Symbiotic dinitrogen fixation and host-plant growth during development of and recovery from phosphorus deficiency

Characterization of nodule growth and function, phosphorus and nitrogen status of plant tissues and host-plant growth of nodulated soybean ( Glycine max L. Merr.) plants developing and recovering from phosphorus deficiency was used to evaluate the role of phosphorus in symbiotic dinitrogen fixation. The sequence of physiological responses during recovery from phosphorus deficiency was; (1) rapid uptake of phosphorus, (2) rapid increases in the phosphorus concentration of leaves and nodules, (3) enhanced growth and function of nodules, (4) increased nitrogen concentrations in all plant organs and (5) enhanced plant growth. The sequence of physiological responses to onset of phosphorus deficiency was; (1) decreased phosphorus uptake, (2) decreased phosphorus concentrations in leaves and nodules, (3) decreased nodule function, (4) decreased nitrogen concentration in plant organs and (5) decreased plant growth. These results, in conjunction with previously published data (Sa and Israel, Plant Physiol. 97: 928–935, 1991), support an interpretation that the total response of symbiotic dinitrogen fixation in soybean plants to altered phosphorus supply is a function of both indirect effects on host-plant growth and more direct effects on the metabolic function of nodules.     

Nitrogen fixation is synchronized with carbon metabolism in Lotus japonicus and Medicago truncatula nodules under salt stress

Abstract

In the present work, the response to NaCl applied at the vegetative stage to Medicago truncatula and Lotus japonicus has been evaluated in order to ascertain whether the effect of salt stress on nitrogen fixation is due to a limitation on nodular carbon metabolism. Results show maximum sucrose synthase (SS) and alkaline invertase (AI) activities were obtained at the vegetative stage, when maximum nitrogenase activity was detected in both species. SS activity decreased with the salt treatment, providing evidence of the regulatory role of this enzyme for the carbon supply to the bacteroids. Phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (MDH) activities could account for higher nitrogen fixation efficiency detected in L. japonicus nodules and isocitrate dehydrogenase (ICDH) activity compensated for the carbon limitations that occur under salt stress. These results support that nitrogenase inhibition in nodules experiencing salt stress is doubt to a carbon flux shortage, as result of carbon metabolism enzymes activities down-regulation.     

Response of nitrogen fixation in relation to nodule carbohydrate metabolism in Medicago ciliaris lines subjected to salt stress

The effect of salt stress on nitrogen fixation, in relation to sucrose transport towards nodules and other sink organs and the potential of sucrose breakdown by nodules, was investigated in two lines of Medicago ciliaris. Under salt stress conditions, the two lines showed a decrease of total biomass production, but TNC 1.8 was less affected by salt than TNC 11.9. The chlorophyll content was not changed in TNC 1.8, in contrast to TNC 11.9. Shoot, root, and nodule biomass were also affected in the two lines, but TNC 1.8 exhibited the higher potentialities of biomass production of these organs. Nitrogen fixation also decreased in the two lines, and was more sensitive to salt than growth parameters. TNC 1.8 consistently exhibited the higher values of nitrogen fixation. Unlike nodules, leaves of both lines were well supplied in nutrients with some exceptions. Specifically, the calcium content decreased in the sensitive line leaves, and the nodule magnesium content was not changed in either line. The tolerant line accumulated more sodium in its leaves. The two lines did not show any differences in the nodule sodium content. Sucrose allocation towards nodules was affected by salt in the two lines, but this constraint did not seem to affect the repartition of sucrose between sink organs. Salt stress induced perturbations in nodule sucrolytic activities in the two lines. It inhibited sucrose synthase, but the inhibition was more marked in TNC 11.9; alkaline/neutral activity was not altered in TNC 1.8, whereas it decreased more than half in TNC 11.9. Thus, the relative tolerance of TNC 1.8 to salt stress could be attributed to a better use of these photoassimilates by nodules and a better supply of bacteroids in malate. The hypothesis of a competition for sucrose between nodules and other sink organs under salt stress could not be verified.     

