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.     

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.     

Studies on octylphenoxy surfactants. Part 2: Effects on foliar uptake and translocation

The effects of octylphenol (OP) and four of its ethoxylated derivatives on uptake into, and distribution within, maize leaf of 2-deoxy-glucose (2D-glucose), atrazine and o, p′-DDT are reported. The surfactants and OP (2 g litre^?1 in aqueous acetone) increased the uptake, at both 1.5 and 24 h, of the three model compounds (applied at 1 g litre^?1) having water solubilities in the g, mg and μg litre^?1 ranges. The uptake of 2D-glucose was positively correlated with the hygroscopicity of the surfactants. The uptake of DDT and atrazine increased with the uptake of the surfactants, being inversely related to their hydrophile:lipophile balance (HLB). Uptake of 2D-glucose and atrazine was enhanced at high humidity, the relative enhancement for atrazine increasing with increasing ethylene oxide (EO) content of the surfactants. A significant proportion of the atrazine and DDT entering the leaf was recovered from the epicuticular wax, the amount of atrazine recovered from the wax increasing with the EO content of the surfactants. The proportion of the surfactants taken up which was recovered from the epicuticular wax was minimal at an EO content of 12.5–16 mole equivalents. The appearance of the deposits on the leaf surface differed markedly among the surfactants, with similar trends for all three chemicals and without visible evidence for infiltration of the stomatal pores. The total quantities of glucose and atrazine translocated were increased by all surfactants but that of DDT was not, despite increases in uptake of up to 7.5-fold. Relative translocation (export from treated region of leaf as a percentage of chemical penetrating beyond the epicuticular wax) was reduced in all cases in the presence of surfactant. Up to 30% of the applied [¹⁴C]chemicals was not recovered from the treated leaf after 24 h. The reduced recovery of 2D-glucose, but not that of atrazine and DDT, was largely attributable to movement out of the treated leaf, with approximately 70% of the chemical taken up being translocated basipetally. Loss of atrazine and DDT was a result of volatilisation. There was no evidence that either [14C]2 D-glucose or [¹⁴C]atrazine was metabolised to [¹⁴C]carbon dioxide.     

Studies of the effects of essential oils isolated from 14 species of Labiatae on the carmine spider mite,Tetranychus cinnabarinus

Essential oils from 14 species of Labiatae were steam-distilled and analyzed. Bean leaf discs freshly sprayed with different concentrations of the acetonic solutions of the oils caused mortality and induced repellency in adult females of the carmine spider mite,Tetranychus cinnabarinus (Boisd.), and egg-laying was reduced. Seven-day-old residues still had some activity. On the basis of EC-50s, the most effective oils were:Lavandula angustifolia xL. latifolia (0.09%);L. angustifolia (0.1%);Melissa officinalis (0.12%);Mentha piperata (1.3%);Salvia fruticosa (1.4%);Ocimum basilicum (1.4%); andRosmarinus officinalis (2.2%).     

Effects of herbicides and herbicide analogs on [14C]leucine incorporation by suspension-cultured Solanum nigrum cells

Assays of [¹⁴C]leucine incorporation were used to measure effects of herbicides on suspensioncultured heterotrophic Solanum nigrum cells. Most herbicidal vs. nonherbicidal chemicals in a set of 47 compounds could be distinguished from each other based on their extent of inhibition of leucine incorporation by S. nigrum cells. Herbicides which failed to inhibit leucine incorporation were photosynthetic inhibitors. Both phytotoxic and nonphytotoxic thiocarbamate analogs (as determined by whole-plant studies) tended to inhibit leucine incorporation. It was concluded that the leucine incorporation screen could detect a majority of compounds tested which are herbicidal, and that it may also be useful to detect compounds which have cellular toxicity which is not observed in the whole plant.     

