Abstract
There are 11 kinds of plasma membrane intrinsic protein OsPIP in rice plant, which were classified in 1 and 2 subfamilies by amino acid sequence. In our study, OsPIP1 subfamily expressed higher than OsPIP2. On the other hand, by using Xenopus oocytes swelling system, water permeability of PIP1 was low, which was around 1/7 of PIP2. Water transport activity of the oocytes, however, increased when PIP1 was coexpressed with PIP2. We therefore examined expression of OsPIP-GFP fusion protein in Xenopus oocytes with a confocal laser scanning microscope; as a result, the intensity of fluorescence in the plasma membrane of OsPIP1-GFP was low compared to OsPIP2-GFP. From these experiments, the water permeability of OsPIP1 might be originally low, or, localization level may be small even if OsPIP1 has an ability to transport water. There is a possibility that OsPIP1 could more located to plasma membrane of the oocytes by coexpressing with OsPIP2, resulting in higher water transport activity of oocytes. Thus we studied a localization change in the cell of OsPIP1 by using DsRed fusion protein and by immunoelectron microscopy, indicating that OsPIP1 subfamily located besides plasma membrane.
