Effect of certain substituted naphthoquinones on growth and respiration of Rhodospirillum rubrum

The effect of dichlone (2,3-dichloro-1,4-naphthoquinone) on photoautotrophic, photoheterotrophic and heterotrophic growth, and respiration of Rhodospirillum rubrum (a nonsulfur purple bacterium) was studied to elucidate the mechanism of action of this toxicant on photosynthetic bacteria. The photosynthetic growth with malate or with hydrogen and CO₂ was inhibited by dichlone. Light respiration of photoheterotrophically grown cells, unlike their dark respiration, was found to be insensitive to dichlone. Although dichlone caused an inhibition of the respiration of dark-grown cells, such cells were able to grow in the presence of dichlone after a lag. Light-dependent ¹⁴C-substrate incorporation by photoheterotrophic or photoautotrophic cells was found to be relatively more sensitive to dichlone than oxidative substrate incorporation by heterotrophic cells. Short-term exposure of the light-grown cells to dichlone resulted in an irreparable loss of their ability to grow photosynthetically and photoassimilate ¹⁴C-substrates. Menadione (2-methyl-1,4-naphthoquinone), a synthetic vitamin K, failed to affect these reactions to a significant extent at comparable concentrations. The findings suggest that dichlone causes an irreversible damage to some primary photosynthetic reaction in chromatophores, whereas the damage caused to the dark heterotrophic metabolism of the cell is less severe and repairable. The inhibitory action of dichlone does not appear to be via the formation of semiquinone free radicals.     

Degradation of ioxynil to CO2 in soil

Degradation of ioxynil (4-hydroxy-3,5-diiodobenzonitrile) to CO₂ was detected in a clay loam, high organic matter content soil. The majority of radioactivity was recovered as ¹⁴CO₂ from both ring-labeled and cyano-labeled ioxynil; however, ¹⁴CO₂ was always released from cyano-labeled ioxynil at a much faster initial rate. No ¹⁴CO₂ was released in treated sterile soil, either aerobically or anaerobically. Production of ¹⁴CO₂ from cyanolabeled and ring-labeled ioxynil was greatly inhibited by HgCl₂ (10^?5M), and p-chloromercuribenzoate (5 × 10^?5M), but slightly inhibited by ferricyanide (10^?4M). No ¹⁴CO₂ was evolved from ring-labeled ioxynil under anaerobic conditions. These observations indicated that the degradation of ioxynil to CO₂ in soil was a microbial action and was oxygen dependent. This is consistent with the known mechanism of oxygenases in degrading benzene rings. Anaerobically, a small amount of ¹⁴CO₂ was released from cyano-labeled ioxynil. Thin-layer chromatographic analyses of the culture supernatant revealed that 3,5-diiodo-4-hydroxybenzamide and 3,5-diiodo-4-hydroxybenzoic acid were intermediate metabolites.     

The distribution and degradation of chlormequat in wheat plants

The distribution and degradation of chlormequat chloride (2-chloro 1,2-¹⁴C ethyltrimethylammonium chloride) was determined after uptake by the roots of summer wheat seedlings. This plant regulator was readily translocated from the roots to the above ground parts and converted into choline. Choline was further metabolized to betaine which upon demethylation yielded finally glycine and serine. Both amino acids were incorporated into a protein fraction.The occurrence of radioactively labeled glycine and serine in the amino acid pool and the evolution of ¹⁴CO₂ from chlormequat treated plants indicated that serine was formed from glycine under the release of ¹⁴CO₂ during photorespiration.One week after the uptake period 82% of ¹⁴C chlormequat taken up by the roots was recovered as the parent compound or as breakdown products in wheat plants. In addition 5% of the amount taken up by the roots was released as ¹⁴CO₂ by the leaves.Fifty per cent of the total amount of chlormequat originally present in roots and leaves was already metabolized after 7.5 days. No evidence has been obtained for the presence of unchanged chlormequat or an unknown metabolite in the nucleic acid or protein fraction.     

