Showing papers on "Frankia published in 1996"
TL;DR: The phylogenetic tree revealed that there was greater diversity among the Alnus-infective strains than among the strains that infect other host plants, and the family Frankiaceae should be emended so that the genera Geodermatophilus and "Blastococcus" are excluded and only the genus Frankia is retained.
Abstract: The members of the actinomycete genus Frankia are nitrogen-fixing symbionts of many species of woody dicotyledonous plants belonging to eight families. Several strains isolated from diverse actinorhizal plants growing in different geographical areas were used in this study. The phylogenetic relationships of these organisms and uncharacterized microsymbionts that are recalcitrant to isolation in pure culture were determined by comparing complete 16S ribosomal DNA sequences. The resulting phylogenetic tree revealed that there was greater diversity among the Alnus-infective strains than among the strains that infect other host plants. The four main subdivisions of the genus Frankia revealed by this phylogenetic analysis are (i) a very large group comprising Frankia alni and related organisms (including Alnus rugosa Sp+ microsymbionts that are seldom isolated in pure culture), to which Casuarina-infective strains, a Myrica nagi microsymbiont, and other effective Alnus-infective strains are related; (ii) unisolated microsymbionts of Dryas, Coriaria, and Datisca species; (iii) Elaeagnus-infective strains; and (iv) “atypical” strains (a group which includes an Alnus-infective, non-nitrogen-fixing strain). Taxa that are related to this well-defined, coherent Frankia cluster are the genera Geodermatophilus, “Blastococcus,” Sporichthya, Acidothermus, and Actinoplanes. However, the two genera whose members have multilocular sporangia (the genera Frankia and Geodermatophilus) did not form a coherent group. For this reason, we propose that the family Frankiaceae should be emended so that the genera Geodermatophilus and “Blastococcus” are excluded and only the genus Frankia is retained.
341 citations
TL;DR: There is genetic diversity among Frankia strains that infect members of the family Casuarinacaeae, contrary to the results of previous molecular studies of isolated strains.
Abstract: DNA extracted directly from nodules was used to assess the genetic diversity of Frankia strains symbiotically associated with two species of the genus Casuarina and two of the genus Allocasuarina naturally occurring in northeastern Australia. DNA from field-collected nodules or extracted from reference cultures of Casuarina-infective Frankia strains was used as the template in PCRs with primers targeting two DNA regions, one in the ribosomal operon and the other in the nif operon. PCR products were then analyzed by using a set of restriction endonucleases. Five distinct genetic groups were recognized on the basis of these restriction patterns. These groups were consistently associated with the host species from which the nodules originated. All isolated reference strains had similar patterns and were assigned to group 1 along with six of the eight unisolated Frankia strains from Casuarina equisetifolia in Australia. Group 2 consisted of two unisolated Frankia strains from C. equisetifolia, whereas groups 3 to 5 comprised all unisolated strains from Casuarina cunninghamiana, Allocasuarina torulosa, and Allocasuarina littoralis, respectively. These results demonstrate that, contrary to the results of previous molecular studies of isolated strains, there is genetic diversity among Frankia strains that infect members of the family Casuarinacaeae. The apparent high homogeneity of Frankia strains in these previous studies probably relates to the single host species from which the strains were obtained and the origin of these strains from areas outside the natural geographic range of members of the family Casuarinaceae, where genetic diversity could be lower than in Australia.
97 citations
TL;DR: In this paper, the root infection by symbiotic N 2 -fixing Frankia and Rhizobium strains was quantified in relation to light and soil properties for seedlings of 12 woody species from a subtropical savanna in southern Texas, USA.
