Characterisation of bound residues of [3H]triforine in the straw of barley grown in the field

Barley was grown in an experimental field and, at the growth stage J (during the stem extension stage when the second node of the stem was formed and the next-to-last leaf just visible), the aerial part of the plants was sprayed with an aqueous emulsion of a mixture of triforine and [³H]triforine (uniformly labelled in the piperazine ring) at the recommended rate of 250 g triforine ha^?1. Barley was harvested when ripe, and the straw was analysed separately. Extraction of the straw with methanol left methanol-insoluble solids containing an amount of radioactivity (the bound residue) which represented 88 % of the tritium (as with all the subsequently quoted percentages, relative to the total tritium incorporated into the straw). Methanol acidified with hydrochloric acid extracted a further 8% of the triforine-derived bound residues as radioactive iminodiacetic acid (0.4%). glycine (3.2%), serine (2.0%), ethanolamine (0.2%) and unidentified compounds (2.2%); a neutral detergent solution extracted a further 3% of the radioactive triforine-derived bound residues as unidentified compounds; these radioactive compounds, which were dissolved by the acidified methanol and by the neutral detergent solution, were thus complexed in the straw to straw constituents. An acid detergent solution extracted a further 58% of the total tritium, which was incorporated by means of σ chemical bonds into the hemicelluloses fraction. Acid hydrolysis of the hemicelluloses yielded a mixture of mono-saccharides; these were converted into a mixture of osazones (50%), recrystallised several times, and had a constant specific radioactivity, indicating that the mono-saccharides were tritiated. The plant solids (which contained 19% of the total tritium), left by the acid-detergent extraction, were processed and separated into the tritium-containing cellulose (13%) and lignin (6%) fractions. No piperazine was observed in the bound residue of straw. Biochemical pathways are suggested for the radioactive metabolites of [³H]triforine.     

Characterisation of bound residues of [3H]triforine in barley grain grown in the field

Barley was grown in an experimental field and at growth stage J (during the stem extension stage when the second node of the stem was formed and the next-to-last leaf was just visible), the aerial part of the plants was sprayed with an aqueous emulsion of a mixture of triforine and [³H]triforine (uniformly labelled in the piperazine ring) at the normal rate of 250 g triforine ha^?1. The barley was harvested when ripe, and the grain was analysed separately. Extraction of the grain with methanol left methanol-insoluble solids containing an amount of radioactivity (the bound residue) which represented 75% of the total radioactivity incorporated into the grain. Methanol acidified with hydrochloric acid extracted a further 7% of the triforine-derived bound residues in the form of radioactive iminodiacetic acid (1.1%), glycine (3.3 %), serine (0.9%), ethanolamine (0.2%) and unidentified compounds (1.5 %); in the grain, these compounds or their precursors had thus been complexed to grain constituents. Aqueous 0.03M sodium hydroxide extracted a further 27% of the total tritium which had been incorporated by means of α chemical bonds into the protein fraction; acid hydrolysis of the proteins yielded radioactive glycine (9.2%), serine (3.9%) and unidentified compounds (13.9%) which could have been a mixture of a large number of other amino-acids. The plant solids (which contained 41% of the total tritium) left after the alkaline aqueous extractions, were processed and separated into tritiated cellulose (4%) and starch (37%) fractions. The starch was hydrolysed and the resulting glucose was converted into the osazone (34%). After being recrystallised several times, the osazone contained a constant specific radioactivity, indicating that [³H]glucose was present. This glucose may be considered as having a carbon skeleton mainly originating biochemically from some metabolites of [³H]triforine; this tritiated glucose may also be considered as indirect evidence of the biochemical oxidation, by transamination, of the metabolites of [³H]triforine; in barley grain, the tritiated glucose (or at least a part of it) was anabolised into proteins. No piperazine was observed in the bound residues in the grain.     

Metabolism of [2,5-14c]piperazine in barley plants

The shoots of barley plants root-treated with [2,5-¹⁴C]piperazine were analysed 30 days after treatment. Methanol extraction left a solid residue which contained 31.9% of ¹⁴C (all percentages refer to the total of ¹⁴C incorporated into the shoots); further extraction with acidified methanol and dimethyl sulphoxide dissolved respectively 3.2% and 5.8% of ¹⁴C. The initial methanol extract contained radioactive piperazine (16.8%), iminodiacetic acid (8.6%), glycine (15.4%), oxalic acid (7.2%), and un-identified compounds (20.1%). In barley, piperazine is the product of the most advanced metabolism so far identified of the fungicide triforine, 1,4-bis(2,2,2-trichloro-1-formamidoethyl)piperazine; the results obtained here show that piperazine is certainly not the end-product of the metabolism of triforine in barley.     

