Dans les cellules végétales, les canaux et les transporteurs anioniques sont essentiels pour les fonctions clés telles que la nutrition, l'homéostasie ionique et la tolérance aux stress biotiques ou abiotiques. Chez Arabidopsis thaliana, les membres de la famille CLC (pour ChLoride Channel), situés sur le tonoplaste, sont requis pour l'homéostasie du nitrate (AtCLCa et AtCLCb) ou impliqués dans la tolérance au sel (AtCLCc).Dans mon travail de thèse, j’ai identifié et caractérisé un canal chlorure, AtCLCg, chez A. thaliana. L'étude de la protéine fusion AtCLCg::GFP a révélé que cette protéine est localisée sur le tonoplaste. Deux lignés mutants indépendants d’insertion ADN-T, atclcg ont été sélectionnés. Les études physiologiques sur ces deux lignés ont démontré qu’AtCLCg joue un rôle dans le passage de chlorure mais pas dans l'homéostasie du nitrate au travers du tonoplaste. En effet, aucune différence de contenu en nitrate (NO3-) racinaire et foliaire n’a été observée entre le sauvage et les mutants dans nos conditions. Par contre, les plantes mutantes présentent un phénotype par rapport au sauvage lorsqu'elles se développent sur milieu de croissance contenant 75 mM NaCl: (i) une diminution de 20% de la masse fraîche ; (ii) une diminution de 16% de la longueur de racines primaires et une réduction de 19% du nombre de racines secondaires ; (iii) une sur-accumulation de 21% et 26% de chlorure et sulfate foliaire, respectivement. Ces phénotypes sont abolis chez les lignés complétées avec 35S::AtCLCg. De plus, les mutants atclcg présentent un phénotype similaire à la présence de 75 mM KCl, mais aucune différence n'est détectée en réponse à 140 mM mannitol. Ce résultat suggère que le phénotype d'hypersensibilité des mutants atclcg dépend du chlorure et non du l'effet osmotique du stress salin.Sachant qu’AtCLCg et AtCLCc partagent un haut degré d'homologie, environ 75% d'identité au niveau des protéines, et que les deux sont impliquées dans la réponse au stress salin de la plante, nous avons généré le double mutant atclcc/atclcg. L’analyse phénotypique a montré que le double mutant ne présente pas un phénotype additif sur milieu de stress 75 mM NaCl. En parallèle, l'analyse de l'expression des gènes a montré qu’AtCLCg est réprimé dans le fond mutant atclcc, et inversement. Par ailleurs, l'analyse de l'expression de gène rapporteur démontre que PAtCLCg::GUS est fortement exprimé dans les cellules du mésophylle alors qu’une forte expression de PAtCLCc::GUS dans les cellules de garde et le pollen est observé. Ainsi, l’ensemble de ces résultats montrent que ces deux protéines AtCLCc et AtCLCg sont impliquées dans la réponse au stress salin de la plante, mais elles n’ont pas de fonction redondante. / In plant cells, anion channels and transporters are essential for key functions such as nutrition, ion homeostasis and, resistance to biotic or abiotic stresses. In Arabidopsis thaliana, members of the ChLoride Channel (CLC) family located on the tonoplast have been shown to be required for nitrate homeostasis (AtCLCa, AtCLCb) or involved in salt tolerance (AtCLCc). In this study, we identified and characterized the chloride channel AtCLCg in A. thaliana. Use of an AtCLCg:GFP fusion revealed the localization of this protein on the tonoplast. Studies on the disruption of the AtCLCg gene by a T-DNA insertion in two independent lines demonstrated that AtCLCg is involved in response to salt stress and not in nitrate homeostasis in our conditions. Although no difference in shoot and root NO3- content is observed, mutant plants show a phenotype compared to wild-type when they are grown on 75 mM NaCl: (i) a decrease by 20% of total plant fresh weight; (ii) a diminution by 16% of primary root length and a reduction by 19% of secondary root number; (iii) an over-accumulation of chloride and sulfate in shoots by 21% and 26% respectively. These phenotypes are abolished in complemented lines with 35S::AtCLCg. atclcg mutants show a similar phenotype in the presence of 75 mM KCl, but no difference is detected in response to 140 mM mannitol. This result suggests that the hypersensitivity phenotype of atclcg mutant depends on the ionic component and not on osmotic effect of salt stress.Knowing that AtCLCg and AtCLCc share a high degree of homology, approximately 75% of identity at protein level, and both are involved in response to salt stress, we generated a clcc/clcg double mutant. Phenotypic analysis showed that the two KO mutations do not have additive effect under salt stress of 75 mM NaCl. In parallel, gene expression analysis showed that AtCLCg is repressed in the clcc mutant background, and conversely. Expression analysis of reporter gene displayed a different pattern for PAtCLCg::GUS, strongly expressed in mesophyll cells, compared with a strong expression of PAtCLCc::GUS in guard cells and pollen. Altogether these results demonstrate that both AtCLCc and AtCLCg are involved in response to salt stress but they are not functionally redundant.