Growth, photosynthetic pigments and photosynthetic activity during seedling stage of cowpea (Vigna unguiculata) in response to UV-B and dimethoate

UV-B (0.4 W m⁻²) irradiation and dimethoate (100 and 200 ppm) treatments, singly and in combination, declined the growth, photosynthetic pigment contents and photosynthesis (O₂ evolution and CO₂-fixation) of cowpea (Vigna unguiculata). Contrary to this, low concentration of dimethoate (50 ppm) caused stimulation on these parameters, while together with UV-B it showed inhibitory effects. Carotenoids (Car) showed varied responses. It was found that carbon-fixation (¹⁴CO₂) was more sensitive to both the stresses than photosynthetic oxygen evolution. Photosynthetic electron transport activity was reduced by both the stresses, however, 50 ppm dimethoate besides inhibiting photosystem II (PSII) and whole chain activity, showed slight stimulation in photosystem I (PSI) activity. The individual effect of two stresses on PSII activity was probably due to interruption of electron flow at oxidation side of PSII which extended to its reaction center following simultaneous exposure. A similar trend was also noticed in case of CO₂ liberation (measured as ¹⁴CO₂ release) in light and dark. Results suggest that dimethoate (100 and 200 ppm) and UV-B alone caused heavy damage on pigments and photosynthetic activity of cowpea, leading to the significant inhibition in growth. Further, the interactive effects of both the stresses got intensified. However, low concentration (50 ppm) of dimethoate showed stimulation, but in combination, it slightly recovered from the damaging effect, caused by UV-B.     

Effect of chlorfenprop-methyl, flamprop-isopropyl and benzoylprop-ethyl on 14C2 fixation in Avena fatua L., Triticum aestivum L. and Hordeum vulgare L.

The effect of chlorfenprop-methyl, flampropisopropyl and benzoylprop-ethyl on ¹⁴CO₂ fixation was followed in wild oat (Avena fatua L.), barley (Hordeum vulgare L., cv. Ametyst), and wheat (Triticum aestivum L., cv. Mironovská). Experimental plants were exposed to a ¹⁴CO₂-enriched atmosphere in a special apparatus 2 h, 1, 3, and 9 days after the herbicide treatment. Chlorfenprop-methyl already inhibited ¹⁴CO₂ fixation in wild oat plants 2 h after the treatment. ¹⁴C-metabolite transport to the roots was strongly decreased. Both ¹⁴CO₂ fixation and ¹⁴C-metabolite level in the roots were significantly depressed in A. fatua when compared with untreated plants at the last sampling time. ¹⁴C incorporation into starch was inhibited from the first day after treatment, and on day 9 was lowered more than ten fold in treated plants. Flamprop-isopropyl inhibited ¹⁴CO₂ fixation in wild oat plants from day 3 after treatment, but benzoylprop-ethyl not until day 9. Both herbicides also decreased ¹⁴C incorporation into starch in A. fatua. Chlorfenprop-methyl also slightly decreased ¹⁴CO₂ fixation in barley on day 9. However, assimilate transport into the roots and ¹⁴C incorporation into starch were not affected. Flamprop-isopropyl inhibited ¹⁴CO₂ fixation in barley plants only on the first day after treatment, and assimilate transport was also reduced. By contrast, no differences from untreated plants were found at the end of the experiment. Benzoylprop-ethyl did not decrease either ¹⁴CO2 fixation or assimilate transport to the roots in wheat, but it inhibited starch synthesis. Atrazine depressed ¹⁴CO₂ fixation in wild oat plants by 91%, in wheat plants by 99% compared with untreated plants. Assimilate transport into the roots was also strongly inhibited. In contrast to atrazine, the effect of chlorfenprop-methyl, flamprop-isopropyl, and benzoylprop-ethyl on CO₂ fixation seems to be secondary.     

A study of ethylene and CO2 evolution from ethephon in tobacco

Buffers and leaf discs of mature tobacco (Nicotiana tabacum L.) were utilized to study [¹⁴C]-ethylene and ¹⁴CO₂ evolution from radiolabeled ethephon, (2-chloroethyl)phosphonic acid. Metabolic fate of [¹⁴C]ethephon in leaf discs was investigated by use of thin-layer chromatography, high-voltage paper electrophoresis, autoradiography, and liquid scintillation spectroscopy. The evolution of labeled ethylene generally increased with increasing buffer pH, buffer volume, and dosage of [¹⁴C]ethephon. [¹⁴C]Ethylene was evolved, increasingly with time, from [¹⁴C]ethephon either added to the buffer or applied to leaf discs. The rate of [¹⁴C]ethylene evolution was maximum during the first day and leveled off on the fourth day. More than 50% of the total [¹⁴C]ethylene evolution over a 96-hr period was recovered during the first 24 hr after [¹⁴C]ethephon application. No ¹⁴CO₂ was evolved when [¹⁴C]ethephon was degraded in the presence of buffer or leaf discs. Only ethephon itself, and no detectable metabolite thereof, was discovered in the methanolic extract of the leaf disc tissue. An insignificant amount of ¹⁴C activity (approximately 2% of the extracted ¹⁴C) was detected in the residue. By means of gas chromatography, it was confirmed that in buffers and tobacco leaf tissue ethephon breaks down to release ethylene but not CO₂.     

