| High salt stress disrupts homeostasis in water potential and ion distribution. This disorder of homeostasis occurs at both the cellular and the whole plant levels. Drastic changes in ion and water homeostasis lead to molecular damage, growth inhibition and even death. Therefore, one important strategy for plants to survive under salt stress is to re-establish the homeostasis in high salt environment. Both ionic and osmotic homeostasis must be restored. The present article analyzed the effect of NaCl stress on the activities and subunits expressions of tonoplast H+-ATPase and H+-PPase, discerned the role of tonoplast H+-ATPase, H+-PPase and Na+/H+ antiporter on the sequestration of Na+ into the vacuole with halophyte Suaeda salsa. The transgenic Arabidopsis plants co-overexpressing of SsNHXI and A VP1 were also been analyzed to examine salt tolerance of the transgenic plants. The results were shown as follows:1 . cDNA cloning and sequence analyzing of subunits B, H and c of tonoplast H+-ATPase in halophyte Suaeda salsaFull cDNA sequences encoding tonoplast H+-ATPase subunits B, H and c were isolated from the cDNA library of halophyte Suaeda salsa through EST analysis. The cDNA of subunit B was 1470 nucleotides long coding for 489 amino acids with a conservative ATP binding site "324-SGSIT-328" and a predicted molecular mass of 54.29 kDa. Amino acid sequence alignment analysis suggested that the V-H+-ATPase B subunit of S. salsa had high homology with other reported V-H+-ATPase subunit B. The H+-ATPase subunit H from S. salsa was a hydrophilic protein with 465 amino acids and a predicted molecular mass of 52.8 kDa, which was encoded by a cDNA with 1398 nucleotides in ORF. Blast analysis indicated that the H+-ATPase subunit H from S. salsa had a high amino acid sequence identity with those coming from plants, but had relatively low sequence identity with those coming from other species. The ORF of the cDNA encoding the H+-ATPase subunit c from S. salsa was 495-bp. The predicated protein had 164 amino acids with amolecular mass of 16.6 kDa. Hydrophobicity analysis suggested that the V-H+-ATPase subunit c from 5. salsa was a transmembrane protein with four transmembrane domains. Earlier experiments indicated the conserve glutamyl residue in the fourth transmembrane domains might participate in the proton translocating across the membranes.CluxtalX analysis indicated that the V-H+-ATPase B, H and c subunits from halophyte S. salsa had high amino acid sequence identity with subunits from Mesembryanthemum crystallinum, which is an inducible CAM species as its growth rate is maximal at moderate salt concentrations. Sequence alignment results suggested that the evolutions of V-H+-ATPase subunits B, H and c were involved in environmental adaptation and these subunits of V-H+-ATPase might have an important role in responses of plants to salt stress. 2. Effect of NaCl treatment on the subunits expressions and activities of H+-ATPase and H+-PPase from Suaeda salsaNorthern blot analysis indicated that the transcription of V-H+-ATPase subunits B, H and c were obviously up-regulated by NaCl stress. The transcripts of mRNA of B and H subunits in 400 mmol/L NaCl-treated plants were significantly higher than those in control during 0-120h and the mRNA levels of B, H and c subunits were also increased under 100 and 400 mmol/L NaCl treatment. The similar up-regulation of subunit B, H (located in the V1 part) and subunit c (located in the V0 part) indicated a coordinate expression of tonoplast H+-ATPase subunits under salt stress.The transcripts of V-H+-ATPase subunits B, H and c were found in the roots, leaves and stems, which confirmed the housekeeping function of the V-H+-ATPase. The expression of subunits B, H and c were greatly higher in young tissues (4-week-old) than those in old tissues (10- week-old), which clearly indicated that the expression of V-H+-ATPase subunits had relationship with plant development. The salt enhanced expression of V-H+-ATPase subunits in roots, shoots and leaves in both young ari...
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