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

The uptake and translocation of [¹⁴C]asulam (methyl 4-aminophenyl-sulphonylcarbamate), [¹⁴C]aminotriazole (1-H-1,2,4-triazol-3-ylamine) and [¹⁴C]glyphosate (N-(phosphonomethyl)glycine) were assessed in Equisetum arvense L. (field horsetail), a weed of mainly horticultural situations. Under controlled-environment conditions, 21°C day/18°C night and 70% r. h., the test herbicides were applied to 2-month-old and 2-year-old plants. Seven days following the application of 0.07-0.09 °Ci (1.14mg) of the test herbicides to young E. arvense, the accumulation of ¹⁴C-label (as percentage of applied radioactivity) in the treated shoots, untreated apical and basal shoots was as follows: [¹⁴C]asulam, 13.2, 0.18 and 1.02%; [¹⁴C] aminotriazole, 67.2, 3.65 and 1-91%; [¹⁴C]glyphosate, 35.9, 0.06 and 0.11%. The equivalent mean values for the accumulation of ¹⁴C-label in 2-year-old E. arvense were [¹⁴C]asulam, 12.0, 1-15 and 1.74%; [¹⁴C]aminotriazole, 58.6, 9.44 and 4.12%; [¹⁴C]glyphosate, 33.1, 0.79 and 2.32%. In the latter experiment, test plants received 0.25-0.30 °Ci (4mg) of herbicide, they were assessed after a 14-day period and the experiment was carried out at 3-week intervals between 2 June and 25 August on outdoor-grown plants. Irrespective of test herbicide or time of application, very low levels of ¹⁴C-label accumulated in the rhizome system. Only 0.2% of the applied radioactivity was recovered in 2-year-old plants and 0.4% in 2-month-old plants. In the young plants [¹⁴C]asulam accumulated greater amounts and concentrations of ¹⁴C-label in the rhizome apices and nodes than [¹⁴C]aminotriazole or [¹⁴C]glyphosate treatments. Inadequate control of E. arvense under field conditions may be due to limited basipetal translocation and accumulation of the test herbicides in the rhizome apices and nodes.     

Effects of the herbicide EPTC and the protectant DDCA on incorporation and distribution of [2-14C]acetate into major lipid fractions of maize cell suspension cultures

The rapid effects of the herbicide EPTC (S-ethyl dipropylthiocarbamate) and the protectant DDCA (N,N-diallyl-2,2-dichloroacetamide) on [2-¹⁴C]acetate incorporation into lipids of maize cell cultures were studied in order to determine whether they act at similar sites of lipid synthesis. DDCA, at 0.05 mM and 0.1 mM, increased the incorporation of [2-¹⁴C]acetate into neutral lipids of a total lipid extract within 2 h. It had very little effect on the major polar lipid constituents. DDCA altered neither the distribution of label within the major lipid classes, nor turnover of the major lipids within 2 h. EPTC (0.1 mM) inhibited overall uptake of [2-¹⁴C]acetate into both neutral and polar lipids by about 30% after a 2-h incubation. The major polar lipid affected was an unidentified glycolipid. In addition to reducing the quantity of lipids synthesized, EPTC changed the lipid profile, altering the distribution of label, mainly within the neutral lipid fraction. A crude membrane fraction from maize cells contained both polar lipids and some neutral lipids. DDCA stimulated [2-¹⁴C]acetate incorporation into different lipid species. EPTC inhibited incorporation of [2-¹⁴C]acetate into both neutral and polar membrane lipids but altered significantly only its distribution into neutral lipids. DDCA (0.1 mM) given together with EPTC (0.2 mM) partially counteracted the effect of EPTC within the neutral lipid fraction. It is suggested that DDCA has a rapid effect on lipid synthesis, but it is probably not sufficient to account for the entire mode of action of the protectant.     

Studies in phytotoxicitya. II. Changes in the concentrations of tricarboxylic acid cycle intermediates associated with phytotoxic effects on leaves

Leaves of dwarf bean and blackcurrant were analysed for their content of some of the acids of the tricarboxylic acid (TCA) cycle after treatment with lime sulphur in order to correlate any changes with the increase in respiration previously reported. In the dwarf bean, a rapid initial decrease in succinic acid was followed by a large increase. This suggested that there was some blocking of the succinic dehydrogenase by the toxic agent. However it is probably important to consider the contribution of the hexose monophosphate (HMP) shunt in the increased respiration and associated metabolic changes as it has been shown that many disruptive agents, both chemical and biological, favour respiration by the HMP rather than the TCA route in plants.     

