(7,14,20,21). Uptake of bromide, chloride and sulfate by excised barley roots is also increased by addition of calcium to the culture solution (3,7,12,20). The presence of calcium and of some other polyvalent cations in culture solutions also influences the ability of roots of barley and many other plants to accumulate potassium in preference to sodium from solutions containing both ions (5, 9).Over the concentration range of about 0.5 to 50 mm, uptake of monovalent cations may be influenced by the accompanying anion (6). When K uptake is limited by anion uptake, addition to culture solutions of calcium salts of anions such as chloride that are rapidly accumulated by excised barley roots may, in addition to any direct effect of calcium ions, stimulate potassium uptake as a result of increased anion uptake. Indeed, Elzam and Hodiges (4) observed that although the addition of CaCl2 to culture solutions increased potassium uptake by excised barley roots, the addition of CaSO4 had no effect. Also, Pitman (17) has shown that slices of beet 1 Present Address: Department of Agricultural Cheniistry, Hokkaido University, Kita-9, Sapporo, Japan. root tissue accumulate more chloride from solutions containing both potassium and calcium than from KCl solutions at the same chloride concentration. Pitman (17) concluded that chloride uptake limited potassium uptake by the beet root tissue and that calcium acted to increase chloride uptake and consequently potassium uptake. The effects of calcium salts on accumulation of potassium and other ions however, are usually attributed to a direct effect of calcium ions without consideration of possible influences of the nature or concentration, of the accompanying anion. The purpose of this study was to attempt to separate the effeicts of calcium ions and the accompanying anion on potassium uptake, and the selectivity for potassium by excised barley roots.
Materials and MethodsExcised barley IHordeum vulgare L., var. Erie) roots were grown essentially as described by Jacobson et al. (9). For each experiment, 50 grams of seed were treated with 75 ml of 10 % '(v/v) HO02 for 10 min. After discarding the H202 solution, the seeds were rinsed with distilled water and then soaked for 24 hr in 1500 ml of aerated distilled water. The seeds were then placed on cheesecloth supported by a nylon screen and covered with another nylon screen and cheesecloth. The screen suipporting the seeds was suspended over 8
PLANT PHYSIOLOGYThe seedlings were grown in a dark chamber at 250. After 2 days the screen and cheesecloth covering the seedlings were removed. After the plants had grown for 3 days, the nutrient solution was replaced with fresh nutrient solution. On the fifth day the nutrient solution was replaced with distilled water and 24 hr later the roots were excised jus't below the screen. The excised roots were rinsed several times with flowing distilled water and placed in 4 liters of aerated distilled water for 1 hr before use in an experiment.The experiments were conducted at 250 using a ratio of ...