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  • 1
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Internodal elongation in floating rice (Oryza sativa L. cv. Habiganj Aman II) is known to be enhanced by treatment with ethylene or gibberellic acid (GA3) at high relative humidity (RH). However, ethylene-induced internodal elongation is inhibited at low RH. while GA3-induced internodal elongation is hardly affected by humidity. We examined the possible involvement of osmoregulation in the stimulation by GA3 of the elongation of internodes at low RH. Submergence and treatment with ethylene or GA33 at 100% RH increased the osmotic potential in internodes of excised stem segments, while GA3 at 20% RH maintained the osmotic potential at a low level. In internodes of stem segments that had been treated with GA3 at 20% RH, the activity of invertase and the level of soluble sugars were almost 2- and 1.5-fold higher, respectively, than those in internodes that had been treated with GA3 at 100% RH. These results indicate that one of the possible mechanisms by which GA3 promotes elongation of internodes at low RH involves the osmoregulation that is achieved by promotion of the synthesis of invertase.
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  • 2
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A review of recent molecular systematic studies of actinorhizal plants and their Frankia endosymbionts is presented. For comparative purposes, a discussion of recent studies pertaining to the evolution of nodulation in the legume-rhizobium system is included. Molecular systematic studies have revealed that actinorhizal plants are more closely related than current taxonomic schemes imply. Broad-based analyses of the chloroplast gene rbcL indicate that all symbiotic root-nodulating higher plants belong to a single large clade. More focused molecular analyses of both legume and actinorhizal hosts within this large clade indicate that symbioses have probably arisen more than once. By comparing host phylogenies and recently published bacterial phylogenies, we consider the coevolution of bacterial symbionts with their actinorhizal hosts.
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  • 3
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Nitrogen-fixing root nodules are formed by Frankia spp. (Actinomycetales) on dicotyledonous hosts such as alders (Alnus spp.). Flavonoid-containing preparations from seed washes of red alder (Alnus rubra Bong.), and individual compounds isolated from such preparations, influenced nodulation of A. rubra by Frankia. Nodulation was enhanced by one flavonoid-like compound, and apparently inhibited by two other such compounds. Four flavonoid-like compounds had no significant effect on nodulation. The seven individual compounds purified from the seed washes were characterized spectrally as possible flavanones and isoflavones. Both the enhancer and the inhibitors appeared to be possible flavanones.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 99 (1997), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Progress in understanding the Frankia-actinorhizal symbiosis has paralleled that of the Rhizobium-legume symbiosis. Previously, these two nitrogen-fixing symbioses have been considered as distinct and unrelated entities. However, it seems likely that many of the developmental stages, and perhaps even the molecular signals, are shared between these two apparently independent associations. For this reason, we propose to emphasize the similarities between the two symbioses by calling for a uniformity of terminology to describe nodule development.
