Ammonium acts systemically while nitrate exerts an additional local effect on Medicago truncatula nodules.

Symbiotic nitrogen fixation (SNF) has a high energetic cost for legume plants; legumes thus reduce SNF when soil N is available. The present study aimed to increase our understanding regarding the impacts of the two principal forms of available N in soils (ammonium and nitrate) on SNF. We continuously measured the SNF of Medicago truncatula under controlled conditions.

Regulation of Symbiotic Nitrogen Fixation in Legume Root Nodules.

In most legume nodules, the di-nitrogen (N)-fixing rhizobia are present as organelle-like structures inside their root host cells. Many processes operate and interact within the symbiotic relationship between plants and nodules, including nitrogen (N)/carbon (C) metabolisms, oxygen flow through nodules, oxidative stress, and phosphorous (P) levels. These processes, which influence the regulation of N fixation and are finely tuned on a whole-plant basis, are extensively reviewed in this paper.

Hidden Nickel Deficiency? Nickel Fertilization via Soil Improves Nitrogen Metabolism and Grain Yield in Soybean Genotypes.

Nickel (Ni)-a component of urease and hydrogenase-was the latest nutrient to be recognized as an essential element for plants. However, to date there are no records of Ni deficiency for annual species cultivated under field conditions, possibly because of the non-appearance of obvious and distinctive symptoms, i.e.

Nitrate application or P deficiency induce a decline in Medicago truncatula N-fixation by similar changes in the nodule transcriptome.

Nitrogen fixation of Medicago truncatula is regulated by the nitrogen status of leaves through inducing a repeatedly occurring 24-h nodule activity rhythm that reduces per day nitrogen fixation. The hypotheses of the present study were that (1) long-term moderate whole-plant P deficiency in Medicago truncatula induces an according daily rhythm in nitrogenase activity comparable to that induced by nitrate application and (2), the changes in the nodule transcriptome that go along with a strong nitrogenase activity decline during the afternoon would be similar under P deficiency or after nitrate supply. The nodules of plants in a low P treatment developed a rhythmic pattern of activity that resembled the pattern following nitrate application.

Short-Term Molecular Acclimation Processes of Legume Nodules to Increased External Oxygen Concentration.

Nitrogenase is an oxygen labile enzyme. Microaerobic conditions within the infected zone of nodules are maintained primarily by an oxygen diffusion barrier (ODB) located in the nodule cortex. Flexibility of the ODB is important for the acclimation processes of nodules in response to changes in external oxygen concentration.

Long-term non-invasive and continuous measurements of legume nodule activity.

Symbiotic nitrogen fixation is a process of considerable economic, ecological and scientific interest. The central enzyme nitrogenase reduces H(+) alongside N2 , and the evolving H2 allows a continuous and non-invasive in vivo measurement of nitrogenase activity. The objective of this study was to show that an elaborated set-up providing such measurements for periods as long as several weeks will produce specific insight into the nodule activity's dependence on environmental conditions and genotype features.

RNA-seq transcriptome profiling reveals that Medicago truncatula nodules acclimate N₂ fixation before emerging P deficiency reaches the nodules.

Legume nodules are plant tissues with an exceptionally high concentration of phosphorus (P), which, when there is scarcity of P, is preferentially maintained there rather than being allocated to other plant organs. The hypothesis of this study was that nodules are affected before the P concentration in the organ declines during whole-plant P depletion. Nitrogen (N₂) fixation and P concentration in various organs were monitored during a whole-plant P-depletion process in Medicago truncatula.

Mechanisms of physiological adjustment of N2 fixation in Cicer arietinum L. (chickpea) during early stages of water deficit: single or multi-factor controls.

Drought negatively impacts symbiotic nitrogen fixation (SNF) in Cicer arietinum L. (chickpea), thereby limiting yield potential. Understanding how drought affects chickpea nodulation will enable the development of strategies to biotechnologically engineer chickpea varieties with enhanced SNF under drought conditions.

The activity of nodules of the supernodulating mutant Mtsunn is not limited by photosynthesis under optimal growth conditions.

Legumes match the nodule number to the N demand of the plant. When a mutation in the regulatory mechanism deprives the plant of that ability, an excessive number of nodules are formed. These mutants show low productivity in the fields, mainly due to the high carbon burden caused through the necessity to supply numerous nodules.

N-feedback regulation is synchronized with nodule carbon alteration in Medicago truncatula under excessive nitrate or low phosphorus conditions.

The aim of the present study was to test the hypothesis that the higher nodule amino acid content induced under certain treatments may play a role in the N-feedback regulation of nitrogenase (EC 1.18.6.

Propane-1,2-diols from dilactides, oligolactides, or poly-L-lactic acid (PLLA): from plastic waste to chiral bulk chemicals.

The preparation of racemic or enantioenriched propane-1,2-diol from dilactides, oligolactides, or poly-L-lactic acid (PLLA) is described. The transformation is carried out as tandem reactions in MeOH, covering hydrolysis and subsequent hydrogenation by using copper chromite as a catalyst. The starting material present undesired side products of the PLLA synthesis or PLLA waste.

An RNA sequencing transcriptome analysis reveals novel insights into molecular aspects of the nitrate impact on the nodule activity of Medicago truncatula.

