The idea that aquaporins may only allow permeation of neutral solutes has been challenged. Members of the group led by Caitlin Byrt, Manchun Zhao and Steve Tyerman have reveal that AtPIP2;1 is permeable to both water and Na+ in heterologous systems. The AtPIP2;1 ionic conductance is inhibited by low pH and Ca2+ similar to previous observations for non-selective cation channels indicating that AtPIP2;1 is a candidate for facilitating Na+ flux across the plasma membrane of root cells and other cells that express PIP2;1, such as guard cells.
Manchun Zhao from her PhD examined the osmotic permeability and CO2 permeability of plasma membranes isolated from leaves to assess co-transport through aquaporins. The permeability to CO2 was not limited by unstirred layers or limitations from carbonic anhydrase used in the method. While showing very different water permeability, plasma membranes from pea and Arabidopsis showed similar CO2 permeability. The temperature dependence of water and CO2 permeation indicated involvement of aquaporins, however, the inhibition of aquaporins reduced water permeability but not CO2 permeability. The two permeabilities were positively correlated but only weakly. These observations help our understanding of the role of aquaporins in mesophyll conductance to CO2, and the proposed co-regulation of water and CO2 transport in leaves.
The two publications about aquaporins are accepted by Plant, Cell & Environment, the link is http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291365-3040/accepted.