Modelling short-term effects of sulphur dioxide. 3. Effects of SO2 on photosynthesis of leaf canopies

The effect of short-term exposure of SO₂ on the photosynthesis of a Faba bean crop was analysed with mobile equipment in the field. Canopy photosynthesis was only affected at high radiation levels and reduced by 4–6% during fumigation with 800 g SO₂ m^–3.The experimental data were used to evaluate the performance of a model for the effects of SO₂ on leaf canopy photosynthesis. The model contained a calculation procedure for canopy photosynthesis, extended with a submodel for SO₂ uptake by leaves and effects of SO₂ on leaf physiology. Diurnal photosynthesis and the effect of SO₂ on canopy photosynthesis were approximated very closely with the model. Possibilities for the application of this approach in crop growth models (operating at a time step of integration of 1 day) are presented and evaluated.Samenvatting Het effect van SO₂ op de fotosynthese van een tuinbonengewas is gemeten met mobiele apparatuur. Gewasfotosynthese werd alleen beïnvloed (4–6% reductie) bij hoge stralingsnivo's tijdens begassing met 800 g SO₂ m^–3.De experimentele gegevens zijn gebruikt om een model voor de effecten van SO₂ op de gewasfotosynthese te evalueren. Het model bestaat uit een rekenprocedure voor de fotosynthese van gewassen dat is uitgebreid met een submodel voor de opname en effecten van SO₂ op de fotosynthese van bladeren. De dagelijkss gang van de fotosynthese en de effecten van SO₂ op de fotosynthese werden nauwkeurig gesimuleerd met het model. Mogelijkheden voor de toepassing van het model in gewasgroeimodellen, die met een tijdstap van één dag werken, wordt gepresenteerd en geëvalueerd.     

Modelling short-term effects of sulphur dioxide. 1. A model for the flux of SO2 into leaves and effects on leaf photosynthesis

A model for the flux of atmospheric SO₂ into leaves and the effects of SO₂ metabolites (S(IV) compounds) on leaf photosynthesis and stomatal resistance is presented. The S(IV) balance in the leaf is determined by the rate of SO₂ uptake and S(IV) removal by oxidation to sulphate. Toxic S(IV) compounds reduce the rate of photosynthesis and induce stomatal closure as a result of feed back control of stomatal resistance by photosynthesis. Other proposed mechanisms, like effects through a pH reduction, are not likely to play a role in short-term effects of realistic SO₂ concentrations. The model contains two key parameters which describe biochemical characteristics: a time coefficient for S(IV) oxidation and a parameter describing the sensitivity of photosynthesis for S(IV).Simulation results demonstrate the potential of plants to avoid extremely toxic concentrations of S(IV) in the leaf by three mechanisms: (i) rapid oxidation of S(IV) to less toxic sulphate, (ii) relatively high resistance to SO₂ uptake and (iii) feed back control between photosynthesis and stomatal resistance. S(IV) concentrations in the leaf and SO₂ concentrations in the stomatal cavities in stable situations are less than 1% of concentrations which build up without these mechanisms. Leaf thickness appears to be an important factor determining the susceptibility of plants to air pollutants. Thin leaves should be more sensitive than thicker leaves. It is concluded that effects of SO₂ on photosynthesis should be related to the uptake per unit of leaf volume instead of the commonly used flux per unit leaf area. The model accurately described the time course of photosynthetic reduction during a short fumigation period and subsequent recovery period.Samenvatting Een model wordt gepresenteerd waarmee de flux van SO₂ vanuit de lucht in het blad en de effecten van SO₂-metabolieten op de bladfotosynthese en stomataire geleidbaarheid kan worden gesimuleerd. De S(IV)-balans in het blad wordt bepaald door de SO₂ opnamesnelheid, en de snelheid van S(IV)-verwerking door met name oxidatie tot sulfaat. Toxische S(IV)-componenten reduceren de fotosynthese en veroorzaken daardoor stomataire sluiting. Andere in de literatuur beschreven mechanismen voor de effecten van SO₂, zoals effecten door een daling van de pH, spelen geen rol op de korte termijn. Het model bevat twee parameters die de biochemische karakteristieken beschrijven: de tijdconstante voor S(IV)-oxidatie en een parameter die de gevoeligheid van de fotosynthese voor S(IV) beschrijft.De simulatieresultaten laten zien dat de plant extreem toxische concentraties in het blad kan voorkomen door: (i) de snelle oxidatie van S(IV) tot sulfaat, (ii) de relatief hoge weerstand voor SO₂-opname en (iii) de stomataire sluiting die een gevolg is van een gereduceerde fotosynthese. S(IV)-concentraties in het blad en SO₂-concentraties in de stomataire holten zijn kleiner dan 1% van de concentratie die zou ontstaan als deze mechanismen niet zouden werken. Bladdikte blijkt de gevoeligheid van planten voor SO₂ in sterke mate te bepalen. De effecten van SO₂ op de fotosynthese dienen te worden gerelateerd aan de opnamesnelheid per eenheid bladvolume, in plaats van bladoppervlak. Het model simuleert de reductie in fotosynthese gedurende een korte begassingsperiode en een herstelperiode nauwkeurig.     

