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The addition of 1 micromolar 2,3,5-triiodobenzoic acid (TIBA) to solutions containing KCl resulted in the inhibition of K and Cl uptake in excised barley roots. The effectiveness of TIBA as an inhibitor increased as the pH of the treatment solution decreased and approached the pK(a) of TIBA. A lag period of approximately 20 minutes existed prior to the onset of TIBA induced inhibition of ion uptake. Respiratory activity was also inhibited by TIBA. The data suggest that in this material, TIBA functions by entering the cytoplasm and inhibiting metabolism. Comparisons made on the effect of added Ca, showed that at pH 5.7 and higher, Ca had no effect on ion uptake whereas at lower pH values the presence of Ca enhanced uptake by offsetting the deleterious effects of H(+).

The ability of 2,3,5-triiodobenzoic acid (TIBA) to alter ion absorption, respiration, carbon metabolism, and the permeability of the cell membranes of excised barley roots has been examined. Roots pretreated in either H(2)O, KCl, or TIBA followed by treatment in KCl, TIBA, or KCl and TIBA demonstrated that inhibition of ion uptake due to TIBA was reversible. These studies also suggest that ions already accumulated within the vacuole remain sequestered after the addition of TIBA, whereas cytoplasmic ions leak out into the external medium. A 20-minute lag period was present prior to the onset of inhibition of O(2) consumption by TIBA. A b-type cytochrome from corn that is apparently associated with the plasmalemma and possibly involved in respiration or ion uptake, or both, was unaffected by TIBA. The addition of TIBA to treatment solutions resulted in the synthesis and accumulation of ethanol. Analysis of organic acids showed that only the malate concentration was affected by treatment with TIBA. A reduction of 26% was noted for malate in the presence of 2 micromolar TIBA. These combined results suggest that the inhibitory action of TIBA in barley roots involves an alteration of mitochondrial respiration and not a direct depolarization of the plasmalemma.

The properties of potassium transport in carrot (Daucus carota L.) suspension culture cells and their isolated protoplasts were examined. Cells cultured in Murashige and Skoog (MS) medium (Plant Physiol 15: 473-497) were potassium saturated and, consequently, they exhibited little net potassium accumulation. Cells that transport and accumulate potassium were derived from the MS-grown cells by culturing them in a potassium-free modified medium. The transport properties of the modified medium cells included: (a) smooth nonsaturating kinetics with 80% of the maximum rates occurring at 0.1 millimolar KCl, (b) linear transport for at least 75 min, (c) alkaline pH optimum, (d) little accompanying anion uptake with increased malate concentrations balancing net increases in positive charge, and (3) little effect on transport by plasmolysis. Potassium transport activity appeared to be 50% lower in protoplasts isolated from the modified medium cells. Nevertheless, the protoplasts exhibited essentially the same kinetics, time course, pH response, and malate adjustment as the intact cells. We concluded from these results that the low potassium cells and their isolated protoplasts are ideally suited to investigating potassium transport at the cell level without the complications associated with multilayered and highly differentiated tissues.

The selective preference of Chlorella pyrenoidosa for alkali metal cations was found to have the order Rb > K > > > Na. It was demonstrated that a cation of higher preference can replace in the cell cations of lower preference by an ion interchange process.The replacement of Na from the cell by K or Rb occurred against high external Na concentrations up to 450 meq/1 Na.It is suggested that the structural selectivity of the Chlorella cell may be amplified by a chromatographic type repetitive selection process, driven by metabolically dependent unsymmetric shape changes of cellular membranes.

The Na and Rb permeability of Chlorella pyrenoidosa were estimated from the rates of radioisotope self-diffusion.The isotopic exchange in absence of net ionic movements followed first order kinetics. This suggested that for sodium, which reached isotopic equilibrium in approximately 90 minutes, the cell behaved as 1 compartment with respect to isotopic exchange. Rubidium in 180 minutes approached isotopic equilibrium by 67%; thus, the existence of a single compartment for Rb has not been demonstrated. Net fluxes, calculated from the isotope exchange data, and expressed on a dry weight and surface area base showed that Na fluxes were approximately 7 times larger than Rb fluxes. Net Na fluxes of 90 milli-equivalents per 100 g dry weight per hour were far in excess of the observed maximum net accumulation of Na. However, Rb fluxes of 13 milliequivalents per 100 g dry weight per hour were of similar magnitude as the rate of Rb accumulation. Thus, permeability could be a limiting factor for Rb but not for Na accumulation. Sodium and Rb fluxes in absence of net ionic movements were inhibited by low temperature, dark air and dark N(2) conditions. This change in flux rates was explained mainly on the basis of metabolically dependent changes in the cell surface layers.Isotope fluxes of Rb were drastically reduced in dark air and dark N(2) in the absence or presence of net cation movements. Dark N(2) essentially eliminated net cation accumulation, whereas dark air had relatively little effect on the net K and Rb accumulation by Chlorella. Thus the 2 major factors involved in net cation accumulation in the Chlorella cell, permeability and processes leading to cation retention, respond differently to metabolic inhibition permitting a separation of these 2 important aspects of cation accumulation.