Submitted by Mario BC (mario@bc.ufrpe.br) on 2017-02-15T13:51:50Z No. of bitstreams: 1 Maria Isabel Leite da Silva.pdf: 1411757 bytes, checksum: d3a9e59e473802e999997d511c7d2197 (MD5) / Made available in DSpace on 2017-02-15T13:51:50Z (GMT). No. of bitstreams: 1 Maria Isabel Leite da Silva.pdf: 1411757 bytes, checksum: d3a9e59e473802e999997d511c7d2197 (MD5) Previous issue date: 2015-11-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Salt stress is a present threat to agricultural production, especially where irrigation makes it necessary for forage crops for animal feed. To minimize this problem, an alternative that has been identified as promising is the use of silicon (Si) via fertilizer, due to the addition of this mineral increase tolerance to salinity of poaceae. Thus, the objective was to evaluate the effect of silicon fertilization on the growth and chemical- bromatological composition of Brachiaria brizantha cv. MG5 in salt stress conditions, using four concentrations of sodium chloride (0, 20, 40 and 60 mmol L-1, equivalent to the electrical conductivity 0, 3.9, 7.5 and 10.9 dS m-1, respectively), and silicon concentrations (0, 1, 2, 3 and 4 mmol L-1) in the nutrient solution, and three cutting times. The experiment was completely randomized in a factorial 4 x 5 x 3 with four replications, where the experimental plot was represented by a pot containing a plant. In the biggest changes in chemical-bromatological composition were due to the sodium chloride concentration in the solution three cuts made. In the three studied cuts the high concentrations of sodium chloride accelerated senescence, reduced growth and nutritive value of Brachiaria brizantha cv. MG5. The concentration of 4 mmol L-1 Si minimized the deleterious effects of sodium chloride in the regrowth of Brachiaria brizantha cv. MG5 in the last two cuts, improving growth. However, the applications of silicon levels were not sufficient to mitigate the deleterious effects of sodium chloride in nutritional value and dry matter production of Brachiaria brizantha cv. MG5 in the three cuts. / O estresse salino é uma ameaça presente na produção agrícola, especialmente onde a irrigação se faz necessária para o cultivo de forragem para a alimentação animal. Para minimizar tal problema, uma alternativa que vem sendo apontada como promissora é o uso do silício (Si) via adubação, em virtude da adição deste mineral aumentar a tolerância das poáceas à salinidade. Dessa forma, objetivou-se avaliar o efeito da adubação silicatada sobre o crescimento e a composição químico-bromatológica da Brachiaria brizantha cv. MG5 em condições de estresse salino, utilizando-se quatro concentrações de cloreto de sódio (0; 20; 40 e 60 mmol L-1, equivalentes às condutividades elétricas 0; 3,9; 7,5 e 10,9 dS m-1, respectivamente) e cinco concentrações de Si (0; 1; 2; 3 e 4 mmol L-1) na solução nutritiva, e três épocas de corte. O experimento foi em delineamento inteiramente casualizado em esquema fatorial 4 x 5 x 3, com quatro repetições, onde a parcela experimental foi representada por um vaso contendo uma planta. Nos três cortes realizados as maiores alterações da composição química-bromatológica ocorreram em função das concentrações do cloreto de sódio na solução. As concentrações altas de cloreto de sódio aceleraram a senescência, reduziram o crescimento e o valor nutritivo da Brachiaria brizantha cv. MG5. A concentração de 4 mmol L-1 de Si minimizou os efeitos deletérios do cloreto de sódio na rebrota da Brachiaria brizantha cv. MG5 nos dois últimos cortes, melhorando o crescimento. No entanto, as aplicações dos níveis de silício não foram suficientes para atenuar os efeitos deletérios do cloreto de sódio no valor nutritivo e na produção de massa seca da Brachiaria brizantha cv. MG5 nos três cortes estudados.

