The phenolic compounds salicylic acid (o-hydroxybenzoic acid) and ferulic acid (4-hydroxy-3-methoxycinnamic acid) inhibited K+ ("Rb+) absorption in excised oat (Avena sativa L. cv. Goodfield) root tissue. Salicylic acid was the most inhibitory. The degree of inhibition was both concentration-and pH-dependent. With decreasing pH, the inhibitory effect of the phenolic increased. During the early stages of incubation, the time required to inhibit K+ absorption was also pH-and concentration-dependent. At pH 4.0, 5 x 10-4 molar salicylic acid inhibited K+ absorption about 60% within 1 minute; whereas, at pH 6.5, this concentration affected absorption only after 10 to 15 minutes. However, at 5 x 10-' molar and pH 6.5, salicylic acid was inhibitory within 1 minute. The capacity of the tissue to recover following a 1-hour treatment in 5 x 10-4 molar salicylic acid ranged from no recovery at pH 4.5 to complete recovery at pH 7.5. The For many years it has been postulated that some plants exert an influence on neighboring plants through the production and release of toxic compounds (13,17). Some of these phytotoxins have recently been shown to inhibit ion absorption (4-6). The most commonly cited class of compounds involved in such toxic activity is that of phenolic compounds, especially derivatives of benzoic and cinnamic acid. Glass (5) efflux from yeast cells in the presence of SA. In a preliminary publication (7), we reported a similar effect of pH and SA on K+ efflux from oat roots. As pH of the medium fell, K+ efflux increased with 5 x 10-4 M SA present. Also, the herbicide 2,4-D inhibited K+ absorption in wheat roots more extensively as pH decreased (18). More recently, Jacobson and Jacobson (9) reported the same effect of pH in barley roots using TIBA. Thus, pH appears to be an important factor to consider when studying phenolic acids and their derivatives.The purpose of this research was to characterize extensively the action of the benzoic acid derivative, SA, on K+ absorption in excised oat root tissue. Our intent was to identify conditions required for inhibition of K+ absorption by SA and to provide the background for studying the physiological processes by which SA acts to inhibit absorption. We investigated the effects of pH, concentration of the inhibitor, and rapidity of action by the compound on K+ absorption. In addition, the absorption of SA itself was measured. We found that pH was a major factor in determining the degree of inhibition of K+ absorption by both SA and FA. We further observed that two parameters, pH and concentration of SA, interacted to produce complex effects on K+ absorption at various times of exposure to SA. MATERIALS

The use of this platelet storage solution in the cryopreservation of platelets yields a significant improvement in their postthaw in vitro recovery and allows for a reduction of the DMSO concentration from 6 to 2 percent, with superior maintenance of in vitro viability and function.

The storage of PCs at refrigerated temperatures inhibits the accumulation of white cell-produced cytokines in the PCs, an effect that could alleviate cytokine-associated febrile transfusion reactions The 4 degrees C storage was also bacteriostatic, which indicates that the storage of PCs at that temperature increases safety by decreasing the potential for sepsis. Thus, the ability to store PCs at 4 degrees C may allow extension of the storage limit beyond 5 days.