Abstract: 1. Root infection by symbiotic N 2 -fixing Frankia and Rhizobium strains was quantified in relation to light and soil properties for seedlings of 12 woody species from a subtropical savanna in southern Texas, USA. 2. None of four rhamnaceous species nodulated, despite the fact that bioassays with a known actinorhizal species yielded 13 nodules per seedling. Celtis pallida (Ulmaceae), Acacia greggii and Acacia berlandieri (Leguminosae) also failed to nodulate even though field populations of these species were characterized by high (2.7-4.2%) foliar nitrogen concentration. 3. Infective rhizobia occurred in all soils studied regardless of soil depth, distance from a host plant or type of plant cover. Plant growth in N-free media and acetylene reduction activity suggested that all nodules were capable of N 2 -fixation. 4. The extent of nodulation varied by species. However, nodulated seedlings were taller, produced more biomass and allocated less biomass to root systems than their non-nodulated counterparts. 5. Numbers of nodules on seedlings of Prosopis glandulosa, the dominant woody species in this subtropical savanna and throughout the south-western USA, were reduced by low light (15% full sunlight) regardless of soil N level; at medium and full sunlight nodule biomass expressed as a fraction of whole plant biomass decreased with increasing soil N. Nodulation of field-grown P. glandulosa appears to be ephemeral, apparently varying with changes in soil moisture. 6. Nodulation and N 2 fixation among woody legumes in subtropical savannas can occur across a broad range of soil conditions and depths with significant impacts on local and regional N-cycles. 7. Field levels of foliar N in species that failed to nodulate in the laboratory were comparable to or greater than those in species capable of nodulation, suggesting that leaf N is not a reliable indicator of N 2 fixation.
80 citations
TL;DR: To study the global diversity of plant-symbiotic nitrogen-fixing Frankia strains, a rapid method was used to isolate DNA from these actinomycetes in root nodules and yielded a unique sequence that places them in a lineage close to bacteria that infect members of the Elaeagnaceae.
Abstract: To study the global diversity of plant-symbiotic nitrogen-fixing Frankia strains, a rapid method was used to isolate DNA from these actinomycetes in root nodules. The procedure used involved dissecting the symbiont from nodule lobes; ascorbic acid was used to maintain plant phenolic compounds in the reduced state. Genes for the small-subunit rRNA (16S ribosomal DNA) were amplified by the PCR, and the amplicons were cycle sequenced. Less than 1 mg (fresh weight) of nodule tissue and fewer than 10 vesicle clusters could serve as the starting material for template preparation. Partial sequences were obtained from symbionts residing in nodules from Ceanothus griseus, Coriaria arborea, Coriaria plumosa, Discaria toumatou, and Purshia tridentata. The sequences obtained from Ceonothus griseus and P. tridentata nodules were identical to the sequence previously reported for the endophyte of Dryas drummondii. The sequences from Frankia strains in Coriaria arborea and Coriaria plumosa nodules were identical to one another and indicate a separate lineage for these strains. The Frankia strains in Discaria toumatou nodules yielded a unique sequence that places them in a lineage close to bacteria that infect members of the Elaeagnaceae.
68 citations
TL;DR: A cDNA clone, pAgthi1, encoding a homologue of yeast Thi4, which is involved in thiazole biosynthesis, was isolated from a library made from poly(A) RNA from actinorhizal nodules of Alnus glutinosa by differential screening with nodule and root cDNA, respectively.
Abstract: A cDNA clone, pAgthi1, encoding a homologue of yeast Thi4, which is involved in thiazole biosynthesis, was isolated from a library made from poly(A) RNA from actinorhizal nodules of Alnus glutinosa by differential screening with nodule and root cDNA, respectively. The corresponding gene, agthi1, was shown to be expressed at high levels in nodules and shoot tips of A. glutinosa, while having low expression levels in roots, flowers, and developing fruits. The function of AgThi1 was demonstrated by yeast complementation studies, in which AgThi1 was able to rescue a yeast thi4 mutant when fused to the yeast Thi4 signal peptide. In A. glutinosa nodules, high levels of agthi1 mRNA were detected in the infected cortical cells and in the pericycle of the nodule vascular system. A homologue of this cDNA, ara6/tz, was identified in Arabidopsis thaliana. ara6 maps in a region of chromosome 5 of Arabidopsis containing the tz locus which is consistent with the fact that ara6transcription is disturbed in two tz mutant lines. ara6/tz is expressed at high levels in chloroplast-containing parenchymatic cells of leaves, inflorescence shoots and flowers of Arabidopsis, and at lower levels in the vascular system.
49 citations
TL;DR: This PCR-RFLP analysis of the PCR amplified nif D-K intergenic spacer (IGS) region was used to cluster 22 Frankia strains of the Elaeagnus host specificity group into seven genomic groups and to measure the degree of genetic similarity among them, indicating that Frankia ability to nodulate with Alnus and Elaeagna is a monophyletic trait shared by three genomic species.
