Changes of the Apoplastic pH and K+Concentration in thePhaseolusPulvinusin situin Relation to Rhythmic Leaf Movements

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Abstract
The apoplastic pH and K+ concentration of the extensor of the Phaseolus primary-leaf pulvinus in relation to rhythmic leaf movements have been investigated with double-barrelled ion-sensitive micro-electrodes. Simultaneous measurements of leaf movement and ion activities in a fine hole of the extensor in situ showed co-existence of ultradian and circadian leaf movements as well as of ultradian and circadian pH changes in the Water Free Space (WFS) of the extensor apoplast in situ. During circadian leaf movement the H+ and K+ activities in the WFS of the extensor change in an antagonistic manner. When extensor cells swell (upward movement of the lamina) the H+ activity increases from approximately pH 6.7 to 5.9 and the K+ concentration decreases from approximately 50 to 10 mol m−3 and vice versa when extensor cells shrink. These changes in the ionic activities in the WFS must be correlated with large changes in the ion content of the DFS and thus support the hypothesis that the cell walls of pulvinar cells serve as reservoirs for K+ and H+.