Our research aimed to reveal the capacity of intercropping with Medicago sativa-rhizobia in the a... more Our research aimed to reveal the capacity of intercropping with Medicago sativa-rhizobia in the amelioration of grapevine growth in agricultural and a Cd/Pb contaminated soils. A local variety of grapevine was cultivated in monocropping and in intercropping with Medicago sativa inoculated or not with its associated rhizobia. Intercropping with alfalfa induced a significant increase in shoot and root biomass of grapevine in the agricultural soil. However, in the contaminated soil, a slight increase in root biomass was observed. Concerning photosynthesis apparatus, we showed that the presence of Cd and Pb in the soil induced a significant decrease in both CO2 assimilation rate and stomatal conductance. Interestingly, intercropping with alfalfa only and with rhizobia alleviate this effect. Similar results are obtained for chlorophyll and carotenoid content. This was associated with a significant decrease in the malondialdehyde level in leaves and roots of grapevine cultivated in interc...
The Sinorhizobium meliloti microsymbiont of Medicago spp. was used in an antibiosis test against ... more The Sinorhizobium meliloti microsymbiont of Medicago spp. was used in an antibiosis test against Phoma medicaginis and in bioprotection assays of Medicago truncatula JA17 from the pathogen. Among 17 S. meliloti strains isolated from root nodules of M. truncatula and Medicago laciniata grown in Tunisian soils, six showed up to 60% growth inhibition of five P. medicaginis strains isolated from infected field-grown M. truncatula. Two S. meliloti strains with differing in vitro effects on P. medicaginis, 10.16/R6 antagonist and 5M6 non antagonist, were used in a bioprotection assay of M. truncatula JA17 from the pathogen. The inoculation of P. medicaginis caused complete root and stem rotting, and the mortality of all treated plantlets. Inoculation of the antagonist S. meliloti strain 10.16/R6 to M. truncatula JA17 infected with P. medicaginis was associated with a significant 65% decrease of vegetative rotting length, an 80% decrease of plant mortality, an increase of root length, and ...
The effect of glyphosate on richness and structure of the Rhizobiaceae and total bacterial commun... more The effect of glyphosate on richness and structure of the Rhizobiaceae and total bacterial communities in an agricultural soil after different treatments was studied. The herbicide was applied on the soil in the presence or the absence of Medicago sativa plants with or without inoculation with the Sinorhizobium meliloti reference strain RCR2011. Terminal-restriction fragment length polymorphism (T-RFLP) profiling showed that this agricultural soil has a high total microbial and rhizobial genetic diversity. To investigate the impact of the herbicide on microbial activity, fluorescein diacetate (FDA) and a panel of three enzymes (phosphatase, catalase, and protease BAA) were assessed. Depending on the type of enzyme tested, the enzymatic activities responded differently to the action of glyphosate, the presence of M. sativa, and the inoculation with RCR2011. The present work gives original insights into the effect of the herbicide on the rhizospheric area of M. sativa with or without rhizobial inoculation by the fact that glyphosate changes microbial diversity and affects soil enzymatic activities.
ABSTRACT In this work, we have compared the physiological responses of alfalfa plants inoculated ... more ABSTRACT In this work, we have compared the physiological responses of alfalfa plants inoculated with either Sinorhizobium meliloti strain S412 (Cu-tolerant) or S112 (Cu-sensitive) in the presence or absence of 0.5 mM of CuSO4. The addition of copper introduced a decrease of nodules number and their dry weight in both symbioses. The interaction established with the Cu-sensitive strain is more affected by copper than that with the tolerant one. In fact, plants inoculated with the sensitive strain revealed a decrease of shoot and roots dry weight larger than that found on plants inoculated with the tolerant strain. However, under copper supply, Medicago sativa with the Cu-tolerant strain did not show any significant changes in both shoot and root biomass production. Under copper excess, great levels of Cu were detected in different parts of the plant with the two symbioses and a great translocation of Cu to aerial parts was shown with the strain S412. Plants with S412 were able to accumulate large quantities of calcium (Ca) in their roots and nodules. While, Ca content decreased drastically in shoot at 0.5 mM of Cu treatment. Moreover, nodulation with S412 allowed plants to maintain high levels of magnesium (Mg) in all tissues and a high iron (Fe) levels in nodules. Results suggest that this symbiotic pair could be used in phytostabilisation of Cu-contaminated soils.