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior / Embora se tenha muitos estudos sobre estresse salino, pouco se conhece sobre os mecanismos individuais de sÃdio (Na+) e cloro (Cl-) na fisiologia de plantas expostas à salinidade. Baseado nisso, objetivou-se, atravÃs deste estudo, avaliar a extensÃo com que os Ãons Na+ e Cl- sÃo acumulados em diferentes partes jovens de feijÃo-caupi [Vigna unguiculata (L.) Walp.] e as suas possÃveis interferÃncias sobre as medidas de transpiraÃÃo. Para comprovar a hipÃtese que os Ãons Na+ e Cl- apresentam modelos diferentes de distribuiÃÃo nas partes vegetativas de feijÃo-caupi e que esse processo nÃo à afetado pela temperatura, foi organizada uma seqÃÃncia metodolÃgica envolvendo trÃs experimentos, onde o experimento I consistiu em avaliar a distribuiÃÃo de Na+ e Cl- em partes jovens de feijÃo-caupi submetido a concentraÃÃes crescentes de NaCl (0; 25; 50; 75 e 100 mM) durante 3 dias, onde ocorreu um maior acÃmulo de cloreto em todas as partes estudadas com exceÃÃo do caule que teve acÃmulo similar de ambos os Ãons. Baseado nessa distribuiÃÃo, utilizou-se a concentraÃÃo de 50mM, pois essa concentraÃÃo nÃo superaria a capacidade de armazenamento e, assim, seria possÃvel, nesse nÃvel, uma recuperaÃÃo (foi mantida durante 6 dias em NaCl e, a partir do 4 dia, as amostras foram divididas em dois lotes). Um lote permanecia com NaCl e o outro trocava a soluÃÃo sem NaCl e assim verificar se essa estratÃgia a planta seria capaz de recuperase. Os resultados corroboram com os obtidos no experimento I com exceÃÃo da primeira folha trifoliolada que acumulou mais Na que Cl. A literatura relata, abundantemente, que nas Ãpocas de verÃo (perÃodo do experimento I), principalmente no semi-Ãrido, as plantas acumulam mais Ãons, onde a temperatura à uma medida de fator climÃtico que pode interferir na distribuiÃÃo de Ãons e esse efeito està ligado à transpiraÃÃo. No experimento III, foi avaliado o efeito combinado de estresse salino e de temperaturas elevadas, com concentraÃÃes de 0 e 100 mM de NaCl e exposiÃÃo a temperaturas de 27; 32; 37 e 42ÂC, separadamente, por um fotoperÃodo de 12 horas. Os resultados corroboram com os obtidos, anteriormente, em que o sÃdio concentrou-se mais nas raÃzes e caules das plantas quando tratadas nas duas Ãltimas temperaturas. Em relaÃÃo ao Ãon cloreto, foi verificado um comportamento similar aos experimentos anteriores, pois este se acumulou, em maior proporÃÃo, nas folhas sob temperaturas de 32 a 42ÂC. Notadamente, o acÃmulo de cloreto està associado à quantidade de Ãgua absorvida durante a aplicaÃÃo do estresse. Em relaÃÃo à transpiraÃÃo, os resultados tambÃm corroboram com os anteriores. Dessa forma, conclui-se que, independente da concentraÃÃo, tempo, recuperaÃÃo e temperatura, o sÃdio à mais concentrado na raiz e caule, enquanto o cloreto concentra-se nas folhas. / Although it has many studies on salinity, little is known about the mechanisms of individual Na+ and Cl- in the physiology of plants exposed to salinity. Based on that meant to use this study to evaluate the extent to which the ions Na+ and Cl- are accumulated in different parts of young cowpea [Vigna unguiculata (L.) Walp.] and the possible interference on the steps of perspiration. To prove the hypothesis that the ions present different models of distribution in vegetative parts of cowpea and this process is not affected by temperature. It organized a string surrounding methodological three experiments. Where will I study was to evaluate the distribution of Na+ and Cl- young in parts of cowpea subjected to increasing concentrations of sodium chloride (0, 25, 50, 75 and 100 mM) for 3 days. In what was a greater accumulation of sodium chloride that in all parts studied, except the stem which accumulation in the equivalent proportions. Based on this distribution used with a concentration of 