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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Root and nodule : lateral organ development in N2-fixing plants
    Xiao, T.T. - \ 2015
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Rene Geurts; Henk Franssen. - Wageningen : Wageningen University - ISBN 9789462572768 - 198
    medicago - wortelknolletjes - endosymbiose - symbiose - mycorrhizae - stikstoffixatie - plantenontwikkeling - moleculaire biologie - medicago - root nodules - endosymbiosis - symbiosis - mycorrhizas - nitrogen fixation - plant development - molecular biology

    Plants are sessile organisms. This characteristic severely limits their ability of approaching nutrients. To cope with this issue, plants evolved endosymbiotic relationships with soil fungi to extend their interface with surrounding environment. In case of arbuscular mycorrhizae (AM) fungi this occurred about 400 million years ago. The AM fungi can interact with most angiosperms. In this symbiotic relationship, the plant get nutrients, especially phosphate, from the fungi, and plants provide carbohydrates to the fungi in return. About 60 million years ago, a group of plants evolved N2-fixing nodule symbiosis. This includes interactions of legumes plants with rhizobium bacteria and actinorhizal plants with Frankia bacteria. Currently, all plant species that are able to establish a nodule symbiosis belong to the Rosid I clade. In the nodule symbioses the bacteria produce ammonia and the plant provides carbohydrates to the bacteria.

    In the root nodule symbiosis, the nitrogen fixing bacteria are hosted in the cell of the root nodule. Although the function and structure of the root nodule are different from the other plant organs, it does share some features with other organs, especially the lateral root. To get further insight into the similarities and differences between root nodule and lateral root, I made use of the model legume (Medicago truncatula) and the non-legume Parasponia (Parasponia andersonii) that is the only genus outside the legumes that forms nodules with rhizobium.

    In Chapter 1, I will give a general introduction on the process of root nodule formation in legume plants. I will mainly focus on nodule organogenesis and the plant hormones that are known to be important for this process. Root nodules are supposed to have a close relationship with lateral roots. Therefore a comparison between lateral root and root nodule development will be included in this introduction.

    Lateral root development has especially been studied in in Arabidopsis. To be able to compare the root and root nodule developmental process, especially at the early stages, a Medicago lateral root development fate map has been made. This will be described in Chapter 2 and showed that in addition to the pericycle, endodermis and cortex are also mitotically activated during lateral root formation. Pericycle derived cells only form part of the stem cell niche as endodermis derived cells also contribute to this.

    In Chapter 3, a Medicago root nodule fate map is presented. In this Chapter, the contribution of different root cell layers to the mature nodule will be described. A set of molecular markers for root tissue, cell cycle and rhizobial infection have been used to facilitate this analysis. The fate map showed that nodule meristem originates from the third cortical layer and many cell layers of the base of the nodule are directly derived from cells of the inner cortical layers, root endodermis and pericycle. The inner cortical cell layers form about 8 cell layers of infected cells while the root endodermis and pericycle derived cells forms the uninfected tissues that are located at the base of the mature nodule. Nodule vascular is formed from the part of the primordium derived from the cortex. The development of primordia was divided in 6 stages. To illustrate the value of this fate map, a few published mutant nodule phenotypes are re-analyzed.

    In Chapter 4, the role of auxin at early stages of Medicago nodule formation is studied. In this chapter auxin accumulation is studied during the 6 stages of primordium development. It is studied by using DR5::GUS as an auxin reporter. Auxin accumulation associates with mitotic activity within the primordium. Previously, it has been postulated by theoretical modelling that the accumulation of auxin during nodulation is induced by a local reduction of PIN (auxin efflux carriers) levels. We tested this theory, but this was hampered due to the low level of PIN proteins in the susceptible zone of the root. It is still possible that auxin accumulation is initiated by a decrease of PIN levels. However, the level of 2 PIN already increase before the first divisions are induced. In young primordia they accumulate in all cells. At later stages PINs mainly accumulate at the nodule periphery and the future nodule meristem. The subcellular position of PINs strongly indicates they play a key role in the accumulation of auxin in primordia.

    Previous studies showed that a group of root apical meristem regulators is expressed in the nodule meristem. In Chapter 5, we tested whether the Medicago nodule meristem expresses PLETHORA genes that are expressed in the root meristem. These PLETHORAs were functionally analysed, by using RNAi approach using a nodule specific promoter. Knockdown of PLETHORAs expression hampers primordium formation and meristem growth. Hence, we conclude rhizobium recruited key regulators of root development for nodule development.