A study has been made of the effects of the inhibitors carbonylcyanide n-chlorophenylhydrazone (CCCP), 3-(3,4-dichkophenyl)-1,14dnethyl urea (DCMU), and of anoxia on the lgt-sensitive membrane potential of VaNsneria leaf cells. The present results are compared with the known effects of these inbibitors on ion transport and photosynthesis (Prins 1974 Ph.D thesis). The membrane potential is composed of a diffusion potential plus an electrogenic component. The electrogenic potential is about -13 millivolts in the dark and -80 millivolts in the light. The inhibitory effect of DCMU and CCCP on the electrogenic mechanisms strongly depends on the light intensity used, the inhibition being less at a higher Light intensity. This is of significance in view of the often conflicting results obtained with these inhibitors. With The present results show that the sensitivity of the membrane potential to inhibitors depends very much on the light intensity used. The meaning of this will be discussed. For Nitella it has been shown that the more negative potential in the light is caused by an electrogenic pump (19,20). Generally, it is assumed that this electrogenic pump is a proton extrusion pump; this may be true for Vallisneria also. MATERIALS AND METHODSPlants of V. spiralis were grown aquatically in a plastic tank on a slightly alkaline soil at room temperature (about 20 C).Leaf strips of 20 x 4 mm were mounted in a modified Mertz chamber (12), except for experiments on the effect of 02, in which small (2-mm) leaf strips were used from the margins of the leaves which are devoid of gas-filled intercellar spaces. By doing this a more rapid exchange of 02 between the cells and the medium was obtained. Cells of the epidermis or outer layer of mesophyll were used. Membrane potentials were measured using 3 M KCl-filled glass microelectrodes. The cells were too small to use the classic two-electrode method for membrane resistance measurements, therefore electrical resistances were measured with the single electrode method of Anderson et al. (1), using 10-kHz current pulses between +5 and -5 namp. Over this range the resistance was ohmic and no rectification was observed. Resistances lower than 1.5 Mgl could not be measured accurately with the set-up used.Despite the recent criticism on this method (6)

The effects of the plant growth substances indoleacetic acid (IAA) and fusicoccin on the transmembrane potential of Avena coleoptile cells (at 27-29 C) were studied. Fusicoccin caused hyperpolarization of the membrane potential which started after a lag of less than 20 seconds, and which on average reached -49 my at an external K+ concentration of 1 mm and -75 my at 0.1 mm K+. IAA caused a hyperpolanzation of -25 my starting after a lag of 7 to 8 minutes. These results suggest that fusicoccin and IAA both activate electrogenic H+ extusion.The growth-promoting compounds IAA and fusicoccin (FC)4 cause a variety of plant cells to excrete protons (2-4, 15, 19).The resulting lowered pH of the wall is believed to induce wall loosening and thus cell elongation (8,12,20). These compounds also stimulate K+ uptake, although the effect of FC is much greater than that of IAA (5).In the absence of hormones 02c+ + 0h+ should be equal to 0°K+ + 0lt+ where 0D+ refers to the total K+ influx, both passive and active, and the other symbols are for K+ efflux and for the influx and efflux of H+. If auxin or FC stimulates 0K+ and 0l,+ equally, there will be no change in the membrane electropotential and the process can be described as an electroneutral K+/H+ exchange, but if 0°+ exceeds 0K+ there will be a hyperpolarization of the membrane potential and the proton excretion can be called electrogenic. With both FC and IAA, proton excretion from oat coleoptiles appears to occur at a more rapid rate than K+ uptake (5). We would expect that both FC and IAA should cause a hyperpolarization of the membrane potential starting at the same time as the H+ excretion.Some measurements of the effects of IAA and FC on PD exist, but the results have been inconclusive. Both hyperpolarization (9) and depolarization (14) of the PD in response to IAA have been found for Avena coleoptiles; in the latter case, the measurements were made hours after application of the hormones. FC causes rapid hyperpolarization in squash cotyledons (16), barley roots (18), and corn roots (7), but its effect on Avena coleoptiles has not been determined. ' In this study, we have examined the time course of IAA and FC-induced changes in the PD and have shown both compounds induce hyperpolarization which appears to be related to the proton excretion found earlier. MATERIALS AND METHODSThe plant material consisted of 15-to 20-mm sections cut from 25-to 32-mm long coleoptiles of Avena sativa, cv. Victory. The plants were grown and the sections were harvested as described earlier (1), except that the manipulations and all experimental procedures were carried out under fluorescent illumination. After removal of the leaves, the sections were peeled (19) and before use were preincubated for a minimum of 1 hr and a maximum of 3 hr in a solution containing 1 mm MES-tris (pH 6), 0.1 mM CaC12, and 0.1 or 1 mm KCI.Transmembrane potential differences were measured with pairs of 3 M KCl-filled glass microelectrodes and the electronic equipment described earlier (10). Segment...