Abstract
Mimosa pudica responds to external stimuli, including touch and heat, and quickly bends its petioles. Water movement through cell membrane occurs during the bending movement, resulting in the rapid loss of turgor pressure of pulvinar extensor motor cells. Thus, aquaporin (AQP) was considered to play a role in this rapid water movement. We have isolated 7 isoforms of plasma membrane intrinsic proteins (PIPs) and examined their water permeability. In the present study, we examine the expression levels of each isoform by RT-PCR. As a result, PIP2;2 and PIP2;3 were expressed in the main pulvinus, and PIP2;2 was abundantly expressed in extensor cells. Change in water permeability of PIPs in response to the rapid movement is thought to be regulated by phosphorylation. Therefore, effects of inhibitors were examined. As results, water permeability of PIP2;2 was improved by the dephosphorylation inhibitor. PKC phosphorylation motif is conserved at the C terminus of PIP2;2, thus mutagenesis was also performed. The result showed that all 3 residues in the motifs of PIP2;2 appear to be important for the phosphorylation-mediated regulation of water permeability.
