Receiv-ed Novem)ber 16, 1956. .Summanwry. Excised roots of barley (Hordcintf vulgare, var. Campana) were incubated in KCl, K2SO, CaCL, and NaCl solutions at concentrations of 10-to 10-2 N.Chanlges in substrate soltution pH, cell sap pH, antI organic acid content of the roots wx ere related to differences in cation and anion absorption. The pH of expressed sap of roots increased when cations were absorbed in excess of anions and decreased wNhen anions were absorbed in excess of cations. The pH of the cell sap shiftedI in response to imbalances in cation and anion uptake in salt solutions as dilute as 10-5. Changes in cell sap pH were detectable within 15 minutes after the rooits were placed in 10-N K2SO. Organic acid changes in the roots were proportional to expressed sap pH chainges induced by unbalanced ion uptake. Changes in organic acid content in respoiise to (lifferenftial cation and anion tupt-ake appear to le associated with the low-vsalt componeiit of ion tiptake.Several investigators (1,5,6,7,8,11, 12) Potassitim, Cl-, and Na+ were extracted by boiling the roots for 10 minutes in each of 3 changes of distilled water (10 ml). The extracts were adjusted to the desired volume by evaporation or dilution. Potassiulm was determined by flame photometric analysis, Na+ by atomic absorption and Cl-by means of a Btuchler-Cotlove automatic chloride titrator. Calcium was determined by flame photometric analysis following oxidation of the sample overnight in a muffle furnace at 4800.Stulfate tuptake was determined with K235S04. After the absorption period, the roots were rinsed for 20 minutes with several changes of non-radioactive 3 X 10-2 N K2S'04. The roots were pressed flat in a planchet anid radioactivity was determined by uise of a gas flow counter. Specific activity of the 35SO2-4 in the substrate solution was estimated by drying an aliquot of the solution in a planchet with 1 ml of a 100 mg/ml sucrose soltttion added to provide self absorption similar to that produtced by the roots.Total organiic acids were determined by the procedure described by Hiatt and Hendricks (5

The influence of NO<-uptake and reduction on ionic balance in barley seedlings (Hordeumn vulgare, cv. Compana) was studied. KNO3 and KCI treatment solutions were used for comparison of cation and anion uptake. The rate of Cl-uptake was more rapid than the rate of NO3-uptake during the first 2 to 4 hours of treatment. There was an acceleration in rate of NO-uptake after 4 hours resulting in a sustained rate of NO3-uptake which exceeded the rate of Cl-uptake. The initial (2 to 4 hours) rate of K+ uptake appeared to be independent of the rate of anion uptake. sorption by roots was balanced by organic acid anion changes, illustrated the intimate involvement of organic acid metabolism in ion accumulation by tissues of higher plants. Subsequently, several investigations have further characterized the nature of the relationship of inorganic ion uptake and organic acid metabolism (4-9, 13-15).The ability of cells to regulate their organic acid anion levels in response to ion uptake imbalances makes it necessary to include organic ion status in any consideration of inorganic ion accumulation. This is particularly pertinent since many organic ions do not readily diffuse through membranes and thus may retain inorganic counterions within a limiting membrane.Under normal physiological conditions, plants absorb similar quantities of inorganic cations and anions, with NO:-being the predominant anion absorbed. Nevertheless, the inorganic cation content in plants is three to six times that of the inorganic anion content (3) because of the reduction and utilization of NO,-.

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The absorption, translocation, and metabolism of N is influenced by the source of N and by the availability and mobility of counter ions for transport. The purpose of this study was to determine the influence of K or Ca on nitrate uptake, translocation, and reduction in barley seedlings (Hordeum vulgare. cv. Compana). Six‐day‐old barley seedlings were grown for 2 to 36 hours in solutions of 1.0 meq/liter KNO3 or Ca(NO3)2, each containing 0.4 meq/liter of CaSO4. Experiments were conducted in a growth chamber at 27 C with a photosynthetic irradiance of 5.3 mW cm−2. Seedlings treated with Ca(NO3)2 (low K) had lower levels of nitrate uptake, nitrate reductase activity, and lower organic acid concentrations than seedlings treated with 1 mM KNO3. The solution pH and the expressed sap pH of roots and shoots of the low K seedlings increased during the experiment. The shoots of the low‐K seedlings had much lower nitrate concentrations and lower levels of nitrate reductase activity than the roots, suggesting that K plays a major role in nitrate translocation. These results support the hypothesis that potassium malate is cycled from the tops to the roots where decarboxylation occurs, providing a source of HCO3‐ for exchange with NO3‐ during absorption.

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