50 mM because it would not exceed the storage capacity and it was possible that a recovery level (it was held for 6 days in NaCl and from the 4th day the samples were divided into two lots. A lot remains NaCl and other exchanges with the solution without NaCl and thus verify that this strategy the plant would be able to recover it. The results corroborated with those obtained in the experiment I except the 1st trifoliate leaves that accumulated more in that Cl. The literature reports that plenty of times in the summer (period of the experiment I), particularly in semi-arid plants accumulate more ions. Where the temperature is a measure of climatic factors that may interfere with the distribution of ions and whether this effect is linked to transpiration. And then we performed the experiment III to assess the combined effect of salinity and high temperatures, in concentrations from 0 to 100 mM NaCl. Exposed to temperatures of 27, 32, 37 and 42 C, separately, during a photoperiod of 12 hours. The results corroborate with those obtained previously in the sodium has focused more on the roots and stems when treated in the last two temperatures. Regarding the chloride ion, was found a behavior similar to previous experiments, as they accumulated in greater proportion in the leaves at temperatures of 32 to 42 C. Notably the accumulation of chloride, is associated withthe amount of water absorbed during the implementation of stress. Regarding transpiration also corroborate the previous results. Thus it appears that regardless of concentration, time, temperature recovery and the ash is more concentrated in the root and stem while chloride is concentrated in the leaves.

O feijÃo-de-corda à uma cultura muito importante na dieta das camadas sociais inferiores. O baixo rendimento dessa cultura faz com que cada vez mais a irrigaÃÃo venha como ferramenta para auxiliar no aumento da produtividade. PorÃm, com o advento da irrigaÃÃo o problema da salinidade aumentou bastante. Neste trabalho, avaliou-se o acÃmulo de sais no solo e a produtividade do feijÃo-de-corda [Vigna unguiculata (L.) Walp.], cv. Epace 10, em funÃÃo da fraÃÃo de lixiviaÃÃo e da salinidade da Ãgua de irrigaÃÃo. O experimento foi realizado durante a estaÃÃo seca na Ãrea experimental do LaboratÃrio de HidrÃulica e IrrigaÃÃo/UFC, seguindo um delineamento em blocos ao acaso, com quatro tratamentos e cinco repetiÃÃes, sendo que cada parcela consistiu de 4 linhas de plantio com o comprimento de 5,0m. No tratamento 1 as plantas foram irrigadas com Ãgua do poÃo (CEa = 0,8 dS m-1), sem fraÃÃo de lixiviaÃÃo; os tratamentos 2, 3 e 4, consistiram de Ãgua salina com CEa de 5,0 dS m-1, sem fraÃÃo de lixiviaÃÃo, com fraÃÃo de lixiviaÃÃo de 0,14 e 0,28, respectivamente. Durante as fases de floraÃÃo e frutificaÃÃo foram feitas quatro avaliaÃÃes de trocas gasosas foliares e trÃs determinaÃÃes dos teores de Na+, Ca+2, K+ e Cl-. Ao final do ciclo foram determinadas parÃmetros de crescimento vegetativo e reprodutivo, bem como o acumulo de sais no solo. A aplicaÃÃo de Ãgua salina provocou acÃmulo de sais no solo, porÃm esses efeitos foram parcialmente revertidos pelo aumento da fraÃÃo de lixiviaÃÃo; a salinidade reduziu a produtividade de grÃo, porÃm nÃo afetou sua qualidade e provocou um aumento de 10% no Ãndice de colheita; a reduÃÃo na produtividade ocasionada pela salinidade da Ãgua deveu-se, em parte, à reduÃÃo na assimilaÃÃo lÃquida de carbono durante as fases de floraÃÃo e frutificaÃÃo, associada aos efeitos osmÃticos e ao acÃmulo de Ãons potencialmente tÃxicos nos tecidos foliares; as fraÃÃes de lixiviaÃÃo nÃo tiveram muita influÃncia na superaÃÃo dos danos provocados pela salinidade sobre a produtividade das plantas. / The cowpea is a very important crop in the diet of the inferior social classes, but its productivity is very low, especially is non-irrigated areas. However, the