bound forms. Plasma samples were collected before and 30 and 60 min after beer administration and analyzed for free and conjugated phenolic acid content. A significant two- to fourfold increase in plasma levels of phenolic acids was detected with peak concentrations at 30 min after beer ingestion. 4-Hydroxyphenylacetic acid was present in plasma mainly as nonconjugated forms while p-coumaric acid was present equally as nonconjugated and conjugated forms. Ferulic, vanillic and caffeic acids were present in plasma predominantly as conjugated forms, with a slight prevalence of sulfates with respect to glucuronates. Our results indicate that phenolic acids from beer are absorbed from the gastrointestinal tract and are present in blood after being largely metabolized to the form of glucuronide and sulfate conjugates. The extent of conjugation is related to the chemical structure of phenolic acids: the monohydroxy derivatives showing the lowest conjugation degree and the dihydroxy derivatives showing the highest one.     

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.     

Detoxication of some naturally occuring phenolics by prairie voles: a rapid assay of glucuronidation metabolism

Mammals detoxicate many phenolic compounds by conjugation with glucuronic acid, and this increases urinary excretion of components of the glucuronic acid pathway. We evaluated a measure of total uronic acid excretion by prairie voles as an index of detoxication of phenolic compounds. Various levels of quercetin and tannic acid were fed at two levels of protein to weanling prairie voles. Uronic acid excretion increased greatly with increased concentrations of dietary phenolics, but was not a simple linear function of phenolic concentration. Voles fed low protein diets excreted more uronic acids than voles fed high protein diets, apparently because of more phenolic-protein complexing in the latter case. Measurement of uronic acid output appears to provide a simple, non-invasive index of detoxication loads in these mammalian herbivores.     

Plant phenolics regulate neoplastic cell growth and survival: a quantitative structure-activity and biochemical analysis

The anti-tumour activities of many plant phenolics at high concentrations (>100 micromol/L) suggest their potential use as dietary supplements in cancer chemoprevention and cancer chemotherapy. However, it is not clear what impact phenolic compounds have at the physiological concentrations obtained through consumption of high phenolic diets on neoplastic cells. In the present study, 54 naturally occurring phenolics were evaluated at physiologically relevant concentrations for their capacity to alter PC12 cell viability in response to serum deprivation, the chemotherepeutic agent etoposide, and the apoptogen C2-ceramide. Surprisingly, novel mitogenic, cytoprotective, and antiapoptotic activities were detected. Quantitative structure-activity relationship modelling indicated that many of these activities could be predicted by compound lipophilicity, steric bulk, and (or) antioxidant capacity, with the exception of inhibition of ceramide-induced apoptosis. Where quantitative structure-activity relationship analysis was insufficient, biochemical assessment demonstrated that the benzoate orsellinic acid blocked downstream caspase-12 activation following ceramide challenge. These findings demonstrate substantive mitogenic, cytoprotective, and antiapoptotic biological activities of plant phenolics on neoplastic cells at physiologically relevant dietary concentrations that should be considered in chemopreventive and chemotherapeutic strategies.     

Carboxylic Acids in Cultured Broth of Sporobolomyces odorus

Carboxylic acids found in the cultured broth of Sporobolomyces odorus AHU 3246 which produces γ-lactones as principles of the aromatic flavor, were analyzed. The concentrate of methylated acids was steam-distilled and in the residue, succinic acid, nonanedioic acid (azelaic acid), undecanedioic acid and 2-hydroxy-3-phenylpropionic acid (β-phenyllactic acid) were identified as their methyl esters by GLC and spectroscopic methods. Phthalic acid and its mono-n-butyl ester were also found, but these compounds were thought to arise from di-n-butyl phthalate, one of impurities of deionized water.     

Biodegradation of aromatic carboxylic acids by Pseudomonas mira

Abstract Biodegradation of aromatic acids (ferulic, vanillic and sipapinic acids) by the soil bacterium Pseudomonas mira was studied by high-pressure liquid chromatography. The presence of glucose in the culture medium slowed down the degradation process but did not affect its mechanism. In addition to vanillic acid and hydroquinone, the products of degradation were found to include acetophenone derivatives. Probably, a mechanism capable of shortening the side chain by spontaneous decarboxylation of unstable 3- keto -3-phenylpropionic acid was present, in addition to the elimination of acetic acid via degradation of the cinnamic acid-type compounds.     