Metabolism of O,O,S-trimethyl phosphorothioate in rats after oral administration of a toxic dose,and the effect of coadministration of its antagonistic thionate isomer

The in vivo metabolism of [¹⁴CH₃S]- and [¹⁴CH₃O]O,O,S-trimethyl phosphorothioate (OOS) was followed in rats after oral administration of threshold or LD₅₀ toxic doses of 20 or 60 mg/kg. Similar metabolic studies were conducted with coadministration of 1% O,O,O-trimethyl phosphorothionate (OOO), which prevented all signs of delayed toxicity, including weight loss. When administered alone, OOS was metabolized mainly (50–60%) via removal of the CH₃S moiety, which was largely converted to expired CO₂. Approximately 20% of the compound was O-demethylated, presumably by conjugation with glutathione, and then further metabolized to CO₂. Major urinary products were identified as O,O-dimethyl phosphoric acid (50–60%) and O,S-dimethyl phosphorothioic acid (～20%). Coadministration of OOO caused a slight decrease (～5%) in the cleavage of the CH₃S moiety, indicated by a reduction in ¹⁴CO₂ from [¹⁴CH₃S]OOS and a quantitatively similar increase in the formation of O,S-dimethyl phosphoric acid. Limited pharmacokinetic studies indicated that OOS was rapidly absorbed and distributed throughout the body. Coadministration of 1% OOO caused a slight increase in the blood half-life of parent OOS when administered at 60 mg/kg. It was concluded that a small proportion of the cleavage of the CH₃S moiety from OOS is involved in the intoxication process, and that this intoxication reaction is specifically inhibited by OOO.     

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.     

Inhibition of carbaryl metabolism by nitrogen in three species of cockroach and one species of locust

The in vivo release of ¹⁴CO₂ arising from decarbamoylation of [¹⁴C]-carbaryl (1-naphthyl methyl-[¹⁴C]-carbamate) injected into male and female Periplaneta americana, Leucophaea maderae, Gromphadorhina portentosa and Schistocerca gregaria was measured up to 50 nmol carbaryl/g body weight. The amount of ¹⁴CO₂ released was proportional to the dose of [¹⁴C]-carbaryl injected and was similar for both sexes of each species. The KD₅₀ values for carbaryl for each species did not correlate with their ability to decarbamoylate carbaryl. The degradation of carbaryl by this pathway is not therefore the limiting factor in determining the overall toxic effect of carbaryl in the four species studied. Decarbamoylation is inhibited by nitrogen in all four species. In P. americana the inhibition is virtually complete, in L. maderae, G. portentosa and S. gregaria the inhibition is 84%, 74% and 51% respectively. The results suggest the involvement of two enzymes, one of which is oxygen dependent. Decarbamoylation studies in air suggest the involvement of two enzymes with differing K_M values. The involvement of aliesterases and mixed function oxidases in the decarbamoylation pathway(s) have not been established so far with this series of experiments.     

The adsorption and degradation of glyphosate in five Hawaiian sugarcane soils*

The rate of aerobic evolution of ¹⁴CO₂ from ¹⁴C-glyphosate labelled in the methylphosphonyl carbon, varied 100-fold within a group of five Hawaiian sugarcane soils. The rate depended inversely on the degree of soil binding, probably associated with the phosphonic acid moiety, and to a less certain extent on soil pH and soil organic matter. After an initial rapid degradation, the rate of ¹⁴CO₂ evolution in three soils reached a constant at 16–21 days which continued to the 60-day termination. The other two soils showed a continually decreasing rate throughout. Two soils released over 50% of the labelled carbon in 60 days, a third released 35%, while the remaining soils released 1.2 and 0.8% respectively. Labelled carbon in the soils after 60 days consisted of glyphosate and one metabolite, aminomethyl-phosphonic acid, with glyphosate predominating in high fixing soils. The ¹⁴C could be extracted almost completely with NaOH solution, and remained mainly in solution after acidification.     