Metabolism of [3H]triforine in barley grown in the field: The unbound radioactive residue

Barley was sown and grown normally in an experimental field. At the growth stage J,

1 Growth stage J: during the stem extension stage; second node of stem formed and next-to-last leaf just visible.

the aerial part of the plants was sprayed with an aqueous emulsion of a mixture of triforine and [³H]triforine (uniformly labelled in the piperazine ring) using the recommended dose rate of about 240g triforine ha^?1. The barley was harvested when ripe and the straw and grain were analysed separately. The total radioactivity concentration was 20 times higher in straw than in grain. In straw and grain, 12 and 25% respectively of the total incorporated radioactivity in each of these tissues was methanol soluble. The composition of the methanol-soluble radioactive residue was investigated and was shown to contain triforine and its metabolites which were free and unbound in barley straw and grain. No radioactive piperazine was observed, in spite of the high detection sensitivity for radioactivity. The concentrations of triforine and its identified metabolites in straw and grain respectively (mg kg^?1, relative to the fresh weight of tissue) were: triforine, 0.034 and 0.0018; N-[(2,2,2-trichloro-1-(piperazin-1-yl)ethyl]formamide), 0.009 and 0.0006; iminodiacetic acid, 0.021 and 0.001; glycine, 0.043 and 0.0033. Other radioactive water-soluble and very polar, unidentified compounds were observed, corresponding to advanced metabolic products of triforine.     

The metabolism of [14C]aldicarb in the root of sugar beet plants

Sugar beet plants were grown in the field, after in-furrow application of [¹⁴C]- aldicarb (3 kg of aldicarb ha^?1) at planting. The ripe sugar beet plants were harvested, and the roots were analysed. The roots were fractionated according to a procedure similar to the normal beet-sugar manufacturing process. Expressed as a proportion of the total radioactivity incorporated into the root, the pulp contained 29.7%, the lime cake 9.7%, the crystallised sugar 17.7% (which gave, with the radioactivity found in the sugar in the molasses, a total of 20.7% of the radioactivity in the total sugar), and the molasses, 42.9%. A part of the labelled carbon from the radio- active aldicarb and its metabolites had thus been metabolised and incorporated into sugar molecules. Except for the radioactivity in the sugar and in the lime cake from the processing, the proportion of radioactive non-conjugated organosoluble compounds was very low (2.6%), and perhaps partially corresponded to the very low amount of aldoxycarb (aldicarb sulphone) in the root (less than 0.001 mg of [¹⁴C]-aldicarb equivalents kg^?1 fresh weight). Hydrolysis of the molasses yielded free radioactive 2-methyl-2-(methylsulphinyl)propan-1-ol (3.1%), 2-mesyl-2-methyl-propan-I-ol (8.9%) and 2-mesyl-2-methylpropionic acid (12.0%) which had been conjugated to plant constituents in the root. The corresponding concentrations (expressed as mg of [¹⁴C]aldicarb equivalents kg^?1 fresh weight of root) were 0.004, 0.011, and 0.016, respectively. No aldicarb, aldicarb sulphoxide or aldoxycarb (nor the corresponding nitrile, generated from aldicarb during the fractionation procedure) was liberated by the hydrolysis, indicating the absence of conjugates of these compounds in the root.     

Metabolism of isopropyl carbanilate (propham) in alfalfa grown in nutrient solution

Alfalfa plants, Moapa variety, were grown in nutrient solution containing isopropylring-[¹⁴C] carbanilate (43.8 μCi/liter propham). After 8 days, 41.2% of the radioactivity initially added to the nutrient culture was recovered; 10.9% of this was from shoots, 3.4% from roots and 26.9% from nutrient medium. Nonextracted residues accounted for 23% of the radioactivity in shoots and 62% of that in roots. The parent herbicide constituted 53 and 38% of the radioactivity extracted from shoots and roots, respectively. The balance of extracted ¹⁴C was polar metabolites which were purified and subjected to enzymatic and acid hydrolysis. Four aglycones were isolated, three of which were purified by thin-layer chromatography and characterized by mass spectrometry. The principal aglycones were: isopropyl-2-hydroxycarbanilate, isopropyl-4-hydroxycarbanilate, and 1-hydroxy-2-propylcarbanilate. The fourth aglycone was not identified.     