The mechanism through which nitrate reduces the activity of legume nodules is controversial. The objective of the study was to follow Medicago truncatula nodule activity after nitrate provision continuously and to identify molecular mechanisms, which down-regulate the activity of the nodules. Nodule H2 evolution started to decline after about 4 h of nitrate application.

Approaches for enhancement of N₂ fixation efficiency of chickpea (Cicer arietinum L.) under limiting nitrogen conditions.

Chickpea (Cicer arietinum) is an important pulse crop in many countries in the world. The symbioses between chickpea and Mesorhizobia, which fix N₂ inside the root nodules, are of particular importance for chickpea's productivity. With the aim of enhancing symbiotic efficiency in chickpea, we compared the symbiotic efficiency of C-15, Ch-191 and CP-36 strains of Mesorhizobium ciceri in association with the local elite chickpea cultivar 'Bivanij' as well as studied the mechanism underlying the improvement of N₂ fixation efficiency.

Growth and nodulation of symbiotic Medicago truncatula at different levels of phosphorus availability.

Medicago truncatula is an important model plant for characterization of P deficiency on leguminous plants at the physiological and molecular levels. Growth optimization of this plant with regard to P supply is the first essential step for elucidation of the role of P in regulation of nodulation. Hence, a study was carried out to address the growth pattern of M.

Comparative Analysis of the Symbiotic Efficiency of Medicago truncatula and Medicago sativa under Phosphorus Deficiency.

Phosphorus (P)-deficiency is a major abiotic stress that limits legume growth in many types of soils. The relationship between Medicago and Sinorhizobium, is known to be affected by different environmental conditions. Recent reports have shown that, in combination with S.

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.

The argon-induced decline in nitrogenase activity commences before the beginning of a decline in nodule oxygen uptake.

Replacement of N(2) by argon in the air around nodules directs nitrogenase electron flow in its total onto H(+) resulting in increased nodule H(2) evolution (total nitrogenase activity (TNA)). However, argon application induces a so-called argon-induced decline in nitrogenase activity (Ar-ID) connected with decreased nodule oxygen permeability. Consequently, TNA measurements tend to underestimate total nitrogenase activity.

Asparagine as a major factor in the N-feedback regulation of N2 fixation in Medicago truncatula.

The objective of this study was to assess whether a whole plant N-feedback regulation impact on nitrogen fixation in Medicago truncatula would manifest itself in shifts of the composition of the amino acid flow from shoots to nodules. Detected shifts in the phloem amino acid composition were supposed to be mimicked through artificial phloem feeding and concomitant measurement of nodule activity. The amino acid composition of the phloem exudates was analyzed from plants grown under the influence of treatments (limiting P supply or application of combined nitrogen) known to reduce nodule nitrogen fixation activity.

The importance of nodule CO2 fixation for the efficiency of symbiotic nitrogen fixation in pea at vegetative growth and during pod formation.

Nodule CO2 fixation is of pivotal importance for N2 fixation. The process provides malate for bacteroids and oxaloacetate for nitrogen assimilation. The hypothesis of the present paper was that grain legume nodules would adapt to higher plant N demand and more restricted carbon availability at pod formation through increased nodule CO2 fixation and a more efficient N2 fixation.

The efficiency of nitrogen fixation of the model legume Medicago truncatula (Jemalong A17) is low compared to Medicago sativa.

Medicago truncatula (Gaertn.) (barrel medic) serves as a model legume in plant biology. Numerous studies have addressed molecular aspects of the biology of M.

Elevated CO2 concentration around alfalfa nodules increases N2 fixation.

Nodule CO2 fixation via PEPC provides malate for bacteroids and oxaloacetate for N assimilation. The process is therefore of central importance for efficient nitrogen fixation. Nodule CO2 fixation is known to depend on external CO2 concentration.

Nitrogen from senescing lower leaves of common bean is re-translocated to nodules and might be involved in a N-feedback regulation of nitrogen fixation.

The objective of the present study was to elucidate whether remobilized N from lower leaves is involved in causing the drop in N(2) fixation during pod-filling in common bean (Phaseolus vulgaris L). Moreover, we addressed the question of whether remobilized N from lower leaves would reach the nodules. Nodulated common bean plants were grown in a growth chamber in quartz sand.

Nitrogen fixation by white lupin under phosphorus deficiency.

Background And Aims: White lupin is highly adapted to growth in a low-P environment. The objective of the present study was to evaluate whether white lupin grown under P-stress has adaptations in nodulation and N2 fixation that facilitate continued functioning.

Methods: Nodulated plants were grown in silica sand supplied with N-free nutrient solution containing 0 to 0.

P-deficiency increases the O2 uptake per N2 reduced in alfalfa.

Nodulated alfalfa (Medicago sativa L. cv. Saranac) plants were grown in hydroponics at P-sufficient and P-deficient supply levels.

Source-sink manipulations suggest an N-feedback mechanism for the drop in N2 fixation during pod-filling in pea and broad bean.

Various legume species show a marked decline in N2 fixation during pod-filling. The objective of this study was to clarify whether this is a result of impaired nodule assimilate supply or whether re-moblised N from senescing lower leaves initiates the phenomenon through an N-feedback impact. In model experiments on pea and broad bean plants during vegetative and reproductive growth, 30 or 60% of green leaves were either excised or individually darkened, thus removing the same photosynthetic capacity yet allowing N to be re-mobilised from darkened leaves.