Uptake and metabolic fate of [14C]-2,4-dichlorophenol and [14C]-2,4-dichloroaniline in wheat (Triticum aestivum) and soybean (Glycine max)

The uptake and metabolism of [14C]-2,4-dichlorophenol (DCP) and [14C]-2,4-dichloroaniline (DCA) were investigated in wheat and soybean. Seeds were exposed to a nutrient solution containing 50 microM of one of two radiolabeled compounds, and plant organs were harvested separately after 18 days of growth. In wheat, uptake of [14C]-2,4-DCP was 16.67 +/- 2.65 and 15.50 +/- 2.60% of [14C]-2,4-DCA. In soybean, uptake of [14C]-2,4-DCP was significantly higher than [14C]-2,4-DCA uptake, 38.39 +/- 2.56 and 18.98 +/- 1.64%, respectively. In the case of [14C]-2,4-DCP, the radioactivity absorbed by both species was found mainly associated with roots, whereas [14C]-2,4-DCA and related metabolites were associated with aerial parts, especially in soybean. In wheat, nonextractable residues represented 7.8 and 8.7% of the applied radioactivity in the case of [14C]-2,4-DCP and [14C]-2,4-DCA, respectively. In soybean, nonextractable residues amounted to 11.8 and 5.8% of the total radioactivity for [14C]-2,4-DCP and [14C]-2,4-DCA, respectively. In wheat, nonextractable residues were nearly equivalent to extractable residues for [14C]-2,4-DCP, whereas they were greater for [14C]-2,4-DCA. In soybean, the amount of extractable residues was significantly greater for both chemicals. However, in both species, nonextractable residues were mainly associated with roots. Isolation of soluble residues was next undertaken using excised shoots (wheat) or excised fully expanded leaves including petioles (soybean). Identification of metabolite structures was made by comparison with authentic standards, by enzymatic hydrolyses, and by electrospray ionization-mass spectrometric analyses. Both plant species shared a common metabolism for [14C]-2,4-DCP and [14C]-2,4-DCA since the malonylated glucoside conjugates were found as the final major metabolites.     

Fate of 14C-ring-labeled 2,4-D, 2,4-dichlorophenol and 4-chlorophenol during straw composting

Experiments were carried out to study the transformation of ¹⁴C-ring-labeled 2,4-D and the two related chlorophenols 4-chlorophenol (4-CP) and 2,4-dichlorophenol (4-DCP) during straw composting under controlled laboratory conditions. Incubation under sterile and nonsterile conditions was done to evaluate the relative importance of the biotic and abiotic processes. Pre-composted straw was treated with the three chemicals. The availability of the different chemicals was monitored during incubations as well as their degradation. Under nonsterile conditions, the mineralization of both chlorophenols reached 20% of the applied compounds, whereas it was 52% for 2,4-D. Transitory water-soluble metabolites of 2,4-D and chlorophenols were formed but they disappeared rapidly. After 21 days, 21% of the 2,4-D and 38% of the 2,4-DCP was stabilized as nonextractable (bound) residues under nonsterile conditions. Bound residues of both chemicals were negligible under sterile conditions. Availability of chemicals as estimated by water extraction decreased during incubation proportionally to mineralization and to the formation of bound residues. The increase in immobilization of the chemical residues was stronger under nonsterile conditions than under sterile conditions. Under nonsterile conditions 71% of the 4-CP was recovered as bound residues, whereas under sterile conditions 30% of the applied 4-CP formed bound residues after formaldehyde addition and only 8% with autoclaved straw. Global microbial activity decreased in the presence of the chlorophenols probably due to their toxic effect. These data indicate that the biological activity associated with straw transformation during composting stimulates the depletion of 2,4-D and chlorophenols by mineralization and by formation of bound residues. Received: 6 September 1996     

Uniformly (14)C-ring-labeled 2,4-dichlorophenoxyacetic acid: a metabolism study in bluegill sunfish, Lepomis macrochirus.

The fate of 2,4-dichlorophenoxyacetic acid (2,4-D), a mixture of [phenyl(U)-(14)C]-2,4-D and unlabeled 2,4-D, in bluegill sunfish was investigated after exposure to approximately 11 ppm under static conditions for 4 days. Total radioactive residues (TRR) in whole fish increased from 0.41 ppm on day 1 to 0.60 ppm on day 3. TRR levels in fillet (edible) and viscera (nonedible) of treated fish on day 4 were 0.41 and 1.9 ppm, respectively. Most residues in both matrices were acetonitrile soluble; small amounts were hexane soluble or unextractable with solvents. Acid and base hydrolyses with ethyl acetate partitioning were used to release the fillet unextractable residues. The identification of 2,4-D and 2,4-dichlorophenol (2,4-DCP) in the fillet was conclusively confirmed by GC-MS analysis. On the basis of the experimental data from this study, a metabolic pathway for 2,4-D in bluegill sunfish in which the 2,4-D is metabolized to 2,4-DCP and conjugates of 2,4-D and 2,4-DCP is proposed.     

