Distribution and Exudation of Allelochemicals in Wheat Triticum aestivum

Wheat allelopathy has potential for weed suppression. Allelochemicals were identified in wheat seedlings, and they were exuded from seedlings into agar growth medium. p-Hydroxybenzoic, trans-p-coumaric, cis-p-coumaric, syringic, vanillic, trans-ferulic, and cis-ferulic acids and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) were identified in both the shoots and roots of 17-day-old wheat seedlings and their associated agar growth medium. Wheat accessions with previously identified allelopathic activity tended to contain higher levels of allelochemicals than poorly allelopathic ones. The allelopathic compounds present in the shoots generally also were identified in the roots and in the agar medium. Allelochemicals were distributed differentially in wheat, with roots normally containing higher levels of allelochemicals than the shoots. When the eight allelochemicals were grouped into benzoic acid and cinnamic acid derivatives, DIMBOA, total coumaric, and total ferulic acids, the amount of each group of allelochemicals was correlated between the roots and the shoots. Most of the allelochemicals identified in the shoots and roots could be exuded by the living roots of wheat seedling into the agar growth medium. However, the amounts of allelochemicals in the agar growth medium were not proportional to those in the roots. Results suggest that wheat plants may retain allelochemicals once synthesized. The presence of allelochemicals in the agar growth medium demonstrated that wheat seedlings were able to synthesize and to exude phytotoxic compounds through their root system that could inhibit the root growth of annual ryegrass.     

Interactions oftrans-cinnamic acid,its related phenolic allelochemicals,and abscisic acid in seedling growth and seed germination of lettuce

Phenolic compounds have been identified as the most common allelochemicals produced by higher plants. Inhibitions of cinnamic acid, its related phenolic derivatives, and abscisic acid (ABA) on seedling growth and seed germination of lettuce were studied.trans-Cinnamic acid, ando-,m-, andp-coumaric acids inhibited the growth of etiolated seedlings of lettuce at concentrations higher than 10^–4 M and seed germination above 10^–3 M. Coumarin inhibited seedling growth and seed germination at 10^–5 M or above. Chlorogenic acid inhibited seedling growth above 10^–4 M, but did not inhibit seed germination at 10^–5–5×10^–3 M. Low concentrations (below 10^–3 M) of caffeic and ferulic acids promoted the elongation of hypocotyls, but higher concentrations (over 10^–3 M) inhibited seedling growth and seed germination. These phenolic compounds and abscisic acid had additive inhibitory effects both on seedling growth and seed germination. The inhibition on lettuce was reversed by caffeic and ferulic acids at concentrations lower than 10^–3 M except for the inhibition of germination by coumarin. These results suggest that in naturetrans-cinnamic acid,o-, m-, p-coumaric acids, coumarin, and chlorogenic acid inhibit plant growth regardless of their concentration. However, caffeic and ferulic acids can either promote or inhibit plant growth according to their concentration.     

Effects of three phenolic acids on chlorophyll content and growth of soybean and grain sorghum seedlings

Experiments were designed to test the hypothesis that interference with chlorophyll metabolism may be one mechanism of inhibition of plant growth in allelopathic interactions. Effects of ferulic,p-coumaric, and vanillic acids on soybean and grain sorghum growth and chlorophyll content were quantified and compared after seedlings were treated with these compounds in a nutrient culture. Following a 6-day treatment cycle, dry weights of soybean seedlings were reduced by both 10^–3 M and 5 × 10^–4 M treatments of ferulic,p-coumaric and vanillic acids. Soybean weight reductions in each case were paralleled by a significant reduction in the concentration (g Chl/mg dry wt) of chlorophylls a and b and total chlorophyll in the unifoliate leaves. Sorghum seedling growth was also reduced by each of the compounds at the 5 × 10^–4 M level, but leaf chlorophyll concentration was not below that of control plants.     

