ARE K-ATPASES OF THE PLASMA-MEMBRANE INVOLVED IN THE CONTROL AND GENERATION OF CIRCADIAN RHYTHMICITY IN PULVINAR MOTOR CELLS OF PHASEOLUS( CHANNELS AND H+)

The circadian leaf movement of Phaseolus coccineus L. is mediated by i on fluxes across the plasma membrane of the pulvinar motor cells. H+-A TPases and K+ channels of the plasma membrane are key molecules which produce the responses to external and internal signals by directing th e flow of ionic osmotica for the swelling and shrinking of the pulvina r motor cells. We investigated the involvement of these molecules in t he circadian rhythmicity of the Phaseolus pulvinus by testing the phas e-shifting effects and/or the period-changing effects of inhibitors of the plasma membrane H+-ATPase, of other treatments which reduce the H + transport across the plasma membrane, and of the K+ channel blocker TEA on the leaf movement rhythm. Four hour pulses of vanadate (0.4 mM) and erythrosin B (8 mu M), of low temperature (3-6 degrees C, down fr om an otherwise constant 23 degrees C) and of TEA (4 mM) shift the pha se of the leaf movement rhythm. The phase response curves are similar in shape and resemble those for cyanide and azide (Mayer, 1981), but d iffer from that of cycloheximide (Mayer and Knoll, 1981). All of these compounds, as well as citrate buffers (10 mM) with pH 4 and 3, shorte n the circadian period when offered continuously via the transpiration stream to the leaves. However the period is not significantly changed by molybdate. These results consistently support the hypothesis that all treatments which inhibit the H+-ATPases and the K+ channels of the plasma membrane and in turn depolarize the membrane potential produce phase shifts or period shortening of the circadian clock controlling leaf movement in Phaseolus. This indicates that the H+-ATPases and the K+ channels of the plasma membrane are key molecules in the coupling of external signals to the circadian clock of pulvinar motor cells and are probably also essential elements of the causal loop generating th e circadian periodicity of the Phaseolus pulvinus.