Turgor-mediated Leaf Movements in Analogy With Stomatal Function and Under the General Aspect of Water Flux Through the Plant: II. Rhythmic Transport of 86Rb and 43K in Trifolium repens L. and Oxalis acetosella L.

Abstract

Microautoradiographic methods were applied to trace (86)Rb and (43)K during the migration within the transpiration stream of Trifolium repens L. and Oxalis acetosella L. During the dark phase of the diurnal cycle, ions moved through the petiole to the insertion of the leaf blade. There the movement stopped. In Oxalis the ions gathered in three distinct spots at the adaxial side of the insertion, each belonging to one of the downwards bending leaflets. In Trifolium the areas of ion accumulation were two little humps at the abaxial periphery of the nodal junction of the inwardly bending leaflets. During the phases of upward movement of the leaflets, Oxalis did not reveal a specific pattern of ion distribution within the pulvinus. However, when Trifolium was loaded during the phases of leaflet opening, (86)Rb and (43)K were mainly found within the parenchymatous bundle sheath of the three laminar pulvini and their junction towards the petiole. The conclusion was that ions are stored within small cells on the flexor side and are removed from there by regulatory processes controlling water and solute flux from the sites of storage to the evaporating surfaces of the leaf blade. Implications on the interpretation of nyctinastic leaf movements are discussed.