Uptake by roots and translocation to shoots of two morpholine fungicides in barley

Despite being lipophilic, morpholine fungicides are systemic in plants. Such transport may be explicable by their protonation (pKa∽7·5) at the pH of plant compartments to yield the more polar cation. This behaviour might be a useful attribute to be incorporated into other classes of lipophilic pesticides. To understand quantitatively the behaviour of the morpholine fungicides, the uptake by roots and transport to shoots in barley of two such ¹⁴C-labelled compounds, dodemorph and tridemorph, were investigated using bathing solutions of differing pH. At pH 5, uptake and transport were small, but increased by approximately two orders of magnitude at pH 8. Tridemorph, the more lipophilic of the two compounds, was highly accumulated by roots at pH 8 and moderately translocated to shoots. In contrast, dodemorph was translocated to shoots at pH 8 with remarkable efficiency, moving into the xylem across the endodermis at 23 times the efficiency of water, though accumulation in roots was less than that of tridemorph. Behaviour at 24 h was largely similar to that at 48 h for both compounds, indicating that uptake and translocation are equilibrium processes maintained over time. Transport to shoots for each compound was directly proportional to the concentrations accumulated in the roots, except at low pH where partitioning into root solids became proportionately more important with such material not being directly available for transport to the xylem across the endodermis. Uptake and transport of these basic fungicides are explained in terms of their partitioning and of their accumulation in acidic plant compartments by ion trapping as the protonated form; this behaviour is discussed in relation to the pKa and lipophilicity of these compounds. © 1998 Society of Chemical Industry     

Relationships between lipophilicity and root uptake and translocation of non-ionised chemicals by barley

The uptake by roots from solution, and subsequent translocation to shoots in barley, of two series of non-ionised chemicals, O-methylcarbamoyloximes and substituted phenylureas, were measured, Uptake of the chemicals by roots was greater the more lipophilic the chemical, and fell to a lower limiting value for polar chemicals. Translocation to the shoots was a passive process, and was most efficient for compounds of intermediate polarity. Both processes had reached equilibrium within 24h of treatment. The reported behaviour of many pesticides in various plant species agrees with the derived relationships, but the detailed mechanisms of these processes are unknown.     

Comparative systemic translocation of several xenobiotics and sucrose

The systemic movement of several xenobiotics was compared in soybean and barley. The more symplastic compounds were also compared to the movement of sucrose. The uptake and efflux from potato tuber tissue was studied and related to the in vivo translocation patterns. The patterns of translocation ranged from primarily apoplastic to ambimobile to symplastic. When the percentage of xenobiotic available for translocation was evaluated there were major differences in patterns of translocation, between plant genera. In barley fenapanil, fenarimol, and oxamyl exhibited primarily apoplastic transport while all three were more ambimobile in soybean. Basipetal transport of oxamyl was 4.2% in barley compared to 30.8% in soybean. Basipetal translocation of benomyl remained very low at 3.0 and 4.1% in barley and soybean, respectively, while sucrose was about 60% in both species. Glyphosate and sucrose were translocated in a similar pattern. The transport of 2,4-D was primarily symplastic, however, retention in the tissue appeared to limit the rate of movement when compared to sucrose. Uptake and efflux of fenapanil, fenarimol, and 2,4-D illustrated the possible role that cellular binding or partitioning may play in systemic translocation. In conjunction with the uptake and efflux, and systemic movement in plants, the octanol/water partition coefficients, log P, for fenarimol and fenapanil, 0.67 and ?0.03, respectively, are correlated with the possible role of cellular binding or partitioning in the systemic movement of xenobiotics.     