Metabolic fate of 2,4-dichlorophenol and related plant residues in rats

This study compared the metabolic fate of [(14)C]-DCP, [(14)C]-residues from radish plants, and purified [(14)C]-DCP-(acetyl)glucose following oral administration in rats. A rapid excretion of radioactivity in urine occurred for [(14)C]-DCP, [(14)C]-DCP-(acetyl)glucose, and soluble residues, 69, 85, and 69% within 48 h, respectively. Radio-HPLC profiles of 0-24 h urine from rats fed [(14)C]-DCP and [(14)C]-DCP-(acetyl)glucose were close and qualitatively similar to those obtained from plant residues. No trace of native plant residues was detected under the study conditions. The structures of the two major peaks were identified by MS as the glucuronide and the sulfate conjugates of DCP. The characterization of a dehydrated glucuronide conjugate by MS and NMR of DCP was unusual. In contrast to soluble residues, bound residues were mainly excreted in feces, 90% within 48 h, whereas total residues were eliminated in both urine and feces. For total residues, the radioactivity in feces was higher than expected from the percentage of soluble and bound residues in radish plants. This result highlighted that less absorption took place when residues were present in the plant matrix as compared to plant-free residues and DCP.     

Inheritance and physiological basis for 2,4-D resistance in prickly lettuce (Lactuca serriola L.)

Experiments were conducted to determine the inheritance and physiological basis for resistance to the synthetic auxinic herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D) in a prickly lettuce biotype. Inheritance of 2,4-D resistance in prickly lettuce is governed by a single codominant gene. Absorption and translocation were conducted using (14)C-2,4-D applied to 2,4-D-resistant and -susceptible biotypes. At 96 h after treatment (HAT), the resistant biotype absorbed less applied 2,4-D and retained more 2,4-D in the treated portion of the leaf compared to the susceptible biotype. The resistant biotype translocated less applied 2,4-D to leaves above the treated leaf and crown at 96 HAT compared to the susceptible biotype. No difference in the rate of metabolism of 2,4-D was observed between the two biotypes. Resistance to 2,4-D appears to originate from a reduced growth deregulatory and overstimulation response compared to the susceptible biotype, resulting in lower translocation of 2,4-D in the resistant prickly lettuce biotype.     

Degradation of [carboxyl-14C] 2,4-D and [ring-U-14C] 2,4-D in 114 agricultural soils as affected by soil organic carbon content

This study compared the degradation of [carboxyl-¹⁴C] 2,4-dichlorophenoxyacetic acid (2,4-D) (C2,4-D) and [ring-U-¹⁴C] 2,4-D (R2,4-D) in 114 agricultural soils (0–15 cm) as affected by 2,4-D sorption and soil properties (organic carbon content, pH, clay content, carbonate content, cation exchange capacity, total microbial activity). The sample area was confined to Alberta, Canada, located 49–60° north longitude and 110–120° west latitude and soils were grouped by soil organic carbon content (SOC) (0–0.99%, 1–1.99%, 2–2.99%, 3–3.99% and >4% SOC). Degradation rates of C2,4-D and R2,4-D followed first-order kinetics in all soils. Although total microbial activity increased with increasing SOC, degradation rates and total degradation of C2,4-D and R2,4-D decreased with increasing SOC because of increased sorption of 2,4-D by soil and reduced bioavailability of 2,4-D and its metabolites. Rates of R2,4-D degradation were more limited by sorption than rates of C2,4-D degradation, possibly because of greater sorption and formation of bound residues of 2,4-D metabolites relative to the 2,4-D parent molecule. Based on the sorption and degradation parameters quantified, there were two distinct groups of soils, those with less than 1% SOC and those with greater than 1% SOC. Specifically, soils with less than 1% SOC had, on average, 2.4 times smaller soil organic carbon sorption coefficients and 1.4 times smaller 2,4-D half-lives than soils with more than 1% SOC. In regional scale model simulations of pesticide leaching to groundwater, covering many soils, input parameters for each pesticide include a single soil organic carbon sorption coefficient and single half-life value. Our results imply, however, that the approach to these regional scale assessments could be improved by adjusting the values of these two input parameters according to SOC. Specifically, this study indicates that for 2,4-D and Alberta soils containing less than 1% SOC, the 2,4-D pesticide parameters obtained from generic databases should be divided by 2.5 (soil organic carbon sorption coefficient) and 1.5 (half-life value).     

