RNA levels of plasma membrane aquaporins inArabidopsis thaliana

The plasmalemma ofArabidopsis thaliana contains several different aquaporins. These members of the major-intrinsic-protein family are permeable and selective for water. The apparent redundancy of aquaporins might be explained by tissue-specific expression of the corresponding gene. In order to investigate and compare the expression levels of five genes for plasma membrane-intrinsic proteins (PIP), PIP1a, PIP1b, PIP1c, PIP2a, and PIP2b, gene-specific RNA probes were generated by transcription of 3' untranslated regions. The probes were applied in RNase protection assays with RNA from different tissues ofA. thaliana. The experiments revealed that PIP1b-RNA is the prominent PIP messenger in all tissues investigated. The expression levels of the remaining PIPs in comparison to PIP1b are low or very low. The findings indicate, that an explanation for the redundancy of plasma membrane aquaporin genes could not be found in an organ-specific expression of them in adult plants.