As our world becomes warmer, agriculture is increasingly impacted by rising soil salinity and und... more As our world becomes warmer, agriculture is increasingly impacted by rising soil salinity and understanding plant adaptation to salt stress can help enable effective crop breeding. Salt tolerance is a complex plant phenotype and we know little about the pathways utilized by naturally tolerant plants. Legumes are important species in agricultural and natural ecosystems, since they engage in symbiotic nitrogen-fixation, but are especially vulnerable to salinity stress. Our studies of the model legume Medicago truncatula in field and greenhouse settings demonstrate that Tunisian populations are locally adapted to saline soils at the metapopulation level and that saline origin genotypes are less impacted by salt than non-saline origin genotypes; these populations thus likely contain adaptively diverged alleles. Whole genome resequencing of 39 wild accessions reveals ongoing migration and candidate genomic regions that assort non-randomly with soil salinity. Consistent with natural selec...
3 ) respectively in saharien and semi arid bioclimatic areas. The characterization of 111 rhizobi... more 3 ) respectively in saharien and semi arid bioclimatic areas. The characterization of 111 rhizobia isolated from nodules of M. truncatula grown on soils from 4 sites, with PCR/RFLP rDNA 16S, showed that S. meliloti was the only Sinorhizobium species in arid areas. Use of REP/PCR emphasized a remarkable genetic polymorphism in this species. The variability between strains is influenced
In this study we investigated effects of Zn supply on germination, growth, inorganic solutes (Zn,... more In this study we investigated effects of Zn supply on germination, growth, inorganic solutes (Zn, Ca, Fe, and Mg) partitioning and nodulation of Medicago sativa This plant was cultivated with and without Zn (2 mM). Treatments were plants without (control) and with Zn tolerant strain (S532), Zn intolerant strain (S112) and 2 mM urea nitrogen fertilisation. Results showed that M. sativa germinates at rates of 50% at 2 mM Zn. For plants given nitrogen fertilisation, Zn increased plant biomass production. When grown with symbionts, Zn supply had no effect on nodulation. Moreover, plants with S112 showed a decrease of shoot and roots biomasses. However, in symbiosis with S532, an increase of roots biomass was observed. Plants in symbiosis with S. meliloti accumulated more Zn in their roots than nitrogen fertilised plants. Zn supply results in an increase of Ca concentration in roots of fertilised nitrogen plants. However, under Zn supply, Fe concentration decreased in roots and increased in nodules of plants with S112. Zn supply showed contrasting effects on Mg concentrations for plants with nitrogen fertilisation (increase) and plants with S112 (decrease). The capacity of M. sativa to accumulate Zn in their nodulated roots encouraged its use in phytostabilisation processes.
World Journal of Microbiology and Biotechnology, 2005
The model legume Medicago truncatula was used to trap natural populations of Sinorhizobium melilo... more The model legume Medicago truncatula was used to trap natural populations of Sinorhizobium meliloti and Sinorhizobium medicae in Tunisian soils to explore their genetic diversity. About 155 Sinorhizobium isolates were trapped from a combination of three soils and four Medicago truncatula populations in order to analyse soil and plant population effects on nodulating Sinorhizobium diversity. The species assignment was done according to the restriction fragment length polymorphism analysis of polymerase chain reaction (PCR/RFLP) of 16S rRNA genes and their infraspecific genetic diversity was assessed with the repetitive extragenic palindromic-polymerase chain reaction (REP-PCR) technique. It appeared that the trapped bacteria were clustered according to the soil of origin, particularly Sinorhizobium medicae isolates. However, regarding the plant population effect, it appeared that no major clustering tendency could be suggested even if the Bulla Regia and Soliman Medicago truncatula populations appeared to nodulate together specific Sinorhizobium medicae genotypes.