    In Chapter 6, we first introduced the non-legume lateral root and nodule fate maps by using Parasponia. In Parasponia nodules the nodule central vascular bundle is completely derived from the pericycle similar as its lateral roots. The nodule infected cells were shown to be derived from cortex. Together with the data obtained in this thesis, this Chapter further discussed several developmental aspects of the different lateral root organs. Especially, it focused on the vasculature and meristem formation of legume and non-legume nodules.

    Comparative and functional analysis of NODULATION SIGNALING PATHWAY 1 (NSP1) and NSP2 in rice and Medicago
    Liu, W. - \ 2013
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Rene Geurts. - S.l. : s.n. - ISBN 9789461736369 - 147
    oryza - medicago - knobbelvorming - symbiose - genen - rhizobium - wortelknolletjes - stikstoffixatie - oryza - medicago - nodulation - symbiosis - genes - rhizobium - root nodules - nitrogen fixation
    Epigenetic control of root and nodule development : the role of plant-specific histone deacetylases and LHP1 in root cell reprogramming
    Schilderink, S. - \ 2012
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Olga Kulikova; Joan Wellink. - S.l. : s.n. - ISBN 9789461734259 - 131
    cellen - epigenetica - wortels - knobbeltjes - plantenontwikkeling - apicale meristemen - medicago - arabidopsis - wortelknolletjes - histonen - cells - epigenetics - roots - nodules - plant development - apical meristems - medicago - arabidopsis - root nodules - histones

    In plants, unlike in animals, most organs develop post embryonically. These organs originate from clusters of undifferentiated dividing cells that form so-called meristems. Differentiated cells can be re-activated to enter the cell cycle and to ultimately give rise to new meristems. These differentiated cells reprogram to become pluripotent cells that are able to give rise to all cell types of the new organ. Examples are the formation of lateral roots from pericycle cells in Arabidopsis and the formation of root nodules from cortical cells in Medicago. In the latter organ rhizobia bacteria in symbiosis with Medicago fix atmospheric nitrogen. The reprogramming of differentiated cells is associated with large changes in gene expression. In this thesis the role of two chromatin modifiers in these reprogramming events is studied; the plant-specific histone deacetylases (HDTs) and LIKE HETEROCHROMATIN PROTEIN I (LHP1).

    In Chapter 2 we show that in Arabidopsis during lateral root formation all four members of the AtHDT family are strongly induced in lateral root founder cells already before the first divisions occur. Furthermore, AtHDT1 and AtHDT2 were shown to be necessary for maintenance of the root stem cell niche and meristem.

    Nodules are formed from fully differentiated root cortical cells. The reprogramming of cortical cells during the formation of nodules is unique to legumes, as cortical cells in other plants are not able to change their cell fate. In Medicago we characterized 3 HDTs and showed that these MtHDTs are involved in cell fate changes and are essential for the formation of nodules (Chapter 3). These MtHDTs are involved in early steps of reprogramming of the cortical cells in nodule initiation, since RNAi knock-down expression of all 3 MtHDTs simultaneously, strongly reduced nodule formation. Microscopic analysis of the small nodules that were still formed revealed these had a normal wt-like proximal part and a disturbed distal part.

    To explain this hybrid phenotype we created a fate map of nodule development by analyzing early stages of nodule formation (Chapter 4). This analysis revealed that the proximal part of nodules contain about 8 layers of fully differentiated cells that directly originate from the nodule primordium, which is derived from the two innermost cortical layers. The nodule meristem originates from the middle cortical layer and further growth of the nodule depends of differentiation and infection of cells originating from this meristem. At the disturbed distal part of the RNAi hybrid nodules, meristem-derived cells do not properly differentiate and are not infected with rhizobia indicating a disturbed meristem function.

    The second chromatin modifier we studied is LHP1, which is known to be involved in several developmental processes in plants, possibly as part of the plant analog of Polycomb Repressive Complex 1 (PRC1). We characterized the Medicago LHP1 homolog (Chapter 5) and showed that LHP1 forms euchromatic complexes that most likely regulate gene expression. MtLHP1 might be involved in proper differentiation of meristem-derived cells in the nodule since knock-down of MtLHP1 resulted in a similar phenotype as seen in MtHDT knock-down nodules.

    Our findings provide new insights on the role of the chromatin modifiers HDTs and LHP1 in reprogramming events in Arabidopsis and Medicago organ development.