Enantiomer resolution and assay of propionic acid-derived herbicides in formulations by using chiral liquid chromatography and achiral gas chromatography

Enantiomers of 6 propionic acid-derived herbicides in the form of their esters were resolved using liquid chromatography with a chiral column. Free acids are converted to methyl esters by means of a BF3-catalyzed reaction. Chromatographic resolutions for 6 of 8 herbicides investigated were in the range of 2 to 4. The method was applied for the simultaneous determination of mecoprop and 2,4-D content and individual mecoprop enantiomers in 2 formulations containing racemic and R-mecoprop in mixture with 2,4-D. Precision and accuracy of content determination was comparable to standard methods, and enantiomer contents were in good agreement with declared values. The enantiomers of dichlorprop and mecoprop were also resolved as diastereomeric menthyl esters by achiral high resolution gas chromatography (HRGC). HRGC data on enantiomer composition were in good agreement with those from the LC method and other data.     

Metabolic fate of [14C] chlorophenols in radish (Raphanus sativus), lettuce (Lactuca sativa), and spinach (Spinacia oleracea)

Chlorophenols are potentially harmful pollutants that are found in numerous natural and agricultural systems. Plants are a sink for xenobiotics, which occur either intentionally or not, as they are unable to eliminate them although they generally metabolize them into less toxic compounds. The metabolic fate of [ (14)C] 4-chlorophenol (4-CP), [ (14)C] 2,4-dichlorophenol (2,4-DCP), and [ (14)C] 2,4,5-trichlorophenol (2,4,5-TCP) was investigated in lettuce, spinach, and radish to locate putative toxic metabolites that could become bioavailable to food chains. Radish plants were grown on sand for four weeks before roots were dipped in a solution of radiolabeled chlorophenol. The leaves of six-week old lettuce and spinach were treated. Three weeks after treatments, metabolites from edible plant parts were extracted and analyzed by high performance liquid chromatography (HPLC) and characterized by mass spectrometry (MS), and nuclear magnetic resonance spectroscopy (NMR). Characterization of compounds highlighted the presence of complex glycosides. Upon hydrolysis in the digestive tract of animals or humans, these conjugates could return to the toxic parent compound, and this should be kept in mind for registration studies.     

Degradation of phenolic and non-phenolic aromatic pollutants by four Pleurotus species: the role of laccase and versatile peroxidase

The ability of Pleurotus eryngii, Pleurotus ostreatus, Pleurotus pulmonarius and Pleurotus sajor-caju to degrade the aromatic pollutants 2,4-dichorophenol (2,4-DCP) and benzo(a)pyrene [B(a)P] in liquid culture and microcosm (using wheat straw as growth substrate and sea sand as a xenobiotic carrier) was investigated by HPLC and ¹⁴CO₂ release from labeled pollutants. We found that 100 μM 2,4-DCP was very quickly transformed by the four fungi, disappearing 24 h after its addition to the liquid cultures. However, a 2-week incubation period was required to transform 100 μM B(a)P up to 75% by P. eryngii and P. pulmonarius. Whereas the fungi were able to begin degradation of the two pollutants with high transformation rates, their complete degradation (mineralization) rates were very low. Mineralization of B(a)P in liquid cultures was only observed with P. eryngii and P. pulmonarius, although the four Pleurotus species studied were able to mineralize this compound in solid state fermentation (SSF). The ligninolytic enzymes laccase and versatile peroxidase (VP), together with aryl-alcohol oxidase (AAO) providing extracellular H₂O₂, were found in liquid cultures. Except AAO, these enzymes were also detected in SSF experiments. In order to investigate the role of ligninolytic enzymes in the process, their action on both pollutants (50 μM) was studied in vitro in the absence and presence of redox mediators. As observed with the fungal cultures, 2,4-DCP was oxidized faster than B(a)P by both laccase (60% transformation after 6 h) and VP (100% transformation after 1 h). Moreover, laccase oxidation was strongly increased (up to 90% transformation after 3 h), by the presence of the mediators 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) or 1-hydroxybenzotriazole (HBT). In the case of B(a)P, the presence of ABTS or HBT was strictly required for oxidation by laccase (25% transformation after 8 h). Degradation of B(a)P was also observed in reactions with VP (40% transformation after 6 h). The results obtained suggest that Pleurotus species can be used in applications focused to the degradation of aromatic pollutants using wheat straw as a growth substrate, and provide the first evidence on the direct transformation of recalcitrant aromatic pollutants by VP.     

