Long distance transport of potassium in cereals during grain filling in detached ears

Ears of wheat plants ( Triticum aestivum L. cv. Kolibri), which were given different and uniform K + ‐nutrition in two experiments, were cut at 2, 4 and 6 weeks after anthesis at 15 cm below the ear. These detached ears were fed 30 m M (experiment 1) or 15, 30, 60 or 90 m M 86 Rb‐K 2 malate (experiment 2) and 146 m M [ 14 C]‐sucrose. After a pulse period of 6 and 4 h, respectively, the ears were transferred to identical non‐labeled solutions for additional 0, 4, 8 or 20 h. About 50% of the K + and sucrose supplied was absorbed by detached ears. This rate declined with plant age and decreasing transpiration. Within the 6 and 4 h uptake period less than 7% of the absorbed K + , but 20% of the sucrose taken up were incorporated into the grain. During the chase period labeled K + in the grain increased to 15% and 14 C even to 50% of total tracer uptake. Incorporation of labeled K + into the grain was not affected by the previous K + nutrition of the plant and was proportional to the K + concentration in the uptake solution. Transition of K + from xylem into phloem during its acropetal transport is assumed. No evidence was found that the grain itself could control its uptake of K + .