ABSTRACT Two cultivars of pea with different sensitivity to bicarbonate (Merveille de Kelvedon, t... more ABSTRACT Two cultivars of pea with different sensitivity to bicarbonate (Merveille de Kelvedon, tolerant and PS210713, sensitive) were cultivated during one month on a nutrient solution containing or not bicarbonate (10 mM). The study indicated that bicarbonate increased the root to shoot ratio much more in the sensitive than in the tolerant one. Bicarbonate reduced iron translocation towards shoots of the two cultivars. This effect was more marked in the sensitive one. The study also showed that bicarbonate provoked a considerable accumulation of iron in roots of the two cultivars. This accumulation was due to iron accumulated in the extraplasm of roots.
The aim of this study was to investigate the effect of NaCl salinity on symbiotic nitrogen fixati... more The aim of this study was to investigate the effect of NaCl salinity on symbiotic nitrogen fixation (SNF) in a Medicago ciliaris-Sinorhizobium medicae symbiosis system, with special emphasis on two genetically pure lines of M. ciliaris developed from germplasm recovered from saline and non-saline lands. Saline treatment (100 mM NaCl) was applied to these two contrasting lines growing in pots in a greenhouse after the appearance of nodules. At the end of the vegetative period, both lines under salt stress registered a decrease in nitrogenase activity, whole plant and organ biomass production and chlorophyll concentration, but the tolerant line TNC 1.8 was much less affected by salt than the sensitive line TNC 11.9. Salinity also provoked a decrease in sucrose phosphate synthase activity (SPS), mainly in TNC 11.9. The decline in leaf SPS in TNC 11.9 was accompanied by salinity-induced membrane oxidative damage in source leaves of the sensitive line, probably induced by a disturbance in soluble sugar/starch partitioning. We report these physiological and biochemical parameters to promote these useful lines as useful germplasm with potential to reveal detailed transcriptomic and metabolomic information and new genetic tools which could assist breeders in improving salinity tolerance and biomass for pasture legumes.
Abstract Hormonal changes in two Medicago ciliaris lines differing in salt tolerance (TNC 1.8 bei... more Abstract Hormonal changes in two Medicago ciliaris lines differing in salt tolerance (TNC 1.8 being more tolerant than TNC 11.9) were studied as possible regulators of growth and symbiotic nitrogen fixation (SNF). After 21 days of saline treatment (100 mM NaCl), four ...
Hormonal changes in two Medicago ciliaris lines differing in salt tolerance (TNC 1.8 being more t... more Hormonal changes in two Medicago ciliaris lines differing in salt tolerance (TNC 1.8 being more tolerant than TNC 11.9) were studied as possible regulators of growth and symbiotic nitrogen fixation (SNF). After 21 days of saline treatment (100 mM NaCl), four ...
The rhizobia present in a single arid region Tunisian soil that nodulate Medicago laciniata and M... more The rhizobia present in a single arid region Tunisian soil that nodulate Medicago laciniata and Medicago truncatula were compared. All isolates, 40 from each host, were Sinorhizobium meliloti based on 16S rRNA polymerase chain reaction restriction fragment length polymorphism (PCR–RFLP) patterns and subsequent confirmation by sequence analysis of the 16S rRNA genes in four representatives from each host species. There was no apparent relationship between Medicago host species of isolation and the nodulating rhizobial genome as determined by repetitive extragenic palandromic PCR. The isolates of M. laciniata were distinguished from those of M. truncatula present in the same soil by variation in PCR–RFLP of nifDK, indicating that this dissimilarity is originally genetic and not geographic. While forming effective symbioses with their own respective isolates, both M. laciniata and M. truncatula formed ineffective true nodules, nodule-like structures, or no nodules at all in cross-inocu...
The purpose of this study was to identify strains of Sinorhizobium meliloti that formed either an... more The purpose of this study was to identify strains of Sinorhizobium meliloti that formed either an effective or completely ineffective symbiosis with Medicago truncatula L. ‘Jemalong A17’ and, subsequently, to determine whether differences existed between their exoH genes. Sinorhizobium meliloti TII7 and A5 formed an effective and ineffective symbiosis with M. truncatula ‘Jemalong A17’, respectively. Using a multilocus sequence typing method, both strains were shown to have chromosomes identical with S. meliloti Rm1021 and RCR2011. The 2260-bp segments of DNA stretching from the 3′ end of exoI through open reading frames of hypothetical proteins SM_b20952 and SM_b20953 through exoH into the 5′ end of exoK in strains TII7 and Rm1021 differed by a single nucleotide at base 127 of the hypothetical protein SM_b20953. However, the derived amino acid sequences of the exoH genes of effective TII7, ineffective A5, and strain Rm1021 were shown to be identical with each other. Therefore, it wo...