环境激素2,4-二氯苯酚对家蚕生殖发育的影响

为了探讨环境激素对鳞翅目昆虫的影响,用添加2,4-二氯苯酚（2,4-DCP）的人工饲料饲养家蚕,调查2,4-DCP对家蚕生殖发育的影响。结果显示,1.60 mmol.kg^-1以下浓度的2,4-DCP,对幼虫和蛹的卵巢生长有促进作用（P〈0.05）;1.60 mmol.kg-1的2,4-DCP对5龄后期快速生长阶段的卵巢表现出抑制作用,但在蛹期卵巢的生长获得补偿。高浓度的2,4-DCP对幼虫期、蛹期卵细胞的生长和发育有一定的促进作用（P〈0.01）。2,4-DCP对家蚕雄性生殖腺的生长、特别是5龄后期精巢的快速生长期表现出一定的抑制作用,在蛹期抑制作用表现十分强烈,1.60 mmol.kg^-1的2,4-DCP使雄蛾蚕的精巢几乎完全退化。2,4-DCP使5龄幼虫的精细胞数量微弱减少,至蛹期精细胞和蛾期精子的数量则显著少于对照（P〈0.01）。1.60 mmol.kg^-1的2,4-DCP使雌蛾的产卵数下降到对照的20%,但造卵数比对照高1.3倍,0.80 mmol.kg^-1以上浓度的2,4-DCP使不受精卵率显著增高（P〈0.05）。2,4-DCP主要通过强烈抑制家蚕雄性生殖腺和生殖细胞的发育以表现出很强的雌激素效应。     

Kinetic modeling of 2,4-dichlorophenoxyacetic acid (2,4-D) degradation in soil slurry by anodic fenton treatment

Anodic Fenton treatment (AFT) has been shown to be a promising technology in pesticide wastewater treatment. However, no research has been conducted on the AFT application to contaminated soils. In this study, the 2,4-D degradation kinetics of AFT in a silt loam soil slurry were investigated for the first time, and the effects of various experimental conditions including initial 2,4-D concentration, Fenton reagent delivery rate, amount of humic acid (HA) addition, and pH were examined. The 2,4-D degradation in soil slurry by AFT was found to follow a two-stage kinetic model. During the early stage of AFT (the first 4-5 min), the 2,4-D concentration profile followed a pseudo-first-order kinetic model. In the later stage (typically after 5 or 6 min), the AFT kinetic model provided a better fit. This result is most likely due to the existence of (*)OH scavengers and 2,4-D sorption on soil. The Fe(2+) delivery rate was shown to be a more significant factor in degradation rate than the H(2)O(2) delivery rate when the Fe(2+)/H(2)O(2) ratios were in the range of 1:2 to 1:10. The presence of HA in soil lowered the AFT rate, most probably due to the competition with 2,4-D for consumption of (*)OH and increased sorption of 2,4-D on soil. The optimal pH for 2,4-D degradation in soil slurry by AFT was observed to be in the range of pH 2-3.     

Effect of molecular complexity and acidity of earthworm faeces humic fractions on glutamate dehydrogenase,glutamine synthetase,and phosphoenolpyruvate carboxylase in Daucus carota α II cells

Carrot cells were grown in cultures supplemented with two hormones [2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (6BAP)] and two humic fractions extracted from earthworm faeces, one with high acidity and a low apparent molecular size (<3500) and the other with low acidity and a large molecular size. 2,4-D stimulated growth through an effect on cell enlargement, while the strongly acidic humic fraction (0.2 mg l^-1) and the weakly acidic fraction (1 mg l^-1) were both less effective. With 4–16 h of pre-incubation, the highly acid humic fraction, mainly alone, induced the best increase in protein content; the effect of the weakly acid humic fraction and the hormones was generally less important. The two humic fractions also differed in their influence on glutamate dehydrogenase activity. After 2 h of pretreatment, the highly acidic fraction increased glutamate dehydrogenase activity, while the other fraction did not affect it. After 4–16 h of pre-incubation, the activity of this enzyme was still not influenced by these humic fractions. The presence of the two hormones did not interfere with the humic matter effects. Glutamine synthetase activity was not affected by a pre-incubation of up to 4 h with the two humic fractions, but it was stimulated after 8–16 h of pre-incubation. A 2,4-D+6BAP mixture stimulated glutamine synthetase activity (from +12 to +50%). Again, the presence of the hormones did not interfere with the effects induced by the humic fractions. After 16 h of pre-incubation, phosphoenolpyruvate carboxylase activity was increased by the highly acidic humic fraction (+93%) and by both humic fractions together (+34%). An explanation of the different incubation times necessary for the humic fractions to exert stimulatory effects on these enzymes is proposed here. The regulatory properties of the strongly acidic humic fraction appeared to depend on the combination of high acidity (expecially carboxylic C) with low molecular size.     

