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The effect of K deficiency on sucrose transport was studied in bean plants from which the cotyledons had been removed soon after germination and which were subsequently grown in culture solution. Labelled sucrose wassupplied to the primary leaf. Mild Kdeficiency depressed translocation. A statistically significant interaction between the presence of K and light was observed. K deficiency had no effect on translocation if the plants had been placed in the dark before the experiment and remained in the dark during the translocationperiod. Maximum correction for differences in the specific activity of the sugar being translocated, as between control and K‐deficient plants (based on sugar analyses in various plant parts), failed to abolish the K effect when the amount of sugar applied was relatively low (high specific activity). On the other hand no effect of K‐deficiency was observed on translocation when the amount of applied sugar was high (low specific activity). In this case 14CO2 fixation was greatly reduced in the controls, but not in the K‐deficient plants. Significant interaction existed between added sugar and K‐deficiency on 14CO2 fixation. All results reported here can be explained on the basis of a scheme whereby K plays a rôle in reversible intermediate steps between sugar formation in the chloroplast and the entry of this photosynthesised sugar into the “translocation pool” where it mixes with exogenous sugar.

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