Sinorhizobium meliloti strain A5, isolated from root nodules of Medicago truncatula growing spont... more Sinorhizobium meliloti strain A5, isolated from root nodules of Medicago truncatula growing spontaneously in Tunisian dry lands, showed better growth performance under different sodium chloride concentrations than the standard reference strain RCR2011. Strain A5 has the ability to grow even at 684 mM NaCl. Two-dimensional (2D) electrophoretic analysis of the salt effect on proteome profiles revealed the greatest change on the 4th day of exposure. The halotolerant strain A5 showed more upregulated protein spots than the standard RCR2011 strain (23% of the analyzed protein spots vs only 10% in strain RCR2011) and fewer downregulated protein spots (28% vs 69%). Proteins over-expressed in salty medium as determined by Matrix-assisted laser desorption ionization time-of-flight mass spectrometry for both strains were identified as an outer-membrane protein, an L-amino-acid binding periplasmic transporter protein, a 50S ribosomal protein (L25), a heat shock protein, and a putative oxidoreductase protein. Down-regulated proteins were identified as a putative iron-binding periplasmic transporter protein, a putative lipoprotein precursor, a putative spermidine/ putrescine-binding periplasmic transporter protein, and a putative amino-acid binding ABC transporter protein. The profile of strain A5 showed higher over-expression of an oxidoreductase and a heat-shock protein, and specifically an induction of a putative oligopeptide ABC transporter ATP-binding protein.
The capacity of nodulating bacteria to survive in soil containing various heavy metal elements ha... more The capacity of nodulating bacteria to survive in soil containing various heavy metal elements has been investigated with the aim of promoting the revegetation of mining sites with Medicago sp. Soil samples were collected from three different mining sites and one agricultural site at a location north of Tunisia. Heavy metal composition analysis showed that the soil samples were contaminated with different concentrations of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn). The forage plant Medicago sativa was able to grow normally and to develop effective nodules in these contaminated soils. Sinorhizobium sp. strains nodulating Medicago sativa plants grown in these mining soil samples were isolated and characterized. The isolated strains were able to grow in soils containing up to 2.5 mM Zn, 0.3 mM Cd, 1 mM Cu and 2 mM Pb. The bioaccumulation was tested for two contrasting strains for each metal. For Cd, Pb, and Zn, strain S532 (tolerant strain) adsorbed lower amounts of metals than sensitive strain S112. For Cu, tolerant strain S412 absorbed more Cu than sensitive strain S112, even though adsorption was similar for these two strains. Our results support the use of Medicago sativa-sinorhizobium symbiosis for the regeneration and enrichment of moderately contaminated soils.
The aim of this study was to investigate the effect of NaCl salinity on symbiotic nitrogen fixati... more The aim of this study was to investigate the effect of NaCl salinity on symbiotic nitrogen fixation (SNF) in a Medicago ciliaris-Sinorhizobium medicae symbiosis system, with special emphasis on two genetically pure lines of M. ciliaris developed from germplasm recovered from saline and non-saline lands. Saline treatment (100 mM NaCl) was applied to these two contrasting lines growing in pots in a greenhouse after the appearance of nodules. At the end of the vegetative period, both lines under salt stress registered a decrease in nitrogenase activity, whole plant and organ biomass production and chlorophyll concentration, but the tolerant line TNC 1.8 was much less affected by salt than the sensitive line TNC 11.9. Salinity also provoked a decrease in sucrose phosphate synthase activity (SPS), mainly in TNC 11.9. The decline in leaf SPS in TNC 11.9 was accompanied by salinity-induced membrane oxidative damage in source leaves of the sensitive line, probably induced by a disturbance in soluble sugar/starch partitioning. We report these physiological and biochemical parameters to promote these useful lines as useful germplasm with potential to reveal detailed transcriptomic and metabolomic information and new genetic tools which could assist breeders in improving salinity tolerance and biomass for pasture legumes.
