Relative Uptake and Translocation of Potassium and Cesium in Barley

The relative rates of uptake of potassium and cesium by excised roots and by intact plants of barley from solutions have been measured by K/sup 42/ and Cs/sup 137/. The results have been expressed as the observed ratio (O.R.): O.R. = (Cs/sup 137//K/sup 42/ plant)/(Cs/sup 137//K/sup 42/ solution). In excised roots, in external concentrations of potassium up to 1.0 meq/l, the O.R. was in the range of 0.15 to 0.25. At a higher concentration (10 meq/U, the O.R. was approximately 0.4, thus indicating a lower selectivity for potassium at this level. In the transfer from root to shoot, a marked effect of potassium concentration on the O.R. was observed. At a concentration of 0.1 meq/l, K/sup 42/was transferred at 10 to 20 times the rate of Cs/sup 137/ (mean O.R. = 0.06). At 10 meq/l, K/sup 42/ was transferred at only twice the rate of Cs/sup 137/ (O.R. = O.5). When the proportions of added stable potassium and cesium in the medium were varied over a very wide range, the O.R. was affected by a factor of less than two. When the rate of potassium uptake was low or when water movement was restricted, the O.R. in the shoots wasmore » greater than unity, showing a greater transference of Cs/sup 137/. (auth)« less