La Dendrologia di Ulisse Aldrovandi

Abstract

Legume-Rhizobium symbiotic nitrogen (N₂) fixation plays a critical role in sustainable nitrogen management in agriculture. The nitrogen fixed by the root nodules not only affects the nitrogen cycle of nature, but is also of great economic importance. A number of physiological and biochemical processes in the nodules are affected by salt stress. The objective of this study was to evaluate the role of arbuscular mycorrhiza (AM) in moderating toxic effects of salt stress on nodular metabolism in Cajanus cajan (L.) Millspaugh (pigeonpea) cv. Manak. Exposure of plants to salinity stress (4, 6 and 8 dSm^?1) caused ionic imbalance, which resulted in increased Na⁺ and reduced K⁺ and Ca²⁺ contents in the nodules. Salinity induced increased synthesis and accumulation of proline and glycine betaine. Salt stress significantly increased the antioxidant enzyme activities in the nodules of all plants. Nodular growth suffered remarkably and a marked decline in nodule biomass was observed under salt stress. Leghemoglobin content and acetylene reduction activity (ARA) also declined under saline conditions. AM could significantly improve nodule dry mass, leghemoglobin content and nitrogenase activity, and phosphorus content under salt stress. Activities of antioxidant enzymes increased markedly in nodules of mycorrhizal-stressed plants. This study suggested a correlation between improved functional efficiency of nodules and higher osmolyte accumulation and enhanced antioxidant enzyme activities of AM plants under stressed conditions relative to the nodules of uninoculated plants.     

Biochar improved nodulation and nitrogen metabolism of soybean under salt stress

To investigate salt stress and biochar application effects on nodulation and nitrogen metabolism of soybeans (Glycine max cv. M7), an experiment was conducted under the control condition. The treatments comprised three biochar rates (non, 50 and 100 g kg^?1 soil) and three salinities (0, 5 and 10 dS m^?1 NaCl), with four replications of treatments. Salt stress diminished the number of nodules and their weights in the soybean roots. Nitrogen content and metabolism decreased in nodules, roots and shoots, while reducing the activity of glutamate dehydrogenase (GDH), glutamine synthetase (GS), glutamine oxoglutarate aminotransferase (GOGAT) and nitrate reductase (NR). Also, salinity brought down root and shoot weight, total plant biomass, chlorophyll content, leaf area (LA) and rubisco activity in the soybean. On the other hand, application of biochar improved nodulation, nitrogen content, rubisco activity, GDH, GS, GOGAT and NR activities in different parts of the soybean and nodules under salt stress, and consequently improved chlorophyll content, LA, root and shoot weight. Both the 50 and 100 g kg^?1 biochar rates showed similar effects in improving nitrogen metabolism and plant performance under salt stress. Generally, biochar increased nodulation and nitrogen metabolism of the soybean under saline conditions.     

Effects of salt stress on growth, photosynthesis and nitrogen fixation in chick-pea (Cicer arietinum L.)

Plants of chick-pea (Cicer arietinum L. cv. ILC1919) inoculated with Mesorhizobium ciceri strain ch-191 were grown in a controlled environmental chamber, and were administered salt (0, 50, 75, and 100 mM NaCl) during the vegetative period. Four harvests (4, 7, 11, and 14d after treatment) were analysed. The aim was to ascertain whether the negative effect of saline stress on nitrogen fixation is due to a limitation on the photosynthate supply to the nodule or a limitation on the nodular metabolism which sustains nitrogenase activity.Plant growth was affected only by the highest NaCl concentration, whereas nitrogenase activity was affected from 50 mM. At the first harvest, Rubisco, PEPC and MDH activities in leaves rose with salt, but fell during the following harvests. The increase of PEPC and MDH in nodules at the two first samplings was clearly related to salt concentration. While 50 mM NaCl increased GS and GOGAT in nodules at some harvests, 100 mM strongly inhibited these activities at all the harvests. The accumulation of proline, amino acids and carbohydrates was clearly related to salt especially in the leaves, whereas in the nodules the protein content was boosted by salt. Although photosynthesis declined with NaCl, the response of nitrogen fixation to salt was more pronounced. This situation, together with carbohydrate accumulation, suggests that the lack of photosynthate does not cause the inhibition of nitrogenase activity under this type of stress. The similar trend observed for the PEPC-MDH pathway and the ARA support the hypothesis concerning the limitation in the supply of energy substrate, mainly malate, to the bacteroids. The accumulation of compatible solutes is more a consequence of damage produced by salt stress than of a protective strategy.     