40 citations
TL;DR: In this article, single-spore isolates of the flexible Elaeagnus-Frankia strain UFI 132715 fulfilled the third and the fourth of Koch's postulates on both Alnus and ElAEagnus axenic plants.
Abstract: Twelve single-spore isolates of the flexible Elaeagnus-Frankia strain UFI 132715 fulfilled the third and the fourth of Koch's postulates on both Alnus and Elaeagnus axenic plants. Seminested nifD-nifK PCR-restriction fragment length polymorphisms provided evidence for the genetic uniformity of the single-spore frankiae with the mother strain and its plant reisolates and allowed their molecular identification directly inside Alnus and Elaeagnus nodules. The clonal nature of these single-spore-purified frankiae should allow safe mutagenesis programs, while their flexible phenotype makes them a powerful tool for understanding the molecular interactions between Frankia strains and actinorhizal plants and for identifying Frankia nodulation genes.
33 citations
TL;DR: Analysis of partial 16S rRNA gene sequences suggests that the Mexican isolates are not Frankia strains but members of a novel clade.
Abstract: Filamentous bacteria isolated from surface-sterilized nodules of Casuarina equisetifolia trees in Mexico were capable of reducing acetylene, a diagnostic test for nitrogenase, but were unable to nodulate their host. Analysis of partial 16S rRNA gene sequences suggests that the Mexican isolates are not Frankia strains but members of a novel clade.
29 citations
TL;DR: Molecular analyses of host plant gene expression in developing nodules have confirmed the occurrence of nodulin proteins and in situ hybridization techniques have been successfully adapted to permit the study of the spatial and temporal patterns of gene expression within actinorhizal nodules.
Abstract: The application of molecular tools to questions related to the genetics, ecology and evolution of actinorhizal symbiotic systems has been especially fruitful during the past two years. Host plant phylogenies based on molecular data have revealed markedly different relationships among host plants than have previously been suspected and have contributed to the development of new hypotheses on the origin and evolution of actinorhizal symbiotic systems. Molecular analyses of host plant gene expression in developing nodules have confirmed the occurrence of nodulin proteins and in situ hybridization techniques have been successfully adapted to permit the study of the spatial and temporal patterns of gene expression within actinorhizal nodules. The use of heterologous probes in combination with nucleotide sequence analysis have allowed a number of nif genes to be mapped on the Frankia chromosome which will ultimately contribute to the development of hypotheses related to nif gene regulation in Frankia. The use of both 16S and 23S rDNA nucleotide sequences has allowed the construction of phylogenetic trees that can be tested for congruence with symbiotic characters. In addition the development of Frankia-specific gene probes and amplification primers have contributed to studies on the genetic diversity and distribution of Frankia in the soil.
20 citations
TL;DR: In situ hybridization studies of the expression of nif genes of Frankia show that the zone of infected mature cells (zone III) is the zone where the nitrogen fixation is the greatest.
Abstract: Summary Actinorhizal nodules or actinorhizae represent the most typical example of modified non pathogenic roots (nodule lobes), induced by signals synthetized by the microsymbiont. The formation of a nodule lobe occurs in four steps: infection of the root hair by Frankia, formation of the prenodule, initiation and nodule lobe infection. The nodule lobe comprises four distinct zones which are the result of the Frankia acropetal growth and of the differentiation of tissues originating from the apical meristem. In situ hybridization studies of the expression of nif genes of Frankia show that the zone of infected mature cells (zone III) is the zone where the nitrogen fixation is the greatest. Similitudes and differences with organogenesis of the nodules of legumes are displayed and the interest of this primitive symbiosis is emphasized.
18 citations
TL;DR: As pioneer species for land revegetation, actinorhizal plants are predisposed to form with mycorrhizal fungi symbiotic associations that are as essential for plant growth as the associations they form with Frankia.
Abstract: Summary As pioneer species for land revegetation, actinorhizal plants are predisposed to form with mycorrhizal fungi symbiotic associations that are as essential for plant growth as the associations they form with Frankia. As expected, mycorrhizas stimulate the development and the N2-fixing activity of the actinorhizal symbiosis by improving mineral nutrition of the host plant. In addition to mycorrhizas, actinorhizal plants are also able to form an unique type of roots called « proteoid roots » or « cluster roots » in response to the detrimental effects of nutrient deficiencies in soil. As an alternative of mycorrhizas, cluster roots are specialized roots capable of assisting plant growth in marginal, nutrient deficient soils. There is no competition between Frankia and mycorrhizal fungi for infection sites but extensive mycorrhizas can affect Frankia growth and the subsequent development of young lobes of actinorhizal nodules. By contrast, the presence of Frankia in planta has no incidence on mycorrhiza...