Degradation of 3-phenylpropionic acid by Haloferax sp. D1227

Haloferax sp. D1227, isolated from soil contaminated with highly saline oil brine, is the first halophilic archaeon to demonstrate the utilization of aromatic compounds (i.e., benzoic acid, cinnamic acid, and 3-phenylpropionic acid) as sole carbon and energy sources for growth. The degradation of 3-phenylpropionic acid in this strain was studied to examine the strategies utilized by Archaea to metabolize aromatic compounds. Based on our findings of (1) the extracellular accumulation of cinnamic acid, benzoic acid, 3-hydroxybenzoic acid, and gentisic acid in cultures of Haloferax D1227 grown on 3-phenylpropionic acid, (2) the presence of an 3-phenylpropionylCoA dehydrogenase, (3) the ATP, CoA, and NAD-dependent conversion of cinnamic acid to benzoylCoA, and (4) the presence of gentisate 1,2-dioxygenase, we propose that Haloferax D1227 metabolizes 3-phenylpropionic acid by initial 2-carbon shortening of the side chain to benzoylCoA via a mechanism similar to fatty acid β-oxidation, fol-lowed by aromatic degradation using a gentisate pathway. The upper aliphatic pathway from 3-phenylpropionic acid to benzoic acid is regulated separately from the lower gentisate pathway. Received: January 7, 1998 / Accepted: July 22, 1998     

人参连作根际土壤中酚酸物质对人参锈腐病菌的化感效应

采用高效液相色谱法对人参连作根际土壤中的酚酸物质进行了分离鉴定,检测发现人参根际土壤中含有没食子酸、水杨酸、3-苯基丙酸、苯甲酸和肉桂酸5种酚酸物质.采用外源添加法研究该5种酚酸物质对人参锈腐病菌的化感效应.结果表明: 5种酚酸对人参锈腐病菌的菌丝生长和孢子萌发都表现出高浓度抑制、低浓度促进的作用.没食子酸、水杨酸和苯甲酸在0.5 mmol·L^-1处理浓度下,3-苯基丙酸和肉桂酸在0.05 mmol·L^-1处理浓度下,均能够显著促进人参锈腐病菌菌丝生长和孢子萌发,并显著加重人参锈腐病病害严重度.     

In vitro study of AMP-deaminase from fish (Cyprinus carpio) treated with hydrolyzable tannins

AMP-deaminase (EC 3.5.4.6) is an enzyme responsible for stabilising adenylate energy changes. The properties of this enzyme are controlled by various ligands of hydrophobic nature. An investigation of enzyme activity alterations under the influence of natural phenolic acids (tannic, ellagic and gallic) which are soluble in water, could evidence the biological toxicity of these compounds. In our study purified AMP-deaminase isolated from white muscle of Cyprinus carpio was exposed to phenolic acids in the concentration range of 1 to 50 microM as well as to tannic acid in the presence of Cu2+ ions (5 microM). On the basis of the obtained results we can conclude that among the tested acids, gallic acid did not contribute to the change in AMP-deaminase activity, whereas ellagic acid diminished its activity at the highest concentration (50 microM). Tannic acid caused a significant decrease in the enzyme activity in comparison to control for all used concentrations. Cu2+ ions alone reduced the activity of AMP-deaminase for all studied concentrations. A combined action of a chosen Cu2+ ions concentration (5 microM) with tannic acid at the concentration higher than 2 microM resulted in a decrease in the enzyme activity, but for lower tannic acid concentration of 1 microM the activity of AMP-deaminase was stimulated. These experiments showed that tannic acid may stop free radical chain reactions only at low concentrations (1 microM) in the presence of Cu2+ ions (5 microM).     

Quantitative analysis of phenolics in selected crop species and biological activity of these compounds evaluated by sensitivity of Echinochloa crus-galli

The purpose of this study was to determine the content of selected phenolic compounds in white mustard, buckwheat, spring barley, oat and rye grown under field conditions. Moreover, the allelopathic efficiency of these compounds was evaluated by sensitivity of Echinochloa crus-galli. The aromatic acids: trans-cinnamic, salicylic, ferulic, chlorogenic, p-hydroxybenzoic, protocatechuic, p-coumaric and vanillic were separated from crop plants by TLC and determined spectrophotometrically. Differences in concentrations of analysed compounds were observed for most of the examined plant species. The highest concentration was noticed for cinnamic acid and ranged from 360 μg·g⁻¹ DW in rye to 2770 μg·g⁻¹ DW in spring barley. The relatively high concentration was noticed for ferulic acid (from 73.8 μg·g⁻¹ DW in buckwheat to 1046 μg·g⁻¹ DW in spring barley) and p-coumaric acid (from 50 μg·g⁻¹ DW in oat to 1499 μg·g⁻¹ DW in buckwheat). The observed differences in the phenolics content between two successive vegetation seasons can reflect the effect of abiotic and biotic environmental factors on the phenolics level in studied plants. In the greenhouse experiment the effect of particular compounds on the growth of Echinochloa crus-galli was also studied. It has been found that the examined phenolics, and especially trans-cinnamic acid and mixture of phenolic compounds, significantly inhibit the growth of Echinochloa crus-galli. The obtained results may contribute to the explanation of the biological activity of some phenolic compounds.     

