Electrophysiology of turgor regulation in marine siphonous green algae.
We review electrophysiological measures of turgor regulation in some siphonous green algae, primarily the giant-celled marine algae, Valonia and Ventricaria, with particular comparison to the well studied charophyte algae Chara and Lamprothamnium. The siphonous green algae have a less negative plasma membrane potential, and are unlikely to have a proton-based chemiosmotic transport system, dominated by active electrogenic K(+) uptake. We also make note of the unusual cellular structure of the siphonous green algae. Hypertonic stress, due to increased external osmotic pressure, is accompanied by positive-going potential difference (PD), increase in conductance, and slow turgor regulation. The relationship between these is not yet resolved, but may involve changes in K(+ )conductance (G (K)) or active K(+) transport at both membranes. Hypotonic turgor regulation, in response to decreased external osmotic pressure, is approximately 3 times faster than hypertonic turgor regulation. It is accompanied by a negative-going PD, although conductance also increases. The conductance increase and the magnitude of the PD change are strongly correlated with the magnitude of hypotonic stress.
Bisson
M A
MA
Department of Biological Sciences, Cooke Hall 109, University at Buffalo, Buffalo, NY 14260, USA. bisson@buffalo.edu
Beilby
M J
MJ
Shepherd
V A
VA
D044784:Chara / Q000502:physiology; D004594:Electrophysiology; D056890:Eukaryota / Q000502:physiology*; D009997:Osmotic Pressure