Correlation between ultrastructural differentiation of bacteroids and nitrogen fixation in alfalfa nodules

Vasse, Jacques; Billy, Françoise de; Camut, Sylvie; Truchet, G.

doi:10.1128/jb.172.8.4295-4306.1990

Cited by 510 publications

(476 citation statements)

References 40 publications

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“…Once in the cytosol, iron can be transported into the symbiosomes, most likely through SEN1 or other VIT homologue (4). In addition, iron is translocated to other organelles for plant ferroprotein synthesis (5). Once the nodule senesces, iron is recycled and transferred back to the vasculature, probably through YSL transporters (6).…”

Section: Resultsmentioning

confidence: 99%

“…4 Subsequently, the endocytic rhizobia differentiate into bacteroids and together with the ''endocytic'' vesicle constitute an organelle-like structure, the symbiosome. 5 In the microaerobic environment achieved within the nodule, bacteroids produce the enzyme nitrogenase, which is directly responsible for nitrogen fixation. 6 There are two main developmental types of nodule: determinate and indeterminate.…”

Section: Introductionmentioning

confidence: 99%

“…1): zone I is the apical meristem, zone II is where rhizobia are released into the host cells and differentiate, zone III is where nitrogen fixation occurs in a microaerobic environment, and zone IV is the senescent zone. 5 Iron plays an essential part in SNF. 8 It is the cofactor of the main enzymes involved in this process, from leghemoglobin, protein responsible for the steady supply of low levels of oxygen in the microaerobic environment in which the reaction takes place, 9 to nitrogenase, the enzyme that catalyzes the reduction of N 2 into two NH 4 + .…”

Section: Introductionmentioning

confidence: 99%

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Iron distribution through the developmental stages of Medicago truncatula nodules

et al. 2013

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Paramount to symbiotic nitrogen fixation (SNF) is the synthesis of a number of metalloenzymes that use iron as a critical component of their catalytical core. Since this process is carried out by endosymbiotic rhizobia living in legume root nodules, the mechanisms involved in iron delivery to the rhizobia-containing cells are critical for SNF. In order to gain insight into iron transport to the nodule, we have used synchrotron-based X-ray fluorescence to determine the spatio-temporal distribution of this metal in nodules of the legume Medicago truncatula with hitherto unattained sensitivity and resolution. The data support a model in which iron is released from the vasculature into the apoplast of the infection/differentiation zone of the nodule (zone II). The infected cell subsequently takes up this apoplastic iron and delivers it to the symbiosome and the secretory system to synthesize ferroproteins.Upon senescence, iron is relocated to the vasculature to be reused by the shoot. These observations highlight the important role of yet to be discovered metal transporters in iron compartmentalization in the nodule and in the recovery of an essential and scarce nutrient for flowering and seed production.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Iron distribution through the developmental stages of Medicago truncatula nodules

et al. 2013

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“…An oxygen-sensing bacterial regulatory cascade controls the expression of the nitrogenase complex and the microaerobic respiratory enzymes that are required to provide energy and reductant to nitrogenase 98 . This cascade is induced by the presence of low oxygen tension within the differentiating bacteroid 89,99,100 . The bacterial regulators include the oxygen-sensing two-component regulatory system FixL and FixJ, NifA, σ 54 and FixK 98 .…”