Our research aimed to reveal the capacity of intercropping with Medicago sativa-rhizobia in the a... more Our research aimed to reveal the capacity of intercropping with Medicago sativa-rhizobia in the amelioration of grapevine growth in agricultural and a Cd/Pb contaminated soils. A local variety of grapevine was cultivated in monocropping and in intercropping with Medicago sativa inoculated or not with its associated rhizobia. Intercropping with alfalfa induced a significant increase in shoot and root biomass of grapevine in the agricultural soil. However, in the contaminated soil, a slight increase in root biomass was observed. Concerning photosynthesis apparatus, we showed that the presence of Cd and Pb in the soil induced a significant decrease in both CO2 assimilation rate and stomatal conductance. Interestingly, intercropping with alfalfa only and with rhizobia alleviate this effect. Similar results are obtained for chlorophyll and carotenoid content. This was associated with a significant decrease in the malondialdehyde level in leaves and roots of grapevine cultivated in interc...
The Sinorhizobium meliloti microsymbiont of Medicago spp. was used in an antibiosis test against ... more The Sinorhizobium meliloti microsymbiont of Medicago spp. was used in an antibiosis test against Phoma medicaginis and in bioprotection assays of Medicago truncatula JA17 from the pathogen. Among 17 S. meliloti strains isolated from root nodules of M. truncatula and Medicago laciniata grown in Tunisian soils, six showed up to 60% growth inhibition of five P. medicaginis strains isolated from infected field-grown M. truncatula. Two S. meliloti strains with differing in vitro effects on P. medicaginis, 10.16/R6 antagonist and 5M6 non antagonist, were used in a bioprotection assay of M. truncatula JA17 from the pathogen. The inoculation of P. medicaginis caused complete root and stem rotting, and the mortality of all treated plantlets. Inoculation of the antagonist S. meliloti strain 10.16/R6 to M. truncatula JA17 infected with P. medicaginis was associated with a significant 65% decrease of vegetative rotting length, an 80% decrease of plant mortality, an increase of root length, and ...
The effect of glyphosate on richness and structure of the Rhizobiaceae and total bacterial commun... more The effect of glyphosate on richness and structure of the Rhizobiaceae and total bacterial communities in an agricultural soil after different treatments was studied. The herbicide was applied on the soil in the presence or the absence of Medicago sativa plants with or without inoculation with the Sinorhizobium meliloti reference strain RCR2011. Terminal-restriction fragment length polymorphism (T-RFLP) profiling showed that this agricultural soil has a high total microbial and rhizobial genetic diversity. To investigate the impact of the herbicide on microbial activity, fluorescein diacetate (FDA) and a panel of three enzymes (phosphatase, catalase, and protease BAA) were assessed. Depending on the type of enzyme tested, the enzymatic activities responded differently to the action of glyphosate, the presence of M. sativa, and the inoculation with RCR2011. The present work gives original insights into the effect of the herbicide on the rhizospheric area of M. sativa with or without rhizobial inoculation by the fact that glyphosate changes microbial diversity and affects soil enzymatic activities.
ABSTRACT In this work, we have compared the physiological responses of alfalfa plants inoculated ... more ABSTRACT In this work, we have compared the physiological responses of alfalfa plants inoculated with either Sinorhizobium meliloti strain S412 (Cu-tolerant) or S112 (Cu-sensitive) in the presence or absence of 0.5 mM of CuSO4. The addition of copper introduced a decrease of nodules number and their dry weight in both symbioses. The interaction established with the Cu-sensitive strain is more affected by copper than that with the tolerant one. In fact, plants inoculated with the sensitive strain revealed a decrease of shoot and roots dry weight larger than that found on plants inoculated with the tolerant strain. However, under copper supply, Medicago sativa with the Cu-tolerant strain did not show any significant changes in both shoot and root biomass production. Under copper excess, great levels of Cu were detected in different parts of the plant with the two symbioses and a great translocation of Cu to aerial parts was shown with the strain S412. Plants with S412 were able to accumulate large quantities of calcium (Ca) in their roots and nodules. While, Ca content decreased drastically in shoot at 0.5 mM of Cu treatment. Moreover, nodulation with S412 allowed plants to maintain high levels of magnesium (Mg) in all tissues and a high iron (Fe) levels in nodules. Results suggest that this symbiotic pair could be used in phytostabilisation of Cu-contaminated soils.