Degradation of the pyrethroid insecticide WL 41706, (±)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate,in soils

The degradation of the insecticide WL 41706, (±)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate, (I), in two soils from Spain and one from the UK has been studied in the laboratory. Samples of (I) labelled separately with ¹⁴C in the benzyl ring (uniform labelling) and at C₍₁₎ of the cyclopropyl ring were used. The insecticide underwent degradation by hydrolysis at the cyano group to form the amide and carboxylic acid analogues. However, the major degradative route was hydrolysis at the ester linkage leading initially to the formation of 3-phenoxy-benzoic acid and 2,2,3,3-tetramethylcyclopropanecarboxylic acid. When a sandy clay soil was treated with [benzyl^?14C]-WL 41706 under balance conditions, ¹⁴CO₂ was evolved at a steady rate and 16 % of the applied radiolabel was detected as ¹⁴CO₂ over a 26 week period. The rate of degradation of I was most rapid on a moist sandy clay (loss of 50 % initial quantity in 4 weeks) but it was considerably slower on dry sandy clay and moist clay soils (> 16 weeks). Under flooded, anaerobic conditions the rate of hydrolysis of the insecticide was slower than under aerobic conditions and the 3-phenoxybenzoic acid and 2,2,3,3-tetramethylcyclopropanecarboxylic acid were found to accumulate over the 24 weeks of the experiment.     

Differential effects of phenoxy herbicides on light-dependent 14CO2 fixation in isolated cells of C3 and C4 plants

Cells were isolated from the developing leaves of Ipomoea aquatica and Digitaria sanguinalis. The effects of phenoxy alkanoic acid herbicides on light-dependent ¹⁴CO₂ fixation and oxygen evolution in these leaf cells were studied. (2,4-Dichlorophenoxy)acetic acid and (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T and 2,4-D) caused a 20% stimulation of ¹⁴CO₂ fixation at 0.8 × 10^?5M and an inhibition at 1 × 10^?4M in I. aquatica leaf cells. Temperature seemed to have a marked influence on such action. No effect or very little effect was observed in the leaf cells of D. sanguinalis. The nonactive (2,4,6-Trichlorophenoxy)acetic acid (2,4,6-T) caused a similar stimulation of CO₂ fixation as 2,4-D and 2,4,5-T at low concentrations in I. aquatica leaf cells, but no inhibition was observed at high concentration. Increase of hight intensity increased the rate of CO₂ fixation in both control and 2,4,6-T-treated cells; however, the percentage of stimulation remained the same. At stimulatory concentration, all three compounds did not cause any stimulation in either photosystem I and II or photosystem II-mediated oxygen evolution. At higher concentrations, the differential effects of 2,4-D and 2,4,5-T on the light-induced CO₂ fixation and photosystem II-mediated oxygen evolution in the I. aquatica leaf cells and D. sanguinalis mesophyll (ms) cells may be attributed in part to their selective action against dicotyledonous plants.     

Microbial dealkylation of trifluralin in pure culture

Mixed populations of soil microorganisms were enriched in the presence of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and 180 pure strains were subsequently isolated. About a third were able to liberate 1.5–6% ¹⁴CO₂ from 0.15 mM [propyl-1-¹⁴C]trifluralin after growing for 21 days on a complex medium. One strain, identified as a Candida sp., showed a ¹⁴CO₂ evolution of 11%. The amount of liberated ¹⁴CO₂ could not be enhanced by adding small concentrations (<3%) of solvents to the culture, by varying the concentration of trifluralin, or by varying the composition of the complex medium. The Candida sp. was unable to cleave the aromatic ring of trifluralin or to use trifluralin as a sole source of carbon or nitrogen. Only traces (< 1%) of dealkylated trifluralin were accumulated in the culture.     

