Unequal distribution of potassium and anions within the Phaseolus pulvinus during circadian leaf movement

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Abstract
Ion and saccharide concentrations in the upper and lower parts of the laminar pulvinus of the primary leaf of Phaseolus vulgaris were measured in relation to the circadian movement. Concentrations of K+, Na+, Ca2+, Mg2+, Cl−, organic acid, NO3−, H2PO4−, fructose and fructose-yielding saccharides in the pulvinus were 75–120, 0.3–0.7, 5–8, 6–12, 40–60, 60–73, 19–35, 2–9 and 1–5 mM, respectively, and the osmotic pressure of the pulvinus was considered to be due to these ions. The cell volume in the expanding part was larger than that in the contracting part. The change of the cell volume altered the molar concentration in the cell sap and therefore the amount of solutes actually transported from the upper to the lower part and vice versa was estimated from the concentration expressed in moles per gram of dry weight. Results showed that K+, Cl−, organic acid (or H+) and NO3− moved from the upper to lower parts or vice versa in the pulvinus in relation to its deformation, keeping the electroneutrality among those ions, whereas Ca2+ and Mg2+ did not move. The difference in the K+ concentration between the upper and lower parts when the leaf was up or down amounted to 30% of the whole osmotic pressure. This lead to the conclusion that the endogenous clock-controlled unequal distribution of K+, Cl−, organic acid (or H+) and NO3− in the pulvinus could be the force for the circadian leaf movement.