Studies on the mode of action of asulam,aminotriazole and glyphosate in Equisetum arvense L. (field horsetail). II: The metabolism of [14C]asulam, [14C]aminotriazole and [14C]glyphosate

The metabolism of [¹⁴C]asulam (methyl 4-aminophenylsulphonylcarbamate), [¹⁴C] aminotriazole (1H-1,2,4-triazol-3-ylamine) and [¹⁴C]glyphosate (N-(phosphonomethyl)glycine) were assessed in Equisetum arvense L. (field horsetail). Following application of the test herbicides (4mg?0.3 °Ci herbicide/shoot) to the shoots of 2-year-old pot-grown plants, the total recovery of ¹⁴C-label after 1 week and 8 weeks was high for all three herbicides (>80-0% of applied radioactivity). Asulam was persistent (>69-7% of recovered radioactivity) in both shoots and rhizomes. Sulphanilamide, a hydrolysis product of asulam, accounted for the remainder of the recovered radioactivity. Aminotriazole showed evidence of conjugation in shoots and rhizomes. The principal ¹⁴C-labelled component in shoots was composed of high proportions of aminotriazole (>76-3%) together with the metabolites: X (ninhydrin positive), β-(3-amino-1,2,4-triazolyl-1-)α-alanine, Y (diazotization positive) and various unidentified compounds. Rhizomes generally contained lower proportions of intact aminotriazole (>59.4%) together with the metabolites X,Y and unidentified compounds. The proportion of aminotriazole did not decrease with time in shoots or rhizomes; however, the ratio of metabolite X: Y moved in favour of Y as the interval after treatment increased. Glyphosate was extensively metabolised in shoots and rhizomes to yield aminomethylphosphonic acid (AMPA) and various unidentified compounds. Differential metabolism appears to be one of the factors which may govern the persistence and toxicity of the test herbicides in E. arvense.     

Metabolism of dibutyl-14C-labeled dibutylaminosulfenyl derivative of carbofuran in the cotton plant

The fate of the di-n-butylaminosulfenyl moiety in 2,3-dihydro-2,2-dimethyl-7-benzofuranyl (di-n-butylaminosulfenyl)(methyl)carbamate (DBSC or Marshal) was studied in the cotton plant at 1, 3, 6, and 10 days following foliage treatment with [di-n-butylamino-¹⁴C]DBSC. Dibutylamine and two major radioactive metabolites were obtained following extraction of the plant tissue with a methanol-buffer containing N-ethylmaleimide (NEM), a sulfhydryl scavenger which was added to prevent the cleavage of the NS bond during the workup procedure. The most adundant radioactive material recovered from plants was identified as a product arising from the reaction between NEM and dibutylamine. Extraction of plant tissue with straight methanol-buffer solution or with methol-buffer containing other sulfhydryl scavengers resulted in 57–86% of the applied radioactivity being recovered as dibutylamine in the organosoluble fraction. When [¹⁴C]dibutylamine was applied to cotton leaves, most of the radioactivity, i.e., 96% of the total recovered radioactivity, was found in the organosoluble fraction as dibutylamine. Dibutylamine is the major metabolite of [di-n-butylamino-¹⁴C]DBSC in the cotton plant.     

Behavior of 14C oryzalin in soil and plants

Radiochemical studies of field soil treated with ¹⁴C oryzalin (3,5-dinitro-N⁴,N⁴-dipropylsulfanilamide) indicated that the compound was readily degradable. One year after soil treatment with oryzalin, 45% of the original radioactivity had dissipated, 25% was extractable, and 30% was “soil bound”. The extractable fraction contained oryzalin and several degradation products, some of which were isolated and identified. No single degradation product accounted for more than 3% of the applied oryzalin. The “soil-bound” radioactivity was extractable with hot alkali. No significant radioactive residues were detectable in either seed or forage of soybean and wheat plants. No specific metabolites of oryzalin were identified in soybean plants. Trace amounts of radioactivity found in plant tissue appeared to be associated with the various plant constituents.     