    The formation of endosymbiotic membrane compartments: membrane identity markers and the regulation of vesicle trafficking
    Ivanov, S. - \ 2012
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Elena Fedorova; Erik Limpens. - S.l. : s.n. - ISBN 9789461733436 - 121
    planten - rhizobium - stikstof - stikstoffixatie - medicago - endosymbiose - celmembranen - blaasjes - biochemische omzettingen - moleculaire biologie - wortels - mycorrhizae - plants - rhizobium - nitrogen - nitrogen fixation - medicago - endosymbiosis - cell membranes - vesicles - biochemical pathways - molecular biology - roots - mycorrhizas

    In symbiosis of plants and arbuscular mycorrhizal fungi as well as in rhizobium-legume symbiosis the microbes are hosted intracellularly, inside specialized membrane compartments of the host. These membrane compartments are morphologically different but similar in function, since they control the exchange of compounds between host and its microsymbiont thus forming a highly specialized symbiotic interface. These are the arbuscules, containing highly branched fungal hyphae, and organelle-like symbiosomes containing rhizobium bacteria. Recent studies have markedly extended our insight in the evolution of the signaling mechanism underlying the formation of these symbiotic interfaces. These studies strongly suggest that rhizobium co-opted the complete signaling mechanism (including lipo-oligosaccharides signal molecules) from the more ancient AM fungi symbiosis. Further, in plant species (Parasponia) where rhizobium nodulation evolved rather recent and independent from legumes, the same lipo-oligosaccharide receptor is essential for the formation of the rhizobium symbiotic interface as well as arbuscules. Therefore it seems likely that rhizobium also co-opted the cellular mechanism controlling arbuscule formation to form a rhizobium symbiotic interface. This would imply that even after co-evolution in legumes the key regulators involved in the formation of these interfaces are similar or even identical.
    In this thesis I have shown that rhizobium symbiosis shares with AM symbiosis molecular and cell biological mechanisms that control symbiotic interface formation. I identified a plant exocytotic pathway marked by two highly homologous vesicle associated membrane proteins (VAMP) that control the formation of the symbiotic interface in both symbioses. RNAi of these two Medicago VAMP genes did not affect non-symbiotic plant development nor nodule formation. However, it hampered the formation of cell wall free regions at infection threads, and therefore blocks symbiosome formation. Further arbuscule formation was blocked, whereas root colonization was not affected. By identifying these VAMPs as common symbiotic regulators in secretory vesicle trafficking, I postulated that during evolution of rhizobium symbiosis pre-existing cellular mechanisms of the AM fungal symbiosis have been co-opted. These findings also revealed a primary role of exocytosis in symbiosome formation and allowed to postulate the apoplastic nature of symbiosome. Using identity markers of endocytotic compartments of plant cell (early endosome and late endosome) such as small GTPases belonging to the Rab family and SNARE (soluble N-ethylmaleimide sensitive factor attachment protein receptor) proteins, I have shown that they never occur on symbiosome membranes at any stage of symbiosome formation and development. This makes untenable long-standing hypothesis that symbiosomes originate from endocytosis-like process and represent endocytic (vacuolar) compartments. Instead symbiosomes have an apoplastic nature. Although symbiosomes have an apoplastic nature they acquire the vacuolar marker MtRab7 when they reach an elongated stage. However, vacuolar SNAREs which execute fusion of membranes are not present on functional symbiosomes, but they do appear on symbiosome membranes at the onset of senescence when symbiosomes are turned into a lytic compartment. Therefore I postulate that the acquisition of Rab7 primes the symbiosomes for degradation by the host. By this the host has full control over its microsymbiont.
    The finding that rhizobium symbiosis has co-opted the signaling mechanism as well as cellular mechanism from AM fungi symbiosis to facilitate an intracellular life style, has major implications for strategies to transfer the nodule symbiosis to non-legume crops. This is a “dream” that is already about a century old. The AM fungal symbiosis is far more ancient than the rhizobial symbiosis. It is also wide spread in the plant kingdom and almost 80% of plant species can establish an AM symbiosis. This implies that plants which are able to interact with AM fungi contain in principle the genes that are necessary for the intracellular accommodation of rhizobium. So the question is no longer why the rhizobium-legume symbiosis is specific for legumes, but why non-legumes are not yet able to establish this symbiosis?

    Co-option of pre-existing pathways during Rhizobium-legume symbiosis evolution
    Lillo, A. - \ 2012
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Rene Geurts. - S.l. : s.n. - ISBN 9789461733443 - 151
    rhizobium - fabaceae - symbiose - evolutie - stikstoffixatie - wortels - fylogenetica - genomen - medicago - eerste wortels - rhizobium - fabaceae - symbiosis - evolution - nitrogen fixation - roots - phylogenetics - genomes - medicago - root primordia