Identification of aromatic dihydroxy acids in biological fluids

3,5-Dihydroxyphenylpropionic acid, 3,5-dihydroxycinnamic acid and 2,3-dihydroxycinnamic acid were detected for the first time to be components of human urine. In the course of this investigation all constitutional isomers of dihydroxy-benzoic, -phenylpropionic, -phenylacetic and -cinnamic acid were synthesized. Mass spectra and retention indices of methyl and trimethylsilyl (TMS) derivatives were determined. In contrast to many other substituted aromatic compounds the mass spectra of methyl and TMS derivatives of dihydroxy aromatic acids often allow a firm distinction to be made between constitutional isomers: TMS derivatives of aromatic acids containing two hydroxy groups located in the ortho position to each other can be recognized by ions resulting from a primary cleavage reaction mainly in the side chain or ester group, followed by loss of tetramethylsilane. In methyl derivatives of 1,2,3-trisubstituted isomers, methoxy groups are lost much more easily from the ions corresponding to the benzylic cleavage than in other isomers. Methyl derivatives of dihydroxycinnamic acids containing at least one methoxy group in the ortho position to the side chain are characterized by a fragmentation reaction, corresponding to the loss of dimethyl ether. TMS and methyl derivatives of 3,5-dihydroxy aromatic acids show unique structure-specific fragmentation reactions.     

Quantitative changes in secondary metabolites of dark-leaved willow (Salix myrsinifolia) exposed to enhanced ultraviolet-B radiation

This is a study of the impact of increased ultraviolet-B (UV-B) radiation on the secondary chemistry of Salix myrsinifolia (dark-leaved willow). For nearly two decades, the loss of stratospheric ozone above the high latitudes of the Northern Hemisphere has increased UV-B radiation (280–320 nm) over the long-term mean. Willows (Salicaceae) are widely distributed in these northern regions. To determine the effects of increased UV-B radiation on willows, the plantlets of three clones of S. myrsinifolia were grown under ambient (3.6 kJ m⁻² day⁻¹) or enhanced (7.18 kJ m⁻² day⁻¹) UV-B irradiance. After the 2-week indoor experiment, the concentrations of UV-B-screening phenolics (flavonoids and phenolic acids) and low-UV-B-screening phenolics (salicylates and condensed tannins) in fresh leaves were investigated and the biomass of leaves, stems and roots was determined. As expected, the total amount of flavonoids in willow leaves clearly increased when plantlets were exposed to higher UV-B irradiation. However, the degree of increase of individual compounds varied: luteolin-7-glucoside, monomethyl-monocoumaryl-luteolin-7-glucoside and one myricetin derivative increased significantly, while the apigenin-7-glucuronide increased only slightly. The enhanced UV-B also increased the amount of p -hydroxycinnamic acid derivative. The UV-B effects on other phenolic acids and tannins were minor. In contrast to the other phenolics, the amounts of two salicylates, salicin and saligenin, decreased under enhanced UV-B irradiation. Our results indicate that the concentrations of both UV-B-screening and low-UV-B-screening phenolic compounds in leaves of S. myrsinifolia may vary in response to elevated UV-B radiation. However, while the UV-B protective flavonoids and phenolic acids accumulate during UV-B exposure, the concentrations of certain salicylates decrease.     

Content of different groups of phenolic compounds in microshoots of Juglans regia cultivars and studies on antioxidant activity

Phenolic and other compounds were extracted from micropropagated axillary shoots (microshoots) of the walnut (Juglans regia L.) cultivars ‘Chandler’, ‘Howard’, ‘Kerman’, ‘Sunland’, and ‘Z₆₃’. Among cultivars, microshoots showed differences in phenolic compounds, phenolic acids, flavonoids, and proanthocyanidins. All cultivars contained the phenolics acids chlorogenic acid, gallic acid, p-coumaric acid; the naphthoquinone juglone; and the flavonoid quercetin. The phenolic acids syringic acid and vanillin were present only in microshoots of ‘Howard’. Microshoot extracts had different antioxidant activity with ‘Kerman’ the highest and ‘Chandler’ the lowest in each of three antioxidant assays: the phosphomolybdenum assay (PPM), reducing power assay, and 2,2-diphenyl-1-picrylhydrazyl-scavenging effect. There was a strong linear relationship between total phenolic compound content of microshoots and increasing antioxidant activity.     