As our world becomes warmer, agriculture is increasingly impacted by rising soil salinity and und... more As our world becomes warmer, agriculture is increasingly impacted by rising soil salinity and understanding plant adaptation to salt stress can help enable effective crop breeding. Salt tolerance is a complex plant phenotype and we know little about the pathways utilized by naturally tolerant plants. Legumes are important species in agricultural and natural ecosystems, since they engage in symbiotic nitrogen-fixation, but are especially vulnerable to salinity stress. Our studies of the model legume Medicago truncatula in field and greenhouse settings demonstrate that Tunisian populations are locally adapted to saline soils at the metapopulation level and that saline origin genotypes are less impacted by salt than non-saline origin genotypes; these populations thus likely contain adaptively diverged alleles. Whole genome resequencing of 39 wild accessions reveals ongoing migration and candidate genomic regions that assort non-randomly with soil salinity. Consistent with natural selec...
3 ) respectively in saharien and semi arid bioclimatic areas. The characterization of 111 rhizobi... more 3 ) respectively in saharien and semi arid bioclimatic areas. The characterization of 111 rhizobia isolated from nodules of M. truncatula grown on soils from 4 sites, with PCR/RFLP rDNA 16S, showed that S. meliloti was the only Sinorhizobium species in arid areas. Use of REP/PCR emphasized a remarkable genetic polymorphism in this species. The variability between strains is influenced
In this study we investigated effects of Zn supply on germination, growth, inorganic solutes (Zn,... more In this study we investigated effects of Zn supply on germination, growth, inorganic solutes (Zn, Ca, Fe, and Mg) partitioning and nodulation of Medicago sativa This plant was cultivated with and without Zn (2 mM). Treatments were plants without (control) and with Zn tolerant strain (S532), Zn intolerant strain (S112) and 2 mM urea nitrogen fertilisation. Results showed that M. sativa germinates at rates of 50% at 2 mM Zn. For plants given nitrogen fertilisation, Zn increased plant biomass production. When grown with symbionts, Zn supply had no effect on nodulation. Moreover, plants with S112 showed a decrease of shoot and roots biomasses. However, in symbiosis with S532, an increase of roots biomass was observed. Plants in symbiosis with S. meliloti accumulated more Zn in their roots than nitrogen fertilised plants. Zn supply results in an increase of Ca concentration in roots of fertilised nitrogen plants. However, under Zn supply, Fe concentration decreased in roots and increased in nodules of plants with S112. Zn supply showed contrasting effects on Mg concentrations for plants with nitrogen fertilisation (increase) and plants with S112 (decrease). The capacity of M. sativa to accumulate Zn in their nodulated roots encouraged its use in phytostabilisation processes.
World Journal of Microbiology and Biotechnology, 2005
The model legume Medicago truncatula was used to trap natural populations of Sinorhizobium melilo... more The model legume Medicago truncatula was used to trap natural populations of Sinorhizobium meliloti and Sinorhizobium medicae in Tunisian soils to explore their genetic diversity. About 155 Sinorhizobium isolates were trapped from a combination of three soils and four Medicago truncatula populations in order to analyse soil and plant population effects on nodulating Sinorhizobium diversity. The species assignment was done according to the restriction fragment length polymorphism analysis of polymerase chain reaction (PCR/RFLP) of 16S rRNA genes and their infraspecific genetic diversity was assessed with the repetitive extragenic palindromic-polymerase chain reaction (REP-PCR) technique. It appeared that the trapped bacteria were clustered according to the soil of origin, particularly Sinorhizobium medicae isolates. However, regarding the plant population effect, it appeared that no major clustering tendency could be suggested even if the Bulla Regia and Soliman Medicago truncatula populations appeared to nodulate together specific Sinorhizobium medicae genotypes.