    Fixed nitrogen is one of the most limiting factors for plant growth. One of the most important nitrogen-fixing systems is the rhizobium root nodule symbiosis. In this Thesis I have studied the legume-rhizobium symbiosis, starting from the idea that part of pre-existing signalling pathways have been co-opted during evolution of this mutualistic interaction. Gene duplications -of which a whole genome duplication (WGD) is the most dramatic variant- are known as important driving forces in evolution of new traits. 56 to 65 million years ago an ancestral legume species within the Papilionoidae subfamily (Papilionoids) experienced a WGD event and subsequently gave rise to several major phylogenetic crowns. I hypothesize that among the orthologous gene pairs maintained are genes that are essential for nodulation. I adopted a phylogenetic strategy to identify new candidate genes involved in the legume-Rhizobium symbiosis
    In a targeted approach, we focussed on the cytokinin phosphorelay pathway. This resulted in the identification of one gene pair encoding type-A Response Regulators (RRs) with a positive regulatory role for these proteins in root nodule formation. Yet the illustrated role for MtRR9 and MtRR11 in rhizobial symbiosis provides a proof of principle of this method to identify gene pairs involved in legume specific characters. An unbiased search for paralogous gene pairs revealed two conserved gene duplications in the NADPH oxidases gene family. NADPH oxidases are reactive oxygen species (ROS) producing enzymes. We identified two sets of duplicated genes that have been maintained after the Papilionoid specific WGD and we show that MtRBOHA and MtRBOHG are redundant, yet essential during symbiosis.
    Moreover, although it is commonly believed that exclusively pericycle cells give rise to the lateral root primordium, similar as seen in Arabidopsis thaliana, we provide morphological evidence that in the studied legume species this is not the case. In both, Lotus and Medicago, also root cortical cell divisions occur during lateral root formation. Furthermore, we found a striking correlation in the cell layers that are recruited during lateral root and nodule primordium formation. This supports the hypothesis that at least parts of the lateral root developmental program have been recruited during evolution of symbiotic root nodules.

    Towards a better understanding of the role of reactive oxygen species in legume root nodules
    Ramos Escribano, J. - \ 2004
    Wageningen University. Promotor(en): Ton Bisseling. - [S.l.] : S.n. - ISBN 9789085040927 - 125
    peulgewassen - arabidopsis - medicago - rhizobium radiobacter - testplanten - wortelknolletjes - wortelharen - symbiose - rna - zuurstof - transformatie - iso-enyzmen - superoxide dismutase - legumes - arabidopsis - medicago - rhizobium radiobacter - test plants - root nodules - root hairs - symbiosis - rna - oxygen - transformation - isoenzymes - superoxide dismutase