Modelling short-term effects of sulphur dioxide. 2. Quantification of biochemical characteristics determining the effect of SO2 on photosynthesis of leaves

A summary version of a model for the SO₂ flux into leaves and effects of SO₂ on the rate of photosynthesis (Kropff, 1989) was used to analyse experimental data on the effects of SO₂ on the rate of photosynthesis with standard statistical techniques. Values for the two key parameters of the model, a sensitivity parameter relating intracellular S(IV) concentration (SO₂, bisulphite and sulphite) to photosynthetic reduction, and a time coefficient for S(IV) oxidation, were estimated from data on photosynthesis during fumigation and subsequent recovery period, by combined non-linear regression of both equations.The pattern of rapid photosynthetic reduction by SO₂ and rapid recovery following fumigation was accurately described with the model for several data sets. Parameter estimates agree very well with experimentally determined values. It is concluded that differences in photosynthetic sensitivity of plants are mainly due to differences in the time coefficient for sulphite oxidation. Variation in leaf thickness may also have contributed to the differences in sensitivity. This approach can be used to parameterize the model for short-term effects of SO₂ on leaf photosynthesis for specific species and environmental conditions from easily obtained data.Samenvatting Een model voor de flux van SO₂ in het blad, het metabolisme van SO₂ in het blad en de effecten van SO₂-metabolieten op de fotosynthese (Kropff, 1989) is gebruikt om gegevens over het effect van SO₂ op de fotosynthese tijdens en na een begassingsperiode te analyseren met standaard statistische technieken. De waarde voor de parameter die de relatie tussen S(IV) en fotosynthese karakteriseert en de waarde van de tijdconstante voor de S(IV)-oxidatie werden voor verschillende data-sets over het verloop van de fotosynthese tijdens en na begassing met SO₂ geschat.De snelle reductie van de fotosynthese na de start van de begassing, het stabiliseren na 1 uur en het snelle herstel na de begassing werden zeer goed met het model beschreven voor de data-sets. De waarden voor de parameters bleken vergelijkbaar met gegevens uit biochemische analyses. Verschillen in gevoeligheid tussen planten voor SO₂ blijken met name te berusten op verschillen in de snelheid waarmee S(IV) wordt geoxideerd. Variatie in bladdikte kan daarnaast van belang zijn geweest. De benadering kan worden gebruikt om inzicht te krijgen in biochemische karakteristieken die de effecten van SO₂ bepalen, met behulp van relatief eenvoudig te verkrijgen data-sets.     

In vitro effects of DDT analogs on trout brain Mg2+-ATPases: I. Specificity and physiological significance

A continuous steady-state assay procedure was used to investigate the effects of DDT and several analogs on the in vitro Mg²⁺-stimulated adenosinetriphosphatase of a trout brain mitochondrial fraction. Pharmacological dissection of the enzyme with oligomycin, dicyclohexyl-carbodiimide, and azide failed to yield a fraction specifically sensitive to the organochlorines. At 25°C, low doses of DDT (≤1.35 μmol/mg of protein) stimulated enzyme activity, while methoxychlor was stimulatory at all doses. Higher doses of DDT and of several analogs caused only 45.5% or less inhibition at 25°C, but inhibition increased at lower temperatures. The physiological significance of these effects is discussed.     

