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.

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Previous investigations with the electron microprobe reveal that the movements of Samanea leaflets are correlated with massive redistribution of K within the pulvinus. Evidence is now presented that Cl moves with K, whether plants are in white light or darkness, whether or not the amplitude of free running oscillations has damped, and whether or not the rhythm has been rephased by phytochrome photoconversion. The mid-extensor to mid-flexor ratio of K + Cl is correlated with leaflet angle under all conditions. Total Cl in both inner cortex and motor region is approximately 0.6 as high as K. The stoichiometry between Cl and the migratory fraction of K is dose to, but not precsely 1:1 in all regions of the pulvinus, suggesting that other ions or systems may also be involved in the balancing of electrical charges.Paired leaflets of Samanea saman (2) and the related plant Albizzia julibrissin (5) open and close with a circadian periodicity during prolonged darkness, and the phase of these rhythmic oscillations can be altered by a properly timed brief pulse of R3 absorbed by phytochrome (11). Such movements are regulated by differential turgor changes in motor cells of the pulvinus, in turn correlated with massive redistribution of K. It was recently shown that Cl balances about 75% of the migratory fraction of K during the opening phase of the rhythm in Albizzia (9). The present study was undertaken to determine whether the distribution of Cl within the pulvinus changes rhythmically during a long dark period, as does K distribution (5, 7), and whether red light pulses that rephase the rhythm affect both K and Cl equally, or either one preferentially. Samanea was used in these investigations, since its pulvinus also has high levels of Cl, and its phytochrome-regulated phase shift curve has been established (1 1).MATERIALS AND METHODS Experimental Conditions. Samanea saman (Jacq.) Merrill plants were grown from seed in controlled chambers with a 16-hr photoperiod, and the usual 8-hr dark period was extended to provide free running conditions for rhythmic experiments. The beginning of the dark period is designated DD = 0. Growing conditions, light sources for converting phytochrome to Pfr (red light 600-690 nm, 5-min exposure, 1.2 J m-2sec-') and Pr (far red light, 710-750 nm, 1.5-min exposure, 9 J m-1sec-') and the dim green safelight have been described (7,8).Electron Microprobe Analysis. K and Cl were analyzed with an electron microprobe (Acton Laboratories Inc., Acton, Mass.) in lyophilized cross-sections of secondary pulvini with diameters of 0.8 to 1.3 mm, taken from the primary and next two leaves of 6-to 8-week-old plants. The smallest pulvini are the most satisfactory experimentally, since the larger the diameter of the pulvinus, the greater is the likelihood that the section will curl during lyophilization and break during pressing. Most of the data in our graphs are from unbroken sections, but in a few cases where complete sections were not available, data from two halfsections of the same pulvinus ...

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