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Potassium-linked Chloride Fluxes during Rhythmic Leaf Movement of Albizzia julibrissin¹

^a Department of Biology, Yale University, New Haven, Connecticut 06520

Transverse sections of Albizzia pulvinules were examined with an electron microprobe to determine ion fluxes associated with turgorcontrolled leaflet movements. K⁺ and Cl^– concentrations are high in the flexor and low in the extensor region of closed pulvini. Both ions migrate out of the flexor and into the extensor during opening as previously described for K⁺. The distribution of these elements is significantly correlated in each phase of the rhythmic cycle examined, but only 50 to 60% of the ionic charge of potassium is balanced by chloride. This value increases to 65 to 85% if one considers only the mobile fraction of the potassium.

The increase in concentration of both ions in the extensor region precedes the decrease in the flexor, thus indicating that there must be a storage reservoir for K⁺ and Cl^–. The inner cortex is suggested as such a reservoir, and plasmodesmata are discussed as a probable pathway for ion movement.