Effects of elevated CO2 and temperature on interactions of grapevine and powdery mildew: first results under phytotron conditions

Journal of Plant Diseases and Protection - This study reports the effect of increased CO2 and temperature on powdery mildew (Erysiphe necatrix) of grapevine evaluated under controlled conditions....     

Virtual Lesion Extension: A Measure to Quantify the Effects of Bacterial Blight on Rice Leaf CO(2) Exchange

ABSTRACT Virtual lesion extension was proposed as a measure to summarize the effects of foliar diseases with single spreading lesions on CO(2)-exchange parameters at the whole-leaf level. Visible lesion plus virtual lesion extension constitute a virtual lesion, in which CO(2) exchange was postulated to be nil. Virtual lesion extension can be derived for each photosynthesis parameter from gas-exchange measurements. Using a leaf-shape function, one-dimensional lesion length was translated into two-dimensional lesion area, and a relationship between visible and virtual severity can be established. The model was applied to measurements of leaf CO(2) exchange in rice leaves infected with Xanthomonas campestris pv. oryzae, the causal organism of rice bacterial blight. The model resulted in a virtual lesion extension of 1.1 cm for the gross CO(2)-exchange rate at light saturation, -3.9 cm for dark respiration rate, and 0 for initial light use efficiency. Reduced light interception due to a visible lesion caused reductions in net CO(2) assimilation, and small virtual lesion extensions only marginally reduced net CO(2) assimilation further. The additional reduction was smaller in case of longer leaves. Measurement of net photosynthesis rate along a transect from the base to the tip of infected leaves indicated that the location on the leaf blade where net photosynthesis decreased from normal to nil was centered around the lesion tip.     

Paraquat tolerant Lolium perenne L.: effects of paraquat on germinating seedlings

A cultivar of Lolium perenne L. (Causeway) selected for tolerance to foliar-applied paraquat was shown also to be tolerant at seed germination and establishment. When seeds were germinated in paraquat solutions (1, 3, 9, 27 ppm), Causeway was more than ten times as tolerant as a normal cultivar of L. perenne. When germination and survival were studied in a soil which had been sprayed with paraquat (0.0, 0.3, 0.9, 2.7 kg/ha) before sowing, Causeway was nearly three times as tolerant as a normal cultivar. Holcus lanatus L. was about equal to normal L. perenne, but Poa trivialis L. was less tolerant. Phytotoxicity was greater in a 10.5% organic than a 4.8% organic soil. It is concluded that the mechanism of paraquat tolerance operates in the non-photosynthetic tissues of germinating seedlings as well as in the photosynthetic tissues of older plants, although the degree of tolerance varies according to the mode and stage of application of the herbicide. There might be advantages in using a paraquat tolerant cultivar of L. perenne when direct drilling grass after sward destruction by paraquat.     

Studies on the biology of black mould (Aspergillus niger) on temperate and tropical onions. 2. The effect of treatments on the control of seedborne A. niger

Treatment of A. niger -inoculated onion seed with benomyl dust (1 g a.i./kg), or a foliar spray of thiram (0·4% a.i./ha) applied to plants grown from inoculated seed under temperate (UK) conditions reduced the incidence of A. niger in harvested crops. Treatment of naturally contaminated Sudanese onion seed with a benomyl + thiram mixture at a rate of 2·5 + 2·5 g a.i./kg or soaking the seed in hot water (15 min at 60°C) reduced the incidence of black mould on bulbs grown in the Sudan in field soil that had not previously been used for onion production. The seed treatments were less effective in crops produced in fields regularly used for onion production. However, incubation of harvested bulbs in moist chambers showed that damage to the internal storage tissue of onion bulbs caused by A. niger was reduced by seed treatment.     