TL;DR: Phylogenetic analysis of actinorhizal plant families is now possible due to the availability of numerous angiosperm sequences of the plastid gene rbcL, and the most parsimonious scenario favored the recurrent evolution of act inorHizal symbiosis.
Abstract: Summary Phylogenetic analysis of actinorhizal plant families is now possible due to the availability of numerous angiosperm sequences of the plastid gene rbcL. A sampling of a 100 rbcL sequences, including representatives of all eight actinorhizal families, was conducted to estimate their phylogenetic relationships. The phylogeny was estimated by neighbor-joining analysis of a matrix of pairwise substitution rates. Bootstrap and double-bootstrap values were estimated. In order to assess the divergent hypotheses of unique or recurrent evolution of actinorhizal symbiosis, character state changes were traced along the branches of the phylogenetic consensus trees obtained, and the number of character changes for each of the two scenarios was calculated. The most parsimonious scenario favored the recurrent evolution of actinorhizal symbiosis. This scenario is supported by the morphophysiological diversity of actinorhizal symbioses and by the relaxed coevolutionary relationships between the host plants and the ...
01 Jan 1996
TL;DR: The nitrogen-fixing actinomycete Frankia has its main ecological niche in the root nodules that are formed with a wide taxonomic range of host plants, called by this fact actinorhizal plants.
Abstract: The nitrogen-fixing actinomycete Frankia has its main ecological niche in the root nodules that are formed with a wide taxonomic range of host plants, called by this fact actinorhizal plants. This generic name comprises more than 200 species of vascular dicotyledonous plants, distributed in 20 genera and eight families [5].
TL;DR: Effective nodules induced on susceptible Alnus glutinosa clones by soil suspensions from a local swamp were analysed cytologically and showed that ineffective nodules contain higher amounts of polyphenols than effective nodules, indicating a plant defense reaction.
Abstract: Summary Several Frankia strains have been shown to induce ineffective, i.e. non-nitrogen fixing nodules, sometimes in a host-plant dependent manner. Previous studies have demonstrated that the resistance to nodulation of Alnus glutinosa by ineffective Frankia strains is genetically determined. In this study, ineffective nodules induced on susceptible Alnus glutinosa clones by soil suspensions from a local swamp were analysed cytologically. Comparisons with effective nodules showed that ineffective nodules contain higher amounts of polyphenols than effective nodules, indicating a plant defense reaction. Polyphenols were found even in the infected cortical cells. In situ hybridization with a Frankia antisense 16S rRNA probe showed that Frankia is degraded at an early stage of development of infected cells. The mRNAs of two plant genes, ag12ar\6 ag13, which had been found to be expressed in the infected cells of effective nodules, were localized in ineffective nodules. Their expression patterns seemed to be ...
TL;DR: In experiments using labeled 1,2-dipalmitoyl phosphatidylcholine and palmitic acid, radioactivity bound rapidly to the insoluble, but solvent-extractable fraction of Frankia cells, suggesting that membrane biosynthesis may be the limiting step for Frankia growth in unamended propionate mineral medium.
Abstract: Frankia isolates from nodules of the genera Casuarina (BR, S21, Thr), Allocasuarina (Allo2), and Gymnostoma (G80) were found to grow exponentially with high biomass yield and minimal sporangia formation in stirred propionate mineral medium when supplemented either with 2.4 μM palmitic acid (C16:0), pentadecanoic (C15:0), heptadecanoic (C17:0), or linoleic (C18:2, cis 9, 12) fatty acids. Strains also grew with lauric (C12:0) or myristic (C14:0) acids, but gave lower biomass yield. Stearic acid (C18:0) produced a good biomass yield, but cultures slowly accumulated sporangia; oleic acid (C18:1, cis-9) was detrimental to growth. Caprylic (C8:0) or capric (C10:0) acids proved to be prejudicial for long-term storage of Frankia strains. In experiments using labeled 1,2-dipalmitoyl phosphatidylcholine and palmitic acid, radioactivity bound rapidly to the insoluble, but solvent-extractable fraction of Frankia cells. In contrast, label from propionic acid accumulated in the cytosolic fraction. Therefore, the beneficial effect of some specific phospatidylcholines or free fatty acids on Frankia growth appears to result from their utilization as building blocks for the membrane, suggesting that membrane biosynthesis may be the limiting step for Frankia growth in unamended propionate mineral medium.