Synergistic inhibitory effects ofp-coumaric and ferulic acids on germination and growth of grain sorghum

The data support the hypothesis that there is a synergistic phytotoxic effect whenp-coumaric and ferulic acids are found together. Equimolar mixtures of both acids showed greater reduction in sorghum seed germination, shoot elongation, and total seedling growth than either phytotoxin caused when alone. Repeated experiments showed mixtures containing 5×10^–3 Mp-coumaric and 5×10^–3 M ferulic acids reduced germination to 34% of controls after 24 hr and 59% by 48 hr. The same concentration of either phenol-treated seeds alone showed 69 and 92% germination at comparable times. The phytotoxic action of the combination approximated the inhibitory effect on germination of 10^–2 M ferulic acid and was a greater reduction than caused by 10^–2 Mp-coumaric treatments. Sorghum seedling growth was more sensitive than germination, with an equimolar mixture of 2.5×10^–4 Mp-coumaric and 2.5×10^–4 M ferulic acids reducing seedling dry weight significantly below weights of seedlings treated separately with 2.5×10^–4 Mp-coumaric or ferulic acids. Further dilutions showed a 1.25×10^–4 M concentration of either phenol was stimulatory to seedling growth, whereas a mixture of these two produced inhibition.     

Evaluation of Ferulic Acid Uptake as a Measurement of Allelochemical Dose: Effective Concentration

Soil solution concentrations of allelopathic agents (e.g., phenolic acids) estimated by soil extractions differ with extraction procedure and the activities of the various soil sinks (e.g., microbes, clays, organic matter). This led to the hypothesis that root uptake of phenolic acids is a better estimator of dose than soil solution concentrations based on soil extracts. This hypothesis was tested by determining the inhibition of net phosphorus uptake of cucumber seedlings treated for 5 hr with ferulic acid in whole-root and split-root nutrient culture systems. Experiments were conducted with 11 ferulic acid concentrations ranging from 0 to 1 mM, phosphorus concentrations of 0.25, 0.5, or 1 mM, and solution pH values of 4.5, 5.5, or 6.5 applied when cucumber seedlings were 9, 12, or 15 days old. The uptake or initial solution concentration of ferulic acid was regressed on ferulic acid inhibition of net phosphorus uptake. Attempts were made to design experiments that would break the collinearity between ferulic acid uptake and phosphorus uptake. The original hypothesis was rejected because the initial ferulic acid solution concentrations surrounding seedling roots were more frequently and consistently related to the inhibition of net phosphorus uptake than to ferulic acid uptake by these roots. The data suggest that root contact, not uptake, is responsible for the inhibitory activity of phenolic acids.     

Simultaneous effects of ferulic andp-coumaric acids on cucumber leaf expansion in split-root experiments

Experiments were conducted to determine how plant responses to mixtures of allelochemicals may change as the proportion of roots in contact with allelochemicals is modified. Thirteen-day-old cucumber seedlings were treated with ferulic and/orp-coumaric acid in a split-root nutrient culture system. Leaf areas were determined just prior to treatment and at harvest, 24 hr after treatment. Ferulic acid was more inhibitory to cucumber leaf expansion thanp-coumaric acid. The effects of ferulic andp-coumaric acids on leaf expansion were additive. For individual acids, mixtures of ferulic andp-coumaric acids in the same container and combinations of ferulic andp-coumaric acids in separate containers, the inhibition of leaf expansion was directly related to the product of the concentration of the acid(s) and the proportion of roots treated with the acid(s). Pretreatment with 0.2 or 0.4 mM ferulic acid and subsequent treatment with 0.5 mM ferulic acid failed to show evidence of acclimation by cucumber seedlings.The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of products named, nor criticism of similar ones not mentioned.     

Allelopathic effect of alfalfa (Medicago sativa) on bladygrass (Imperata cylindrica)

Greenhouse and laboratory experiments were conducted at the Agricultural and Water Resources Research Center Station, Baghdad, in 1985 and 1986 to investigate the possible allelopathic potential of alfalfa (Medicago saliva L.) and its decomposed residues on bladygrass (Imperata cylin-drica L. Beauv.), a noxious weed in Iraq, and to isolate, characterize, and quantify possible allelopathic agents in alfalfa residues and root exudates. Results indicated that decomposed alfalfa roots and their associated soil produced a 51–56% reduction in bladygrass seed germination. Root and shoot length of bladygrass seedlings were reduced by an average of 88%. Decayed and undecayed mixtures of alfalfa roots and soil at 0.0151 (w/w) inhibited bladygrass seedlings reproduced from rhizomes by 30 and 42%. It was found that root exudates of alfalfa seedlings caused significant reduction in shoot and root dry weights of bladygrass seedlings when alfalfa and bladygrass were grown together in nutrient culture. Caffeic, chlorogenic, isochloro-genic,p-coumaric,p-OH-benzoic, and ferulic acids were detected in alfalfa root exudates and residues. The highest amount (126 fig phenolic acids/g soil) of these compounds was found in alfalfa root residues after six months of decomposition in soil.     