The degradation of dinitramine (N3,N3-diethyl 2,4-dinitro-6-trifluoromethyl-m-phenylenediamine) in soil

Radioactive dinitramine (1) was incorporated at $\text{1}\text{2}$ Ib/acre (0.6 ppm) in Anaheim silty loam soil and its degradation studied over an 8-month period. For both specifically—¹⁴CF₃ and -Ring-UL-[¹⁴C] labeled (1), only ca. 20% of the radioactivity was lost from the incorporated zone. Mehanol- or acetonitrile-extractable radioactivity decreased rapidly over the initial 60 days reaching 20% after 244 days. Two compounds were isolated and characterized as (1), 0.05 ppm, and 6-amino-1-ethyl-2-methyl-7-nitro-5-trifluoromethylbenzimidazole (2), 0.06 ppm. Two other compounds were tentatively identified by TLC as monodealkylated dinitramine (3), 0.01 ppm, and 6-amino-2-methyl-7-nitro-5-trifluoromethylbenzimidazole (4), 0.01 ppm, Sodium hydroxide (10%) and anionic surfactant (10%) were effective in removing up to 50% of the residual bound radioactivity (i.e., nonacetonitrile extractable), while dimethylamine (25%) released 26%; extraction by acid was less effective.     

Selectivity of 2,4-D in Solanum ptycanthum Dun. and Lycopersicon esculentum Mill.

In controlled environmental studies, a marked difference was observed between the growth pattern of tomato and eastern black nightshade plants that received doses of 2,4-D ranging from 28 to 952 g a.e. ha^?1. The highest dose of 2,4-D reduced the dry weight of eastern black nightshade and tomato by approximately 15 and 50%, respectively, when compared with controls. Although the height of both species was reduced by all doses of 2,4-D, eastern black nightshade plants produced secondary shoots, which compensated for any potential loss in dry weight that otherwise may have occurred. Tomato plants did not produce secondary shoots. After application of ¹⁴C-2,4-D to tomato and eastern black nightshade, the pattern of ¹⁴C absorption and translocation was similar in both plant species. However, there was significantly more radioactivity recovered in tomato (72%) than in eastern black nightshade (52%) plants, 72 h after treatment. Assay radioactivity in the nutrient solution of hydroponically grown plants indicated that 7·0 and 27·9% of the applied radioactivity was exuded from the roots of tomato and eastern black nightshade, respectively, within 72 h after treatment. Assay of plant extracts by thin layer chromatography revealed that the amount of radioactivity that remained as unaltered 2,4-D was 73 and 49% in tomato and eastern black nightshade, respectively, 72 h after treatment. Thus the greater tolerance of eastern black nightshade appeared to be due to greater rates of 2,4-D metabolism and/or greater rates of herbicide elimination by root exudation.     

Alfalfa metabolism of propham

Root-treated alfalfa absorbs, translocates, and metabolizes [phenyl-¹⁴C]isopropyl carbanilate ([¹⁴C]propham). After 7 days of root treatment, the distribution of radiolabel was 73% for shoots and 27% for roots. Shoots and roots were extracted and separated into the polar, nonpolar, and solid residual components using a mixture of chloroform, methanol and water. The insoluble residues accounted for approximately 40% of the ¹⁴C found in shoots and roots. The nonpolar fraction (6.1% of the radiolabel in shoots and roots) was not characterized, but was shown to be some component other than parent propham. Propham was not found in either shoots or roots. The polar metabolites were partly purified on Amberlite XAD-2. Cellulase-liberated aglycones were derivatized and separated by high-performance liquid and gas-liquid chromatography. The infrared, nuclear magnetic resonance, and mass spectral data showed that the polar metabolites of alfalfa shoots and roots were glycoside conjugates of isopropyl 2-hydroxycarbanilate (2-hydroxypropham) and isopropyl 4-hydroxycarbanilate (4-hydroxypropham). Conjugated 4-hydroxypropham accounted for 45.9% of the ¹⁴C in the shoots and 3.4% of the ¹⁴C in the roots. Conjugated 2-hydroxypropham accounted for 3.4% of the ¹⁴C in the shoots and 1.4% of the ¹⁴C in the roots.     