    Biological N2 fixation is carried out exclusively by prokaryotes, either in the free-living form or in mutualistic symbioses with green algae, legumes and actinorhizal plants. The most agronomica1ly relevant symbiosis is, by fàr, that formed between soil rhizobia and legume roots. In addition, the input of fixed N2 by this symbiosis into agricultural systems represents an economical and environmentally- friendly altemative to chemical fertilization. Therefore, the improvement of the efficiency of symbiotic N2 fixation, both under physiological and stressful conditions, is highly desirable.
    The process of N2 fixation occurs in specialized organs, called nodules, that are formed as a result of a complex exchange of molecular signals (flavonoids, Nod factors) between the rhizobia and the host plant. During nodule formation, bacteria differentiate into bacteroids, which express the nitrogenase enzymatic complex. This catalyzes; the reduction of N2 to ammonium, requires ATP, Mg2+ and an electron donor, and is irreversibly inactivated by O2. During the last few years, the very early stages of nodule formation are being dissected at the molecular level. It is clear that the signal transduction pathway, which is triggered after binding of compatible Nod factors to receptors, involves oscillatory changes in cytoplasmic calcium, ethylene and protein kinases. Several lines of evidence indicate that reactive oxygen species (ROS) are also involved in signal transduction during nodule formation as well as in natural and stress- induced nodule senescence. However, critical questions remain to be answered: what specific ROS and at what specific step(s) of nodulation do they participate, how can Nod factors suppress the plant's defensive response, or how ROS production escapes control during nodule senescence.
    In this thesis we have devised three strategies that may be of value for the cellular and molecu1ar study of symbiosis and in particular ROS metabolism in nodules. First, we report a novel method that allows the isolation of root hairs, with high yield and purity, from the model legume M. truncatula. We also found in M. truncatula a protein, MtRH2, homologous to pea PsRH2, that is specifically localized in the root epidermis. This feature was exploited to monitor the root hair isolation procedure and can also be used for specific expression of antioxidant enzymes in root hairs. A second strategy that may be helpful to study the function of ROS is gene inactivation. We show that A. rhizogenes-mediated RNA interference (RNAi) is a fast and effective tool for this purpose. The introduction of RNAi in legumes and Arabidopsis using Agrobacterium rhizogenes based transformation was set up with genes with a known knockout phenotype. The efficiency of the technique was demonstrated by using RNAi to knock-down the KOJAK gene of Arabidopsis, which is involved in root hair development. We also show that RNAi silencing is restricted to the epidermal cells where RNAi constructs are expressed. A third strategy to study ROS metabolism is the overexpression of important antioxidant enzymes, such as superoxide dismutases (SODs), in transgenic legumes. Three lines of transgenic alfalfa (M. sativa) were designed to overexpress, respectively, MnSODs in chloropIasts, MnSOD in mitochondria and FeSODs in chloropIasts. Analysis of SOD composition in these plants led us to discover a novel compensatory effect in the activities of MnSOD and FeSOD in the leaves, which was not due to changes in mRNA levels. We also provide evidence that SOD activity in plants is regulated at least partially at the post-translational level and that FeSOD performs important antioxidant functions other than the scavenging of superoxide radicals generated in photosynthesis. Finally, in this thesis we discuss the significance, applications and prospects of the work done in the light of current research on nodule formation and senescence.
    Role of ROP GTPases and Nod factor signaling in Medicago root nodule infection
    Mirabella, R. - \ 2004
    Wageningen University. Promotor(en): Ton Bisseling, co-promotor(en): Rene Geurts. - [S.l.] : S.n. - ISBN 9789085040484 - 160
    wortelknolletjes - medicago - fosfoglyceraat kinase (gtp) - actine - genexpressie - signaaltransductie - root nodules - medicago - phosphoglycerate kinase (gtp) - actin - gene expression - signal transduction
    Teelt van luzerne heeft zijn beperkingen
    Boxem, Tj. - \ 1999
    Praktijkonderzoek Rundvee, Schapen en Paarden. Praktijkonderzoek 12 (1999)1. - ISSN 1386-8470 - p. 30 - 31.
    groenvoeders - medicago - plantenvoeding - oogsten - voer - voedingswaarde - luzerne - green fodders - medicago - plant nutrition - harvesting - feeds - nutritive value - lucerne
    Een sterk punt van luzerne is dat het in zijn eigen stikstofbehoefte kan voorzien door binding van stikstof uit de lucht. Daarmee speelt luzerne ook een gunstige rol in een vruchtwisselingsplan. Luzerne is daarom het meest interessant voor de biologische veehouderij of onder zware MINAS regelgeving.
    Expression of the Sinorhizobium meliloti C4-dicarboxylate transport gene during symbiosis with the Medicago host plant
    Boesten, B. - \ 1999
    Agricultural University. Promotor(en): A. van Kammen. - S.l. : S.n. - ISBN 9789058080943 - 121
    rhizobium - symbiose - medicago - regulatie - transport - rhizobium - symbiosis - medicago - regulation - transport

    During symbiosis between Sinorhizobium meliloti and the Medicago host plant, the energy required to fix atmospheric nitrogen, is derived from the plant photosynthate. Current evidence indicates that C 4 -dicarboxylates (dCA) are the major and probably only source of carbon provided to the bacteroids in sufficiently high amounts to support symbiotic N 2 -fixation. The ability of the microsymbiont to take up dCA is essential for the establishment of an effective symbiosis. The dct A gene codes for a high affinity dCA permease (DctA). The regulatory dct BD genes code for a two-component regulatory system. Under free-living conditions, the regulatory dct BD genes are essential for activation of the dct A promoter. Bacteroids isolated from nodules induced by regulatory dct BD mutants take up dCA efficiently. This demonstrated that in the specific environment of the nodule, regulatory molecules other than DctBD, are involved in the expression of the dct A promoter.

    The aim of this work was to study the regulation of the dct A gene during symbiosis of S.meliloti with the Medicago host plants and in particular to characterise this alternative mechanism of symbiotic activation (ASA). Using gene fusions of the dct A expression signals to the lac Z reporter gene, in combination with histochemical staining of plant tissue, the regulation of the S.melilotidct A gene was studied in situ during the symbiosis with the Medicago host plants. The major findings of this work are the following.

    1) The ASA mechanism is only active at the late stages of the symbiosis.

    First, it is established that in a wild-type background, the dct A gene is expressed during the early and late stages of symbiosis (A). In contrast in nodules induced by a regulatory dct B or dct D mutant, a distinct late symbiotic pattern of dct A expression was observed (B). This meant that the ASA is an exclusive late symbiotic mechanism. The temporal and spatial pattern of DctBD-independent dct A expression in nodules induced on the alfalfa host plant was always very similar to that of the nif H gene fusion. This late symbiotic manifestation of the ASA means that the early expression of dct A observed in wild-type nodules is necessarily DctBD dependent.

    2) The ASA requires sequences downstream of the dct A promoter for activity.