Phenolic acids affect photosynthesis and protein synthesis by isolated leaf cells of velvet-leaf

The effects ofp-coumaric, ferulic, chlorogenic, and vanillic acids on photosynthesis and protein synthesis by isolated leaf cells of velvetleaf (Abutilon theophrasti Medik) were investigated. Photosynthesis and protein synthesis were measured in cell suspensions by the incorporation of¹⁴CO₂ and [¹⁴C]leucine, respectively. None of the tested phenolic acids except vanillic reduced photosynthesis by more than 50% at the highest concentration and 30 min of incubation. At 100M concentrations and 60-min incubation periods,p-coumaric, ferulic, chlorogenic, and vanillic acids inhibited photosynthesis by 33, 37, 57, and 65%, respectively. Ferulic acid was the most inhibitory to protein synthesis and reduced the incorporation of [¹⁴C]leucine by 50% at about 1.0M after 60 min of incubation. At the highest concentrations tested in this study, vanillic and ferulic acids were inhibitory to photosynthesis and protein synthesis, respectively, whereas chlorogenic andp-coumaric acids did not inhibit either physiological process. The maximum inhibition of protein synthesis by chlorogenic acid was 19% and by vanillic acid was 28% at 100M concentrations. Chlorogenic, vanillic, andp-cou-maric acids at 0.1M caused increased protein synthesis over the untreated control. Overall, photosynthesis was more sensitive than protein synthesis to the four phenolic acids tested.Florida Agricultural Experiment Station Journal Series No. 9228.     

Effects of phenolic acids on germination and early growth of herbaceous woodland plants

Four herbaceous plant species from woodland (clearings),Deschampsia flexuosa, Scrophularia nodosa, Senecio sylvaticus, andChamaenerion angustifolium, were tested for their sensitivity to phenolic acids. Seven commonly occurring phenolic compounds were used in a germination experiment in concentrations ranging from 0.01 to 10 mM, i.e., salicylic,p-hydroxybenzoic, syringic, caffeic, vanillic,p-coumaric, and ferulic acids. Germination was delayed rather than inhibited. Radicle elongation was strongly affected; at lower concentrations stimulatory effects were observed, whereas at high concentrations radicle elongation was severely reduced. Salicylic acid was the most effective phenolic compound, whereas caffeic acid caused no effects. Early growth was studied in more detail in a second experiment withDeschampsia flexuosa andSenecio sylvaticus and the phenolic acids, ferulic and p-coumaric acid. Primary root length, number and length of secondary roots, and dry weight were stimulated at 0.01 mM but were inhibited at 10 mM of both compounds. The results are discussed in view of the allelopathic relations between trees and herbaceous understory vegetation.     

Effects of ferulic andp-coumaric acids in nutrient culture of cucumber leaf expansion as influenced by pH

