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Xylem translocation and root uptake of weak electrolytes were investigated with the pressure chamber technique (PCT) using de-topped soybean plants. Two compounds were organic bases (fenpropimorph and imazalil) and four were organic acids (bentazone, primisulfuron-methyl, rimsulfuron and triasulfuron). The compounds covered a wide range of log KOW and pKa values. Concentrations in external solution and in xylem sap were measured by HPLC at pH values in external solution of 4.5, 6.5 and 8.5. For weak bases, translocation was higher at low pH and the transpiration stream concentration factors (TSCF) were in the range 0.31-0.95. At pH 8.5, the concentrations in leaking xylem sap were very low for fenpropimorph, and steady-state was probably not reached. For weak acids, TSCF values derived with external pH from 4.5 to 8.5 were in the range 0.55-1.50 for primisulfuron-methyl, 0.64-1.35 for rimsulfuron, 0.81-0.93 for triasulfuron and 0.69-0.92 for bentazone. The variation of TSCF of the weak electrolytes was much smaller in these PCT experiments than in recent experiments with intact plants. The likely reason is that de-topped soybean plants in the pressure chamber seemed to be unable to regulate their xylem sap pH, which was almost identical to the pH in external solution. Without pH differences, the ion-trap process, which is responsible for accumulation or exclusion of weak acids and bases in the xylem of living plants, does not take place. Model simulations carried out for intact and de-topped plants supported this hypothesis. By variation of the pH of the xylem sap, good agreement between measurements and simulations could be achieved. 相似文献
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Stefan Trapp 《Pest management science》2000,56(9):767-778
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 KOW, pKa 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 相似文献
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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 Kow (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. 相似文献
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Fernando Sicbaldi Gian Attilio Sacchi Marco Trevisan Attilio A. M. Del Re 《Pest management science》1997,50(2):111-119
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 Kow; 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 Kow was observed. The highest TSCF values were measured for those compounds with log Kow 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 Kow values below as well as above 3. © 1997 SCI. 相似文献
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