ABSTRACT Two cultivars of pea with different sensitivity to bicarbonate (Merveille de Kelvedon, t... more ABSTRACT Two cultivars of pea with different sensitivity to bicarbonate (Merveille de Kelvedon, tolerant and PS210713, sensitive) were cultivated during one month on a nutrient solution containing or not bicarbonate (10 mM). The study indicated that bicarbonate increased the root to shoot ratio much more in the sensitive than in the tolerant one. Bicarbonate reduced iron translocation towards shoots of the two cultivars. This effect was more marked in the sensitive one. The study also showed that bicarbonate provoked a considerable accumulation of iron in roots of the two cultivars. This accumulation was due to iron accumulated in the extraplasm of roots.
The aim of this study was to investigate the effect of NaCl salinity on symbiotic nitrogen fixati... more The aim of this study was to investigate the effect of NaCl salinity on symbiotic nitrogen fixation (SNF) in a Medicago ciliaris-Sinorhizobium medicae symbiosis system, with special emphasis on two genetically pure lines of M. ciliaris developed from germplasm recovered from saline and non-saline lands. Saline treatment (100 mM NaCl) was applied to these two contrasting lines growing in pots in a greenhouse after the appearance of nodules. At the end of the vegetative period, both lines under salt stress registered a decrease in nitrogenase activity, whole plant and organ biomass production and chlorophyll concentration, but the tolerant line TNC 1.8 was much less affected by salt than the sensitive line TNC 11.9. Salinity also provoked a decrease in sucrose phosphate synthase activity (SPS), mainly in TNC 11.9. The decline in leaf SPS in TNC 11.9 was accompanied by salinity-induced membrane oxidative damage in source leaves of the sensitive line, probably induced by a disturbance in soluble sugar/starch partitioning. We report these physiological and biochemical parameters to promote these useful lines as useful germplasm with potential to reveal detailed transcriptomic and metabolomic information and new genetic tools which could assist breeders in improving salinity tolerance and biomass for pasture legumes.
Abstract Hormonal changes in two Medicago ciliaris lines differing in salt tolerance (TNC 1.8 bei... more Abstract Hormonal changes in two Medicago ciliaris lines differing in salt tolerance (TNC 1.8 being more tolerant than TNC 11.9) were studied as possible regulators of growth and symbiotic nitrogen fixation (SNF). After 21 days of saline treatment (100 mM NaCl), four ...
Hormonal changes in two Medicago ciliaris lines differing in salt tolerance (TNC 1.8 being more t... more Hormonal changes in two Medicago ciliaris lines differing in salt tolerance (TNC 1.8 being more tolerant than TNC 11.9) were studied as possible regulators of growth and symbiotic nitrogen fixation (SNF). After 21 days of saline treatment (100 mM NaCl), four ...
The rhizobia present in a single arid region Tunisian soil that nodulate Medicago laciniata and M... more The rhizobia present in a single arid region Tunisian soil that nodulate Medicago laciniata and Medicago truncatula were compared. All isolates, 40 from each host, were Sinorhizobium meliloti based on 16S rRNA polymerase chain reaction restriction fragment length polymorphism (PCR–RFLP) patterns and subsequent confirmation by sequence analysis of the 16S rRNA genes in four representatives from each host species. There was no apparent relationship between Medicago host species of isolation and the nodulating rhizobial genome as determined by repetitive extragenic palandromic PCR. The isolates of M. laciniata were distinguished from those of M. truncatula present in the same soil by variation in PCR–RFLP of nifDK, indicating that this dissimilarity is originally genetic and not geographic. While forming effective symbioses with their own respective isolates, both M. laciniata and M. truncatula formed ineffective true nodules, nodule-like structures, or no nodules at all in cross-inocu...
The purpose of this study was to identify strains of Sinorhizobium meliloti that formed either an... more The purpose of this study was to identify strains of Sinorhizobium meliloti that formed either an effective or completely ineffective symbiosis with Medicago truncatula L. ‘Jemalong A17’ and, subsequently, to determine whether differences existed between their exoH genes. Sinorhizobium meliloti TII7 and A5 formed an effective and ineffective symbiosis with M. truncatula ‘Jemalong A17’, respectively. Using a multilocus sequence typing method, both strains were shown to have chromosomes identical with S. meliloti Rm1021 and RCR2011. The 2260-bp segments of DNA stretching from the 3′ end of exoI through open reading frames of hypothetical proteins SM_b20952 and SM_b20953 through exoH into the 5′ end of exoK in strains TII7 and Rm1021 differed by a single nucleotide at base 127 of the hypothetical protein SM_b20953. However, the derived amino acid sequences of the exoH genes of effective TII7, ineffective A5, and strain Rm1021 were shown to be identical with each other. Therefore, it wo...