TL;DR: Responsibility of the seedlings to the inoculation with the soil from the rhizosphere of damaged alder trees from six field sites differs, even though no correlation was found relating growth to the health status of the trees, and some of the preliminary results from experiments testing the influence of these symbioses are reported.
Abstract: During the last few years alder has declined in South Bohemia. The possible role of mycorrhizal and actinorhizal symbioses is reviewed and some of the preliminary results from experiments testing the influence of these symbioses on alder growth and the influence of eutrophication on the development of these symbioses are reported. Seedlings ofAlnus glutinosa were inoculated with arbuscular mycorrhizal (AM) fungi and the actinomyceteFrankia in experiment 1, and with rhizosphere soil collected from field sites with different degrees of alder damage in experiment 2. In both experiments, a solution containing nitrate, ammonia and phosphorus in concentrations simulating eutrophic waters, was applied. Both symbioses markedly promoted the growth of the seedlings in experiment 1. The plants inoculated with the rhizosphere soil microflora in experiment 2 were larger than the control plants. Response of the seedlings to the inoculation with the soil from the rhizosphere of damaged alder trees from six field sites differs, even though no correlation was found relating growth to the health status of the trees. Nutrient treatment did not have any effect on the growth of seedlings in either experiment. The dry weight ofFrankia was greater in mycorrhizal plants compared to nonmycorrhizal plants and mycorrhizal colonization is reduced inFrankia inoculated plants supplemented with phosphorus in experiment 1. Nitrogen enhanced mycorrhizal colonization in nodulated plants which were not supplemented with phosphorus no effect of nitrogen on actinorhiza was observed.
TL;DR: The characterization of several C. glauca transcripts identified by sequence analysis of cDNA clones is presented, showing the presence of symbiotic genes involved in Casuarina-Frankia symbiosis.
Abstract: Summary Casuarinas are actinorhizal tropical trees belonging to the family Casuarinaceae and are capable of forming nitrogen fixing root nodules with an actinomycetal microorganism known as Frankia. In order to identify genes involved in Casuarina-Frankia symbiosis, a Casuarina glauca root nodule cDNAs library was constructed and screened differentially with root and nodule cDNA probes. Here, we present the characterization of several C. glauca transcripts identified by sequence analysis of cDNA clones. In order to study the symbiotic genes in Casuarina glauca root nodules, two genetic transformation systems were developed in Casuarinaceae using Agrobacterium rhizogenes and Agrobacterium tumefaciens. Expression of symbiotic genes was studied in transgenic root nodules.
TL;DR: Spores of Frankia strain ACN1AG, immobilized in calcium alginate beads, germinated to produce colonies that increased in protein content and showed nitrogenase activity, opening the possibility of using beaded spores as inocula.
Abstract: Spores of Frankia strain ACN1AG, immobilized in calcium alginate beads, germinated to produce colonies that increased in protein content and showed nitrogenase activity. Air dried immobilized spores remained viable for at least 15 days in dry condition, making the storage and transport of Frankia strains easy. This also opens the possibility of using beaded spores as inocula.
01 Jan 1996
TL;DR: Nodule development, structure, and metabolism will be compared between both systems, indicating that actinorhizal symbioses represents a more primitive situation with a less sophisticated pattern of signal exchange than it is the case for the program of legume nodules.