Relationships between lipophilicity and the distribution of non-ionised chemicals in barley shoots following uptake by the roots

Determinations were made of the distribution of two series of non-ionised chemicals, ^O-methylcarbamoyloximes and substituted phenylureas, in barley shoots, following uptake by the roots from solution. The concentrations in basal and central shoot sections became constant after 24 to 48 h for all but the most lipophilic chemical studied, and were then greatest for the more lipophilic chemicals. Amounts in the leaves generally increased up to 72 or 96 h, when degradation balanced translocation. The accumulation of chemical in the lower section of shoots can be ascribed to a partitioning process similar to that in roots, the chemical being partitioned between the shoot and the xylem transpiration stream; this uptake could be estimated from the octan-1-01/water distribution coefficients, and was predicted to be greatest for compounds for which log K_ow=4. 5.     

Transport via xylem of atrazine, 2,4-dinitrotoluene, and 1,2,3-trichlorobenzene in tomato and wheat seedlings

Transport of atrazine (ATR), 2,4-dinitrotoluene (DNT), and 1,2,3-trichlorobenzene (TCB) from roots to shoots via xylem of wheat and tomato seedlings was measured following a 24-h exposure of plant roots to hydroponic solutions of these organic compounds. Transport of the compounds from roots to shoots reached equilibrium within 24 h, consistent with an earlier finding. Low concentrations of TCB were detected in the final external solution and the xylem efflux of control wheat seedlings. This suggested that there was a fast foliar uptake of TCB and its downward movement via phloem of the wheat seedlings. Concentrations of DNT, ATR, and TCB in xylem effluxes of wheat and tomato increased significantly with increases of their external concentrations. The translocation stream concentration factors (TSCF), i.e., the ratios of the concentrations in xylem sap to those in external solution, of the compounds with tomato seedlings followed the order of ATR > DNT >> TCB, which was inversely correlated with the log K_ow (the octanol–water partition coefficient) of the compounds. The observed xylem transports of DNT and TCB from roots to shoots with wheat seedlings were lower than those with tomato seedlings. ATR exhibited a high xylem transport with the two plant species, which resulted presumably from an atrazine–metal complex formation.     

Physicochemical factors affecting the uptake by roots and translocation to shoots of amine bases in barley

The uptake by barley roots from nutrient solution and subsequent transport to shoots of two series of amine bases were measured over 6 to 72 h. The compounds were chosen to span systematically ranges of lipophilicity (assessed using 1-octanol/water partition coefficients, K_ow) and pKa that would include commercial pesticide amines. In a series of six substituted phenethyl amines, strong bases with pKa∽9·5, all the compounds were strongly taken up by roots from solutions of pH 8·0; uptake declined substantially as the pH was lowered to 5·0, especially for the compounds of intermediate lipophilicity (log K_ow 2 to 3). This uptake could be ascribed to three processes: (i) accumulation of the cation inside the root cells due to the negative charge on the plasmalemma, as given by the Nernst equation and important only for the polar compounds which have low permeation rates through membranes; (ii) accumulation into the vacuole by ion-trapping, which was the dominant process at high pH for all compounds and at all pH values for the compounds of intermediate lipophilicity; (iii) partitioning on to the root solids, substantial only for the most lipophilic compounds. Translocation to shoots was proportional to uptake by roots, this ratio being independent of external pH for each compound and being optimal for the compounds of intermediate lipophilicity. Such proportionality was also observed in a series of three weaker bases of intermediate lipophilicity, in which compounds of pKa 7·4 to 8·0 were also well taken up and translocated whereas the very weak base 4-ethylaniline (pKa 5·03) was much less so. Tests with quaternised pyridines confirmed that organic cations move only slowly through membranes. The observed behaviour of the amines could be modelled reasonably well assuming that transport within the plant was dominated by movement across membranes of the non-ionised species, and this appeared to be true even for the most lipophilic phenethylamine (log K_ow 4·67) studied, though its long-distance movement would be as the protonated species. © 1998 Society of Chemical Industry     

Physico-chemical factors affecting uptake by roots and translocation to shoots of weak acids in barley