Comparative study of nitrogen fixation and carbon metabolism in two chick-pea (Cicer arietinum L.) cultivars under salt stress

Two cultivars of Cicer arietinum with differential tolerance to salinity have been compared by analysing growth, photosynthesis, nodulation, nitrogenase activity, and carbon metabolism in the nodule cytosol. The aim was to help elucidate the relationships between, on the one hand, sucrose and malate metabolism in nodules and, on the other, the inhibition of nitrogen fixation under salt stress. Chick-pea cultivars Pedrosillano (sensitive) and ILC1919 (tolerant) inoculated with Mesorhizobium ciceri strain Ch-191 were grown in a controlled environmental chamber and were treated with salt (0, 50, 75, and 100 mM NaCl) from sowing to harvest time (28 d). Plant growth and photosynthesis were more affected by salt in Pedrosillano than in ILC1919. Also the effect of salt on nodulation and nitrogen fixation was much more pronounced in Pedrosillano. The increase in nodular mass in ILC1919 can partially counteract the inhibition of nitrogenase activity. The enzymes of sucrose breakdown were inhibited by NaCl, but in ILC1919 a rise in alkaline invertase was observed with salinity, which could compensate for the lack of the sucrose synthase hydrolytic activity. The activity of PEPC was stimulated by salt in ILC1919. Also, this cultivar showed higher malate concentrations in root nodules.     

Inadequate iron supply and high bicarbonate impair the symbiosis of peanuts (Arachis hypogaea L.) with different Bradyrhizobium strains

In the present study, we examined the effects of iron deficiency in an acid solution and in an alkaline solution containing bicarbonate on the growth and nodulation of peanuts inoculated with different bradyrhizobial strains or supplied with fertilizer nitrogen.Inadequate iron supply in acid solution decreased the number of nodule initials, nodule number and nodule mass. Alleviating the iron deficiency increased acetylene reduction but not bacteroid numbers in nodules. Nitrogen concentrations in shoots of inoculated plants increased as iron concentrations in solution increased when determined at day 30 but not at day 50. Higher iron concentrations in solution were required for maximum growth of plants reliant on symbiotic nitrogen fixation than for those receiving fertilizer nitrogen.Adding bicarbonate to the solution with 7.5 M Fe markedly depressed nodule formation. This effect was much more severe than that of inadequate iron supply alone. Bicarbonate also decreased nitrogenase activity but did not decrease bacteroid concentrations in nodules.Both NC92 and TAL1000 nodulated peanuts poorly when bicarbonate was present. However, an interaction between iron concentrations in acid solutions and Bradyrhizobium strains on nodulation of peanuts was observed. Alleviating iron deficiency increased the number of nodule initials and nodules to a much greater extent for plants inoculated with TAL1000 than for plants inoculated with NC92.     

Phloem‐derived γ‐aminobutyric acid (GABA) is involved in upregulating nodule N2 fixation efficiency in the model legume Medicago truncatula

Nitrogen fixation in legumes is downregulated through a whole plant N feedback mechanism, for example, when under stress. This mechanism is probably triggered by the impact of shoot‐borne, phloem‐delivered compounds. However, little is known about any whole‐plant mechanism that might upregulate nitrogen fixation, for example, under N deficiency. We induced emerging N‐deficiency through partial excision of nodules from Medicago truncatula plants. Subsequently, the activity and composition of the remaining nodules and shifts in concentration of free amides/amino acids in the phloem were monitored. Furthermore, we mimicked these shifts through artificial feeding of γ‐aminobutyric acid (GABA) into the phloem of undisturbed plants. As a result of increased specific activity of nodules, N₂ fixation per plant recovered almost completely 4–5 d after excision. The concentration of amino acids, sugars and organic acids increased strongly in the upregulated nodules. A concomitant analysis of the phloem revealed a significant increase in GABA concentration. Comparable with the effect of nodule excision, artificial GABA feeding into the phloem resulted in an increased activity and higher concentration of amino acids and organic acids in nodules. It is concluded that GABA might be involved in upregulating nodule activity, possibly because of its constituting part of a putative amino acid cycle between bacteroids and the cytosol.     