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confidence: 99%

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

et al. 2007

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Nitrogen-fixing rhizobial bacteria and leguminous plants have evolved complex signal exchange mechanisms that allow a specific bacterial species to induce its host plant to form invasion structures through which the bacteria can enter the plant root. Once the bacteria have been endocytosed within a host-membrane-bound compartment by root cells, the bacteria differentiate into a new form that can convert atmospheric nitrogen into ammonia. Bacterial differentiation and nitrogen fixation are dependent on the microaerobic environment and other support factors provided by the plant. In return, the plant receives nitrogen from the bacteria, which allows it to grow in the absence of an external nitrogen source. Here, we review recent discoveries about the mutual recognition process that allows the model rhizobial symbiont Sinorhizobium meliloti to invade and differentiate inside its host plant alfalfa (Medicago sativa) and the model host plant barrel medic (Medicago truncatula).The recent completion of the Sinorhizobium meliloti genome sequence, and the progress towards the completion of the Medicago truncatula genome sequence, have led to a surge in the molecular characterization of the determinants that are involved in the development of the symbiosis between rhizobial bacteria and leguminous plants. Aromatic compounds from legumes called flavonoids first signal the rhizobial bacteria to produce lipochitooligosaccharide compounds called Nod factors 1 . Nod factors that are secreted by the bacteria activate multiple responses in the host plant that prepare the plant to receive the invading bacteria. Nod factors and symbiotic exopolysaccharides induce the plant to form infection threads, which are thin tubules filled with bacteria that penetrate into the plant cortical tissue and deliver the bacteria to their target cells. Plant cells in the inner cortex internalize the invading bacteria in host-membrane-bound compartments that mature into structures known Correspondence to G.C.W. gwalker@mit.edu. Competing interests statementThe authors declare no competing financial interests. DATABASES Invasion of plant rootsAlthough plant roots are exposed to various micro-organisms in the soil, their cell walls form a strong protective barrier against most harmful species. The early steps in the invasion of barrel medic (M. truncatula) and alfalfa (Medicago sativa) roots by S. meliloti are characterized by the reciprocal exchange of signals that allow the bacteria to use the plant root hair cells as a means of entry. Initial signal exchangeFlavonoid compounds (2-phenyl-1,4-benzopyrone derivatives) produced by leguminous plants are the first signals to be exchanged by host-rhizobial symbiont pairs 1 (FIG. 1). Flavonoids bind bacterial NodD proteins, which are members of the LysR family of transcriptional regulators, and activate these proteins to induce the transcription of rhizobial genes 1,2 . For example, the M. sativa-derived flavonoid luteolin stimulates binding of an active form of NodD1 to an S. meliloti 'nod-box' p...

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“…Simultaneously with infection, inner root cortical cells dedifferentiate to form a nodule primordium and then a nodule meristem (11,14,19). The persistent activity of the meristem, located at the outer extremity of the nodule, ensures nodule elongation for a number of weeks (41). While the meristem is active, rhizobia are released from the infection threads into the plant cell cytoplasm (5,14,17,24).…”

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confidence: 99%

Root nodulation of Sesbania rostrata

et al. 1994

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The tropical legume Sesbania rostrata can be nodulated by Azorhizobium caulinodans on both its stem and its root system. Here we investigate in detail the process of root nodulation and show that nodules develop exclusively at the base of secondary roots. Intercellular infection leads to the formation of infection pockets, which then give rise to infection threads. Concomitantly with infection, cortical cells of the secondary roots dedifferentiate, forming a meristem which has an "open-basket" configuration and which surrounds the initial infection site. Bacteria are released from the tips of infection threads into plant cells via "infection droplets," each containing several bacteria. Initially, nodule differentiation is comparable to that of indeterminate nodules, with the youngest meristematic cells being located at the periphery and the nitrogen-fixing cells being located at the nodule center. Because of the peculiar form of the meristem, Sesbania root nodules develop uniformly around a central axis. Nitrogen fixation is detected as early as 3 days following inoculation, while the nodule meristem is still active. Two weeks after inoculation, meristematic activity ceases, and nodules then show the typical histology of determinate nodules. Thus, root nodule organogenesis in S. rostrata appears to be intermediate between indeterminate and determinate types.

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Correlation between ultrastructural differentiation of bacteroids and nitrogen fixation in alfalfa nodules

Cited by 510 publications

References 40 publications

Iron distribution through the developmental stages of Medicago truncatula nodules

Iron distribution through the developmental stages of Medicago truncatula nodules

How rhizobial symbionts invade plants: the Sinorhizobium–Medicago model

Root nodulation of Sesbania rostrata

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