Differential effects of phenoxy herbicides on light-dependent CO2 fixation in isolated cells of C3 and C4 plants

Cells were isolated from the developing leaves of Ipomoea aquatica and Digitaria sanguinalis. The effects of phenoxy alkanoic acid herbicides on light-dependent ¹⁴CO₂ fixation and oxygen evolution in these leaf cells were studied. (2,4-Dichlorophenoxy)acetic acid and (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T and 2,4-D) caused a 20% stimulation of ¹⁴CO₂ fixation at 0.8 × 10⁻⁵M and an inhibition at 1 × 10⁻⁴M in I. aquatica leaf cells. Temperature seemed to have a marked influence on such action. No effect or very little effect was observed in the leaf cells of D. sanguinalis. The nonactive (2,4,6-Trichlorophenoxy)acetic acid (2,4,6-T) caused a similar stimulation of CO₂ fixation as 2,4-D and 2,4,5-T at low concentrations in I. aquatica leaf cells, but no inhibition was observed at high concentration. Increase of hight intensity increased the rate of CO₂ fixation in both control and 2,4,6-T-treated cells; however, the percentage of stimulation remained the same. At stimulatory concentration, all three compounds did not cause any stimulation in either photosystem I and II or photosystem II-mediated oxygen evolution. At higher concentrations, the differential effects of 2,4-D and 2,4,5-T on the light-induced CO₂ fixation and photosystem II-mediated oxygen evolution in the I. aquatica leaf cells and D. sanguinalis mesophyll (ms) cells may be attributed in part to their selective action against dicotyledonous plants.     

Microbial metabolism of propanil and 3,4-dichloroaniline

A Pseudomonas sp. which grew on 4-chloroaniline as a sole source of carbon and nitrogen was able to degrade 15% of 0.05 mM [¹⁴C]3,4-dichloroaniline to ¹⁴CO₂ within 10 days in presence of 1.5 mM 4-chloroaniline. The catabolic enzymes which degraded 3,4-dichloroaniline to CO₂ were inducible by 4-chloroaniline and by 3,4-dichloroaniline. However, their activity was much lower on 3,4-dichloroaniline than on 4-chloroaniline. The strain showed no significant growth on 3,4-dichloroaniline as a sole source of carbon and nitrogen. Soils supplemented with [ring-¹⁴C]propanil and the Pseudomonas sp. evolved 25–50% ¹⁴CO₂ within 5 days. The ¹⁴CO₂ evolution remained below 1% in absence of the Pseudomonas sp.     

Influence of glyphosate on selected plant processes

Biochemical effects of glyphosate have been examined with a variety of plant materials using mostly merislematic or actively growing tissues. The accumulation of chlorophyll was severely retarded and photosynthetic CO₂ uptake was inhibited to a lesser extent. These inhibitory effects could not be alleviated by the simultaneous admixture of divalent cations. Glyphosate enhanced the initial substrate-induction of nitrate reductase, but repressed induction of nitrite reductase, in Ihe latter case correlating with both inhibition of chlorophyll accumulation and CO₂ uptake. Inhibition of macromolecule synthesis in single node buds of Agropyron repens(L.) Beauv. was due partly to inhibition of ¹⁴C-precursor uptake. The specific activity of soluble acid phosphatase was enhanced as was the evolution of ethane. Ethylene production was not greatly affected. A marked decrease in microsomal protein was observed but the specific activities of several microsomal enzymes did not decline. Glyphosate had little inhibitory effect on the activity of microsomal ATPases in vitro.     

Mineralisation of the herbicide linuron by Variovorax sp. strain RA8 isolated from Japanese river sediment using an ecosystem model (microcosm)

BACKGROUND: Linuron is a globally used phenylurea herbicide, and a large number of studies have been made on the microbial degradation of the herbicide. However, to date, the few bacteria able individually to mineralise linuron have been isolated only from European agricultural soils. An attempt was made to isolate linuron‐mineralising bacteria from Japanese river sediment using a uniquely designed river ecosystem model (microcosm) treated with ¹⁴C‐ring‐labelled linuron (approximately 1 mg L^?1). RESULTS: A linuron‐mineralising bacterium that inhabits river sediment was successfully isolated. The isolate belongs to the genera Variovorax and was designated as strain RA8. Strain RA8 gradually used linuron in basal salt medium (5.2 mg L^?1) with slight growth. In 15 days, approximately 25% of ¹⁴C‐linuron was mineralised to ¹⁴CO₂, with 3,4‐dichloroaniline as an intermediate. Conversely, in 100‐fold diluted R2A broth, strain RA8 rapidly mineralised ¹⁴C‐linuron (5.5 mg L^?1) and more than 70% of the applied radioactivity was released as ¹⁴CO₂ within 3 days, and a trace amount of 3,4‐dichloroaniline was detected. Additionally, the isolate also degraded monolinuron, metobromuron and chlorobromuron, but not diuron, monuron or isoproturon. CONCLUSION: Although strain RA8 can grow on linuron, some elements in the R2A broth seemed significantly to stimulate its growth and ability to degrade. The isolate strictly recognised the structural difference between N‐methoxy‐N‐methyl and N,N‐dimethyl substitution of various phenylurea herbicides. Copyright © 2010 Society of Chemical Industry     