Cucumber seedlings were grown in 5 mM MES [2-(N-morpholino)ethanesulfonic acid] -buffered nutrient solutions adjusted to a pH of 5.5, 6.25, or 7.0. Nutrient solutions were changed on alternate days. Seedlings were treated for a two-day period with various concentrations (0–1 mM) of ferulic acid,p-coumaric acid, or mixtures of these phenolic acids when 16 days old. Leaf growth, dry weight, and water utilization of the seedlings; pH of the solutions; and disappearance of the phenolic acids from nutrient solutions were monitored. Leaf area expansion of cucumber seedlings was inhibited by both ferulic andp-coumaric acid, and the magnitude of these inhibitions was influenced by concentration and pH. Inhibition of leaf area expansion was greater at pH 5.5 and nominal at pH 7.O. Ferulic acid was more inhibitory thanp-coumaric acid. The effect of pH on growth was best described by data for mean relative rates of leaf expansion. For example, the mean relative rates of leaf expansion by both acids at 0.5 mM for the 16- to 18-day growth period (treatment period) were reduced by 45, 31, and 8% for the pH 5.5, 6.25, and 7.0 treatments, respectively. The dry weight of seedlings at harvest (day 22) was significantly reduced for seedlings grown in the pH 5.5 and 6.25 treatments, but not for the pH 7.0 treatment. There was, however, one exception; the dry weight of seedlings treated withp-coumaric acid solutions adjusted to a pH of 5.5 was not significantly reduced. Water utilization by the seedlings was reduced by both ferulic andp-coumaric acid. Again, the impact of ferulic acid was greater thanp-coumaric acid. The effect of ferulic acid on water utlization decreased with increasing pH of the nutrient solution. The pH effects were not so consistent forp-coumaric acid. The effects of equimolar mixtures of the two phenolic acids were additive for all variables measured. There was a linear correlation between mean relative rates of leaf expansion and water utilization.Paper No. 9693 of the Journal Series of the North Carolina Agricultural Research Sevice, Raleigh, North Carolina. Mention of a trademark or a propriety product does not constitute a guarantee or warranty of the product by the Agricultural Research Service and does not imply its approval to the exclusion of other products that may be suitable.     

Use of water and EDTA extractions to estimate available (free and reversibly bound) phenolic acids in Cecil soils

Sterile and microbe reinfested Cecil A_p and B_t soil materials amended with 0 to 5 µmol/g of ferulic acid,p-coumaric acid,p-hydroxybenzoic acid, or vanillic acid were extracted after varying time intervals with water, EDTA, or NaOH to characterize sorption of cinnamic and benzoic acid derivatives and to determine the effectiveness of water and EDTA extractions in estimating concentrations of free and reversibly bound phenolic acids in soils. Basic EDTA (0.5 M, pH 8) extractions and water extractions provided good estimates of both free and reversibly bound cinnamic acid derivatives, but not of benzoic acid derivatives. Neutral EDTA (0.25 M, pH 7) and water extractions, however, were effective for both cinnamic and benzoic acid derivatives Rapid initial sorption of both cinnamic and benzoic acid derivatives was followed by slow long-term sorption of the cinnamic acid derivatives. Slow long-term sorption was not observed for the benzoic acid derivatives. The amount of sorption of phenolic acids in soil materials was directly related to the concentration of phenolic acids added to soil materials. The addition of a second phenolic acid to the soil materials did not substantially affect the sorption of each individual phenolic acid. Sodium hydroxide extractions, which were made only after phenolic acids in phenolic acid-amended and non-amended soil material were depleted by microbes, confirmed that neutral EDTA and water extractions of soils can be used to make accurate estimates of baseline (residual) levels of free and reversibly bound phenolic acids available to soil microbes and, thus, potentially to seeds and roots.The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of products named, nor criticism of similar ones not mentioned.     

Influence of Pretreatment Stresses on Inhibitory Effects of Ferulic Acid, an Allelopathic Phenolic Acid

Experiments were conducted to determine the potential for acclimation (i.e., increased tolerance) to allelopathic phenolic acids resulting from pretreatment of seedlings with allelochemical (ferulic acid), drought, or nutrient stress. Cucumber seedlings were exposed to pretreatment stresses in a nutrient culture system for nine days, starting with day 3. Seedlings were subsequently treated for 5 hr with 0, 0.25, 0.5, or 0.75 mM ferulic acid. Acclimation (tolerance) was quantified by percentage inhibition of net phosphorus uptake. Seedlings grown with ferulic acid or drought pretreatment stresses were more tolerant to subsequent ferulic acid treatments (i.e., inhibition of net phosphorus uptake by ferulic acid was reduced). Nutrient pretreatment stress eliminated the inhibitory activity of ferulic acid on net phosphorus uptake. The results suggest that a general acclimation response to a variety of pretreatment stresses can confer an increased tolerance of plants to allelopathic phenolic acids such as ferulic acid.     