irrigation in semi-arid areas has been associated to soil salinization. The study had the objective to evaluate the effect of water salinity and the leaching fraction on the growth and the productivity of grains of cowpea plants (Vigna unguiculata), cv, Epace 10. The experiment was set up in the experimental area of the LaboratÃrio de HidrÃulica e IrrigaÃÃo/UFC, during the dry season. A completely randomized block design, with five repetitions, was adopted. Each experimental unit consisted of 4 lines of plantation of 5.0 m. The treatments studied were:: 1. Well water with ECw of 0.8 dS m-1 (without leaching fraction); 2. saline water with ECw of 5.0 dS m-1 (without leaching fraction); 3. saline water with ECw of 5.0 dS m-1 with leaching fraction of 0.14; and 4. saline water with ECw of 5.0 dS m-1 with leaching fraction of 0.28. During the flowering and fruit development four measurements of gas exchange and three determinations ion concentrations (Na+, Ca+2, K+, and Cl-) were performed. At the end of the crop cycle, some parameters of vegetative growth and plant yield, and salt accumulation in the soil were observed. The saline water application provoked salt accumulation in the soil profile, but this effect was partially reverted by the increase of the leaching fraction. Salinity reduced plant yield, but it did not affect its quality and caused a 10% increase in the harvest index. The reduction in plant yield was related, at least in part, to decrease in net assimilation of carbon during flowering and fruit development due to osmotic effects and to accumulation of potentially toxic ions. In general, the increase in leaching fraction did not reduce the effect of the salinity on plant development.

Abiotic stresses are responsible for limiting crop production worldwide. Among diverse abiotic stresses, drought and salinity are the most challenging. Plants under these conditions have diverse strategies for tolerating stress. Osmotic adjustment and osmoprotection occur in plants during salinity and drought stress through accumulation of compatible solutes to a high level without interfering with cellular metabolism. Polyols (sugar alcohols) including sorbitol and ribitol are one such class of compatible solutes. Using plants of wild-type (WT) and three genetically-modified lines of tomato (Solanum lycopersicum cv. ‘Ailsa Craig’), an empty vector line ‘TR22’, and 2 sdh anti-sense lines ‘TR45’, and ‘TR49’ designed to severely limit sorbitol metabolism, the objective of this work was to characterize the sorbitol cycle in tomato in response to abiotic stresses. Sorbitol and ribitol content, as well as the enzymatic activities, protein accumulation, and gene expression patterns of the key sorbitol cycle enzymes ALDOSE-6-PHOSPHATE REDUCTASE (A6PR), ALDOSE REDUCTASE (AR), and SORBITOL DEHYDROGENASE (SDH), were measured in mature leaves in response to drought stress by withholding water and by using polyethylene glycol as a root incubation solution to mimic drought stress, to salt stress by incubating roots in NaCl solution, and to incubation of roots in 100 mM sorbitol and ribitol. A6PR, not previously reported for tomato, and AR both exhibited increased activity correlated to sorbitol accumulation during the drought osmotic, and salt stresses, with SDH also increasing in WT and TR22 to metabolize sorbitol. The level of sorbitol accumulation was considerably lower than that of the common sugars glucose and fructose so was not enough to have a significant impact on tissue osmotic potential but could provide other important osmoprotective effects. Use of the sdh antisense lines indicated that SDH has the key role in sorbitol metabolism in tomato as well as a likely role in ribitol metabolism. Like sorbitol, ribitol also accumulated significantly more in the antisense lines during the stresses. Expression and/or