Gating of Plant Aquaporins
The gating of aquaporins is carried out to stop the flow of water through the pore of the protein. This may be carried out for a number of reasons, i.e. plant contains low amounts of cellular water due to drought. The gating of an aquaporin is carried out by an interaction between a gating mechanism and the aquaporin which causes a 3D change in the protein so that it blocks the pore and thus disallows the flow of water through the pore. In plants it has been seen that there are at least two forms of aquaporin gating. These are gating by the dephosphorylation of certain serine residues, which has been linked as a response to drought, and the protonation of specific histidine residues in response to flooding. The phosphorylation of an aquaporin has also been linked to the opening and closing of a plant in response to temperature.
Plasma membrane intrinsic proteins are found, as their name suggests in the plasma membrane of plant cells. There are two PIP subgroups, PIP1 and PIP2, due to the distinct differences in their peptide sequence. PIP1s commonly have lower water channel activity than PIP2s although it is not understood why. Also not understood, but the water channel activity of PIP1s has been seen to increase when in the tetramer form with PIP2s.