When seedlings ofPhaseolus vulgariswith leaves in the daytime position (almost horizontal to the ground) were turned upside-down during the light period, their leaves moved upward away from the ground after about 20 min and ceased moving after about 1.5 h. But when seedlings with leaves in the night time position (directed downward) were turned upside-down, their leaves moved downward toward the ground after about 30 min and stopped moving about 2 h later. Thus,Phaseolusprimary leaves showed positive or negative geotropic responses that correspohded to the dark or light period.This geotropic response of primary leaves was accompanied by the redistribution of K+, Cl−and NO3- in the laminar pulvinus. These facts suggest that the circadian endogenous clock that is assumed to exist inPhaseolus vulgarishas at least two regulation echanisms; one which measures time and another which determines leaf postition in relation to gravity by changing the ion distribution in the pulvin
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