Studies on the mode of action of asulam in bracken (Pteridium aquilinum L. Kuhn) I. Absorption and translocation of [14C]asulam

Studies of the absorption and translocation of foliage-applied ring-labelled [¹⁴C]asulam [methyl (4-aminobenzenesulphonyl) carbamate] were carried out using glasshouse and field-grown bracken plants. Translocation of ¹⁴C from the treated frond was primarily according to a 'source to sink’pattern with intense accumulation of radioactivity in the metabolically active sinks viz. rhizome apices, frond buds, root tips and young frond tissue. In the case of field bracken, translocation and distribution of ¹⁴C was extensive in the rhizome system, accumulation occurring in the active as well as dormant buds situated on the non-frond-bearing and storage rhizome branches. Treatment of fully expanded fronds with 100μl of [¹⁴C]asulam (1 mg, 1.0–1.5 μCi) as 2 μl droplets resulted in a rapid initial uptake during the first week, followed by progressive entry and distribution with time. Basipetal translocation to the rhizome system was positively correlated with total uptake. High humidity (95%) and high temperature (30°C) stimulated uptake and subsequent basipetal translocation to a considerable degree. Uptake was greater through the stomatal-bearing abaxial than through the adaxial cuticle. Incorporation of a surfactant (Tergitol-7, 0.1%) increased penetration by up to 30%. Uptake declined markedly as the frond aged, while translocation was predominantly acropetal in young treated fronds, becoming exclusively basipetal when the fronds matured. Optimum uptake and maximum distribution of [¹⁴C]asulam in the rhizome and its associated buds was achieved when treatments were applied to almost fully expanded fronds. The translocated ¹⁴C (asulam and possibly some of its metabolites) showed a considerable degree of persistence in the rhizome system, 8% of the applied activity still remaining in the rhizome 40 weeks after treatment.     

Studies on the chiral isomers of fonofos and fonofos oxon: II. In vitro metabolism

The in vitro metabolism of the chiral isomers of fonofos and fonofos oxon in the presence of mouse liver mixed-function oxidase and serum esterase was investigated. The metabolism of ³⁵S-labeled phenyl-(S)_P-fonofos mediated by mixed-function oxidase took place stereoselectively, resulting predominantly in (R)_P-fonofos oxon. Similarly, (R)_P-fonofos was converted to (S)_P-oxon. In each case, however, a significant amount of racemization occurred. Other products were diphenyl disulfide and diphenyl disulfide oxide. In addition to stereospecificity, the oxidative metabolism of (R)_P-fonofos proceeded at a rate faster than that of (S)_P-fonofos. Stereoselective rate differences also were observed in mouse or rat serum-catalzyed degradation of the fonofos oxon enantiomers, the (S)_P isomer being degraded about twofold faster than its enantiomer. The differences in toxicities of the isomers of fonofos and fonofos oxon were consistent with the in vitro metabolism data.     

Studies on the colonization of axenically grown tomato plants by a GFP-tagged strain of Clavibacter michiganensis subsp. michiganensis

In this study, colonization and disease development of axenically-grown tomato plants by Clavibacter michiganensis subsp. michiganensis (Cmm), the causative agent of bacterial wilt and canker, was investigated. For this, a spontaneous rifampicin resistant strain of Cmm was tagged with a marker that expressed a green fluorescent protein (GFP) in a stable way and which possessed a similar virulence to the parental strain. In vitro plants were drop-inoculated at the stem base and the population dynamics was determined by dilution pour-plating in a selective medium. At 3 h after inoculation, Cmm was already present in low densities in roots, stems and leaves. At 16 dpi, Cmm was found throughout the entire plant in high densities of ca. 10¹⁰ cfu g^?1. Symptoms developed in the in vitro plants typical for Cmm, such as canker, wilting and growth reduction. The presence of Cmm in vascular and parenchymatic tissue of in vitro tomato plants was confirmed by epifluorescence stereo- and confocal laser scanning microscopy. This study showed that in vitro tomato plants can be effectively used for detailed studies on interactions between Cmm and its host, in particular if a GFP-tagged strain of the pathogen is used.