activity of A6PR, AR, and SDH were also induced by the polyols, although it is not clear if the induction was due to a polyol signal, the osmotic effect of the incubation solution, or both. In addition, a unique post-abiotic stress phenotype was observed in the sdh anti-sense lines. After both drought and salt stresses and during a recovery phase after re-watering, the antisense lines failed to recover. This may have been due to their accumulation of ribitol. The sdh anti-sense lines were uniquely sensitive to ribitol but not sorbitol, with an apparent foliar and seed germination toxicity to ribitol. The determination that sorbitol, and perhaps ribitol as well, plays a role in abiotic responses in tomato provides a cornerstone for future studies examining how they impact tomato tolerance to abiotic stresses, and if their alteration could improve stress tolerance.

Soil salinity is a widespread problem that limits crop yield throughout the world. The accumulation of soluble salts in the soil can inhibit plant growth by increasing the osmotic potential of interstitial water, inducing ion toxicity and nutrient imbalances in plants. Over the last decade, considerable effort has been put into developing economical and effective methods to reclaim these damaged soils. Phytoremediation is a technique that uses plants to extract, contain, immobilize and degrade contaminants in soil. The most common process for salt bioremediation is phytoextraction which uses plants to accumulate salt in the shoots, which is then removed by harvesting the foliage. As developing significant plant biomass in saline soils is an issue, a group of free-living rhizobacteria, called plant growth promoting rhizobacteria (PGPR), can be applied to plant seeds to aid plant growth by alleviating salt stress. The principle objective of this research was to test the efficacy of PGPR in improving the growth of plants on salt-impacted soils through greenhouse and field studies. In this research, previously isolated PGPR strains of Pseudomonas putida. UW3, Pseudomonas putida UW4, and Pseudomonas corrugata CMH3 were applied to barley (Hordeum valgare C.V. AC ranger), oats (Avena sativa C.V. CDC baler), tall wheatgrass (Agropyron elongatum), and tall fescue (festuca arundinacea C.V. Inferno). PGPR effects on plant growth, membrane stability, and photosynthetic activity under salt stress were examined. Greenhouse studies showed that plants treated with PGPR resulted in an increase in plant biomass by up to 500% in salt-impacted soils. Electrolyte leakage assay showed that plants treated with PGPR resulted in 50% less electrolyte leakage from membranes. Several chlorophyll a fluorescence parameters, Fv/Fm, effective quantum yield, Fs, qP, and qN obtained from pulse amplitude modulation (PAM) fluorometry showed that PGPR-treated plants resulted in improvement in photosynthesis under salt stress. Field studies showed that PGPR promoted shoot dry biomass production by 27% to 230%. The NaCl accumulation in plant shoots increased by 7% to 98% with PGPR treatment. The averaged soil salinity level at the CMS and CMN site decreased by 20% and 60%, respectively, during the 2008 field season. However, there was no evidence of a decrease in soil salinity at the AL site. Based on the improvements of plant biomass production and NaCl uptake by PGPR observed in the 2008 field studies, the phytoremediation efficiency on salt-impacted sites is expected to increase by 30-60% with PGPR treatments. Based on the average data of 2007 and 2008 field season, the time required to remove 25% of NaCl of the top 50 cm soil at the CMS, CMN and AL site is estimated to be six, twelve, and sixteen years, respectively, with PGPR treatments. The remediation efficiency is expected to accelerate during the remediation process as the soil properties and soil salinity levels improve over time.

