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Byline: Fengyun Zhao (1,2), Zenglan Wang (1), Quan Zhang (1), Yanxiu Zhao (1), Hui Zhang (1) Keywords: Na.sup.+/H.sup.+ antiporter; Salt tolerance; SsNHX1; Suaeda salsa; Transgenic rice Abstract: Salt stress is one of the most serious factors limiting the productivity of agricultural crops. Increasing evidence has demonstrated that vacuolar Na.sup.+/H.sup.+ antiporters play a crucial role in plant salt tolerance. In the present study, we expressed the Suaeda salsa vacuolar Na.sup.+/H.sup.+ antiporter SsNHX1 in transgenic rice to investigate whether this can increase the salt tolerance of rice, and to study how overexpression of this gene affected other salt-tolerant mechanisms. It was found that transgenic rice plants showed markedly enhanced tolerance to salt stress and to water deprivation compared with non-transgenic controls upon salt stress imposition under outdoor conditions. Measurements of ion levels indicated that K.sup.+, Ca.sup.2+ and Mg.sup.2+ contents were all higher in transgenic plants than in non-transformed controls. Furthermore, shoot V-ATPase hydrolytic activity was dramatically increased in transgenics compared to that of non-transformed controls under salt stress conditions. Physiological analysis also showed that the photosynthetic activity of the transformed plants was higher whereas the same plants had reduced reactive oxygen species generation. In addition, the soluble sugar content increased in the transgenics compared with that in non-transgenics. These results imply that up-regulation of a vacuolar Na.sup.+/H.sup.+ antiporter gene in transgenic rice might cause pleiotropic up-regulation of other salt-resistance-related mechanisms to improve salt tolerance. Author Affiliation: (1) Key Laboratory of Plant Stress, Life Science College, Shandong Normal University, Wenhua East Road No. 88, 250014, Jinan, Shandong Province, PR China (2) Life Science College, Shandong Science and Engineering University, 255049, Zibo, Shandong Province, PR China Article History: Registration Date: 10/11/2005 Received Date: 07/09/2005 Accepted Date: 20/10/2005 Online Date: 28/01/2006 Article note: Fengyun Zhao and Zenglan Wang contributed equally to this work. M. R. Godge and A. Purkayastha made equal contributions and hence should be treated as joint first authors for this paper.