Relationships between Phenolic Acid Concentrations,Transpiration, Water Utilization,Leaf Area Expansion,and Uptake of Phenolic Acids: Nutrient Culture Studies

Phenolic acid treatments of cucumber seedlings (Cucumis sativus cv “Early Green Cluster”) inhibited transpiration, water utilization, leaf area, and absolute and relative rates of leaf expansion. The cinnamic acids, ferulic and p-coumaric acids, were two to five times more inhibitory than the benzoic acids, p-hydroxybenzoic acid and vanillic acid. When phenolic acid concentrations were maintained at inhibitory concentrations through multiple successive treatments, percent inhibition of water utilization remained relatively constant for a given concentration and phenolic acid, percent inhibition of leaf area initially increased and then leveled off to a constant percent, and percent inhibition of transpiration and rates of leaf area expansion declined over time. Subsequently, p-coumaric acid was chosen as the model compound for further study. When p-coumaric acid was inhibitory, percent inhibition of transpiration, water utilization, and rates of leaf area expansion of actively growing leaves rapidly declined (i.e., was lost) as p-coumaric acid concentrations surrounding roots decreased. Absolute and relative rates of leaf expansion, for example, declined approximately 12 and 14%, respectively, for every 0.1 mM decline in p-coumaric acid concentration. Uptake of p-coumaric acid by cucumber seedling roots was continuous over the 24- or 36-hr periods monitored, but was not consistently related to the initial p-coumaric acid treatment concentrations. However, declining p-coumaric acid concentrations monitored at 6- or 12-hr intervals over the 24- or 36-hr periods continued to be highly correlated to the initial p-coumaric acid treatment concentrations. A 25% depletion by 13-d-old cucumber seedlings took 8.5, 12, 19.5, 25, and 29.5 hr for 0.125-, 0.25-, 0.5-, 0.75-, and 1-mM treatments, respectively. Uptake during periods when phenolic acid concentrations and root uptake (depletion from solution) were related appeared to represent periods dominated by apoplastic movement into the intercellular spaces of roots. Uptake during periods without this relationship likely represented periods dominated by symplastic movement. The ability of cucumber seedlings to modify active phenolic acid concentrations surrounding their roots suggests that cucumber seedling can directly influence the magnitude of primary and secondary effects of phenolic acids through feedback regulation.     

Inhibition of cucumber leaf expansion by ferulic acid in split-root experiments

Experiments were conducted to determine how the proportion of a root system in contact with an allelopathic compound may affect seedling responses. Cucumber seedlings grown in a split-root nutrient culture system were given either single (1 mM) or multiple applications (0.5 mM) of ferulic acid. Seedlings receiving single applications were left in the treatment solutions for two days and then harvested, while seedlings receiving multiple applications had their solutions changed every other day for a total of three changes. Leaf areas were determined daily starting with the initial ferulic acid treatment. Mean absolute and mean relative rates of leaf expansion were inversely related to the proportion of the root system in ferulic acid solution. Leaf expansion was inhibited primarily during the first 24 hr after each treatment. A partial recovery of growth occurred during the second 24-hr period following each treatment. Root length was reduced by ferulic acid. These results suggest that information on root and allelochemical distribution in soils is important when assessing the potential of allelopathic interactions between plants.Paper No. 11940 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina 27695-7643. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of products named, nor criticism of similar ones not mentioned.     

