Francisco Ligero

Effects of salt stress on growth and nitrogen fixation by pea, faba-bean, common bean and soybean plants

The effects of salinity on growth, nodulation, acetylene reduction activity (ARA), nodule leghemoglobin (Lb) content and respiratory capacity of bacteroids from pea (Pisum sativwn cv. Lincoln), faba-bean (Vicia faba L. var. minor cv. Alborea), bean (Phaseolus vulgaris cv. Contender) and soybean (Glycine max L. var. Williams) were determined. The depressive effect of saline stress (50 and 100 mM NaCl) on dry weight and ARA of nodules was directly related to the salt-induced decline in dry weight and N content in shoots. The results indicate that P. savitum was the legume most severely affected by salinity, whereas G. max was the most salt-tolerant species. Saline stress was also responsible for a decrease in cytosolic protein of nodules, specifically Lb; this effect was more pronounced in pea and bean nodules than in soybean and faba-bean nodules. Bacteroids isolated from soybean and bean nodules exhibited higher respiratory activity in the absence of energy-yielding substrates than those isolated from pea and faba-bean plants. Salt added directly to the incubation mixture of bacteroids inhibited O2 uptake of bacteroids isolated from nodules of each legume. However, salt treatment of plants decreased respiratory capacity only in pea and faba-bean bacteroids. Inhibition of ARA under moderate saline stress may be related to the drop in bacteroid respiration. Under severe stress both the reduction in Lb content and inhibition of bacteroid respiration may be involved in salt-induced inhibition of nitrogen fixation.

Inoculation and nitrate alter phytohormone levels in soybean roots: differences between a supernodulating mutant and the wild type

Abstract. The levels of different cytokinins, indole-3-acetic acid (IAA) and abscisic acid (ABA) in roots of Glycine max [L.] Merr. cv. Bragg and its supernodulating mutant nts382 were compared for the first time. Forty-eight hours after inoculation with Bradyrhizobium, quantitative and qualitative differences were found in the roots endogenous hormone status between cultivar Bragg and the mutant nts382. The six quantified cytokinins, ranking similarly in each genotype, were present at higher concentrations (30–196% on average for isopentenyl adenosine and dihydrozeatin riboside, respectively) in mutant roots. By contrast, the ABA content was 2-fold higher in Bragg, while the basal levels of IAA [0.53 μmol (g DW)−1, on average] were similar in both genotypes. In 1 mM NO3−-fed Bragg roots 48 h post-inoculation, IAA, ABA and the cytokinins isopentenyl adenine, and isopentenyl adenosine quantitatively increased with respect to uninoculated controls. However, only the two cytokinins increased in the mutant. High NO3− (8 mM) markedly reduced root auxin concentration, and neither genotypic differences nor the inoculation-induced increase in auxin concentration in Bragg was observed under these conditions. Cytokinins and ABA, on the other hand, were little affected by 8 mM NO3−. Root IAA/cytokinin and ABA/cytokinin ratios were always higher in Bragg relative to the mutant, and responded to inoculation (mainly in Bragg) and nitrate (both genotypes). The overall results are consistent with the auxin-burst-control hypothesis for the explanation of autoregulation and supernodulation in soybean. However, they are still inconclusive with respect to the inhibitory effect of NO3−.

Evolution of ethylene from roots of medicago sativa plants inoculated with rhizobium meliloti

Summary The evolution of ethylene from roots of Medicago sativa plants uninoculated and inoculated with Rhizobium meliloti was measured for plants grown in test tubes under axenic conditions.Three maxima of ethylene evolved were always observed.These appeared 9-11, 19-23, and 27-30 days after sowing.Ethylene released from roots of inoculated plants showed a considerable increase compared with uninoculated plants.Results showed that ethylene is an important factor in the control of nodule development, maintenance, and senescence.

Detoxification of semisolid olive-mill wastes and pine-chip mixtures using Phanerochaete flavido-alba

Semisolid olive-mill residues, pine chips, and mixtures of both residues contain phytotoxic components capable of inhibiting germination and vegetative growth in plants. Solid-state cultures of Phanerochate flavido-alba on pine chips or mixtures of both residues reduce these phytotoxic effects in fermented substrates. The phenol and lipid contents in cultures detoxified by this fungus also decreases.

Salinity effects on growth analysis and nutrient composition in four grain legumes. Rhizobium symbiosis

Abstract The effect of salinity on growth response, nitrogen (N) fixation and tissue mineral content was investigated for four legumes: faba bean (Vicia faba L), pea (Pisum sativum L), soybean (Glycine max L), and common bean (Phaseolus vulgaris L). Plants were grown in a vermiculite culture system supplied with a N‐free nutrient solution with the addition of 0, 50, and 100 mM NaCl. Plants were harvested at the beginning of the flowering period and the dry weights of shoots and roots and acetylene reduction activity (ARA) were evaluated at the same time plant tissues were analysed for N, potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) contents. The depressive effect of saline stress on ARA of nodules was directely related to the salt induced decline in dry weight and N content in shoots. Growth inhibition by NaCl treatments was greater for the pea than for other legumes, whereas the soybean was the most salt‐tolerant Saline stress also affected the N content in shoots and roots. In general th...

Influence of host genotypes on growth, symbiotic performance and nitrogen assimilation in faba bean (Vicia faba L.) under salt stress

Fifteen genotypes of faba bean (Vicia faba L.) were inoculated with salt-tolerant Rhizobium leguminosarum biovar. viciae strain GRA 19 in solution culture with 0 (control) and 75 mM NaCl added immediately after transplanting. Genotypes varied in their tolerance of high levels of NaCl. Physiological parameters (dry weight of shoot and root, number and dry weight of nodules) were not affected by salinity in lines VF46, VF64 and VF112. Faba bean line VF60 was sensitive to salt stress. Host tolearance appeared to be a major requisite for nodulation and N2 fixation under salt stress. Tolerant line VF112 sustained nitrogen fixation under saline conditions. Activity of the ammonium assimilation enzymes glutamine synthetase and glutamate synthase, and soluble protein content, were reduced by salinity in all genotypes tested. Evidence presented here suggests a need to select faba bean genotypes that are tolerant to salt stress.

Effects of NaCl on growth and nitrogen fixation and assimilation of inoculated and KNO3 fertilized Vicia faba L. and Pisum sativum L. plants

Faba bean (Vicia faba L. var. minor cv. Alborea) and pea (Pisum sativum L. cv. Lincoln) plants, inoculated with Rhizobium leguminosarum biovar. viciae strain GRA19, were treated with salt (100 mM NaCl) and/or nitrate (8 mM KNO3) to test whether plants grown with inorganic-nitrogen are more tolerant to salinity than plants entirely reliant upon fixed nitrogen. According to the growth inhibition recorded, pea plants dependent on dinitrogen fixation proved more tolerant to salt stress than those N-fertilized, in contrast to results obtained for faba bean plants. This study therefore confirms that plants dependent on nitrogen fixation are not always more sensitive to salinity than are N-fertilized plants. Nitrate addition did not reduce the specific nitrogenase activity in pea, but did in faba bean. However, nodulation was inhibited in both legumes. The specific nitrogenase activity was more affected by salt treatment in N-fertilized plants for both legumes. The activity of the enzymes mediating ammonium assimilation in nodules (GS, NADH-GOGAT) was inhibited by salt stress both in N-fixing and in N-fertilized pea and faba bean plants.

Evolution of ethylene from roots and nodulation rate of alfalfa (Medicago sativa L.) plants inoculated with Rhizobium meliloti as affected by the presence of nitrate

Summary Ethylene has been reported as an inhibitor of root nodulation of legumes inoculated with Rhizobium. The inhibitory effect of fixed nitrogen on the establishment of the Rhizobium-legume symbiosis is well-known although not too much is understood of the mechanisms involved. Alfalfa plants inoculated with R. meliloti were cultured in mineral solution containing different nitrate concentrations. The results obtained show a clear positive correlation between nitrate concentration and the quantity of ethylene released from roots. This fact could be an explanation of the inhibitory effect on nodulation shown by the application of fixed nitrogen to legume culture.

Nitrate- and Inoculation-enhanced Ethylene Biosynthesis in Soybean Roots as a Possible Mediator of Nodulation Control

Summary Root ethylene biosynthesis has been studied in soybean (Glycine max [L.] Merr.) cv. Bragg plants and its supernodulating (nts382 and nts1007) and non-nodulating (nod49 and nod139) mutants. Regardless of NO3 treatment, inoculation with Bradyrhizobium japonicum significantly increased root ethylene evolution rate, reaching a plateau between 24 and 48 h after inoculation, with the rates being significantly higher in 8 mmol L−1 fed roots (high) than in those given 1 mmol L-1 (low) during the time of experiment. This Inoculation Stimulated Ethylene Release (ISER) response appears to be related to the infection process and nodule development, as treatment with Ag+ (an inhibitor of ethylene action) at the moment of inoculation markedly increased nodule number of Bragg plants under both high and low NO3 concentrations. Compared with the parental Bragg, the near-isogenic nodulating mutants used in this study showed normal ethylene biosynthesis ability (ethylene evolution and ACC oxidase activity), although significant quantitative differences were detected among them. Whether these differences are causally related to the nodulation phenotype is not known. Our previous observations on the involvement of endogenous ethylene in the control of nodule number in alfalfa are therefore also applicable to soybean, a determinate nodule type legume. The results further suggest that effects other than an alteration of ethylene biosynthesis might have also been caused by the nts mutations.

Genotypic differences in nitrogen assimilation in Vicia faba: Effect of nitrate

Five inbred lines and a commercial cultivar of field-bean (Vicia faba) were inoculated with a strain of Rhizobium leguminosarum bv. viciae and grown, with or without nitrate, under axenic conditions in a growth chamber. There were significant (p<0.01) differences between lines in N yield, both in N-free solution (N2 fixed, fully symbiotic) and with added NO3−. Increase in the N yield of NO3−-fed plants compared with fully symbiotic plants also varied between genotypes, with line VF109 being the least responsive to NO3−. This may indicate nitrate tolerance in relation to N2 fixation. The indication was supported by the observations that nodule development and nodule activity (acetylene reduction) were less inhibited in VF109 in the presence of 8 mM NO3− than in the other lines of Vicia faba. Glutamine synthetase and glutamate synthase (GOGAT) activities appeared to be related to genotypic differences in symbiotic efficiency. This finding suggests that assays of nodule glutamine synthetase and NADH-glutamate synthase might be used in Vicia faba breeding programs to indicate capacity for symbiotic N2 fixation, particularly in the presence of NO3−. ei]Section editor: B G Rolfe