Biodegradation of chlorinated phenols in subsurface soils

Microcosm studies were employed to determine the subsurface biodegradation rates of phenol, 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP). Soil samples were taken from sites in Pennsylvania and Virginia from depths up to 31 m, and all samples contained significant microbial populations. Soil from both sites readily biodegraded all five compounds. Biodegradation rates increased as initial concentrations increased, and all biodegradation rates appeared to follow first-order kinetics with regard to the initial compound concentrations. Biodegradation rates for the five compounds followed the order: phenol = 2-CP > 2,4,6-TCP > 2,4-DCP. PCP was degraded more slowly than phenol or 2-CP, but similarly to 2,4,6-TCP and 2,4-DCP. Different soils exhibited different degradation rates, and the soil characteristics that may influence the rates are discussed. The data suggest that biological degradation is a significant attenuation mechanism for phenol and its chlorinated derivatives in subsurfaces saturated and unsaturated zones.     

不同植物激素对冬凌草愈伤组织增殖及褐化的影响

研究了不同种类的植物激素对冬凌草叶片诱导愈伤组织及褐化的影响,结果表明:培养基中植物激素的种类、浓度及其组合对愈伤组织增殖及褐变影响较大。适宜浓度的2,4-D、IAA和NAA生长素、KT和6-BA细胞分裂素及GA3,能不同程度地减轻或抑制褐化,促进愈伤组织的生长,其中以2,4-D(2.5) KT(0.2) GA3(0.2)效果最好。     

Effects of 2,4-d on nitrogen fixation and carbon dioxide evolution in a soil microcosm

Two concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) 1.7 kg ha^?1 and 3.4 kg ha^?1 were applied to oats (Avena sativa L. ‘Orbit’) grown in terrestrial microcosms in a sandy soil. Carbon dioxide evolution and non-symbiotic N₂ fixation (C₂H₂ reduction) were measured weekly. On day 70 of the study, 2,4-D was applied a second time at the same application rates and soil CO₂ evolution and N₂ fixation were measured more frequently. Soil CO₂ evolution over 24 h period was significantly decreased by 40 to 50% at both application rates of 2,4-D. This response lasted less than 7 days. Nitrogen fixation was unaffected by 2,4-D except for an unexplained decrease observed in the 1.7 kg ha^?1 treatment 35 days after 2,4-D application. This effect was not observed on the following sampling date. The second application of 2,4-D failed to produce any significant change in soil CO₂ evolution or N₂ fixation. From these studies we conclude soil microbial populations either degraded or became acclimated to 2,4-D as a result of the initial application and that 2,4-D has no significant adverse effect on N₂ fixation or soil CO₂ evolution.     

提高小麦×玉米杂交产生单倍体胚频率的研究

为了提高小麦×玉米杂交单倍体胚的产生频率，采用了2,4-D中含有不同体积浓度的二甲基亚砜和不同的激素处理组合两种方法诱导小麦×玉米产生单倍体，研究其对得胚率的影响。结果表明，就平均得胚率而言，在二甲基亚砜激素浓度处理中，最佳的二甲基亚砜体积浓度为3.0%（得胚率为17.0%），而且各不同浓度的处理均高于对照（9.7%）；在不同激素配比试验中，2,4-D+3%二甲基亚砜单独处理的得胚率（7.3%）﹥2,4-D两次处理(6.9%)﹥2,4-D与2,4-D+3%二甲基亚砜配合处理(5.5%)﹥2,4-D一次处理(2.9%)。     