The uptake from solution of maleic hydrazide, flamprop and a series of phenoxyacetic acids by roots, and their subsequent translocation to shoots, was measured in barley. Both uptake and translocation increased as the pH of the solution decreased, the magnitude of the change varying amongst the chemicals tested. Uptake by roots could be accounted for by the ion-trap mechanism, which assumes that entry of the chemicals occurs largely by passive diffusion of the undissociated form of the acids, with passage of the anions across the cell membranes being very slow. The ratio of the permeability of the cell membranes to the undissociated and dissociated forms of the acids was estimated from the accumulation in roots, and in the phenoxyacetic acid series this ratio was maximal (4×10⁵) for compounds of intermediate lipophilicity. Maleic hydrazide and flamprop had much lower ratios, 1.8×10² and 10³ respectively; the value for flamprop was much less than for phenoxyacetic acids of similar lipophilicity, such as 2, 4- dichlorophenoxyacetic acid, indicating that lipophilicity may not be the sole factor determining the behaviour of weak acids in plants. Translocation to shoots was approximately proportional to the chemical concentrations in the roots.     

Root Uptake and Xylem Translocation of Pesticides from Different Chemical Classes

A pressure-chamber technique was used to study the root uptake and xylem translocation of some fungicides, herbicides and an insecticide from different chemical classes in detopped soybean roots. Physiological parameters such as K⁺ leakage from roots, K⁺ concentrations in the xylem sap, and protein and ATP levels in the root cells were measured so as to evaluate any potential damage of this technique to the root system. HPLC was used to quantify the compounds in the xylem sap. The pressure-chamber technique has proved useful to study the root uptake and translocation of pesticides, does not damage the root system, and allows one to obtain appreciable volumes of xylem sap that can be analysed directly by HPLC, thus avoiding dependence on the availability of radio-labelled compounds. The concentration of each pesticide in the xylem sap showed a steady-state kinetic profile. Non-linear regression analysis was used to calculate the steady-state concentration and the time required to achieve 50% of the steady-state concentration (TSSC₅₀). TSSC₅₀ was well correlated with log K_ow; the more lipophilic the compound the more time was required to reach the steady-state concentration. The efficiency of translocation was assessed by the transpiration stream concentration factor (TSCF) and a non-linear relationship between TSCF and log K_ow was observed. The highest TSCF values were measured for those compounds with log K_ow values around 3, a lipophilicity value similar to that reported earlier in an analogous experiment with detopped soybean plants but slightly higher than that reported in earlier experiments with intact barley plants. Lower TSCF values were obtained with chemicals with log K_ow values below as well as above 3. © 1997 SCI.     

土层水分非均匀供应下施锌对玉米植株中Ca、Fe、Mn、Cu吸收积累的影响

进行分层盆栽试验,模拟田间土壤剖面上下层水分不均匀分布条件,研究表层土壤施锌对玉米植株吸收Ca、Fe、Mn和Cu养分的影响。结果表明:上层土壤干旱抑制了苗期玉米植株生长,降低了地上部Ca、Fe、Mn分配比例。上层土壤干旱情况下,增加下层土壤水分供应,并没有提高植株生长和养分元素的吸收量。施锌明显促进了玉米地上部生长,在土壤水分充足时,施锌对植株生长效果更明显。不论土壤水分状况如何,施锌显著降低了植株中Ca、Fe、Mn、Cu浓度,对植株吸收积累Fe有拮抗作用;上层土壤干旱条件下,施锌还降低了地上部和整株中Mn以及根部Cu的积累量。施锌对植株体内Ca、Fe、Mn、Cu向上运输没有显著性影响。研究表明土壤表层干旱条件下,即使增加土壤水分,尚不能提高玉米植株生长和对Ca、Fe、Mn、Cu等养分的吸收利用。施用锌肥可以提高作物对土壤水分利用,但要注意对作物吸收Fe与Mn的拮抗作用,适当配合铁锰等养分供应。     

