Cation Chelating Agents Affect Leaf Movement via Leakage and not by Inhibition of Contractile Proteins)

Abstract

Vanden Driessche (1978) proposed that EDTA prevents the seismonastic leaf movement (the closing movement) of the pinnules (tertiary pulvini) ofMimosa via inhibition of the contraction of Ca (2)?,?-regulated contractile proteins. However, the effects of EGTA and EDTA on the leaf movement of the laminar pulvinus ofPhaseolus coccineus L. and the primary pulvinus ofMimosa pudica L. are contrary to the effects measured at the tertiary pulvini (pinnules) ofMimosa or Al- bizzia. EGTA and EDTA (5 to 25 m M) inhibit the upward (opening) movement and induce a downward (closing) movement of the laminar pulvinus ofPhaseolus and the primary pulvinus ofMimosa. High EGTA and EDTA concentrations «freeze» these pulvini in the night (closed) position of the leaves, whereas the tertiary pulvini ofMimosa andAlbizzia in the day (open) position. However, there is evidence that these contrary leaf movement reactions of the different pulvini are due to structural differences and not to different actions of these substances. In excised flexor and extensor tissues of the laminar pulvinus ofPhaseolus EDTA and EGTA induce a netto efflux of osmotica in hypotonic solutions. DMSO (5 to 10%, v/v), which change also the permeability of membranes, induces, similar to EDTA, an opening of the pinnules (tertiary pulvini) ofMimosa in light and dark and inhibit the seismonastic or dark-induced closing movement. However, in the laminar pulvinus ofPhaseolus , DMSO (3 to 5 %) induces a closing movement and «freezes» the lamina in the physiological night position. We conclude therefore, that leakage of osmotica induces night (closed) position in such pulvini, which are lowered during the night and elevated during the day, and day (open) position in such pulvini, which are elevated during the night and lowered during the day. Thus experiments with EDTA give no evidence that contractile proteins play an essential role in the mechanism of circadian, nyctin- astic, or seismonastic leaf movements.