Why Phenolic Acids Are Unlikely Primary Allelochemicals in Rice

Allelopathy in rice (Oryza sativa, L.) effective against weeds has been found in about 3.5% of tested rice germplasm in both laboratory and field experimentation. However, the allelochemicals responsible for growth inhibition of rice-associated weeds have not yet been identified. In the literature, phenolic acids are often mentioned as putative allelochemicals. If phenolic acids commonly reach growth inhibitory concentrations in rice ecosystems, it must be expected that the degree of tolerance to phenolic acids will vary among traditional rice cultivars or plant species adapted to rice environments having inherently different phenolic acid concentrations. Phenolic acids concentrations are normally greater in submerged than in aerobic soils. A dose–response study, however, showed that seedlings of rice cultivars adapted to submerged anaerobic soils did not have higher level of tolerance against p-hydroxybenzoic acid than did seedlings of varieties adapted to aerobic upland soils. Moreover, traditional rice cultivars had no greater tolerance than did improved cultivars that were recently bred for traits other than tolerance of phenolic acids. Similarly, there were no differences in tolerance of p-hydroxybenzoic acid between two Echinochloa weed species adapted to either anaerobic or aerobic growth conditions. Thus, neither the rice cultivars nor weed species had evolved different tolerance levels against the phenolic acid. However, all rice cultivars had significantly greater tolerance of p-hydroxybenzoic acid than did either weed species. In a second experiment, the rates at which rice plants released phenolic acids into solution cultures were measured for at least one month, the time period of greatest allelopathic activity following planting under field conditions. The maximum release rate of phenolic acids during the first month of growth was approximately 10 g/plant/day. At a conventional plant density, the release rate of phenolic acids would be approximately 1 mg/m²day. This order of release rate cannot provide concentrations remotely close to phytotoxic levels determined for these rice cultivars and weed species. The results presented in this paper do not preclude the possibility that phenolic acids might be one component in a mixture of chemicals that, when present simultaneously, are allelopathic.     

Chemo‐enzymatic synthesis of lipophilic ferulates and their evaluation for antioxidant and antimicrobial activities

An efficient chemo‐enzymatic synthesis of ferulic acid‐based structured lipids mimicking triacylglycerol with a pendant phenolic moiety was carried out for the first time. Initially, ferulic acid was reduced to coniferyl alcohol, followed by its esterification with fatty acids. The key step in the synthesis was dihydroxylation of the olefinic side chain of coniferyl ester, which was eventually esterified with fatty acids to generate phenolic structured lipids. Two such compounds of varying fatty acid chain lengths were synthesized in good yield. Structural confirmation of both compounds is based on IR, ¹H and ¹³C NMR, and MS techniques. The synthesized compounds were tested for in vitro antioxidant and antimicrobial activities. Both compounds exhibited moderate to good antioxidant activity. The phenolic structured lipid with only shorter‐chain fatty acids showed antibacterial activity. Both compounds did not show any antifungal activity.     

Effects of Microbial Utilization of Phenolic Acids and their Phenolic Acid Breakdown Products on Allelopathic Interactions

Reversible sorption of phenolic acids by soils may provide some protection to phenolic acids from microbial degradation. In the absence of microbes, reversible sorption 35 days after addition of 0.5–3 mol/g of ferulic acid or p-coumaric acid was 8–14% in Cecil A_p horizon and 31–38% in Cecil B_t, horizon soil materials. The reversibly sorbed/solution ratios (r/s) for ferulic acid or p-coumaric acid ranged from 0.12 to 0.25 in A_p and 0.65 to 0.85 in B_t horizon soil materials. When microbes were introduced, the r/s ratio for both the A_p and B_t horizon soil materials increased over time up to 5 and 2, respectively, thereby indicating a more rapid utilization of solution phenolic acids over reversibly sorbed phenolic acids. The increase in r/s ratio and the overall microbial utilization of ferulic acid and/or p-coumaric acid were much more rapid in A_p than in B_t horizon soil materials. Reversible sorption, however, provided protection of phenolic acids from microbial utilization for only very short periods of time. Differential soil fixation, microbial production of benzoic acids (e.g., vanillic acid and p-hydroxybenzoic acid) from cinnamic acids (e.g., ferulic acid and p-coumaric acid, respectively), and the subsequent differential utilization of cinnamic and benzoic acids by soil microbes indicated that these processes can substantially influence the magnitude and duration of the phytoxicity of individual phenolic acids.     