Uptake and translocation of some pesticides by hypocotyls of radish seedlings

Some of the factors affecting absorption and translocation of pesticides by the hypocotyls of intact radish (Raphanus sativus, L., cv. Black Spanish) seedlings have been studied, particular attention being given to the triazine herbicides simazine, atrazine and atraton. Uptake and translocation appear to be largely passive processes and by contrast with foliar absorption seem to be unaffected by humidity, con-centration, light and by the aqueous solubilities of the compounds. Diffusion across the tissues of the hypocotyl, rather than rate of transpiration, appears to determine the rate at which atrazine and simazine are translocated to the cotyledons. For several pesticides there is a qualitative relationship between the percentages of the compounds translocated to the upper portion of the shoots and their partition coefficients in oil/water systems. In conclusion, some consideration is given to the relative importance of uptake by roots and shoots under field conditions.     

Effects of sterol biosynthesis-inhibiting fungicides and plant growth regulators on the sterol composition of barley plants

A number of sterol biosynthesis-inhibiting (SBI) fungicides and plant growth regulator analogs were applied as root drenches to barley seedlings and their effect on the total sterol composition of the roots and shoots was measured by gas-liquid chromatography. Prochloraz was found to be inactive in this system, probably because of poor uptake, while the other compounds could be divided into two groups according to their mode of action as assessed by sterol profiling. The morpholines tridemorph and fenpropimorph inhibited the enzyme cycloeucalenol—obtusifoliol isomerase whereas triadimenol, nuarimol, paclobutrazol, and triapenthenol (RSW 0411) inhibited the enzyme responsible for the removal of the C-14 methyl group. Effects of individual diastereo-isomers and enantiomers of some compounds on sterol profiles were compared with their known fungicidal and anti-gibberellin properties. Shoot growth was reduced by all the compounds tested, paclobutrazol, nuarimol, and triapenthenol being the most effective. As well as inducing accumulation of abnormal sterols, SBI fungicide treatment changed the ratio of campesterol to stigmasterol and sitosterol. It is hypothesized that this may reflect changes in membrane architecture and may offer an explanation for the increased frost hardiness sometimes observed with SBI fungicide-treated plants.     

Modelling uptake into roots and subsequent translocation of neutral and ionisable organic compounds

A study on uptake of neutral and dissociating organic compounds from soil solution into roots, and their subsequent translocation, was undertaken using model simulations. The model approach combines the processes of lipophilic sorption, electrochemical interactions, ion trap, advection in xylem and dilution by growth. It needs as input data, apart from plant properties, log K_OW, pK_a and the valency number of the compound, and pH and chemical concentration in the soil solution. Equilibrium and dynamic (steady‐state) models were tested against measured data from several authors, including non‐electrolytes as well as weakly acidic and weakly basic compounds. Deviations from the measured values led to further development of the model approach: sorption in the central cylinder may explain the small transpiration stream concentration factor of lipophilic compounds. For non‐electrolytes, the model predicted uptake and translocation with high accuracy. For acids and bases, the tendency of the results was satisfactory. The dynamic model and the equilibrium approach gave similar results for the root concentration factor. The calculation of the transpiration stream concentration factor was more accurate with the dynamic model, but still gave deviations up to factor of ten or more. The dominating process for monovalent weak electrolytes was found to be the ion trap effect. © 2000 Society of Chemical Industry     

Effects of micro-organisms on the absorption of inorganic nutrients by plants

Micro-organisms concentrated in the rhizosphere can influence the absorption of inorganic nutrients by plants. The effects were investigated by comparing uptake of nutrients in plants grown in the presence and absence of micro-organisms in both water culture and soil. In water culture, at phosphate concentrations below about 1.0 part/million competition occurs between barley plants and a microflora of casual laboratory contaminants resulting in reduced absorption and translocation of phosphate. In the presence of micro-organisms nitrogen uptake from nitrate was increased and from ammonium ions decreased; uptake of metal from solutions of ferric, zinc and manganous salts and EDTA chelates was enhanced. The results for plants grown in specific soils confirmed that competition from micro-organisms can reduce uptake of phosphate and molybdenum by the plants. The direct effect of rhizosphere micro-organisms can be demonstrated only in special circumstances but such studies aid our understanding of plant nutrition.     