Soil salinity is a widespread problem that limits crop yield throughout the world. The accumulation of soluble salts in the soil can inhibit plant growth by increasing the osmotic potential of interstitial water, inducing ion toxicity and nutrient imbalances in plants. Over the last decade, considerable effort has been put into developing economical and effective methods to reclaim these damaged soils. Phytoremediation is a technique that uses plants to extract, contain, immobilize and degrade contaminants in soil. The most common process for salt bioremediation is phytoextraction which uses plants to accumulate salt in the shoots, which is then removed by harvesting the foliage. As developing significant plant biomass in saline soils is an issue, a group of free-living rhizobacteria, called plant growth promoting rhizobacteria (PGPR), can be applied to plant seeds to aid plant growth by alleviating salt stress. The principle objective of this research was to test the efficacy of PGPR in improving the growth of plants on salt-impacted soils through greenhouse and field studies. In this research, previously isolated PGPR strains of Pseudomonas putida. UW3, Pseudomonas putida UW4, and Pseudomonas corrugata CMH3 were applied to barley (Hordeum valgare C.V. AC ranger), oats (Avena sativa C.V. CDC baler), tall wheatgrass (Agropyron elongatum), and tall fescue (festuca arundinacea C.V. Inferno). PGPR effects on plant growth, membrane stability, and photosynthetic activity under salt stress were examined. Greenhouse studies showed that plants treated with PGPR resulted in an increase in plant biomass by up to 500% in salt-impacted soils. Electrolyte leakage assay showed that plants treated with PGPR resulted in 50% less electrolyte leakage from membranes. Several chlorophyll a fluorescence parameters, Fv/Fm, effective quantum yield, Fs, qP, and qN obtained from pulse amplitude modulation (PAM) fluorometry showed that PGPR-treated plants resulted in improvement in photosynthesis under salt stress. Field studies showed that PGPR promoted shoot dry biomass production by 27% to 230%. The NaCl accumulation in plant shoots increased by 7% to 98% with PGPR treatment. The averaged soil salinity level at the CMS and CMN site decreased by 20% and 60%, respectively, during the 2008 field season. However, there was no evidence of a decrease in soil salinity at the AL site. Based on the improvements of plant biomass production and NaCl uptake by PGPR observed in the 2008 field studies, the phytoremediation efficiency on salt-impacted sites is expected to increase by 30-60% with PGPR treatments. Based on the average data of 2007 and 2008 field season, the time required to remove 25% of NaCl of the top 50 cm soil at the CMS, CMN and AL site is estimated to be six, twelve, and sixteen years, respectively, with PGPR treatments. The remediation efficiency is expected to accelerate during the remediation process as the soil properties and soil salinity levels improve over time.

Large, membrane-bound vacuoles of plant cells are suitable organelles for the compartmentation of ions. These vacuoles contain Na+/H+ antiporters for movement of Na+ within the organelle in exchange for H+. They provide an efficient mechanism to prevent the occurance of detrimental outcomes of Na+ accumulation in the cytosol. Identification of AtNHX1 gene that confers resistance to salinity by expressing a Na+/H+ antiport pump facilitates the understanding of the salt stress tolerance mechanisms of plants. The aim of the present study was to isolate and clone the Arabidopsis thaliana AtNHX1 coding sequence for transformation of Nicotiana tabacum plants via Agrobacterium tumefaciens mediated gene transfer. For this purpose, total RNA was isolated from Arabidopsis thaliana plants and cDNA synthesis was performed. AtNHX1 (1614bp) was amplified by using cDNA of Arabidopsis via specific primers. The amplified PCR product was verified by sequencing. AtNHX1 coding sequence was cloned into the plant transformation vector pCVB1 and 10 independent putative transgenic tobacco plants were obtained via Agrobacterium tumefaciens mediated gene transfer sysytem. Transfer of selected 8 putative transgenic plants to soil provided the regeneration of T1 seeds. Germination of the seeds under different salt treatments (0, 50, 100, 150, 200, 250 mM NaCl) was observed for evaluating the salt tolerance of transformed plants. The 82% and 60% of the transgenic T1 seeds were germinated on 150 mM NaCl and 200 mM NaCl containing media, respectively. In contrast the germination percentage of wild type tobacco seeds under 150 mM NaCl and 200 mM NaCl concentrations were 39% and 21%, respectively. The germination rate of the transgenic T1 seeds were significantly higher (p=0,001) when compared to the control seeds especially under high salt stress conditions (150 and 200 mM NaCl). Taken all together, our results demonstrated that the germination efficiencies and growth of the plants transformed with AtNHX1 were higher than the wild type tobacco plants under high salt concentrations.

