Programme Contents

Modelling the response of ion transporters to hyperosmotic shock in cells of salt-sensitive Chara australis and salt-tolerant Lamprothamnium succinctum

We compared the response of salt-sensitive Chara australis and salt-tolerant Lamprothamnium succinctum to hyperosmotic shock. Media osmolarities were increased to 285 mOsmol/kg by adding sorbitol. Current-voltage scans were obtained as function of time in sorbitol medium. The data were modelled by a parallel combination of proton pump, inward and outward rectifiers and background currents (Beilby & Walker, 1996).

The response of Lamprothamnium succinctum was to increase the average membrane potential up to −151 ± 10 mV (n=5) after 148 ± 74 minutes (Al Khazaaly & Beilby, 2007). Modelling indicated increased rate of proton pumping. The half activation potential of the inward rectifier depolarized above the resting membrane potential, so K⁺ ions could be imported into the cell, contributing to turgor regulation. In contrast to Lamprothamnium succinctum, most Chara australis cells became strongly depolarized, conductive and showed varying rate of plasmolysis. The Chara australis proton pump responded to osmotic shock, but did not maintain rates high enough to keep membrane potential negative. Eventually all cells became plasmolysed and their conductance increased considerably to 5.5 S.m⁻² and higher. The failure of Chara to regulate turgor (Bisson & Bartholomew, 1984) appears to arise from insufficient activation of the proton pump to turgor decrease.

Al Khazaaly, S. & Beilby, M.J. (2007). Modeling ion transporters at the time of hypertonic regulation in Lamprothamnium succinctum (Characeae, Charophyceae). Charophytes 1(1): 28-47.

Beilby, M.J. & Walker, N.A. (1996). Modeling the current-voltage characteristics of Chara membranes. I. the effect of ATP and zero turgor. Journal of Membrane Biology 149: 89-101.

Bisson, M. & Bartholomew, D. (1984). Osmoregulation or turgor regulation in Chara. Plant Physiology 74: 252-255.