Electrophysiology of Turgor Regulation in Marine Siphonous Green Algae

Abstract

Abstract. 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 decrease external osmotic pressure, is 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.

Putting the N in dinoflagellates

“…The Na + versus H + powered-transport in, respectively, marine and freshwater/terrestrial organisms, is however not an absolute rule. For example, the freshwater chlorophyte Ankistrodesmus braunii requires Na + for the transport of ${\mathrm{P}\mathrm{O}}_4^{3-}$, while Charales living in brackish waters typically use H + symporters for nutrient transport (Ullrich and Glaser, 1982; Bisson et al, 2006). The strong negative membrane potential of characean cells is thought to enable H + -symport even in alkaline environments (Bisson et al, 2006).…”

“…For example, the freshwater chlorophyte Ankistrodesmus braunii requires Na + for the transport of ${\mathrm{P}\mathrm{O}}_4^{3-}$, while Charales living in brackish waters typically use H + symporters for nutrient transport (Ullrich and Glaser, 1982; Bisson et al, 2006). The strong negative membrane potential of characean cells is thought to enable H + -symport even in alkaline environments (Bisson et al, 2006). Notably, Charales are also able to use Na + -coupled transport for ${\mathrm{P}\mathrm{O}}_4^{3-}$, urea and Cl - (Sanders et al, 1985; Walker et al, 1993; Reid et al, 2000).…”

Phylogeny and Molecular Evolution of the Green Algae

“…Transplant experiments with the giant-celled Acetabularia, conducted by Joachim Hämmerling, demonstrated that the nucleus of a cell contains the genetic information that directs cellular development, and postulated the existence of messenger RNA before its structure was determined (Hämmerling, 1953). Acetabularia, along with other giant-celled green algae (Valonia, Chara and Nitella), has also served as an experimental organism for electro-physiological research and studies of cell morphogenesis (Menzel, 1994;Mandoli, 1998;Shepherd et al, 2004;Bisson et al, 2006;Mine et al, 2008). The charophyte Mougeotia played a key role in outlining the role of phytochrome in plant development (Winands & Wagner, 1996).…”

Osmosensing and osmoregulation in unicellular eukaryotes

“…While potassium ion flux has been identified as mainly responsible for turgor regulation (Bisson et al 2006), the molecular details of osmotic regulation have not been resolved. Microalgae osmoregulate mainly through the use of contractile vacuoles (Heywood 1978;Buchmann and Becker 2009) and some accumulate compatible osmolytes like glycerol (Avron 1986;Husic and Tolbert 1986), and in some cases mannitol (Iwamoto and Shiraiwa 2005).…”