    We also found that certain gene fusions lacking the extreme N-terminal domain of the dct A coding region did not respond to the ASA. This was remarkable since these gene fusions appeared to be correctly regulated by the DctBD system under free-living conditions. In contrast, gene fusions containing the first 8 amino-acids of the dct A coding region were efficiently activated by the ASA (B). We concluded that some cis-acting nucleotide sequences, located immediately downstream of the dct A promoter in the beginning of the coding region, are required for ASA activity

    3) The UAS sites of the dct A promoter are not essential for ASA activity.

    Inline Figure 1

    During symbiosis dct A:: lac Z gene fusions lacking the upstream activator sites (UAS) were expressed in wild-type nodules (D) and at a similar level in a dct D mutant background (E). The pattern of temporal and spatial expression in a wild-type nodule (D) was similar to that observed for DctBD independent activation of other gene fusions containing the UAS (B). We concluded that the UAS, which are indispensable for the activation by the DctBD system, are not essential for the activation of the dct A promoter by the ASA.

    4) The alternative symbiotic activator requires NifA.

    We observed gene fusions lacking the UAS sequences are efficiently expressed in the wild-type and dct D mutant backgrounds (D;E), but were not activated in nodules formed by a nif A mutant strain (F).

    Working with the Medicago truncatula host plant, we found that in nodules induced by a dct D mutant strain, the dct A gene was not expressed efficiently. We also observed that the nif A gene is expressed in these nodules at a level, which is strongly reduced in comparison to the level of nif A expression in nodules induced on M.sativa . We concluded that an efficient expression of the nif A gene is required for ASA activity.

    5) The ASA is not essential for symbiotic N 2 -fixation.

    Monitoring dct A activity with the dct A:: lac Z gene fusions which are not activated by the ASA, demonstrated that the DctBD system alone is sufficient to express the dct A promoter during symbiosis. Additionally we observed that although the ASA does not function in nodules induced on the Medicago truncatula host plant, these nodules were efficient for symbiotic N 2 -fixation. This indicates that activation of the dct A promoter by the ASA is not required for symbiotic N 2 -fixation.

