Change in potassium distribution in a Phaseolus pulvinus during circadian movement of the leaf

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Phaseolus moves its leaves upward and downward with circadian period. This movement of the leaf results from the differential change in the turgor on opposite sides of the pulvinus. Concentrations of K^+, Na^+, Mg^<++>, and Ca^<++> in the upper and lower halves of the pulvinus and the water content of cells on both sides of it were analyzed in relation to the deformation of the pulvinus. The results showed that (1) the pulvinus was de-formed by expansion and contraction of the cells on its opposite sides; (2) among the four cations, the K^+ concentration was markedly high in both halves of the pulvinus; (3) the osmotic pressure of the upper and lower halves were nearly equal during the rhythmic deformation of the pulvinus; (4) the expansion and contraction of the cells on the opposite sides of the pulvinus have a positive correlation only with a change in the K^+ concentration expressed in terms of μmoles per mg protein; (5) the concentrations of other cations such as Na^+, Mg^<++>, Ca^<++>, expressed in terms of μmoles per mg protein, did not change during the circadian deformation of the pulvinus. Thus, the rhythmic K^+ movement seems to be the basis for pulvinar turgor movements. With respect to the mechanism of K^+ movement, three possibilities are discussed.
日本植物生理学会の論文