| Although considerable progress has been achieved in salt tolerant breeding by genetic transformation, few transgenic plants can grow and yield normally under high salinity stress. Salt stress responses in plants are complex processes, which involved in the coordination of multiple genes. Single gene transformation is hard to solve the problem which might need either the multiple gene transformation or cross-breeding of plants containing different stress-tolerance genes. Osmotic adjustment is the main mechanism of salinity tolerance in many plants. The plant has two ways in maintaining homeostasis under salt stress. One is the development of high capacity to synthesize and accumulate compatible solutes, including proline and betaine. The other is to uptake or exclude of some ions through various antiporters and proton pumps. To evaluate the effects of combined salt tolerant mechanisms, BADH gene from Atriplex hortensis was introduced into the T2 progeny of transgenic tomato (L. esculentum 'Moneymaker') line X1OEA1 containing AtNHX1 by Agrobacterium-mediated transformation. PCR, Southern blot, RT-PCR and betaine measurement indicated that BADH was integrated into the genome of T2 progeny of line X1OEA1 and functional properly. Physiological responses of the double gene transplant to 200 mM NaCl treatment, reflected by photochemical efficiency of PSâ…¡(Fv/Fm), relative electronic conductivity (Rc/Rc'), chlorophyll content (Chla~+b, Chla/b) and net photosynthetic rate (Pn), were better than those in X1OEA1. Our results showed that 'multigene transformation' could further improve salt tolerance of plant. Furthermore, we optimized the tomato transformation system. The results proved that Timentin is a better antibiotic than Cefotaxim for the effective transformation of tomato.
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