Water channels are important for osmotic adjustments of yeast cells at low temperature.
The importance of aquaporin expression in water permeability in Saccharomyces cerevisiae was assessed by measuring the osmotic water permeability coefficient (P(f)) and the activation energies (E(a)) from both hypo- and hypertonic experiments performed with whole protoplasts from four strains differing in aquaporin level of expression: parental, double-deleted and overexpressing AQY1 or AQY2. Double-deleted (lower P(f)) and AQY1-overexpressing strains (higher P(f)) presented linear Arrhenius plots with E(a) consistent with fluxes mainly through the lipids [16.3 kcal mol(-1) (68.2 kJ mol(-1))] and with a strong contribution of channels [9.6 kcal mol(-1) (40.2 kJ mol(-1))], respectively. The Arrhenius plots for the parental (swelling experiments) and overexpressing AQY2 strains (swelling and shrinking experiments) were not linear, presenting a break point with a change in slope around 23 degrees C. The E(a) values for these strains, calculated for temperatures ranging from 7 to 23 degrees C, were lower [9.5 kcal mol(-1) (39.7 kJ mol(-1))] than the values obtained from 23 to 38 degrees C [17 kcal mol(-1) (71.1 kJ mol(-1))]. This behaviour indicates that only in the lower temperature range did the water fluxes occur predominantly via the water channels. The permeabilities for each strain relative to the deletion strain show that an increase in permeability due to the presence of aquaporins was more relevant at low temperatures. Following our results, we propose that water channels play an important role for osmotic adjustment of yeast cells at low temperature.
Soveral
Graça
G
Faculdade de Farmácia, Universidade de Lisboa, 1649-003 Lisboa, Portugal.|REQUIMTE, Dept Química, FCT-UNL, 2829-516 Caparica, Portugal.
Veiga
Alexandra
A
Centro de Engenharia Biológica, FC-UL, C2, 1749-016 Lisboa, Portugal.|Instituto Superior de Agronomia, 1349-017 Lisboa, Portugal.
Loureiro-Dias
Maria C
MC
Centro de Engenharia Biológica, FC-UL, C2, 1749-016 Lisboa, Portugal.
Tanghe
An
A
Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven and Department of Molecular Microbiology, Flanders Interuniversity Institute for Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium.
Van Dijck
Patrick
P
Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven and Department of Molecular Microbiology, Flanders Interuniversity Institute for Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium.
Moura
Teresa F
TF
REQUIMTE, Dept Química, FCT-UNL, 2829-516 Caparica, Portugal.
D020346:Aquaporins / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D018628:Gene Dosage; D016014:Linear Models; D017711:Nonlinear Dynamics; D009994:Osmolar Concentration; D011523:Protoplasts / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology; D013223:Statistics as Topic; D013696:Temperature; D014867:Water / Q000378:metabolism*; D014882:Water-Electrolyte Balance
C115153:AQY1 protein, S cerevisiae; C422454:AQY2 protein, S cerevisiae; D020346:Aquaporins; D029701:Saccharomyces cerevisiae Proteins; D014867:Water