Soil salinity negatively affects agricultural production in Turkey by decreasing the yield and quality. Direct introduction of stress related genes by genetic engineering is one of the most rapid approaches to develop stress tolerant crops. In this study, TaNHX1 gene was isolated from bread wheat and three different local wheat cultivars were transformed with overexpression vectors containing TaNHX1 gene by using Agrobacterium-mediated and particle bombardment gene transfer techniques. Immature embryo and inflorescence of Triticum durum cv. Kiziltan-91 and Triticum aestivum cv. Y&uuml / regir-89 and mature embryo of Triticum durum cv. Mirzabey-2000 were used as an explant. In this manner, totally 8960 and 5650 explants were used during particle bombardment and Agrobacterium-mediated transformation, respectively. Moreover, leaves of Nicotiana tabacum cv. Petit Havana were transformed by TaSTR gene to develop salt resistant transgenic tobacco plants by using Agrobacterium-mediated transformation. Stable expression and inheritance of the transgenes was confirmed by both genetic and molecular analyses. T1 progeny showed segregation of the transgenes in a typical Mendelian fashion in most of the plants. Expression of TaSTRG in tobacco was evaluated by physiological and biochemical analysis, such as germination test, root length and MDA analysis. In addition to the nuclear transformation, chloroplast transformation of tobacco was performed with Xyl10B gene responsible for the synthesis of hyperthermostable xylanase enzyme. Stable integration of transgenes and homoplasmy were confirmed with PCR and Southern blotting.

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Identification of salt- resistant tree species and genotypes is needed for rehabilitation of lands affected by salinity in Mexico. This dissertation consists of four studies for analyzing the responses of Pinus leiophylla seedlings to salt. In the first study, resistance to salt stress was studied in six-month-old seedlings from eight different sources of seed collected from the areas with contrasting precipitation levels. Plants from the xeric areas were shorter and had smaller stem diameters but were less sensitive to salt stress and recovered faster from salt injury compared with the plants from mesic sites, suggesting that morphological and physiological adaptations to drought were helpful with salt stress resistance. In the second study, fascicle needle production and tissue ion accumulation were examined in NaCl-treated three-month-old seedlings from two populations of the xeric origin and two populations from the mesic areas. Seedlings from the xeric population of San Felipe developed fewer fascicles and had shorter needles compared with seedlings from the remaining three populations. NaCl treatment delayed the emergence of fascicles and reduced the fascicle needle production and needle length. However, the extent of needle injury and ion accumulation in shoots were lower in the San Felipe seedlings compared with the other studied populations. In the third study, the effects of branch pruning and seedling size on total transpiration and accumulation of Na+ and Cl- in tissues were examined. Total plant transpiration, as affected by plant size and branch pruning, was correlated with Na+ and Cl- needle concentrations and needle necrosis. Branch pruning reduced ion accumulation in the shoots and needle necrosis levels in short seedlings but not in the tall seedlings. In the fourth study, sprouting and physiological responses of 16 month-old-seedling to salt were examined. NaCl treatment concentrations of 100, 150, and 200 mM reduced gas exchange and root hydraulic conductance, caused needle injury and triggered sprouting of adventitious shoots. Sprouting from the upper parts of the main stem and lateral branches was three times greater with 100 and 150 mM NaCl compared with 200 mM NaCl treatment but, at the base of the stem, sprout numbers were similar for all NaCl treatments.

Control of intracellular ion homeostasis is pivotal to plant salt tolerance. Plants have developed a number of mechanisms to keep ions at appropriate concentrations. Both transporters and channels on the plasma membrane play important roles in this function. Plant cyclic nucleotide-gated channels (CNGCs) in the plasma membrane are non-selective monovalent and divalent cation channels. So far, most studies on plant CNGCs have been conducted on heterologous systems. In planta, reverse genetic studies revealed the role of different CNGCs in cation uptake, transport and homeostasis. However, there is little information available about the functional characteristics of plant CNGCs. Among the 20 members of this protein family in Arabidopsis, only AtCNGC2 has been functionally identified as an ion channel; therefore, more functional characterization needs to be done on other members of this protein family. Several CNGCs were suggested to be involved in K+, Ca2+ and Na+ uptake and transport, but available information is scarce. This study investigated the relationship between CNGC10 and ion transport in Arabidopsis, with a particular emphasis on the involvement of CNGC10 in salt tolerance. Arabidopsis thaliana wild type (WT) and two AtCNGC10 antisense lines (A2 and A3) were used to characterise the impact of different level of salt stress on (i) root growth, ion concentration in tissues, ion fluxes across the root surface and intracellular ion concentration and pH at the seedling stage, and (ii) photosynthesis and ion concentration in tissues at the flowering stage. Plants of both antisense lines had higher K+ and lower Ca2+ and Mg2+ concentrations in shoots than WT plants when grown in non-salt control 1/4 Hoagland solution. Altered K+, Ca2+ and Mg2+ internal concentrations in AtCNGC10 antisense lines compared with WT plants under non-salt conditions indicated disturbed long distance ion transport, especially xylem loading/retrieval and/or phloem loading. The results of ion fluxes across the root surface also suggested that AtCNGC10 might be involved in transport of K+, Ca2+ and Mg2+ in tissue. Under sudden salt exposure, higher Na+ efflux and smaller K+ efflux in both antisense lines suggested that AtCNGC10 channels are involved in Na+ and K+ transport. The shoots of AtCNGC10 antisense lines A2 and A3 contained higher Na+ concentrations and significantly higher Na+/K+ ratios compared to WT, resulting in impaired photosynthesis and increased salt sensitivity in A2 and A3 than in WT plants. In contrast, seedlings of both antisense lines exposed to salt stress had lower shoot Na+/K+ ratios and longer roots than WT seedlings, indicating that A2 and A3 were more salt-tolerant than WT in the seedling stage, likely because growth is less dependent on photosynthesis in the seedling than in the flowering stage. These results suggested CNGC gene might play a different role during different developmental stages and in various plant organs.