Carbon metabolism and bacteroid respiration in nodules of chick-pea (Cicer arietinum L.) plants grown under saline conditions

ABSTRACT

The present work investigates the relationships between nitrogen fixation, carbon metabolism and oxygen consumption by bacteroids of Mesorhizobium ciceri in root nodules of chick-pea plants. Its aim was to establish whether some of the compounds which accumulate under salt stress may be used as respiratory substrates by bacteroids to fuel their own metabolism and nitrogenase activity. Plants were grown in a growth chamber, and salt stress was induced by adding 50 mM NaCl to the nutrient solution at sowing. The data presented here show a rise in fermentative metabolism in nodules of chick-pea plants exposed to high salinity, and suggest that proline, lactate or ethanol, may play an important role as energy-yielding substrates for bacteroids in this plant species. The bacteroids could utilize glucose as a respiratory substrate both under control and saline conditions, while malate did not appear to be the preferred substrate in the presence of salt.     

Metabolic changes in soybean nodules after inhibition of nitrogen fixation by treatment with oxygen

Metabolites that accumulated in soybean [Glycine max (L.) Merr.]nodules after inhibition of nitrogen fixation were analysedto determine what carbon compounds the bacteroids might obtainfrom their host. Exposure of roots of intact soybean plantsto 100% O₂ for 5 min caused a decrease in acetylene reductionactivity within 10 min and then the activity recovered onlyslowly. Analysis of carbohydrates, organic acids, volatile compoundsand amino acids in extracts of nodules revealed that succinate,malate and alanine all accumulated within 10 min after treatmentwith O₂. The concentrations of sucrose, acetone, tyrosine, valine,isoleucine, leucine, and ornithine in the nodules increasedslowly after such treatment. The results are discussed in termsof carbon sources for supporting nitrogen fixation of soybeanbacteroids. Key words: Glycine max, carbon metabolism, nitrogen fixation, nodules     

Carbohydrates in Soybean Nodules: II. DISTRIBUTION OF COMPOUNDS IN SEEDLINGS DURING THE ONSET OF NITROGEN FIXATION

During the first few days of nitrogen fixation activity by soybean (Glycine max (L.) Merr) root nodules, d-chiro-inositol, myo-inositol, sucrose, alpha,alpha-trehalose, and maltose accumulate rapidly and reach concentrations several fold greater than concentrations in other plant organs. Concentrations of d-pinitol in nodules (>/=1.0 milligrams per gram fresh weight) were similar to concentrations in leaf blades. The concentration of fructose in nodules was lower than concentrations in other plant organs.Comparison of nonnodulated roots, nodulated roots (after removal of nodules), and nodules indicated that nodules may compete successfully with roots for carbohydrates, especially the disaccharides sucrose, alpha,alpha-trehalose, and maltose. Based on the isolation of protoplasts and bacteroids, it was tentatively concluded that the highest concentrations of cyclitols in soybean nodules are located in the infected region and that, inside infected cells, the highest concentrations of d-pinitol and myo-inositol are outside of bacteroids.Evidence for the identification of d-chiro-inositol and maltose in soybean nodules is presented.     

Soybean genotypic differences in sensitivity of symbiotic nitrogen fixation to soil dehydration

Nitrogen fixation activity by soybean (Glycine max (L.) Merr.) nodules has been shown to be especially sensitive to soil dehydration. Specifically, nitrogen fixation rates have been found to decrease in response to soil dehydration preceding alterations in plant gas exchange rates. The objective of this research was to investigate possible genetic variation in the sensitivity of soybean cultivars for nitrogen fixation rates in response to soil drying. Field tests showed substantial variation among cultivars with Jackson and CNS showing the least sensitivity in nitrogen accumulation to soil drying. Glasshouse experiments confirmed a large divergence among cultivars in the nitrogen fixation response to drought. Nitrogen fixation in Jackson was again found to be tolerant of soil drying, but the other five cultivars tested, including CNS, were found to be intolerant. Experiments with CNS which induced localized soil drying around the nodules did not result in decreases in nitrogen fixation rates, but rather nitrogen fixation responded to drying of the entire rooting volume. The osmotic potential of nodules was found to decrease markedly upon soil drying. However, the decrease in nodule osmotic potential occurred after significant decreases in nitrogen fixation rates had already been observed. Overall, the results of this study indicate that important genetic variations for sensitivity of nitrogen fixation to soil drying exist in soybean, and that the variation may be useful in physiology and breeding studies.     

