An estuarine species of the alga Vaucheria (Xanthophyceae) displays an increased capacity for turgor regulation when compared to a freshwater species

Abstract

Turgor regulation is the process by which walled organisms alter their internal osmotic potential to adapt to osmotic changes in the environment. Apart from a few studies on freshwater oomycetes, the ability of stramenopiles to turgor regulate has not been investigated. In this study, turgor regulation and growth were compared in two species of the stramenopile alga Vaucheria, Vaucheria erythrospora isolated from an estuarine habitat, and Vaucheria repens isolated from a freshwater habitat. Species were identified using their rbcL sequences and respective morphologies. Using a single cell pressure probe to directly measure turgor in Vaucheria after hyperosmotic shock, V. erythrospora was found to recover turgor after a larger shock than V. repens. Threshold shock values for this ability were >0.5 MPa for V. erythrospora and <0.5 MPa for V. repens. Recovery was more rapid in V. erythrospora than V. repens after comparable shocks. Turgor recovery in V. erythrospora was inhibited by Gd(3+) and TEA, suggesting a role for mechanosensitive channels, nonselective cation channels, and K(+) channels in the process. Growth studies showed that V. erythrospora was able to grow over a wider range of NaCl concentrations. These responses may underlie the ability of V. erythrospora to survive in an estuarine habitat and restrict V. repens to freshwater. The fact that both species can turgor regulate may indicate a fundamental difference between members of the Stramenopila, as research to date on oomycetes suggests they are unable to turgor regulate.

Mechanisms underlying turgor regulation in the estuarine alga Vaucheria erythrospora (Xanthophyceae) exposed to hyperosmotic shock

“…We have shown in our previous study that V. erythrospora survives and grows in media with salinities close to that of freshwater (Muralidhar et al . ). A reversed antiporter may be plausible under these conditions, provided the membrane potential and cytosolic pH support the energetics.…”

“…; reported as synonym V. sessilis ), which also regulates turgor as shown in our previous study (Muralidhar et al . ; reported as synonym V. repens ).…”

“…It was subsequently cultured in agarized modified f/2 medium with an osmolality of 247 mOsmol kg −1 , as described previously (Muralidhar et al . ). Osmolality measurements were made with a Wescor (model 5500; Wescor, Logan, UT, USA) vapour pressure osmometer.…”

“…The pressure probe apparatus was as described previously (Muralidhar et al . ). Data acquisition for these probe experiments was conducted with PowerLab 4/20 (Model ML840; ADInstruments, Bella Vista, NSW, Australia) read out using LabChart 7 (version 7.2.1, ADInstruments).…”

“…We have previously reported the ability of Vaucheria repens, a freshwater species, and Vaucheria erythrospora, an estuarine species, to regulate turgor in response to hyperosmotic shock using real-time pressure measurements (Muralidhar et al 2013). V. erythrospora was found to tolerate a wider range of external solute concentrations both in culture over a long period and when exposed to a sudden osmotic change.…”