Arabidopsis Thaliana plant plasma membrane aquaporins shut down at low citoplásmico pH.

MOIRA SUTKA; KARINA ALLEVA; COLETTE TOURNAIRE-ROUX; MARIO PARISI; CHRISTOPHE MAUREL; GABRIELA AMODEO

Bariloche, Argentina,

Congreso; XXXII Reunión Anual de la Sociedad Argentina de Biofísica - Bariloche Protein Symposium.; 2003

Sociedad Argentina de Biofísica - Sociedad Argentina de Bioquímica y Biología Molecular

Mechanisms that regulate water permeability (Pf) in plants are ba-sic to understand plant responses under limiting factors like abiotic stress. One of the proposed candidates involved in aquaporin modulation is pH (J. Mcmb. Biol., 2002 187:175-184; Plant. J., 2002 30:71-81). In order to understand its action we performed the following approaches: 1 ) At the cell level, isolatcd leaf protoplasts showed very low Pf values (10-20 µ.m.s"') in the presence of an acidic bath medium (pH 5.5) when employing a developed micropi­pette technique combined with video microscopy. 2) At the mem­brane level, when plasma membrane vcsicles were purified and studied using stopped flow spectrophotometry. we found that Pf was blocked by protons when medium pH was lowered on both sides of the membrane. In these experiments, when vcsicles were equilibrated at different pH (final concentration 10 mM of buffer) Pf showed a half-inhibition at pH values of 7.2-7.5. 3) At the mo-lecular level, PIPs were expressed in Xenopus oocytes. In osmotic swelling assays, Pf was markedly sensitive (85%) to a 10 min pre-treatment by sodium acetate (pH 6.0) which induced a marked cy-tosolic acidification. These findings clearly demonstrate not only that pH allows short-term regulation of aquaporin activity but also that these proteins can be directly blocked by an intracellular acidification.