Short term regulation in plant aquaporin water pathways

KARINA ALLEVA, MOIRA SUTKA, RICARDO DORR, MARIO PARISI AND GABRIELA AMODEO

Río de Janeiro, RJ-Brasil

Congreso; XXVIII Congresso da Sociedade Brasileira de Biofísica, V Congreso IberoAmericano de Biofísica; 2003

SOBLA (Sociedad de Biofisicos latinoamericanos)

Aquaporins are widespread structures that facilitate water exchange. Their presence not only supports their high water permeability role but also holds the molecular basis for its regulation. In plants, aquaporins can affect physiological processes by changing their expression pattern (long-term regulation) or be directly activated/inactivated (short-term regulation). We have previously characterized water transfers in root. The present work presents novel contributions to the characterization of the short-term regulatory mechanisms in plant cell membranes. Results are summarized as follows: Water permeability (Pf) in isolated plasma membrane vesicles protected against dephosphorylation (526±27 mm.s-1, n=6) was not different to non-protected ones (542±40 mm.s-1) implying that dephosphorylation does not inactive these channels. In isolated tonoplast vesicles, Pf is high (297±62 mm s-1, n=5), strongly reduced (84%) with HgCl2 (n=4) and its activation energy is low (Ea=6.5±0.3 kcal.mol-1). All these facts are consistent with water movements through the aquaporin structure. The effect of low pH (5.6) reduces Pf 42% (n=4). In plant plasma membrane vesicles, Pf is higher (526±27 mm.s-1±SEM, n=6) compared to other plasma membranes, slightly inhibited by HgCl2 (20%) and with low Ea (2.9±0.3 kcal.mol-1). At low pH (5.6), Ea is also enhanced (14.1±5.9 kcal.mol-1), and Pf is strongly reduced in agreement with values reported for transport through a lipid bilayer. Divalents cations also affected Pf, Ca2+ showing a strong inhibition (95%) when compared to Ba2+ (only 30%) and Mg2+ (none). Half-reduction in water transport was obtained for 200 mM free Ca2+. Supported by FONCYT PICT/99-5145, UBACyT IJ2003 and IFS-C3052 (GA).