    Teelt van luzerne
    Schans, D.A. van der; Zwanepol, S. ; Jukema, A. ; Boxem, T. ; Nijssen, K. - \ 1998
    Lelystad : Praktijkonderzoek voor de Akkerbouw en de Vollegrondsgroenteteelt (Teelthandleiding 84) - 55
    medicago - nederland - luzerne - teelt - teelthandleidingen - akkerbouw - medicago - netherlands - lucerne - cultivation - cultivation manuals - arable farming
    In de teelthandleiding luzerne is informatie over de teelt, oogst en voedingsaspecten van luzerne te vinden.
    Voedergewassen op droogtegevoelige gronden zonder beregening
    Stienezen, M. ; Everts, H. ; Snijders, P. ; Schans, D. van der - \ 1998
    Praktijkonderzoek Rundvee, Schapen en Paarden. Praktijkonderzoek 11 (1998)3. - ISSN 1386-8470 - p. 28 - 31.
    droge stof - zea mays - maïs - triticale - medicago - beta vulgaris - suikerbieten - zandgronden - voedergrassen - dry matter - zea mays - maize - triticale - medicago - beta vulgaris - sugarbeet - sandy soils - fodder grasses
    Een te grote onttrekking van grondwater is de oorzaak dat het grondwaterpeil in sommige gebieden de laatste decennia aanzienlijk is gedaald. De landbouw neemt ongeveer eenderde van de grondwateronttrekking voor haar rekening. Het beleid zoekt naar mogelijkheden om het gebruik van grondwater door de landbouw te beperken
    Fractioneren van gras en luzerne
    Kasper, G.J. - \ 1998
    Landbouwmechanisatie 49 (1998)3. - ISSN 0023-7795 - p. 47 - 48.
    briketten - briketteren - graslanden - medicago - korrelvoer - voer - eiwitten - biologie - scheiding - fractionering - zuiveren - briquettes - briquetting - grasslands - medicago - pelleted feeds - feeds - proteins - biology - separation - fractionation - purification
    Gewasfractionering is de mechanische scheiding van gewassen in een aantal fracties voor een betere benutting van het oorspronkelijke materiaal. Het is een proces waarbij de bladrijke plant sterk gekneusd en samengeperst wordt. Hierdoor ontstaat een relatief eiwitrijke en een vezelarme sapfractie en een vezelrijke perskoek
    Luzerne beperkt alternatief voor gras
    Meijer, R. ; Walbeek, M. van - \ 1996
    Praktijkonderzoek Rundvee, Schapen en Paarden. Praktijkonderzoek 9 (1996)2. - ISSN 1386-8470 - p. 21 - 22.
    diervoedering - graansoorten - melkvee - melkveehouderij - ontwikkeling - voer - groei - medicago - voedingswaarde - kuilvoer - jonge dieren - animal feeding - cereals - dairy cattle - dairy farming - development - feeds - growth - medicago - nutritive value - silage - young animals
    Op droogtegevoelige gronden zonder beregening kan worden overwogen om luzerne te telen.
    Waarde gedroogde luzerne goed vast te stellen
    Boxem, Tj. - \ 1994
    Praktijkonderzoek / Praktijkonderzoek Rundvee, Schapen en Paarden (PR), Waiboerhoeve 7 (1994)5. - ISSN 0921-8874 - p. 38 - 41.
    diervoedering - ontwikkeling - voer - groei - medicago - voedingswaarde - kuilvoer - jonge dieren - voedergrassen - animal feeding - development - feeds - growth - medicago - nutritive value - silage - young animals - fodder grasses
    Uit onderzoek op ROC Aver Heino waarbij graskuil en luzernekuil zijn vergeleken bleek dat jongvee op luzernekuil volgens de berekende energie-opname uit de voederwaardeschatting ruim 300 gram per dier per dag zou kunnen groeien, maar in werkelijkheid was de groei ruim 650 gram. Dit betekent dat door het jongvee uit luzernekuil aanmerkelijk meer energie is gehaald dan op basis van analyse is ingerekend.
    Veevoedkundige waarde gras- en luzernebrok
    Boxem, Tj. - \ 1993
    Lelystad : Proefstation voor de Rundveehouderij, Schapenhouderij enPaardenhouderij (Publikatie / Proefstation voor de Rundveehouderij, Schapenhouderij en Paardenhouderij 79) - 15
    rundvee - medicago - voedermiddelbewerking - voedergrassen - cattle - medicago - feed processing - fodder grasses
    Van F.e zijde wordt gedacht dat de voederwaarde van luzernebrok zeker zo goed of zelfs aanzienlijk beter is dan die van goed gewonnen grasbrok. Het is echter de vraag of deze zienswijze juist is. Mede op verzoek van de Vereniging van Nederlandse Groenvoederdrogerijen is in het winterseizoen 1991/92 een drietal proeven uitgevoerd om na te gaan of de groei van vrouwelijk jongvee overeenkwam met de potentiële groei volgens de vastgestelde voederwaarde van rantsoenen met gras- of luzernebrok.
    Ontwikkeling bedrijfssysteem met luzerne op Cranendonck
    Subnel, B. ; Boxem, Tj. ; Walbeek, M. van - \ 1993
    Praktijkonderzoek / Praktijkonderzoek Rundvee, Schapen en Paarden (PR), Waiboerhoeve 6 (1993)5. - ISSN 0921-8874 - p. 51 - 57.
    graansoorten - droge stof - bedrijfssystemen - voer - medicago - nederland - voedingswaarde - kuilvoer - cereals - dry matter - farming systems - feeds - medicago - netherlands - nutritive value - silage
    Luzerne kan in droge jaren zonder kunstmatige beregening tot hoge opbrengsten komen en heeft geen stikstofbemesting nodig.
    Een jaar luzerne op Cranendonck
    Subnel, B. ; Werf, J. van der - \ 1992
    Praktijkonderzoek / Praktijkonderzoek Rundvee, Schapen en Paarden (PR), Waiboerhoeve 5 (1992)4. - ISSN 0921-8874 - p. 24 - 28.
    groenbemesters - medicago - green manures - medicago
    Luzerne is een voedergewas dat in veel landen in de wereld, zoals de VS, Canada en Australië, een belangrijk deel van het rantsoen voor melkvee uitmaakt.
    Inhibition of nodulation of lucerne (Medicago sativa L.) by calcium depletion in an acid soil.
    Pijnenborg, J.W.M. ; Lie, T.A. ; Zehnder, A.J.B. - \ 1990
    Plant and Soil 127 (1990). - ISSN 0032-079X - p. 31 - 39.
    medicago - bodem - calcium - zure gronden - kattekleigronden - stikstofbindende bacteriën - symbiose - rhizobium - medicago - soil - calcium - acid soils - acid sulfate soils - nitrogen fixing bacteria - symbiosis - rhizobium
    Biological nitrogen fixation by lucerne (Medicago sativa L.) in acid soils
    Pijnenborg, J. - \ 1990
    Agricultural University. Promotor(en): A.J.B. Zehnder; T.A. Lie. - S.l. : Pijnenborg - 112
    medicago - assimilatie - stikstof - zure gronden - kattekleigronden - medicago - assimilation - nitrogen - acid soils - acid sulfate soils

    Growth of lucerne( Medicago sativa L.) is poor in soils with values of pH-H2O below 6. This is often due to nitrogen deficiency, resulting from a hampered performance of the symbiosis withRhizobium meliloti. This thesis deals with the factors affecting biological nitrogen fixation by lucerne in acid soils.