Abstract: Since decades, research has been performed to answer the question whether the ability to form an endophytic symbiosis with N 2 -fixing bacteria can be transferred to agriculturally important crops Here, two root nodule symbioses between angiosperms and N 2 -fixing bacteria, Rhizobium /legume and symbioses between the actinomycetous bacterium Frankia and actinorhizal plants, will be described In contrast to Rhizobium , which with one exception, can only enter symbioses with plants of the legume family, Frankia can enter symbioses with plant species from eight different families, mostly perennial woody shrubs While extensive research has been done on physiological, ecological molecular and genetic aspects of Rhizobium /legume symbioses, molecular studies on actinorhizal symbioses have been started only recently Nodule development, structure, and metabolism will be compared between both systems, indicating that actinorhizal symbioses represents a more primitive situation with a less sophisticated pattern of signal exchange The developmental program of actinorhizal nodules shows less differences from the one of lateral roots than it is the case for the program of legume nodules Also in contrast to legume nodules, there is a considerable diversity in actinorhizal symbioses regarding the differentiation of the endosymbiont in symbiosis and the oxygen protection systems provided by the plant The implications of this comparison will be discussed
01 Jan 1996
TL;DR: Responsibility of the seedlings to the inoculation with the soil from the rhizosphere of damaged alder trees from six field sites differs, even though no correlation was found relating growth to the health status of the trees, and some of the preliminary results from experiments testing the influence of these symbioses are reported.
Abstract: During the last few years alder has declined in South Bohemia. The possible role of mycorrhizal and actinorhizal symbioses is reviewed and some of the preliminary results from experiments testing the influence of these symbioses on alder growth and the influence of eutrophication on the development of these symbioses are reported. Seedlings ofAlnus glutinosa were inoculated with arbuscular mycorrhizal (AM) fungi and the actinomycete Frankia in experiment 1, and with rhizosphere soil collected from field sites with different degrees of alder damage in experiment 2. In both experiments, a solution containing nitrate, ammonia and phosphorus in concentrations simulating eutrophic waters, was applied. Both symbioses markedly promoted the growth of the seedlings in experiment 1. The plants inoculated with the rhizosphere soil microflora in experiment 2 were larger than the control plants. Response of the seedlings to the inoculation with the soil from the rhizosphere of damaged alder trees from six field sites differs, even though no correlation was found relating growth to the health status of the trees. Nutrient treatment did not have any effect on the growth of seedlings in either experiment. The dry weight of Frankia was greater in mycorrhizal plants compared to nonmycorrhizal plants and mycorrhizal colonization is reduced in Frankia inoculated plants supplemented with phosphorus in experiment 1. Nitrogen enhanced mycorrhizal colonization in nodulated plants which were not supplemented with phosphorus no effect of nitrogen on actinorhiza was observed.
Journal Article•
Journal Article•
TL;DR: To isolate plant endophytes to be utilized as an inoculum in adapted species, Frankia typical morphological characteristics were presented and A. cordobensis and C. quinquenervia had a good aerial development but its fixing nitrogen ability was low, as a plant growth promoting rhizobacteria (PGPR).
Abstract: Frankia is an actinomycete that fixes atmospheric nitrogen in actinorhizal symbiosis (in non-legume plants). Atriplex cordobensis is an important Chaco Arido forage species due to the high nitrogen content. The aim of this paper was to isolate plant endophytes to be utilized as an inoculum in adapted species. A. cordobensis seedlings of 30 days were inoculated with isolated strains of Atriplex cordobensis, Colletia hystrix, Trevoa trinervis, Talguenea quinquenervia and 4-6 strains of Retanilla ephedra, courtesy of the University of Chile. A complete randomized design with 9 replications was performed. The infective ability of the strains was established through the re-isolation of the endophytes in QMOD artificial medium. The infectivity was evaluated by means of: plant aerial part length, leaf number, number and length of internodes, dry weight and total nitrogen content. The symbiotic effectivity, inoculation response and fixed nitrogen quantity were calculated. All strains treated on A. cordobensis presented Frankia typical morphological characteristics. A. cordobensis and C. hystrix showed the best nitrogen fixing effectivity, T. quinquenervia had a good aerial development but its fixing nitrogen ability was low, as a plant growth promoting rhizobacteria (PGPR). All strains were infective and A. cordobensis and C. hystrix apported the highest nitrogen amount to the plants.
TL;DR: The exponential growth was improved for some strains of Frankia nodulating actinorhizal plants belonging to the Casuarinaceae family and the complex proteolytic system, an excretion of exo-proteins and to use some isoenzyms to characterize these strains.
Abstract: Summary Here we present some methodologies developed for the study of the biology and genetic diversity of Frankia nodulating actinorhizal plants belonging to the Casuarinaceae family. First, the exponential growth was improved for some strains. This permitted to describe their complex proteolytic system, an excretion of exo-proteins and to use some isoenzyms to characterize these strains. We have also studied the preliminary microbial signals that follow exposure of host-plant to flavonoids. In a second part, the genetic diversity of Frankia nodulating Casuarinaceae was studied. The isolation step was avoided by a direct characterization of the endosymbiont inside the nodule. A genetic diversity was shown among Frankia associated to Casuarinaceae in Australia, whereas previous studies on isolated strains had shown an important genetic homogeneity.
