Diurnal Rb+ Transport from Roots to the Laminar Pulvinus in Phaseolus vulgaris L.

The primary leaves of kidney bean (Phaseolus vulgaris L.) open under light and close in the dark by the deformation of the pulvinus resulting from diurnal distribution changes of K+, Cl−, organic acid (or H+) and NO3−. When Rb+ was added as a tracer of K+ to the seedlings through their roots, it was transported to the pulvinus cells during the light period but not during the dark period. Transpiration occurred vigorously in the light but almost stopped in the dark. We concluded that Rb+ absorbed by the roots was carried to the pulvinus by the transpiration stream.