    In a field experiment, lucerne seeds were either inoculated withR.meliloti only,or inoculated and pelleted with lime, before sowing in a sandy soil of pH 5.2. Lime-pelleting significantly improved the establishment of the seedlings. This was caused by earlier nodulation, as evidenced by the formation of crown nodules,i.e.the nodules on the upper 10 mm of the seedling taproot. The number of seedlings carrying crown nodules tripled from 18% to 56%, 26 days after sowing as a result of lime-pelleting. The dry matter yield and nitrogen fixation of the plants at later stages showed a close correlation with crown nodulation.

    To minimize the problems inherent to field experiments,e.g.costs and labour, besides pots, rhizotrons (small root boxes made of plastic petri dishes) were developed to study the symbiosis under controlable conditions in the laboratory (Chapter 2). Comparative trials showed that crown nodulation in pots was practically similar to that in the field. In rhizotrons, the early root development and nodule formation could continuously be observed. moreover, lime- pelleting resulted in a greater increase of crown nodulation (5% to 90%) during a shorter incubation period (14 days).

    R.melilotibacteria are notorious for their acid sensitivity. As a consequence the increased crown nodulation by lime-pelleting might be the result of a better proliferation of these bacteria, thus resulting in a higher chance of root infection. To verify this hypothesis, the effect of lime-pelleting on the survival of inoculated R.meliloti around the seed was recorded during a period of 12 days following sowing. In the initial 12 hours a strong increase in rhizobial numbers coincided with the germination of the seed. Little differences in multiplication were measured in the presence or absence of a lime-pellet. To obtain optimal nodulation in this soil, however, lime-pelleting was a prerequisite and at least 10 5cells ofR.meliloti per seed were required. In the absence of lime, only a few plants nodulated, even when the number of rhizobia was increased to 10 7per seed (Chapter 3).

    The nodulation effect of lime-pelleting could not be explained by a better rhizobial multiplication. The benefit of CaC0 3 can be due to either neutralization of soil acidity and/or to the input of calcium.Tostudy the pH changes in the rhizosphere while leaving the spatial arrangement of the soil intact, the following method was deviced: The soil was covered with a thin layer of agar containing the pH indicator bromocresol purple. To prevent the contamination of agar with soil particles, a nylon gauze was used to keep the soil separated from the agar. Quantitative pH measurements were done by inserting a micro-electrode into the agar after 3 hours of contact with the soil. The validity of the data obtained by this method was investigated by comparing the results with those obtained using standard procedures for pH measurement in a soil-water suspension (Chapter 4).

    Using the agar-contact method, it was shown that the benefit of lime on the nodulation of lucerne was largely (80%) due to neutralization of acidity, and to a lesser extent (20%) to the supply of calcium. For nodulation, soil-pH measured around lime-pelleted seeds, should at least be 5.8. Untreated roots were also able to induce a pH-increase of 0.6 units at 6 days after sowing (d.a.s.) or later, but only very few plants nodulated. These results, obtained with soil-grown plants, confirm earlier findings with hydroponically grown plants, that nodulation is sensitive for acidity only during the early phase of the process (0 to 3 d.a.s.) (Chapter 5).

    The soil already contained 1.2 meq of calcium per 100 g. Hence, the contribution of calcium in the lime effect was rather small. When the native calcium was removed with a specific calcium chelator (EGTA). crown nodulation could further be reduced to 12%. However, an additional complication was the acidification that accompanied the chelation of soilcalcium, with soil-pH dropping from 6.1 to 5.2. This problem could be overcome by applying small agar blocks containing the chelator. This technique allowed local application and temporal treatment of the root with EGTA. It was shown that the nodulation could be inhibited by calcium depletion only during the first day (Chapter 6). Obviously, the early phase of the nodulation of lucerne in acid soil is transiently susceptible to low calcium availability, similar to the transient sensitivity to low pH.

    Effect of legumes on soil mineral nitrogen and response of potatoes to nitrogen fertilizer
    Neeteson, J.J. - \ 1989
    In: Effects of crop rotation on potato production in the temperate zones : proceedings of the international conference on Effects of crop rotation on potato production in the temperate zones, held in August 14 - 19, 1988, Wageningen, The Netherlands / Vos, J., van Loon, C.D., Bollen, G.J., Kluwer (Developments in plant and soil sciences vol. 40) - ISBN 9780792304951 - p. 89 - 93.
    braak - medicago - nitraten - nitrieten - stikstof - aardappelen - rotaties - bodem - solanum tuberosum - fallow - medicago - nitrates - nitrites - nitrogen - potatoes - rotations - soil - solanum tuberosum
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