中文摘要：

Na^＋／H^＋反向运输蛋白基因（NHX）是在细菌、植物和动物体内普遍存在的一类膜蛋白基因家族。迄今已在模式植物拟南芥中分离出AtNHX1、AtNHX2、AtNHX3、AtNHX4、AtNHX5和AtNHX6共6个成员，并发现部分成员对盐胁迫有不同程度的响应。以AtNHX1和AtNHX6的cDNA核苷酸序列为信息探针，基于可利用的杨树EST数据库和毛果杨全基因组测序结果，通过电子杂交辅助的克隆技术，从毛白杨形成层cDNA中分离得到长度分别为1635bp和1709bp的2个cDNA，其分别含有编码544个和526个氨基酸残基的完整开放阅读框。由它们所推导的蛋白质序列与拟南芥、水稻、小麦和玉米的NHX1和NHX6基因的蛋白质序列高度同源，同源性分别为79％、76％、69％和74％以及82％、82％、27％和26％，故将其命名为PtNHX和PtNHX6（GenBank注册号分别为AY660749和AY832912）。Southern杂交分析表明，PtNHX和PtNHX6均为低拷贝基因（或有一些高度同源的基因），在杨树基因组中以1—4个拷贝形式存在。组织特异性RT—PCR结果显示，PtNHX1和PtNHX6基因在杨树根、茎和叶片中均有表达，但其表达模式稍有不同：PtNHX1在根部、形成层、未成熟木质部、成熟叶和嫩叶中均高度表达，在韧皮部和成熟木质部中有少量表达，而PtNHX6在根部、成熟叶和嫩叶中表达丰度较高，在韧皮部、形成层、未成熟木质部表达丰度较低，在成熟木质部中表达丰度极低。NaCI诱导的杨树叶片差异表达RT-PCR检测结果初步表明，PtNHX1和PtNHX6基因均受盐诱导表达，当溶液中NaCl浓度在100—400mmol·L^-1内，随着盐浓度的提高，PtNHX和PtNHX6基因的表达丰度逐渐增强，但超过400mmol·L^-1后，其表达丰度均有所降低，这与所测定的叶片ABA含量匹配。

英文摘要：

The Na^＋/H^＋ antiporter is a ubiquitous membrane protein gene family of bacteria, plants and mammals. In Arabidopsis thaliana, six NHX isoforms have been identified to date and some of which have a major function in response to NaCl. The Populus NHX1 and NHX6 cDNA isolation was performed by underlying the electronic cloning technique, based on the Populus EST databases and P. trichocarpa genome sequence using AtNHX1 and AtNHX6 nucleotide cDNA sequence information. Two cDNA clones encoding NHX were isolated from the cDNA prepared from cambial zone of Populus tomemosa by the RT-PCR method. These two cDNAs are 1 635 bp and 1 709 bp in length with corresponding open reading frames （ORFs） which are capable of encoding the protein of 544 and 526 amino acids （ aa）, respectively. The deduced aa sequence of the PtNHXI and PtNHX6 （ GenBank accession number AY660749 and AY832912） proteins shares 79% , 76% , 69% , 74% and 82 % ,82 %, 27 % ,26 % identity with the other recently isolated A. thaliana, Oryza sativa, Triticum aestivum and Zea mays NHX1 and NHX6 , respectively. When poplar genomic DNA was digested with selected restriction enzymes and then analysed on a Southern blot, we found one to four bands that were labelled, suggesting a low-copy gene （or a few highly homologous genes） within the poplar genome. Tissue differential expression indicated that PtNHX1 and PtNHX6 transcripts have their mRNA products in roots, stems and leaves, but have some differences in PtNHX1 and PtNHX6 gene. As for PtNHX1 , it was expressed predominantly in roots, cambium, immature xylem, young leaf and mature leaf, with some expression in the phloem and mature xylem zone of the stem. The PtNHX6 transcripts are the most abundant mRNA products in roots, young and mature leaf, and a low-abundance was detected in phloem, cambium and xylem. To confirm the possible regulation of PtNHX1 and PtNHX6 gene expression by NaCl, the RT-PCR detection of the expression abundance of the PtNHX1 and PtNHX6 genes was performed at different N