TL;DR: The first succesful isolation of Frankia from the nodules of Polish Alnus glutinosa have been described, and the isolate was capable of forming N 2 -fixing symbiotic root nodules on AlnUS glut inosa seedlings.
TL;DR: The roots of Alnus hirsuta seedlings treated with Al grew better in height, root length and fresh weight in the presence of Frankia than those uninoculated with Frankia.
Abstract: This study was conducted to compare the growth and mineral nutrient composition of Alnus hirsuta seedlings when treated with different aluminum concentrations and acidic nutrient solutions with and without Frankia inoculation and to examine microscopic changes in the roots treated with different aluminum levels with and without Frankia inoculation. When inoculated with Frankin, A. hirsura seedlings without A1 treatment showed the greatest growth rate in height; root length and fresh weight. The seedlings treated with Al grew better in height, root length and fresh weight in the presence of Frankia than those uninoculated with Frankia. As the concentration of Al treatments increased, the concentration of Al in both shoot and root increased regardless of Frankia inoculation. As the concentration of treated Al increased, the concentration of cations (Ca, Mg, K) in the tissue decreased. The root tissues treated with A1 showed the following microscopic characteristics as compared to those without Al treatment;...
01 Jan 1996
TL;DR: In this article, the authors studied plant gene expression during the development and function of actinorhizal nodules of Alnus glutinosa, by characterizing cDNA clones isolated from a nodule cDNA library.
Abstract: Plants that can be nodulated by actinomycetes of the genus Frankia are collectively called actinorhizal plants and comprise mostly woody plant species. Compared to Rhizobium- legume interactions, actinorhizal symbioses are poorly understood, especially in their molecular aspects. The goal of the research described in this thesis is to study plant gene expression during the development and function of actinorhizal nodules of Alnus glutinosa, by characterizing cDNA clones isolated from a nodule cDNA library, Chapter 1 gives an overview about the development and functioning of actinorhizal nodules, in comparison with legume- Rhizobium interactions. By differential screening, several A. glutinosa cDNA clones were isolated, representing genes expressed at markedly elevated levels in actinorhizal nodules compared to roots. These cDNAs were found to encode products involved in nitrogen metabolism (chapter 2), a hitherto unknown metabolic pathway (chapter 3), and senescence (chapters 4 and 5). Like in legume nodules, ammonium assimilation in actinorhizal nodules is performed by the common glutamine synthetase (GS)/glutamate synthase (GOGAT) pathway. The exported form of fixed nitrogen in Alnus nodules is citrulline. Two cDNA clones isolated were found to encode products related to nitrogen metabolism. pAg 11 encoded a glutamine synthetase (GS), the key enzyme responsible for ammonium assimilation; pAg 118 encoded an acetylornithine transaminase (AOTA) which is involved in the biosynthesis of citrulline (chapter 2). By determining their sites of expression new insight was gained in reassimilation of ammonium in actinorhizal nodules. One nodule-specific clone, pAg 135, was found to encode a polypeptide homologous to a fatty acid reductase, but since fatty alcohols are not found in A. glutinosa nodules it remains to be examined in which metabolic pathway Ag 135 is active (chapter 3). A cDNA (pAg13) encoding a proline-rich polypeptide was also isolated. Apart from proline, the potential mature peptide was also rich in glutamic acid. In situ hybridization showed that this gene was expressed in infected cells during endosymbiont degradation and in the nodule pericycle (chapter 4). Ineffective root nodules that cannot fix nitrogen because the Frankia bacteria do not form vesicles, can be induced by certain Frankia strains on A. glutinosa. They represent compact structures and contain higher amounts of polyphenols than the effective nodules. A comparison of ag13 expression between effective and ineffective nodules of A. glutinosa is presented, implying that ag13 expression is indeed correlated with senescence (chapter 5). So far, about 15 nodule-specific/enhanced cDNA clones have been isolated and identified in Alnus glutinosa nodules. In chapter 6, the results currently achieved in plant molecular studies on Alnus glutinosa nodules are summarized and discussed.
01 Jan 1996