Determination of extractable and non-extractable radioactivity from prairie soils treated with carboxyl- and ring-labelled [14C]2,4-D

Ring- and carboxyl-labelled [¹⁴C]2,4-D were incubated under laboratory conditions, at the 2 g/g level, in a heavy clay, sandy loam, and clay loam at 85% of field capacity and 20 1C. The soils were extracted at regular intervals for 35 days with aqaeous acidic acetonitrile, and analysed for [¹⁴C]2,4-D and possible radioactive degradation products. Following solvent extraction, a portion of the soil residues were combusted in oxygen to determine unextracted radioactivity as [¹⁴C]carbon dioxide. The remaining soil residues were then treated with aqueous sodium hydroxide, and the radioactivity associated with the fulvic and humic soil components determined. In all soils there was a rapid decrease in the amounts of extractable radioacitivity, with only 5% of that applied being recoverable after 35 days. All recoverable radioactivity was attributable to [¹⁴C]2,4-D, and no [¹⁴C]-containing degradation products were observed. This loss of extractable radioactivity was accompanied by an increase in non-extractable radioactivity. Approximately 15% of the applied radioactivity, derived from carboxyl-labelled [¹⁴C]2,4-D, and 30% from the ring-labelled [¹⁴C]2,4-D was associated with the soil in a non-extractable form, after 35 days of incubation. After 35 days, less than 5% of the radioactivity from the carboxyl-labelled herbicide, and less than 10% of the ringlabelled material, was associated with the fulvic components derived from the three soils. Less than 5% of the applied radioactivities were identifiable with any of the humic acid components. It was considered that during the incubation [¹⁴C]2,4-D did not become bound or conjugated to soil components, and that non-extractable radioactivity associated with the three soil types resulted from incorporation of radioactive degradation products, such as [¹⁴C]carbon dioxide, into soil organic matter.     

Metabolism of [14C]dieldrin in bluegill fish

The exposure of bluegill fish to 50 parts per billion [¹⁴C]dieldrin in a static system resulted in the absorption of 73.00% of the radioactivity in 48 hr. Following transfer of the fish to clean water, only 16.20% of the absorbed radiolabel was eliminated in 23 days. Out of the 93.65% of the absorbed radioactivity recovered, 9 radioactive spots were isolated which included unchanged dieldrin (74.39%), pentachloroketone (8.17%), and aldrin-trans-diol (8.04%) as major metabolites.     

The degradation of methazole in soil. II. Studies with methazole,methazole degradation products and diuron

[¹⁴C]-Labelled methazole, 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU), 1-(3,4-dichlorophenyl)urea (DCPU), and diuron were incubated in soil at 20°C and field capacity soil moisture content. Decomposition followed first-order kinetics; half-lives for degradation of these four compounds were 2.4, 144, 30 and 108 days respectively. The amount of DCPMU and DCPU that could be extracted decreased with time and the decrease was accompanied by the generation of an equivalent amount of ¹⁴CO₂. This was not so in the studies with diuron and methazole, however, and the decrease in the concentrations of radioactivity extracted from soil treated with these compounds could not be entirely accounted for as carbon dioxide. It is concluded that the unextractable radiochemical that was present was DCPMU. Methazole appeared to be degraded through DCPMU to 3,4-dichloroaniline (DCA) with the production of only traces of DCPU.     

Metabolism of N-hydroxymethyl dimethoate and N-desmethyl dimethoate in bean plants

N-Hydroxymethyl [carbonyl-¹⁴C] dimethoate (0.43 ppm) and N-desmethyl [carbonyl-¹⁴C] dimethoate (0.50 ppm) were stem-injected into bean plants (Phaseolus vulgaris) in two separate experiments. Plants were harvested periodically, extracted, fractionated, and analyzed for metabolites. The resulting pattern of metabolites formed from the administration of these two compounds was different. Radioactivity was not detected in the organic fraction 2 days after N-desmethyl dimethoate administration. N-Desmethyl dimethoate was rapidly broken down to dimethoate carboxylic acid and other polar metabolites, then further degraded into materials which became part of the plant constituents. N-Hydroxymethyl dimethoate was quite stable in the plant. Most of the material not remaining as parent became rapidly conjugated and constant levels of conjugate were maintained. Very little radioactivity was bound in the plant marc. The metabolic pathway of these compounds is as follows: N-hydroxymethyl to the glucoside or N-desmethyl derivative; the N-desmethyl metabolite degrades primarily to the carboxylic acid but also to N-desmethyl dimethoxon, either of which in turn may be degraded to dimethoxon carboxylic acid. The conversion of -NHCH₂OH to -NH₂ is a slow reaction so that conjugation becomes the route of choice when the plant is treated with N-hydroxymethyl dimethoate.     

