Early salt-stress effects on expression of genes for aquaporin homologues in the halophyte sea aster (Aster tripolium L.)

Six partial PCR fragments that encode aquaporin homologues in the halophyte sea aster Aster tripolium were cloned using genomic DNA and cDNA as templates. The deduced amino acid sequences were highly similar to those of other major intrinsic proteins (MIPs) in plants. The expression patterns of sea aster mip genes in leaves and suspension-cultured cells during a 24-hr NaCl stress period were studied with PCR samip (sea aster major intrinsic protein) fragments. Three samip (A-C) fragments were obtained by PCR with genomic DNA as templates, and 3 samip (D-F) fragments were obtained by RT-PCR Among the 6 genes, expression of Samip A, B and C was significantly inducible by salt stress. The level of Samip A, B and C mRNAs was dependent on NaCl concentration in both whole plants and cultured cells. However, no significant accumulation of Samip transcripts was observed in salt-adapted cells. These observations suggest that Samip A, B and C genes play an important role in the early salt-adaptable stage in sea asters.