In this study, 14 days old lentil seedlings (Lens culinaris Medik cv. Sultan), which were subjected to 7 days of drought (20% PEG 6000), and salt (150 mM NaCl ) stress , were examined in a comparative manner for the effects of drought and salt stress treatments. In shoot and root tissues physiological parameters such as wet-dry weight, relative water content, root-shoot lengths, membrane electrolyte leakage, and lipid peroxidation in terms of malondialdehyde (MDA) were determined. H2O2 content, proline accumulation and chlorophyll fluorescence analysis were also performed. Changes in the activity of antioxidant enzymes such as superoxide dismutase (SOD: EC 1.15.1.1), catalase (CAT: EC 1.11.1.6) ascorbate peroxidase (APX: EC 1.11.1.11) and glutathione reductase (GR: EC 1.6.4.2) were observed upon stress treatments. In salt treated lentil seedlings, significant decreases in wet-dry weight, RWC, shoot-root length and chlorophyll fluorescence measurements indicated a sensitivity, when compared to drought treated plants. Higher MDA concentration and higher electrolyte leakage amounts are supported these results. APX, GR and proline seem to play important roles in antioxidant defense against salt stress for both tissues by removing reactive oxygen species and protecting macromolecules and membranes. GR and proline are also maintains the main protective mechanism against drought stress effects. SOD is active in drought stressed roots and salt stressed shoots, where the H2O2 contents are also observed to be increased.

Salinity usually reduces plant growth in terms of height and biomass, but can increase secondary metabolite production. This frequently reported observation in guayule (Parthenium argentatum Gray, Asteraceae) was investigated for possible mechanisms.Osmotic and specific ion effects of four chloride salts (CaCl2, MgCl2, KCl, and NaCl) on leaf anatomical and plant physiological parameters were studied. One-year-old plants of guayule line AZ 2 were grown under two salt concentrations (750 ppm and 1500 ppm) for each salt type (plus a control) in sand culture (semi-hydroponic) for eight weeks under controlled greenhouse conditions in Tucson, Arizona.Growth in height decreased with increasing salt concentration. Shoot dry weight, rubber, and resin contents, however, showed no significant differences between treatments, indicating no effect from either salt concentration or salt type. There was a trend for increasing rubber content with increasing salt concentration, although not statistically significant. At the same time, net CO2 gas exchange rates decreased significantly with increasing salinity.With increasing salt concentration, guayule showed osmotic effects in terms of height, indicating a lower hydraulic conductivity. Although plants of higher salt concentrations utilized significantly less water, they had the same shoot dry weights, rubber, and resin contents. Salt-stressed plants therefore achieved higher water use efficiencies. The diurnal net CO2 gas exchange rates were significantly reduced with increasing salinity; the nocturnal net CO2 gas exchange rates showed no significant difference between the treatments.Anatomically, it was found that the stomata were raised or elevated above the epidermis, and supported by upwardly curving cells. When guayule was grown under salt treatments, the trichomes were found to include deposits of material. Trichomes might act as a detoxification repository for excess ions. Although the physiological significance of raised stomata is unknown, it is hypothesized that the unique combination of raised stomata, indumentum, and multiple layers of palisade parenchyma allows for an overall high photosynthetic capacity and performance. During stress conditions such as salinity or drought, guayule might activate an internal CO2 concentrating mechanism, i.e., bicarbonate/CO2 pump, internal CO2 recycling, or PEP carboxylation activity.