Relationship between boron and calcium in the N2-fixing legume–rhizobia symbiosis

Because boron (B) and calcium (Ca²⁺) seem to have a strong effect on legume nodulation and nitrogen fixation, rhizobial symbiosis with leguminous plants, grown under varying concentrations of both nutrients, was investigated. The study of early pre‐infection events included the capacity of root exudates to induce nod genes, and the degree of adsorption of bacteria to the root surface. Both phenomena were inhibited by B deficiency, and increased by addition of Ca²⁺, resulting in an increase of the number of nodules. The infection and invasion steps were investigated by fluorescence microscopy in pea nodules harbouring a Rhizobium leguminosarum strain that constitutively expresses green fluorescent protein. High Ca²⁺ enhanced cell and tissue invasion by Rhizobium, which was highly inhibited after B deficiency. This was combined with an increased B concentration in nodules of plants grown on B‐free medium and supplemented with high Ca²⁺ concentrations, and that can be attributed to an increased B import to the nodules. Histological examination of indeterminate (pea) and determinate (bean) nodules showed an altered nodule anatomy at low B content of the tissue. The moderate increase in nodular B due to additional Ca²⁺ was not sufficient to prevent the abnormal cell wall structure and the aberrant distribution of pectin polysaccharides in B‐deficient treatments. Overall results indicate that the development of the symbiosis depends of the concentration of B and Ca²⁺, and that both nutrients are essential for nodule structure and function.     

Lipid and hydrocarbon production byBotryococcus spp. under nitrogen limitation and anaerobiosis

The production of lipids and hydrocarbons in batch cultures of the algaeBotryococcus braunii andB. protuberans has been studied with respect to nitrogen limitation under aerobic and anaerobic conditions. Nitrogen deficiency significantly decreased the dry weight, chlorophylla and protein contents but the amounts of carotenoids, carbohydrates and lipids increased in both the species. Nitrogen starvation gave a 1.6-fold increase in lipid content. Anaerobiosis under nitrogen deficient conditions gave greater lipid production than anaerobiosis in nitrogen supplemented medium. Under nitrogen deficiency, the hydrocarbon fraction increased and the polar lipids decreased. Anaerobiosis induced hydrocarbon synthesis more significantly than nitrogen deficiency but decreased other non-polar and polar lipids.     

Organic acid accumulation may inhibit N2 fixation in phosphorus-stressed lupin nodules.

Nodulated lupins (Lupinus angustifolius cv. Wonga) were hydroponically grown under conditions of low phosphate (LP) or adequate phosphate (HP) to assess the effect of phosphoenolpyruvate carboxylase (PEPC)-derived organic acids on nitrogen assimilation in LP nodules. LP conditions are linked to altered organic acid metabolism, by the engagement of PEP metabolism via PEPC. In LP nodules, the enhanced organic acid synthesis may reduce the available organic carbon for nitrogen assimilation. The diversion of carbon between the organic acid- and amino acid pools was assessed through key nodular enzymes and (14)CO(2) metabolism. Under LP conditions, increased rates of organic acid synthesis via PEPC and malate dehydrogenase (MDH), coincided with reduced nitrogen assimilation via aspartate aminotransferase (AAT), aspartate synthetase (AS) and glutamine synthetase (GS)/glutamate synthase (GOGAT) activities. There was a preferential metabolism of nodular (14)CO(2) into organic acids and particularly into malate. High malate levels were associated with reduced N(2) fixation and synthesis of amino acids. These results indicate that phosphorus deficiency can enhance malate synthesis in nodules, but that excessive malate accumulation may inhibit N(2) fixation and nitrogen assimilation.     

Proline accumulation has prevalence over polyamines in nodules of Medicago sativa in symbiosis with Sinorhizobium meliloti during the initial response to salinity

Background and aims

Polyamines are cationic molecules that play an important role in the plant response to environmental stresses. The aim of this work is to determine the role of these compounds in the response to salinity of Medicago sativa plants in symbiosis with the soil bacteria Sinorhizobium meliloti.

Methods

M. sativa plants inoculated with S. meliloti were subjected to 100 and 150 mM NaCl treatments. The concentration of nodular polyamines was determined in relation to the nitrogen fixation parameters, proline accumulation, and oxidative damage. In addition, polyamines concentrations were analyzed in different nodular fractions as well as the effect of exogenous polyamines in the nodulation response.

