Water and solute transfers are regulated by pH in Beta vulgaris root vacuoles.

MOIRA SUTKA, GABRIELA AMODEO, RICARDO DORR Y MARIO PARISI.

Campinas, Sao Pablo, Brasil

Congreso; IV Congreso de Biofísica del Cono Sur. XXIX Reunión Anual de la Sociedad Argentina de Biofísica; 2000

SAB, Sociedad de Biofisica Brasilera, SOBLA

Vacuoles represent 90% of a plant cell and are responsible of cell volume regulation and pH homeostasis. In this study, vacuoles were isolated from sugar beet root cells, equilibrated in an isotonic mannitol solution and their volume changes studied using videomicroscopy. A rather complex volume response was observed, probably reflecting both water and solute movements when vacuoles were exposed to anisosmotic conditions by modifying mannitol concentration or when mannitol was partial and isosmotically replaced by urea. If vacuoles were pre-incubated in the presence of HgCl2 a reduction in the equilibrium volume was observed under hyposmotic conditions. This reduction was concentration-dependent and prevented by b-mercaptoethanol pretreatment. Volume change was completely abolished with 300 mM HgCl2. Volume changes induced by a hyposmotic challenge were also strongly dependent on medium pH. The response to medium hyposmolarity was completely abolished at pH 6.6, being this effect fully reversible. These results can be interpreted accepting that mercury sensitive water channels are blocked by low pH during the hyposmotic challenge. Unexpectedly, water permeability was apparently not affected by medium acidification in hyperosmotic experiments, while solute (mannitol permeability) would be reduced. It is concluded that proton concentration differently affects water and solute permeabilities during hyposmotic or hyperosmotic challenges