| Uptake and translocation of cations play essential roles in plant nutrition, signal transduction, growth, and development. Among them, potassium (K~+) and sodium (Na~+) have been the focus of numerous physiological studies because K~+ is an essential macronutrient and the most abundant inorganic cation in plant cells, whereas Na~+ toxicity is a principal component of the deleterious effects associated with salinity stress. Maintaining a low Na~+, high K~+ state especially in shoot is a bacis strategy for plants to tolerate high soil salinity.SsHKT1 from Suaeda salsa, encodes a cation transporter of HKT family. At first, it was found to be a process to uptake K~+ when plants deprived of potassium. Now HKT-type transporters are shown to function as a K~+-Na~+ cotransporter or Na~+ transporter. It has recently been demonstrated that HKT-type transporters appear to play key roles in salt tolerance. In Arabidopsi, AtHKT1 has been proposed to influx Na~+ into roots, recirculate from shoots to roots, controls retrieval of Na~+ from the xylem or facilitates Na~+ homeostasis.SsHKT1 can complement the Saccharomyces cerevisiae mutant defective in K~+ uptake, suggest that it is a high affinity K~+ transporter but we didn't find SsHKT1 can mediate Na~+ transport in yeast. In this research, SsHKT1 (1.65kb) were inserted into binary plant vector pROKâ…¡. The resulting plasmid were mobilized to Agrobacterium tumefaciens strain GV3101 which was used for plant transformation. The genes were introduced into AtHKT1 mutant sas2-1 (ecotype Landsberg) by Agrobaterium tumefaciens-mediated transformation with floral-dipping method under the control of CaMV 35S promoter. Transformants were selected for their ability to grow on medium containing kanamycin (40mg/L). Several homozygous lines transformed with SsHKT1 were selected and used for further molecular and physiological determination. Whether the gene was transformed into the Arabidopsis was confirmed by PCR and RT-PCR. We want to study the function of SsHKT1 in plant in this method.Molecular and physiological determination result of SsHKT1 homozygous transformants:1. Isolation of the transgenic lines genome DNA as template, PCR analysis indicated that SsHKT1 gene had been integrated into all of the transgenic plants'genomes.2. Total RNA of transgenic lines was isolated, RT-PCR analysis revealed the expression of SsHKT1 gene in T3 plants of transgenic lines.3. The K~+ content in shoot and root of SsHKT1 transgenic lines are much higher than in sas2-1 after different concentration K~+ treatment.4. The Na~+ content of shoot and root in SsHKT1 transgenic lines are similar to that in sas2-1, higher in shoot and lower in root than that in the wild type after different concentration NaCl (0, 50, 75, 100mmol/L) treatment.5. The percentage of surviving plants of transformants are similar to sas2-1, and lower than the wild type after treatment of LiCl.Summarily, expressing of SsHKT1 gene increased K~+ content of transgenic plants under normal or high K~+ treatment. The results suggest that the SsHKT1 is a K~+ thansporter. The transgenic lines appeared salt accumulate in shoot and lower Na~+ content in root which similar to sas2-1 in normal condition and especially in treatment with NaCl. The survival percentage of transgenic plants didn't increased in treatment with LiCl. It shows that SsHKT1 has no much influence to the Na~+ content of transgenic plants. We didn't find the evidence of Na~+ recirculation or xylem retrieval function of SsHKT1.
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