Effects of ferulic acid,an allelopathic compound,on net P,K, and water uptake by cucumber seedlings in a split-root system

Since distribution of allelopathic compounds in soils is highly variable, injurious effects by such compounds should be related to the frequency of contact with roots. Experiments were conducted to determine how P, K, and water uptake of cucumber seedlings were affected as the fraction of roots in contact with ferulic acid (FA) was increased. Seedlings were grown in Hoagland's nutrient solution for 14 days and then transferred to 0.5 mM CaSO₄ solution for 24 hr before being placed into a split-root culture system. The containers in the system were filled with 0.5 mM concentrations of KH₂PO₄ and CaSO₄ or 0.5 mM concentrations of KH₂PO₄, CaSO₄, and ferulic acid (FA). Net uptake of P by seedlings (milligrams per seedling) decreased in a curvilinear (concave) manner as the fraction of the roots in contact with FA increased. Net uptake of K (milligrams per seedling) and water (milliliters per seedling) by seedlings decreased linearly as the fraction of the roots in contact with FA increased. Net uptake of P, K, and water by seedlings was reduced 57, 75, and 29%, respectively, when the whole root system was exposed to FA. Net P and K uptake of roots (milligrams per gram root fresh weight) not in contact with FA decreased in a linear and curvilinear (convex) manner, respectively, as the fraction of roots in contact with FA increased. Net P and K uptake of roots in contact with ferulic acid increased in a linear and curvilinear (convex) manner, respectively. Net water uptake of roots (milliliters per gram root fresh weight) not in contact with FA increased in a curvilinear (concave) manner as the frequency of the roots in contact with FA increased. Net water uptake of roots in contact with FA did not show a trend. Transpiration (milliliters per square centimeter) was reduced in a linear manner as the fraction of roots in contact with FA increased. A very slight compensation by roots not in contact with FA for roots in contact with FA was observed for net water uptake rates. No compensation for P and K uptake rates was observed.Paper Mo. 12421 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina 27695-7643. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentioned.     

Soybean (<Emphasis Type="Italic">Glycine max</Emphasis>) Root Lignification Induced by Ferulic Acid. The Possible Mode of Action

Ferulic acid, in the form of feruloyl CoA, occupies a central position as an intermediate in the phenylpropanoid pathway. Due to the allelopathic function, its effects were tested on root growth, H(2)O(2) and lignin contents, and activities of cinnamyl alcohol dehydrogenase (CAD, EC 1.1.1.195) and peroxidase (POD, EC 1.11.1.7) from soybean (Glycine max (L.) Merr.) root seedlings. Three-day-old seedlings were cultivated in half-strength Hoagland's solution (pH 6.0), with or without 1.0 mM ferulic acid in a growth chamber (25 degrees C, 12/12 hr light/dark photoperiod, irradiance of 280 mumol m(-2) s(-1)) for 24 or 48 hr. Exogenously supplied ferulic acid induced premature cessation of root growth, with disintegration of the root cap, compression of cells in the quiescent center, increase of the vascular cylinder diameter, and earlier lignification of the metaxylem. Moreover, the allelochemical decreased CAD activity and H(2)O(2) level and increased the anionic isoform PODa5 activity and lignin content. The lignin monomer composition of ferulic acid-exposed roots revealed a significant increase of guaiacyl (G) units. When applied jointly with piperonylic acid (an inhibitor of the cinnamate 4-hydroxylase, C4H), ferulic acid increased lignin content. By contrast, the application of 3,4-(methylenedioxy) cinnamic acid (an inhibitor of the 4-coumarate:CoA ligase, 4CL) with ferulic acid did not. Taken together, these results suggest that ferulic acid may be channeled into the phenylpropanoid pathway (by the 4CL reaction) and, further, may increase the lignin monomer amount solidifying the cell wall and restricting the root growth.     

Inhibition and recovery of cucumber roots given multiple treatments of ferulic acid in nutrient culture

Ferulic acid, a frequently cited allelopathic agent, inhibited photosynthesis, leaf expansion, and root elongation of cucumber seedlings grown in aerated nutrient cultures in a growth chamber. Other effects were a reduction in the proportion of radioactivity fixed by photosynthesis translocated to roots, a stimulation in secondary root initiation, and an increase in root-shoot ratios. Inhibition of leaf expansion and root elongation induced by multiple ferulic acid treatments was rapidly lost once ferulic acid was removed from the root environment. The changes in general root morphology, i.e., average root length and root number, associated with ferulic acid treatments, were partially reversed or not affected when ferulic acid was removed from the root environment.Paper No. 11411 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, North Carolina 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentioned.