The Effect of Gibberellic Acid, when Applied to the Rooting Medium, on Nodulation and Nitrogen Fixation in Gram (Cicer arietinum)

Plants of a pure line variety, G 24, of Cicer arietinum L. were grown in sand culture. After an initial dose of a complete nutrient solution, a nitrogen free nutrient solution was supplied to the sand at intervals and a standard rhizobial culture was added twice. The plants were treated with two concentrations of gibberellic acid (20 mg/I and 100 mg/I) through the rooting medium. At suitable intervals two pots from each treatment were sampled. Observations were made regarding the earliest initiation of nodulation, the number, weight and colour of nodules and the nitrogen content of different plant organs under various treatments. GA₃ treatments enhanced nodule initiation. While 20 mg/1 somewhat enhanced nodule number, weight and nitrogen content, 100 mg/I caused detrimental effects in the long run. Pod formation was delayed with GA₃, the effect being much more pronounced with the higher concentration used. Pod and seed weights under 20 mg/1 GA₃ were almost comparable to the control, but 100 mg/I proved very deleterious.     

Silicon promotes nodule formation and nodule function in symbiotic cowpea (Vigna unguiculata)

Applying silicon in the form of metasilicic acid (H₄SiO₃) or silicic acid (H₄SiO₃) to Bradyrhizobium -infected, hydroponically grown cowpea seedlings resulted in a significant ( P 0.05) increase in the number of nodules, nodule dry matter, and nitrogen fixed on a per plant basis. Total dry matter of plants increased with silicon supply, and the differences were significant ( P 0.05) at the higher silicon concentrations. Cowpea plants cultured in sand were also assessed for their response to silicic acid. Nodule number and nodule mass increased with silicon supply to sand cultured plants, though nitrogen fixation was unaltered. Although silicon is not essential for growth of cowpea, it is important for nodule formation and nodule functioning in hydroponically grown plants. Consequently, data collected and conclusions drawn from earlier glasshouse experiments, which have excluded silicon from nutrient solutions, may be flawed. Future studies on nodulation and nitrogen fixation using legumes in liquid culture must therefore include silicon as a nutrient element.     

Influence of cadmium stress and arbuscular mycorrhizal fungi on nodule senescence in Cajanus cajan (L.) Millsp

Cadmium (Cd) causes oxidative damage and affects nodulation and nitrogen fixation process of legumes. Arbuscular mycorrhizal (AM) fungi have been demonstrated to alleviate heavy metal stress of plants. The present study was conducted to assess role of AM in alleviating negative effects of Cd on nodule senescence in Cajanus cajan genotypes differing in their metal tolerance. Fifteen day-old plants were subjected to Cd treatments--25 mg and 50 mg Cd per kg dry soil and were grown with and without Glomus mosseae. Cd treatments led to a decline in mycorrhizal infection (MI), nodule number and dry weights which was accompanied by reductions in leghemoglobin content, nitrogenase activity, organic acid contents. Cd supply caused a marked decrease in nitrogen (N), phosphorus (P), and iron (Fe) contents. Conversely, Cd increased membrane permeability, thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H2O2), and Cd contents in nodules. AM inoculations were beneficial in reducing the above mentioned harmful effects of Cd and significantly improved nodule functioning. Activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) increased markedly in nodules of mycorrhizal-stressed plants. The negative effects of Cd were genotype and concentration dependent.     

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, Nodulation and Nitrogen Fixation in Cowpea and Mung Beans

The effects of salt stress on growth, nodulation, and nitrogen accumulation in cowpea (Vigna sinensis) and mung beans (Vigna aureus) were studied in sand culture. Salinity (NaCl) retarded the growth of leaves, stem and roots of both the crops. Root growth of mung beans was more sensitive to the increase in salt stress than that of cowpea. The relative growth rates of stressed plant parts declined initially but were subsequently higher than those of control for a period, suggesting that the plants tended to adapt to unfavourable environment even while being stressed. The total nodule number, weight and nitrogen content per plant decreased due to salt treatment, which interfered with the initiation of nodules but not with their further development. There was a considerable fall in the nitrogen fixation efficiency of mung beans under saline environment; it was not so in cowpea.     

Cooperative Action of Rhizobium meliloti Nodulation and Infection Mutants during the Process of Forming Mixed Infected Alfalfa Nodules

Alfalfa plants co-inoculated with Rhizobium meliloti nodulation (Nod-) and infection mutants deficient in exopolysaccharide production (Inf-EPS-) formed mixed infected nodules that were capable of fixing atmospheric nitrogen. The formation of infected nodules was dependent on close contact between the inoculation partners. When the partners were separated by a filter, empty Fix- nodules were formed, suggesting that infection thread formation in alfalfa is dependent on signals from the nodulation and infection genes. In mixed infected nodules, both nodulation and infection mutants colonized the plant cells and differentiated into bacteroids. The formation of bacteroids was not dependent on cell-to-cell contact between the mutants. Immunogold/silver staining revealed that the ratio of the two mutants varied considerably in colonized plant cells following mixed inoculation. The introduction of an additional nif/fix mutation into one of the inoculation partners did not abolish nitrogen fixation in mixed infected nodules. The expression of nif D::lacZ fusions additionally demonstrated that mutations in the nodulation and infection genes did not prevent the nif genes from being expressed in the mutant bacteroids.     

Effect of Nitrogen Fertilization and Growth Suppression on Pitch Canker Development on Loblolly Pine Seedlings

One-yr-old loblolly pine seedlings of two half-sib families, grown in sand, were fertilized three times per week with nutrient solution containing 20 μg/ml (low) or 80 μg/ml (high) nitrogen. Nitrogen concentration in the nutrient solution was either constant throughout the experiment, or interehanged after the inoculation of stems or shoots with Fusarium subglutinans, 55 days after initiation of fertilization. Growth was suppressed by a weekly excision of shoots branching from the stem apex. Either high nitrogen nutrition or shoot excision generally enhanced canker elongation on stem inoculated plants; the combination of both was extremely conducive for disease development. With intact plants of family 8–68, interchange of pre-inoculation low nitrogen nutrition with high nitrogen after inoculation enhanced canker elongation and rate of wilt. Nitrogen content varied in wood, bark and needles, as well as with time intervals, but was consistently in accordance with nitrogen level in the nutrient solution. In shoot excised plants, nitrogen content was higher than in the respective treatment without shoot excision. The higher nitrogen nutrient accelerated disease development on inoculated shoots, compared to low nitrogen, on both pine families. With respective treatments, stem cankers were larger and rates of shoots exhibiting lesions or wilt were higher on plants of family 8–68 than on 8–61. It is postulated that the disease enhancing effect associated with higher nitrogen content in stem tissues results from an increased nitrogen availability to the pathogen.     

Media optimization of Parietochloris incisa for arachidonic acid accumulation in an outdoor vertical tubular photobioreactor

The green alga Parietochloris incisa contains a significant amount of the nutritionally valuable polyunsaturated fatty acid and arachidonic acid (AA) and is being considered for mass cultivation for commercial AA production. This study was primarily aimed to define a practical medium formulation that can be used in commercial mass cultivation that will contribute to a substantial increase in the AA productivity of P. incisa with concomitant reduction of nutritional cost. The effect of nutrient limitation on growth and AA content of this microalga was explored in a batch culture in outdoor conditions using a vertical tubular photobioreactor. The study was conducted in two parts: the first was primarily focused on the effect of different nitrogen concentration on growth and AA content and the second part compares nitrogen deprivation, combination of nitrogen and phosphorus deprivation, and combined overall nutrient limitations at different levels of deprivation under low and high population densities. Since complete nitrogen deprivation hampers lipid and AA accumulation of P. incisa, thus, a critical value of nitrogen supply that will activate AA accumulation must be elucidated under specific growth conditions. Under the present experimental conditions, 0.5?g(-1) sodium nitrate obtained a higher AA productivity and volumetric yield relative to the nitrogen-deprived culture corresponding to 36.32?mg?L(-1)?day(-1) and 523.19?mg?L(-1). The combined nitrogen and phosphorus limitation seemed to enhance AA productivity better than nitrogen deprivation alone. The effect of overall nutrient limitation indicates that acute nutrient deficiency can trigger rapid lipid and AA syntheses. The effect of light as a consequence of culture cell density was also discussed. This study therefore shows that the nutrient cost can be greatly reduced by adjusting the nutrient levels and culture density to induce AA accumulation in P. incisa.     

Concentration-dependent influence of quercetin on nodulation process and the main characteristics of soybean inoculated with Bradyrhizobium japonicum

Soybean plants cv. Corsoy were grown in greenhouse conditions on sterilized quartz sand. They were inoculated with Bradyrhizobium japonicum, strain 542. The plants were treated with different concentrations of quercetin (ranging from 10 nM to 1M) at regular intervals during the experiment. The experiment was terminated at flower development. The following parameters, important for symbiosis efficiency were determined: shoot, root and nodule weights, nodule number, total leghemoglobin in the nodules,total nitrogen and soluble protein concentrations in shoots and roots, as well as chlorophyll concentration in the leaves.The results obtained partly confirmed the earlier findings that quercetin inhibits nodulation since increasing quercetin concentration decreased the number of nodules. However, at very low concentrations, quercetin stimulated the number of nodules. Quercetin also exerted a stimulating influence on other characteristics of the plant and nodules which did not correlate with nodule number and quantity of N fixed. These are: nodule weight, leghemoglobin concentration, total soluble protein content in shoots and roots as well as shoot and root weight.     

Effect of soil moisture stress on legume-rhizobium symbiosis in soybeans

Summary In a pot culture experiment, the influence of soil moisture stress at different physiological stages of soybean, cv. Hark, on nodulation, symbiosis and nitrogen accumulation was studied. Moisture stress reduced leghemoglobin content of root nodules and nitrogen uptake by plants. It had no effect on number of bacteroids. Stress at mid bloom and rapid pod filling stages reduced yield and seed protein content. However, these parameters were not affected by stress at nodule initiation and early flowering stages, though, flower initiation and maturity of the plant were delayed. Moisture stress at any stage did not alter nitrogen status of roots.     

The influence of colchicin on root nodule formation inTrifolium Pratense

Summary Addition of colchicin to nutrient solutions supplied to red clover plants had an inhibitory effect on root development and nodulation. At the lowest colchicin concentrations, a small, non-significant increase in the number of nodules was often observed; in a few experiments a barely significant increase in the number of nodules developing was observed up to concentrations of 10 mg per 1.Colchicin did not influence the growth of Rhizobium and growth of the bacteria in the presence of colchicin (10 mg per 1) had no effect on their subsequent infectivity or ability to fix nitrogen.Treatment with colchicin resulted in the formation of increased numbers of polyploid cells of the clover roots. In addition, it induced the development of deformed root-hairs which probably facilitated infection by Rhizobium and the formation of infection threads.The nodules developing at colchicin concentrations of 10 mg per 1 and higher were small, had an abnormal structure and were ineffective in nitrogen fixation.It is concluded that any stimulatory effect of colchicin on nodulation does not necessarily require to be associated with an increase in the number of polyploid cells in the root cortex. The effect of colchicin can be fully accounted for, initially by the greater number of infections resulting from the development of increased numbers of deformed root hairs, and subsequently by the reduced inhibitory action of the ineffective nodules on the formation of further nodules.     

Never too many? How legumes control nodule numbers

Restricted availability of nitrogen compounds in soils is often a major limiting factor for plant growth and productivity. Legumes circumvent this problem by establishing a symbiosis with soil-borne bacteria, called rhizobia that fix nitrogen for the plant. Nitrogen fixation and nutrient exchange take place in specialized root organs, the nodules, which are formed by a coordinated and controlled process that combines bacterial infection and organ formation. Because nodule formation and nitrogen fixation are energy-consuming processes, legumes develop the minimal number of nodules required to ensure optimal growth. To this end, several mechanisms have evolved that adapt nodule formation and nitrogen fixation to the plant's needs and environmental conditions, such as nitrate availability in the soil. In this review, we give an updated view on the mechanisms that control nodulation.     

Carbon Metabolism, Nitrogen Assimilation, and Seed Yield of Cowpea (Vigna unquiculata L. Walp.) Grown in an Adverse Temperature Regime

When grown in an environment known not to favour the productionof large seed yields (warm days-cool nights; 33–19 °C),non-nodulated plants of cowpea cv. K 2809 supplied with abundantinorganic nitrogen not only assimilated N more rapidly but alsoproduced larger total dry weights and seed yields than plantsdependent on Rhizobium CB 756. Remobilization of nitrogen fromvegetative organs started sooner in nitrate-dependent than innodulated plants and contributed 69 and 47%, respectively, tothe N content of mature fruits. Plants dependent on nodulesrelied more on current assimilation of nitrogen during the laterstages of fruit growth than those given inorganic N; they alsoutilized a larger proportion of shoot-derived photosynthatesin growth of organs below ground and in the respiratory activitiesof both nodules and supporting roots. Although nitrate-dependentplants developed larger shoot systems than those relying onnodules, the distribution of carbon and nitrogen to leaves decreasedmarkedly as branches extended during early reproductive growth.The respiration of roots on nodulated plants became more efficientduring the later stages of fruit growth whereas the populationof secondary nodules present at this stage of development respiredless efficiently (mg C consumed per mg N assimilated) than theprimary nodules present earlier during development.     

Phosphorus deficiency increases nodule phytase activity of faba bean–rhizobia symbiosis

The effect of phosphorus deficiency on growth, nodulation and phytase activity was studied in glasshouse for four symbioses involving two faba bean cultivars, namely Aguadulce (AG) and Alfia (AL), and two local rhizobial isolates, namely RhF1 and RhF2. The P deficiency was applied by adding 25 µmol of Pi plant^?1 week^?1 to nutrient solution, whereas the sufficient control received 125 µmol plant^?1 week^?1. At flowering stage, the plants were harvested for assessment of growth and nodulation, P and N contents in organs as well as activities of phytase and phosphatases in nodules. The latter were highly stimulated by P deficiency, particularly for AL–RhF1 symbiosis for which shoot growth and P content were not affected by P deficiency. Using in situ RT-PCR, the expression of a plant histidine acid phytase HAP gene was detected in the nodule cortex under P deficiency. It is concluded that high nodule phytase activity constitutes a mechanism for faba bean plants to adapt their nitrogen fixation to P deficiency.     

Effects of continuous nitrogen application and nitrogen preconditioning on nodulation and growth ofCeanothus griseus varhorizontalis

Rooted cuttings ofCeanothus griseus varhorizontalis were irrigated with 0, 10, 20, 50, 75 or 100ppm nitrogen as NH₄NO₃ for eight weeks prior to inoculation with infectiveFrankia. After inoculation, half of the plants for each treatment nitrogen level continued to be irrigated with the preconditioning nitrogen level and half were given no more supplemental nitrogen. For plants continuously receiving nitrogen, nodule initiation (nodule number) was inversely correlated with increasing supplemental nitrogen levels, and suppressed above 50 ppm N. Leaf nitrogen above 2% in continuous-N plants correlated with greatly reduced or suppressed nodulation. Plants maintained after inoculation without supplemental nitrogen showed influence of the prior nitrogen treatment on nodulation. Preconditioning at 50 ppm and above greatly reduced the number of nodules formed. The evidence suggests that stored internal nitrogen can regulate nodulation.Plant biomass accumulated maximally when nodulation was suppressed, at 75 and 100 ppm supplemental N applied continuously. Internode elongation during the nodulation period occurred only on nodulated plants, or in the presence of supplemental N (10 ppm and above).     

The effect of cobalt on the growth of young lucerne on a siliceous sand

Summary The nodulation and growth of young lucerne plants on a moderately acid siliceous sand were greatly increased by inoculation and the application of lime. In addition cobalt treatment significantly increased the yield of nitrogen per nodulated plant and the amount of nitrogen fixed per nodulated plant but had no effect on non-nodulated plants. Cobalt significantly increased the fresh weight of nodules per plant, due to greater nodule size. Furthermore the amount of nitrogen fixed per unit fresh weight of nodular tissue was substantially increased. The effects of cobalt on symbiotic nitrogen fixation led to significant increases (29 to 77 per cent) in the dry-matter yield of lucerne tops.     

Growth, nitrogen fixation and ammonium assimilation in common bean (Phaseolus vulgaris): effect of phosphorus

The impact of phosphorous nutrition on plant growth, symbiotic N₂ fixation, ammonium assimilation, carbohydrate and amino-acid accumulation, as well as on nitrogen, phosphorus and ATP content in tissues in common bean ( Phaseolus vulgaris ) plants was investigated. Plants inoculated with Rhizobium tropici CIAT899 were grown in Leonard jars under controlled conditions, with P-deficient (0 and 0.1 m M ), P-medium (0.5, 1 and 1.5 m M ) and P-high (2 m M ) conditions in a N-free nutrient solution. The P application, increased leaf area, whole plant DW (67%), nodule biomass (4-fold), and shoot and root P content (4- and 6-fold, respectively) in plant harvested at the onset of flowering (28-days-old). However, P treatments decreased the total soluble sugar and amino acid content in vegetative organs (leaf, root and nodules). The root growth proved less sensitive to P deficiency than did shoot growth, and the leaf area was significantly reduced at low P-application. The absence of a relationship between shoot N content, and P levels in the growth medium could indicate that nitrogen fixation requires more P than does plant growth. The optimal amount for the P. vulgaris – R. tropici CIAT899 symbiosis was 1.5 m M P, this treatment augmented nodule-ARA 20-fold, and ARA per plant 70-fold compared with plants without P application.     

Effect of plant nutrient supply on nodule effectiveness and rhizobium strain competition for nodulation ofLotus pedunculatus

Summary The effect of nutrient supply on nodule formation and competition between Rhizobium strains for nodulation ofLotus pedunculatus was studied. Limiting plant growth by decreasing the supply of nutrients in an otherwise nitrogen-free medium, increased the size but decreased the number and the nitrogenase activity of nodules formed by a fast-growing strain of Lotus Rhizobium (NZP2037). In contrast decreasing nutrient supply caused only a small decline in the size, number and nitrogenase activity of nodules formed by a slow-growing strain (CC814s). Providing small quantities of NH₄NO₃ (50 to 250 g N) to plants grown with a normal supply of other nutrients stimulated nodule development by both Rhizobium strains and increased the nitrogenase activity of the NZP2037 nodules. Differences in the level of effectiveness (nitrogen-fixing ability) of nodules formed by different Rhizobium strains on plants grown with a normal supply of nutrients were less apparent when the plants were grown with decreased nutrient supply or when the plants were supplied with low levels of inorganic N.Inter-strain competition for nodulation ofL. pedunculatus between the highly effective slow-growing strain CC814s and 7 other fast- and slow-growing strains, showed CC814s to form 42 to 100% of the nodules in all associations. The greater nodulating competitiveness of strain CC814s prevailed despite changes in the nutrient supply to the host plant. A tendency was observed for partially effective Lotus Rhizobium strains to become more competitive in nodule formation when plant growth was supplemented with low levels of inorganic nitrogen.     

α-Aminoadipic Acid and α,ɛ-Diaminopimelic Acid in Inoculated Pea Plants (Pisum sativum) and Root Nodule Bacteria (Rhizobium leguminosarum)

Observations were made on the content of α-aminoadipic acid and α-aminophimelic acid (DAP) in pea plants, nodules and Rhizobium leguminosarum, strain HT3. The preparations were purified by ion exchange chromatography, Qualitative analyses were made by paper chromatography, and quantitative analyses by means of an automatic amino acid analysator. In the whole plant and seeds the content of α-aminoadipic acid soluble in 70% ethanol varied between 10 and 80 μg/g dry weight. The shoot and red nitrogen fixing nodules contained more of this acid than roots and green inactive nodules. In the insoluble fraction of the shoot its concentration was 0.4-0.6 mg/g dry weight. α-Aminoadipic acid was not found in free living rhizobia, which again contained a considerable amount of α-aiaminopimelic acid, about 0.5 mg/g dry weight. The synthesis of DAP was intensive also in root nodules. In red nodules, which fixed molecular nitrogen, the content of DAP was 2.1 mg/g dry weight and in green inactive nodules 1.3 mg/g dry weight. It was shown that in the nodules DAP is closely connected with cell wall peptides of bacteroids. DAP could not be found in pea plants outside the nodules.