铁炮百合的胚性愈伤组织诱导和植株再生

以铁炮百合(又称麝香百合)杂种系品种‘White heaven’的组培苗叶片为外植体,研究了不同种类和浓度的激素对愈伤组织诱导和植株再生的影响,并通过叶片位置、接种方式以及光暗等不同处理进一步优化胚性愈伤组织的诱导。结果表明:以组培苗基部叶片为外植体,采用叶片近轴面向上的接种方式,在MS+1.0mg.L-12,4-D+0.1mg.L-16-BA的培养基上暗培养可诱导出胚性愈伤组织,诱导率可达65.74%;经石蜡切片鉴定可观测到球形胚和心形胚。最佳分化和生根培养基分别为MS+0.1mg.L-1NAA和1/2MS+0.5mg.L-1IBA,分化率达81.48%,生根率达91.67%。结果还显示2,4-D在百合胚性愈伤组织的诱导中起到了关键作用。     

Flavone C-glycoside,phenolic acid,and nitrogen contents in leaves of barley subject to organic fertilization treatments

From the leaves of barley, Hordeum vulgare, one new flavone C-glucoside and three known flavone glucosides were isolated and characterized by (1)H and (13)C NMR and MALDI-TOF-MS. The novel flavone C-glucoside was isovitexin 7-O-beta-[6' "-O-(E)-p-coumaroyl]glucoside (6' "-coumaroylsaponarin), and the known compounds were isovitexin 7-O-beta-[6' "-O-(E)-feruloyl]glucoside, isoorientin 7-O-beta-[6' "-O-(E)-feruloyl]glucoside, and tricin 7-O-beta-glucoside. The sum of all the flavone glycosides and soluble phenolic acids in the leaves decreased with increased rate of plant nutrients given in animal manure and with increased crop yield. All of the major phenylpropanoids showed the same general response to nutrient level. The concentration of nitrogen in the leaves was not directly related to nutrient application or to contents of phenylpropanoids.     

Comparative degradation of [14C]-2,4-dichlorophenoxyacetic acid in wheat and potato after Foliar application and in wheat, radish, lettuce, and apple after soil application

The fate of 2,4-dichlorophenoxyacetic acid (2,4-D) applied foliarly as the 2-ethylhexyl ester (EHE) to wheat and potatoes, to the soil as the dimethylamine (DMA) salt under apple tree canopies, and preplant as the free acid for wheat, lettuce, and radish was studied to evaluate metabolic pathways. Crop fractions analyzed for (14)C residues included wheat forage, straw, and grain; potato vine and tubers; and apple fruit. The primary metabolic pathway for foliar application in wheat is ester hydrolysis followed by the formation of base-labile 2,4-D conjugates. A less significant pathway for 2,4-D in wheat was ring hydroxylation to give NIH-shift products 2,5-dichloro-4-hydroxyphenoxyacetic acid (4-OH-2,5-D), 4-OH-2,3-D, and 5-OH-2,4-D both free and as acid-labile conjugates. The primary metabolic pathway in potato was again ester hydrolysis. 2,4-D acid was further transformed to 4-chlorophenoxyacetic acid and 4-OH-2,5-D. For the soil applications, (14)C residues in the crops were low, and characterization of the (14)C residues indicated association with or incorporation into the biochemical matrix of the tissue. The degradative pathways observed in wheat are similar to those characterized in other intact plant studies but differ from those in studies in wheat cell suspension culture in that no amino acid conjugates were observed.     

Phenoxyacetic acid residue incorporation in cell walls of soybean (Glycine max.)

The metabolism of [(14)C] phenoxyacetic acid (POA) and the formation of bound residues were studied in soybean leaves and stems. POA was metabolized to 4-HO-POA and to 4-HO-POA glucoside, and a significant fraction of the radioactivity was incorporated in the cell walls (CW). An extraction procedure of CW polymers was developed to specifically isolate the radioactivity associated with each of them. In leaves, the radioactivity showed a preferential distribution into the hemicelluloses and lignins, while pectins and lignins were the most radioactive CW polymers in stems. The identified bound metabolites were 4-HO-POA, POA, and phenolic residues. The latter and POA were essentially incorporated into the lignin fractions and were linked to the benzylic carbons of lignin monomers. 4-HO-POA, the major bound residue, was more evenly distributed in CW polymers. It was esterified to noncellulosic polysaccharides and lignins, but in the latter, contrary to other POA residues, it was mainly linked at the gamma-carbon of propanoid side-chains of lignin monomers. That type of linkage suggested an enzymatic incorporation of 4-HO-POA in CW, contrary to others residues which have an opportunistic lignin incorporation. That incorporation of 4-HO-POA in CW polymers looks like that of endogenous hydroxycinnamic acids.