Cell elongation and revolving movement in Phaseolus vulgaris L. twining shoots

In Phaseolus vulgaris L., the shoot displays a revolving movement that occurs rhythmically in a highly regular manner. Previous data led to think that revolving movement is driven by turgor and volume changes in the epidermal cells of the bending zone. To document this hypothesis, the time course of in situ cell length variations in the bending zone was measured during the movement of the shoot and related to the phase of the revolving movement. Each ten minutes, a photograph of cells was taken and the revolving movement was simultaneously recorded using time-lapse microphotography and video-monitoring. In the moving part of the shoot, epidermal cells displayed partly reversible length variations during their growth. Data were processed by Fourier analysis to determine whether or not a periodicity exists. Rhythm in cell length variations was evidenced only when initial cell lengths were ranged between 60 and 120 mu m. In this case, the period corresponds to that of the revolving movement. Thus, revolving movement is related to partly reversible length variations in the cells of the bending zone. These results agree with the hypothesis of an involvement of turgor mediated volume changes in the revolving movement.