Degradation of the herbicide [14C]-diclofop-methyl in soil under different conditions

The degradation of the herbicide diclofop-methyl, ( ± )-methyl 2-[4-(2,4-dichloro-phenoxy)phenoxy]propionate, was investigated in two agricultural soils under aerobic and anaerobic conditions. Using two differently labelled forms of [¹⁴C]-diclofop-methyl the qualitative as well as the quantitative formation of extractable metabolites was followed for 64 days. The mineralisation of the uniformly labelled aromatic rings was pursued by monitoring the ¹⁴CO₂ generated for 25 weeks. As a first step of the degradation a very rapid hydrolysis of the ester bond was detected under all conditions. Diclofop, the corresponding substituted propionic acid formed, was extensively degraded under aerobic conditions, the final product being ¹⁴CO₂. As an intermediate, a compound later identified by GLC/MS to be 4-(2,4-dichlorophenoxy)phenol, was found in the extracts. Furthermore, traces of six other unknown metabolites were detected. Under anaerobic conditions the degradation proceeded to a small extent. At most 3% of the applied radioactivity was accounted for by the degradation product 4-(2,4-dichlorophenoxy)phenol. No other metabolite, including ¹⁴CO₂, was observed, implying lack of any further degradation.     

Influence of monuron on photosystem II and light-dependent 14CO2 fixation in isolated cells of C3 and C4 plants

Cells were isolated from the developing leaves of Ipomoea aquatica (water spinach), a C₃ plant, and three kinds of C₄ plants, namely, Digitaria sanguinalis (NADP⁺-specific malate dehydrogenase type), Panicum miliaceum (NAD⁺-specific malic enzyme type), and Panicum texanum (phosphoenopyruvate carboxy kinase type), to study the effect of monuron on light-dependent ¹⁴CO₂ fixation and oxygen evolution. Bundle sheath cells, except for those of D. sanguinalis, and mesophyll cells of all plants fixed approximately the same amount of ¹⁴CO₂. Monuron, at the range used (2 to 10 × 10^?7M), showed strong inhibition in the mesophyll cells of water spinach and in bundle sheath cells of P. miliaceum and P. texanum and moderate inhibition in the mesophyll cells of all C₄ plants. In the bundle sheath cells of D. sanguinalis the low rate of ¹⁴CO₂ fixation was stimulated to some extent by the addition of malate and ribose 5-phosphate. The I₅₀ value was 6 × 10^?7M for the sensitive cells. Monuron inhibited the oxygen evolution of all seven cell types and their I₅₀ values varied between 3 × 10^?7 to 6 × 10^?7M. The differential response of isolated plant cells from different species to light-dependent CO₂ fixation in the presence of monuron may also be involved in urea herbicide selectivity and undoubtedly is due to the differential photosynthetic pathways present nn them.     

Absorption,translocation and metabolism of the herbicide naproanilide in tobacco

Naproanilide [2-(2-naphthyloxy)propionanilide] has a high activity against dicotyledonous weeds in rice fields, but is very safe to rice. This study was designed to clarify the absorption and translocation of radiolabelled naproanilide in tobacco plants and the metabolism in tobacco callus. The results indicated that naproanilide is translocated easily to the upper part of tobacco plants. Distribution of radioactivity in tobacco plants at the 7th day was shown to be 0.88, 0.24 and 0.03%, and at the 14th day 1.71, 1.86 and 2.32% of the total activities of [¹⁴C]naproanilide in root, stem and leaf, respectively. When compared to earlier results obtained with rice, the translocation rate in tobacco is much higher and might therefore contribute a possible mechanism of herbicidal selectivity. Metabolites including NOP [2-(2-naphthyloxy)propionic acid], NOPM [methyl 2-(2-naphthyloxy)propionate], 2-naphthol, 2,3-naphthalenediol, 2,6-naphthalenediol, 2,7-naphthalenediol and 2-hydroxy-1,4-naphthoquinone were identified in tobacco callus by co-chromatography.