Sinorhizobium meliloti strain A5, isolated from root nodules of Medicago truncatula growing spont... more Sinorhizobium meliloti strain A5, isolated from root nodules of Medicago truncatula growing spontaneously in Tunisian dry lands, showed better growth performance under different sodium chloride concentrations than the standard reference strain RCR2011. Strain A5 has the ability to grow even at 684 mM NaCl. Two-dimensional (2D) electrophoretic analysis of the salt effect on proteome profiles revealed the greatest change on the 4th day of exposure. The halotolerant strain A5 showed more upregulated protein spots than the standard RCR2011 strain (23% of the analyzed protein spots vs only 10% in strain RCR2011) and fewer downregulated protein spots (28% vs 69%). Proteins over-expressed in salty medium as determined by Matrix-assisted laser desorption ionization time-of-flight mass spectrometry for both strains were identified as an outer-membrane protein, an L-amino-acid binding periplasmic transporter protein, a 50S ribosomal protein (L25), a heat shock protein, and a putative oxidoreductase protein. Down-regulated proteins were identified as a putative iron-binding periplasmic transporter protein, a putative lipoprotein precursor, a putative spermidine/ putrescine-binding periplasmic transporter protein, and a putative amino-acid binding ABC transporter protein. The profile of strain A5 showed higher over-expression of an oxidoreductase and a heat-shock protein, and specifically an induction of a putative oligopeptide ABC transporter ATP-binding protein.
The capacity of nodulating bacteria to survive in soil containing various heavy metal elements ha... more The capacity of nodulating bacteria to survive in soil containing various heavy metal elements has been investigated with the aim of promoting the revegetation of mining sites with Medicago sp. Soil samples were collected from three different mining sites and one agricultural site at a location north of Tunisia. Heavy metal composition analysis showed that the soil samples were contaminated with different concentrations of cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn). The forage plant Medicago sativa was able to grow normally and to develop effective nodules in these contaminated soils. Sinorhizobium sp. strains nodulating Medicago sativa plants grown in these mining soil samples were isolated and characterized. The isolated strains were able to grow in soils containing up to 2.5 mM Zn, 0.3 mM Cd, 1 mM Cu and 2 mM Pb. The bioaccumulation was tested for two contrasting strains for each metal. For Cd, Pb, and Zn, strain S532 (tolerant strain) adsorbed lower amounts of metals than sensitive strain S112. For Cu, tolerant strain S412 absorbed more Cu than sensitive strain S112, even though adsorption was similar for these two strains. Our results support the use of Medicago sativa-sinorhizobium symbiosis for the regeneration and enrichment of moderately contaminated soils.
The aim of this study was to investigate the effect of NaCl salinity on symbiotic nitrogen fixati... more The aim of this study was to investigate the effect of NaCl salinity on symbiotic nitrogen fixation (SNF) in a Medicago ciliaris-Sinorhizobium medicae symbiosis system, with special emphasis on two genetically pure lines of M. ciliaris developed from germplasm recovered from saline and non-saline lands. Saline treatment (100 mM NaCl) was applied to these two contrasting lines growing in pots in a greenhouse after the appearance of nodules. At the end of the vegetative period, both lines under salt stress registered a decrease in nitrogenase activity, whole plant and organ biomass production and chlorophyll concentration, but the tolerant line TNC 1.8 was much less affected by salt than the sensitive line TNC 11.9. Salinity also provoked a decrease in sucrose phosphate synthase activity (SPS), mainly in TNC 11.9. The decline in leaf SPS in TNC 11.9 was accompanied by salinity-induced membrane oxidative damage in source leaves of the sensitive line, probably induced by a disturbance in soluble sugar/starch partitioning. We report these physiological and biochemical parameters to promote these useful lines as useful germplasm with potential to reveal detailed transcriptomic and metabolomic information and new genetic tools which could assist breeders in improving salinity tolerance and biomass for pasture legumes.
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