Intracellular pH sensing is altered by plasma membrane PIP aquaporin co-expression

BELLATI JORGE, ALLEVA KARINA, SOTO GABRIELA, VITALI VICTORIA, SUTKA MOIRA,

Buzios, Brasil

Congreso; VII Iberoamerican Congress of Biophysics; 2009

The plant plasma membrane barrier can express aquaporins (PIP1 and PIP2) that show two intriguing aspects: i) the potential of modulating whole membrane water permeability by co-expression of both types, recently been distinguished for showing a differential capacity to reach the plasma membrane (Plant Cell 16:215-28, 2004); and ii), the faculty to reduce water permeation through the pore after cytoplasmic acidification (Nature. 425:393-7, 2003), as a consequence of a gating process. Objectives: Our working hypothesis is that these two key features might enhance plasticity to the membrane water transport capacity if they jointly trigger any cooperative interaction. In previous work, we proved by biophysical approaches that the plasma membrane of the halophyte Beta vulgaris storage root present highly permeable aquaporins that can be shut down by acidic pH (J Exp Bot. 57:609-21, 2006). We took advantage of this preparation to test our proposed hypothesis. Methods: Root Beta vulgaris PIPs were therefore subcloned and expressed in Xenopus oocytes. Results: Co-expression of BvPIP1;1 and BvPIP2;2 not only enhance oocyte plasma membrane water permeability synergistically showing a sevenfold increment but also reinforces pH inhibitory response from partial (75%) to a complete shut down (99%), when lowering cytoplasmic pH to 6.0. This pH dependent behavior shows that PIP1-PIP2 co-expression accounts for a different pH sensitivity by shifting the inhibitory response in almost one pH unit (EC50 pH 6.1 to pH 6.9) compared to BvPIP2;2 expressed alone. Conclusion: These results show for the first time that PIP co-expression impacts modulating the membrane water permeability through the pH regulatory response, enhancing in this way membrane versatility to adjust its water transfer capacity.