Results

The concentration of nodular polyamines decreased by the salinity in correlation with the nitrogenase activity after 2 and 4 weeks of salt treatment while spermine accumulated after 6 weeks. On the contrary, proline accumulation was induced by the salinity at all time points. The analysis of different nodular fractions showed the highest polyamines concentration in bacteroids being homospermidine the most abundant.

Conclusion

Proline accumulation had prevalence over polyamines at the earliest response to salinity probably due to nitrogen limitation under salt stress conditions and the existence of a common precursor for both compounds in the nodule. Nevertheless, after long salt exposure, spermine was also accumulated. The analysis of different nodular fractions indicated the bacteroidal origin of polyamines in nodules being homoespermidine, one of the most abundant.     

The Effects of Salinity on Nitrogen Fixation and Trehalose Metabolism in Mycorrhizal Cajanus cajan (L.) Millsp. Plants

Arbuscular mycorrhizal (AM) fungi exist widely in natural ecosystems as well as in salt-affected soils and are considered suitable candidates for bio-amelioration of saline soils. Plants respond to salinity by accumulating sugars and other low-molecular-weight compatible solutes. One such compound is trehalose, which has been found to play an important role as a stress protectant. The aim of the present investigation was to study interactions between an AM fungus and salinity stress on growth, nitrogen fixation, and trehalose metabolism in Cajanus cajan (L.) Millsp. (pigeonpea). Two genotypes [Sel 85N (salt-tolerant) and ICP 13997 (salt-sensitive)] were subjected to saline treatments with and without mycorrhizal inoculations. Salinity reduced plant biomass (shoot and root) in both genotypes and resulted in a decline in shoot-to-root ratio (SRR); however, a smaller decline was observed in Sel 85N than in ICP 13997. AM colonization was reduced with increasing salinity levels but mycorrhizal responsiveness (MR) increased. Genotypic variability in nitrogen fixation and trehalose metabolism in response to salinity and mycorrhization was observed. An increment in nodule number was accompanied by a reduction in dry mass. Subsequently, nodular activity (leghemoglobin, acetylene-reduction activity [ARA], nitrogen content) was reduced under soil salinity, which was more profound in ICP 13997 than in Sel 85N. The symbiotic association with Glomus mosseae led to significant improvement in plant dry mass and nitrogen-fixing potential of nodules under salt stress. Salinity led to an increase in trehalose-6-P synthetase (TPS) and trehalose-6-P phosphatase (TPP) activities resulting in increased trehalose content in nodules, which was accompanied by inhibition of trehalose catabolism (trehalase activity). AM plants had lower trehalase activity under saline and nonsaline conditions. Thus, a symbiotic relationship between plant roots and G. mosseae might have resulted in salinity tolerance in a genotype-dependent manner.     

Influence of boron and calcium on the tolerance to salinity of nitrogen-fixing pea plants

The effects of different levels of B (from 9.3 to 93 M B) and Ca (from 0.68 to 5.44 mM Ca) on plant development, nitrogen fixation, and mineral composition of pea (Pisum sativum L. cv. Argona) grown in symbiosis with Rhizobium leguminosarum bv. viciae 3841 and under salt stress, were analysed. The addition of extra B and extra Ca to the nutrient solution prevented the reduction caused by 75 mM NaCl of plant growth and the inhibition of nodulation and nitrogen fixation. The number of nodules recovered by the increase of Ca concentration at any B level, but only nodules developed at high B and high Ca concentrations could fix nitrogen. Addition of extra B and Ca during plant growth restored nodule organogenesis and structure, which was absolutely damaged by high salt. The increase in salt tolerance of symbiotic plants mediated by B and Ca can be co-related with the recovery of the contents of some nutrients. Salinity produced a decrease of B and Ca contents both in shoots and in nodulated roots, being increased by the supplement of both elements in the nutrient solution. Salinity also reduced the content in plants of other nutrients important for plant development and particularly for symbiotic nitrogen fixation, as K and Fe. A balanced nutrition of B and Ca (55.8 M B, 2.72 mM Ca) was able to counter-act the deficiency of these nutrients in salt-stressed plants, leading to a huge increase in salinity tolerance of symbiotic pea plants. The necessity of nutritional studies to successfully cultivate legumes in saline soils is discussed and proposed.