Effect of phenolic acids and phenolics from plant cell walls on rumenlike fermentation in consecutive batch culture

Information on the interaction between mixed populations in the rumen and plant phenolics is required to fully elucidate the limitations of phenolic compounds on forage digestibility. The objective of this study was to examine the degradation of Italian ryegrass (Lolium multiflorum L.) hay incubated with mixed ruminal populations in consecutive batch culture (CBC) with or without phenolic acids or phenolic compounds extracted from plant cell walls. Each CBC consisted of a series of 10 cultures (3 replicates per culture) inoculated (10%, vol/vol) in sequence at 48-h intervals with microbial suspension from the previous set of cultures. All cultures were grown on a semidefined medium containing Italian ryegrass hay, and each CBC was initiated with an inoculum from the rumen. Rumenlike fermentation characteristics were maintained in control CBCs by repeated inoculum transfer. Treatment CBCs were transferred as described above, but cultures 5, 6, and 7 were incubated in the presence of trans-p-coumaric, cis-p-coumaric, or trans-ferulic acid or phenolics extracted from the cell walls of maize stem or barley straw. Mean apparent dry matter disappearance in control CBC cultures was 495 mg per g of hay, whereas the presence of phenolics reduced the initial dry matter disappearance by 6.3 to 25.6%. trans-p-Coumaric acid and, to a lesser extent, the phenolics from cell walls of maize stem were the most inhibitory compounds for dry matter disappearance and for the production of volatile fatty acids; trans-p-coumaric acid altered the molar ratio of acetate/propionate/butyrate. The CBC further showed variations in the ability of the rumen microbial population to adapt to phenolic compounds.     

Effect of phenolic acids and phenolics from plant cell walls on rumenlike fermentation in consecutive batch culture.

Information on the interaction between mixed populations in the rumen and plant phenolics is required to fully elucidate the limitations of phenolic compounds on forage digestibility. The objective of this study was to examine the degradation of Italian ryegrass (Lolium multiflorum L.) hay incubated with mixed ruminal populations in consecutive batch culture (CBC) with or without phenolic acids or phenolic compounds extracted from plant cell walls. Each CBC consisted of a series of 10 cultures (3 replicates per culture) inoculated (10%, vol/vol) in sequence at 48-h intervals with microbial suspension from the previous set of cultures. All cultures were grown on a semidefined medium containing Italian ryegrass hay, and each CBC was initiated with an inoculum from the rumen. Rumenlike fermentation characteristics were maintained in control CBCs by repeated inoculum transfer. Treatment CBCs were transferred as described above, but cultures 5, 6, and 7 were incubated in the presence of trans-p-coumaric, cis-p-coumaric, or trans-ferulic acid or phenolics extracted from the cell walls of maize stem or barley straw. Mean apparent dry matter disappearance in control CBC cultures was 495 mg per g of hay, whereas the presence of phenolics reduced the initial dry matter disappearance by 6.3 to 25.6%. trans-p-Coumaric acid and, to a lesser extent, the phenolics from cell walls of maize stem were the most inhibitory compounds for dry matter disappearance and for the production of volatile fatty acids; trans-p-coumaric acid altered the molar ratio of acetate/propionate/butyrate. The CBC further showed variations in the ability of the rumen microbial population to adapt to phenolic compounds.     

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.     

Phenolic substances as allelopathic agents arising during the degradation of rye (Secale cereale) tissues

Rye seedlings, tillering plants and crop residues were allowed to decompose in model incubation experiments. Young tissues gave rise to high concentrations of allelochemicals, whereas crop residues did not produce inhibitors. Seven phenolic acids were identified in the investigated materials; p-hydroxybenzoic protocatechuic, gallic, vanillic, syringic, p-coumaric, ferulic as well as benzoic acid. However, neither the level of these acids nor the total content of phenolic compounds corresponded to the level of phytotoxicity determined in bioassays. This demonstrated that, apart from phenolics, other unidentified water-soluble organic compounds were also responsible for the toxicity of rye decomposition products. The study was conducted within program CPBP 04.10.03. The study was conducted within program CPBP 04.10.03.