Arabidopsis thaliana plant plasma membrane aquaporins shut down at low cytoplasmatic pH

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

Bariloche, Argentina

Congreso; XXVII Reunión Anual de la Sociedad Argentina de Biofísica, XXXIX Reunión Anual de la Sociedad Argentina de Investigaciones Bioquímicas; 2003

SAB,SAIB

Mechanisms that regulate water permeability (Pf) in plants are basic to understand plant responses under limiting factors like abiotic stress. One of the proposed candidates involved in aquaporin modulation is pH (J. Memb. 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, isolated leaf protoplasts showed very low Pf values (10-20 mm.s-1) 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 vesicles 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 vesicles 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 molecular 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 cytosolic 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.