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  • 5
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Actinomycetes from the genus Frankia are able to form symbiotic associations with more than 200 different species of woody angiosperms, so called actinorhizal plants. Many actinorhizal plants are infected via deformed root hairs. Factor(s) eliciting root hair deformation in actinorhizal symbioses have been found to be released into the culture medium, but the factor(s) has (have) not yet been characterized. In the present work, we describe the constitutive production of factor(s) by Frankia strain ArI3 causing root hair deformation on Alnus glutinosa. Deformation was detected after 4–5 h of incubation with both Frankia cultures and their cell-free culture filtrates. When culture filtrate was used, deformation was concentration dependent. A contact time of 2 min between culture filtrate and host roots was sufficient to induce subsequent root hair deformation. No root hair deformation on A. glutinosa could be detected with purified Nod factors from Rhizobium meliloti or R. leguminosarum biovar viciae. No correlation was found between Frankia strains belonging to different host specificity groups and their ability to deform root hairs on A. glutinosa. However, strains not able to deform root hairs on A. glutinosa were also unable to nodulate.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 99 (1997), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 7
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We have characterized a full-length cDNA (hb-Cg1F) that represents symbiotic mRNA hemoglobin (hb) from Casuarina glauca root nodules. In situ hybridization was used to examine the correlation between hb-Cg1F mRNA and the state of the Frankia infection process. The efficiency of in situ hybridization using DIG-labeled vs [35S]-labeled probes was compared. The expression of hb-Cg1F gene is induced in young infected host cells prior to the detection of Frankia nifH mRNA. Since Frankia does not form vesicles in C. glauca nodules, it is proposed that Hb is necessary to reduce the O2 concentration in the cytoplasm of the host cells before the nif genes are expressed.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 99 (1997), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Nucleotide sequences of nifHD from Frankia strain EuIKl were determined and analysed. The 3.2-kb and 5.5-kb BamHI fragments of a genomic clone were previously shown to contain nifHD-like sequences and to be contiguous, based on hybridization experiments and partial sequencing data. Sequence analysis of about 3.0 kb from these fragments revealed two open reading frames and beginning of a third in the same orientation, each of which showed high degree of sequence homology with nifH, nifD and nifK, respectively. The deduced amino acid sequence of the nifH ORF, consisting of 861 bp, showed sequence similarity of about 91% with those of other Frankia strains, whereas that of nifD ORF, consisting of 1458 bp, showed about 85% similarity. Intergenic sequence between nifH and nifD was 45 bp and between nifD and nifK was 61 bp. The 5’of nifH revealed putative Shine-Dalgarno sequences; however, a sequence resembling a typical nif-promoter or NifA binding site was not found. Northern hybridization of RNA from the nodules showed that nifHDK were transcribed into a polycistronic mRNA in the symbiont of Elaeagnus umbellata.
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 99 (1997), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Molecular methods based on DNA or rRNA hybridization are powerful tools in microbial ecology for the specific detection and enumeration of bacteria unbiased by the limitations of culturability. A promising alternative to the analysis of Frankia populations in root nodules by methods based on rRNA extraction or on DNA extraction followed by the polymerase chain reaction (PCR) is the whole cell hybridization technique. This technique includes the microscopic detection of labeled probes hybridized to specific target sequences on marker molecules such as rRNA in fixed microbial cells. The analysis of uncultured Frankia populations in root nodules can reliably be performed on a subgroup level when digoxigenin-labeled oligonucleotide probes or in vitro transcripts directed against an actinomycetes-specific insertion on the 23S rRNA are used. Digoxigenin-labeled probes are more suitable for in situ detection of Frankia than fluorescent probes since the sensitivity is higher and problems arising from the autofluorescence of cells and plant material are avoided. All these strategies, however, require pretreatments to increase the permeability of vesicles, hyhae and spores.
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  • 10
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Our understanding of the actinorhizal symbiosis, in particular of the Frankia-Ceanothus association, has been hampered by the failure to isolate infective strains in pure culture. Recently, the polymerase chain reaction (PCR) has been utilized to amplify regions of the Frankia genome, allowing analysis of the microsymbiont genome without first isolating the microbe in pure culture. Root nodules were collected from six Ceanothus spp. common to the coastal regions of the Santa Monica Mountains of southern California. Individual lobes were surface-sterilized, total DNA was extracted and amplified using prokaryotic-specific primers. To assess the genetic diversity of Frankia endophytes in the population studied, the BOX primer was used to generate genomic fingerprints of prokaryotic nodule inhabitants using rep-PCR. Fingerprint patterns fell into twelve distinct groups indicating the occurrence of genetic diversity of Frankia in the nodules sampled. DNA extracts of individual lobes that gave distinct BOX-PCR fingerprints were also amplified by PCR using primers directed against conserved regions of the 16S ribosomal RNA gene. The nucleotide sequences of the PCR products were determined and aligned with the corresponding region from other taxa for phylogenetic analysis. The sequences from Ceanothus nodules share a common ancestor to that of the Elaeagnus–infective strains.
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