The effect of chlorffenprop-methyl on 32P uptake, transport and metabolism in Avena fatua L. and Hordeum vulgare L.

The eflect of chlorfenprop-methyl on plant weight, root uptake, transport and metabolism of ³²P in wild oat and barley plants was examined 4 h. 1, 3 and 9 days after treatment. The fresh weight of treated wild oat plants became significantly less than that of the controls by day 9. There was no significant effect on the weight of barley plants during this period. Uptake of ³²P by treated wild oat planus progressively decreased during the experiment and by day 9 was significantly 70% less yhan that in the control: uptake by barley plants showed a significant 30% increase by day 9. Transport of ³²P to the shoots followed a similar pattern. In wild oat plants, transport was significantly inhibited at all sampling dales by 44–91%. In barley plants. ³²P transport to the shoots tended to be enhanced by day 9 after herbicide treatment. Metabolism of ³²P in wild oat plants was affected 4 h after treatment. The content of ³²-P in individual fractions (inorganic, organic, lipidic, and nucleic acid P) was lower in treated plants, especially in the shools. In barley plants. ³²P incorporation into the individual fractions was initially inhibited 4 h after treatment, but later corresponded to that found in the control.     

Performance and uptake of some carbendazim-producing fungicides applied as seed treatments to spring barley,in relation to their physicochemical properties

The performance of carbendazim and its chemical precursors benomyl, thiophanatemethyl and methyl 4-(2-aminophenyl)-3-thioallophanate ( I ) ( “NF48” ) as systemic fungicidal seed treatments on barley was investigated. In field trials all treatments significantly decreased smut (Ustilago nuda) at 3.2 g kg^-1 of seed; the order of effectiveness was I > benomyl > thiophanate-methyl > carbendazim. Control of barley mildew (Erysiphe graminis) followed a similar pattern but results were less clear-cut. Measurements of uptake and translocation from seeds, treated with radiolabelled fungicide and planted in pots of Woburn soil in a controlled environment room, showed that seedlings accumulated much more I than the other compounds over 28 days. This substantial early uptake into leaves could explain why I was particularly effective against smut in the field trials. Comparisons of amounts taken up. with solubility in water, octanol/water partition coefficient, extent of adsorption on soil and pK_a values suggested that the effects of these properties on availability in the soil solution may be more important than their influence on penetration into the root in determining relative uptake and disease control in the case of localised applications such as seed treatments.     

结实期水分与氮素对水稻氮素利用与养分吸收的影响

以武育粳3号和汕优63为材料,研究了结实期水分与氮素对水稻氮素利用与养分吸收的影响。结果表明:随氮素水平的提高,稻株吸氮量增加,氮素的利用率、产谷效率和营养器官的氮素转运率下降,稻草中氮的滞留量提高;氮肥促进了稻株对P、K的吸收;水分胁迫降低了稻株的吸氮能力,但提高了氮素的利用率、产谷效率和营养器官的氮素转运率;水分胁迫降低了稻株对P、K的吸收,但提高了对P的利用率;水分与氮肥有明显的互作效应,在一定的氮肥水平下,轻度的水分胁迫,可不降低产量或提高产量,同时提高了水稻的氮素利用率,减少稻田氮的损失。     

Physicochemical properties of agrochemicals: Their effects on foliar penetration

Uptake and translocation of 26 chemicals (herbicides, fungicides, growth regulators, insecticides and model compounds), formulated with and without ‘Ethylan TU’ (NP8) surfactant, have been determined 24, 48 and 72 h after spraying onto leaves of maize, rape, strawberry and sugar beet. Eight of the chemicals may be classified as polar (log partition coefficient (P) < 0) and 18 as lipophilic (log P 0·8-4·6). Chemicals penetrated more readily into waxy leaves of rape and strawberry than into less-waxy sugar beet, whilst lowest rates were observed for maize. Rates of uptake varied from exceedingly low (< 2% 72 h after application) for uracil, maleic hydrazide, isoproturon and methyl phenylurea applied to maize, to rapid (>98% within 24 h of application) for acephate and triadimefon applied to strawberry leaves. The effects of NP8 on rates of chemical uptake were classified into 4 types, viz:-