A specific and sensitive assay to quantify the herbicidal activity of chloroacetamides

Based on a recently discovered property of chloroacetamide herbicides—the inhibition of the incorporation of oleic acid into sporopollenin of Scenedesmus acutus—a rapid quantitative test was developed for chloroacetamide-type herbicidal activity. In this test, algal cells are incubated for 3 h with [¹⁴C]oleic acid, saponified and the lipids (including non-saponifiable ones) extracted and discarded. The radioactivity incorporated into the residual non-lipid fraction is determined, and inhibition of this incorporation is used as a marker of chloroacetamide-type activity. Twenty-two agrochemical compounds were screened in this assay, which was found to be very sensitive, a 50% inhibition being reached with submicromolar herbicide concentrations. It is specific to chloroacetamides and related amides, since all these herbicides tested were potent inhibitors, while other herbicides were not. Highest inhibition was shown by cafenstrole followed by butachlor, fluthiamid, metazachlor, alachlor, dimethenamid, metolachlor and mefenacet. For these herbicides (with the exception of butachlor) sensitivity in the test was positively correlated (r=0·984) with their phytotoxic effect on the alga. © 1998 SCI     

Metabolism of the fungicide triforine in barley plants

The metabolic fate of [³H]-triforine in barley plants has been studied. 15 and 30 days after treatment, unchanged triforine amounted to 57.5 and 43.2% respectively, and of three soluble metabolites detected, piperazine (0.3 and 4.0%) and N-[2, 2,2-trichloro-1-(piperazin-1-yl)ethyl] formamide (12.9 and 8.4%), the latter for the first time as a metabolite in plants, were identified using t.1.c. with four solvent systems. The solid residue contained 23.1 and 38.2% of bound label after 15 and 30 days respectively.     

Studies on the site of uptake by plants of chlortoluron and terbutryne

Experiments were done to observe the pattern of early root development of radish (Raphanus raphatnistrum L.) and perennial ryegrass (Lolium perenne L.), the mobility of chlortoluron following application to the soil surface, the effect of protecting the subterranean shoots of four plant species on their response to chlortoluron and terbutryne and the relative quantities of ¹⁴C-labelled chlortoluron taken up by radish and Avenu fatua from root and shoot zone exposure. Both chlortoluron and terbutryne appear to be able to enter the plants examined, Alopecurus myosuroides, Stellaria media, perennial ryegrass and radish, through roots and shoots. It is suggested that shoot uptake is relatively more important for plants like perennial ryegrass than for those whose roots develop more quickly and invade the soil above the seed, such as radish. The quantities of radioactive chlortoluron taken up from soil containing 400 ng g^?1 showed that less than 3 ng per plant could reduce A. fatua fresh weight by 17–40% while over 30 ng per plans had little effect on radish. By comparison 2 kg ha^?1 chlortoluron applied to the soil surface of pots which were sub-irrigated for 3 weeks gave a concentration of 170 ng g^?1 in the layer of soil 10–12 mm from the surface. It is suggested that for shallow germinating species with herbicides of physical and phytotoxic properties similar to chlortoluron, the solvent action of rainfall, together with diffusion, is enough to allow the transport of toxic quantities to the target plant although any leaching action is likely to increase activity.     

Uptake,distribution and metabolic fate of 3H-triforine in plants. II. Long-term experiments

Uptake of ³H-triforine by tomato and barley seedlings from soil with a high organic matter content was much less efficient than from aqueous suspensions, even though the period of exposure was much longer—at least 1 week (“long-term treatment”) vs 1 day (“short-term treatment”). After transplanting to fresh soil, part of the label in the roots was lost probably by desorption. Distribution of label in tomato shoots was as irregular as after short-term treatment; label was virtually confined to the leaves which expanded before about 14 days after cessation of the treatment. In shoots of barley seedlings which were pretreated in an aqueous suspension of ³H-triforine for 1 day before being subjected to a long-term soil treatment, almost all radioactivity present could be ascribed to uptake during the pretreatment phase. The distribution pattern strongly resembled that obtained after short-term treatment, hardly any label being found in leaves which unfolded after the pretreatment phase. Rates of conversion of ³H-triforine in barley shoots depended to some extent on whether or not seedlings were transplanted to fresh soil after 1 week.