• (i) low rates, with limited enhancement by NP8;
• (ii) high rates unaffected by NP8;
• (iiii) marked enhancement by NP8 within 24 h; and
• (iv) continuous enhancement by NP8 over 0-72 h.

Translocation into the tissues immediately adjacent to the target site was greater for waxy than less-waxy plants, enhancement by NP8 was attributed to its effects on penetration rather than to surfactant interactions at the sub-cuticular level. Logarithms of physicochemical properties (partition coefficient, water solubility S, molecular weight MW), together with deposit area and melting point (m.p.) values were used to investigate relationships with uptake and translocation. In most cases the variability could not be described adequately in a simple linear form. Regressions using the entire group of 26 chemicals also showed poor correlations between uptake patterns and individual variables. Polynomials in log S, log P, log MW and m.p. were used to test for complex relationships. A quadratic polynomial in log P, log S and m.p. accounted for slightly more (77%) of the variability between the means for total uptake than a cubic polynomial in log P and log S (75%). Although both regressions were significant, the ‘lack of fit’ indicated that other factors need to be included to account fully for the variability in rates of uptake and translocation.     

The nature of bound residues derived from triforine in barley plants

The shoots of barley plants root-treated with [³H]-triforine fungicide (uniformly labelled in the piperazine ring) were analysed 30 days after treatment. Methanol extraction left a solid plant residue which contained 33% of the total ³H which had been incorporated into the shoots. Methanol acidified with hydrochloric acid extracted a further 18% of the triforine-derived bound residues as N-[2,2,2-trichloro-1-(piperazin-1-yl)ethyl]formamide (8%), and piperazine (10%). In the plants, these compounds had thus been complexed to plant constituents. Hot dimethyl sulphoxide (DMSO) extracted a further 13% of the total ³H, leaving a solid residue (mainly cellulose) which contained 2% of ³H, perhaps incorporated into the cellulose. Evaporation of the solvent from the DMSO extract gave a solid, the radioactivity of which (13%) could not be extracted by methanol. A part (7%) of this radioactivity could be released by successive hydrolysis with amyloglucosidase and β-glucosidase, which generated a complex mixture of polar and water soluble unknown radioactive compounds not including piperazine. These latter compounds would be the products of extensive metabolism of triforine (and its metabolite piperazine) bound to, or incorporated into starch. Most (11%) of the radioactivity of this solid could be released by hydrochloric acid hydrolysis, which also generated a complex mixture of polar and water soluble unknown radioactive compounds not including piperazine; a part (4%) of them could have been associated with lignin in the plant.     

干旱区绿洲土壤外源Pb对油菜生长和吸收Cd、Zn的影响

以干旱区绿洲土壤和油菜为供试对象,通过Cd-Zn和Cd-Pb-Zn胁迫下的盆栽试验研究了Cd-Zn污染绿洲土壤条件下Pb的介入对油菜生长及吸收和迁移Cd、Zn的影响。结果表明,Pb的介入促进了油菜茎叶的生长,在较低水平(Cd≤1.8mg·kg-1、Zn≤300mg·kg-1)时促进了根系的生长,而在较高水平(Cd>1.98mg·kg-1、Zn>300mg·kg-1)时则抑制了根系的生长;Pb的介入促进了油菜对Cd、Zn的吸收,但并未影响油菜对Cd、Zn吸收的变化趋势;Pb的介入促进了油菜对Cd、Zn的富集,却抑制了对Cd、Zn的迁移。