Current Plant Science and Biotechnology in Agriculture, 1995
One of the most fundamental aspects in biology is the regulation of biochemical pathways, which i... more One of the most fundamental aspects in biology is the regulation of biochemical pathways, which is brought about by an interplay between signals, genetic elements and transacting factors. Our knowledge of the signals involved in nodulation and nitrogen fixation is progressing rapidly but our understanding of their mechanisms of action is rather poor. In this overview we will deal with signals known or assumed to be involved in the various steps which lead to nodulation and nitrogen fixation. Rhizobium will be the leading microsymbiont but, when appropriate, other microbes will be dealt with. Because of severe space limitation many valuable references had to be omitted.
Current Plant Science and Biotechnology in Agriculture, 1993
Bradyrhizobium japonicum, a Gram negative soil bacterium, has the ability to establish a nitrogen... more Bradyrhizobium japonicum, a Gram negative soil bacterium, has the ability to establish a nitrogen-fixing symbiosis with soybean, siratro, cowpea, and a few other leguminous plants. This process is termed nodulation and the plant is induced to form a new nitrogen-fixing organ, the nodule. B. japonicum is a member of the family Rhizobiaceae which also includes Rhizobium, Azorhizobium, and Agrobacterium species. In Rhizobium, Azorhizobium, and Bradyrhizobium species the bacterial nodulation (nod or nol) genes are necessary for the establishment of the symbiosis with their respective host plant. The expression of the nodulation genes is controlled, in part, by the product of the nodD gene which encodes a positive transcriptional regulator. Induction of the nodulation genes also requires the presence of specific plant flavonoids. In the case of the association between B. japonicum and soybean, these nod gene-inducing flavonoids are isoflavones (e.g., genistein, daidzein, and their corresponding glycosides, Smit et al. 1992).
The sym-plasmid pRLl can be transferred to Agrobacterium tumefaciens. Exconjugants of A.tumefacie... more The sym-plasmid pRLl can be transferred to Agrobacterium tumefaciens. Exconjugants of A.tumefaciens harbouring pRL1::Tn5 produce medium bacteriocin and are able to nodulate on Vicia sativa (Van Brussel et al., 1982). Transfer of the self-transmissable plasmid pRL1 to A. tumefaciens was much lower than to Rhizobium. Transfer of pRL1 only occurred when 1062 pRL1 was the donor strain and transfer frequencies were very low e.g. 10-6 (table 1, lines 1, 2). Using A. tumefaciens pRL1::Tn5 as a donor the plasmid could be retransferred to 1062 and 5039 with equal frequencies (10-4). When now these two strains, harbouring pRL1::Tn5-A (the A stands for the transfer via A. tumefaciens) were used as donors pRL1::Tn5-A was transferred to A. tumefaciens in both cases with a rather high frequency (10-4). The resulting transconjugants A. tumefaciens pRL1::Tn5-A produced medium bacteriocin and nodulated V. sativa. The extra plasmid in these exconjugants was larger than the original pRL1 viz. 180 Mdal in stead of 135 Mdal. This large plasmid appeared to be a cointegrate between pRL1::Tn5 and pRL8, a 100 Mdal plasmid of 1062 (Johnston et al., 1982), because it was incompatible with pRL8. So pRL1 can only be transferred to A. tumefaciens as a cointegrate. This explains the low transfer frequencies when 1062 pRL1 is the donorstrain and the normal transfer frequencies when the cointegrate has been established.
Biology and Molecular Biology of Plant-Pathogen Interactions, 1986
Agrobacterium tumefaciens is the causative agent of the plant tumour, crown gall. The molecular b... more Agrobacterium tumefaciens is the causative agent of the plant tumour, crown gall. The molecular basis of the tumour induction by A. tumefaciens is the transfer and subsequent expression of a defined part, the T-DNA, of the Ti-plasmid, a large plasmid, from the bacterium to the plant cell [1]. The processes occurring between the first bacterium-plant contact and the expression of the T-DNA in planta are almost unknown. At least eight virulence (Vir) operons are involved, whose functions are essential for tumour formation on all plants or which influence the host range. Many of the Vir genes are located on the Ti-plasmid [2] but some Vir genes are located on the chromosome [3].
Current Plant Science and Biotechnology in Agriculture, 1998
Over the last decades it has become evident that also in rice (Oryza saliva) biological nitrogen ... more Over the last decades it has become evident that also in rice (Oryza saliva) biological nitrogen fixation by bacteria, e. g. Azospirillum brasilense and Herbaspirillum seropedicae can make significant contributions to the nitrogen input of this plant (Boddey et al. 1995). In analogy to the root nodule symbiosis between Rhizobium bacteria and leguminous plants, interactions with signal molecules may take place between the associated partners. Our study aims to find these signals.
Introduction The root-nodule bacteria Rhizobium, Bradyrhizobium and Azorhizobium (collectively rh... more Introduction The root-nodule bacteria Rhizobium, Bradyrhizobium and Azorhizobium (collectively rhizobia) invade and nodulate the roots of their host plants via either wounds or root hairs. The choice is made by the host plant, e.g. the same rhizobial strain infects Vigna roots via root hairs and Arachis roots via wounds (Sen & Weaver, 1984), whereas another strain infects Parasponia via root epidermal cracks and Macroptilium via root hairs (Marvel et al ., 1985). Shortly before or during root invasion, rhizobia induce cell divisions in the root cortex, resulting in formation of a nodule primordium. Through infection threads (tip-growing tubular structures containing invading rhizobia) and/or between cortical cells the rhizobia migrate towards the growing primordium, are endocytosed by young nodule cells, and differentiate into dinitrogenfixing bacteroids (see also Brewin et al ., this volume). Rhizobial invasion of most agronomically important legumes such as pea ( Pisum sativum ), soybean ( Glycine max ) and bean ( Phaseolus vulgaris ) occurs through root hairs. Infection of a living plant cell is an unusual phenomenon in plant–bacteria interactions. Plants are open organisms. At many sites, the intercellular space of a plant is in direct contact with the environment, e.g. in stomata, hydathodes or wounds resulting from emergence of lateral roots. A plant is used to regular visits of (plant-associated) bacteria to its interior. Therefore, wound-infection by rhizobia is a normal phenomenon whereas root hair infection is special.
Recognition in Microbe-Plant Symbiotic and Pathogenic Interactions, 1986
The nodulation of leguminous plants by the soil bacterium Rhizobium is a multi-step process in wh... more The nodulation of leguminous plants by the soil bacterium Rhizobium is a multi-step process in which both plant genes and bacterial genes are involved (Vincent 1980). Many bacterial genes involved in the nodulation process have been shown to reside on plasmids, which are generally called Sym plasmids (Hooykaas et al 1981). These nod genes can be divided in common and host-specific genes, depending on whether they can be complemented by the corresponding genes of other fast-growing Rhizobia (Djordjevic et al 1985a; Fisher et al 1985; Wijffelman et al 1985). The genetic organization and the function of the common nod genes A, B, C, D, I, J of R. leguminosarum, R. trifolii and R. meliloti is very homologous, whereas the organization of the host-specific nodulation functions is more different (Djordjevic et al 1985b; Egelhoff et al 1985; Rossen et al 1984; Schofield et al 1986; Spaink et al, this volume; Torok et al 1984). The nodD gene of all three species is the only nod gene which is transcribed constitutively, whereas the other nod operons are not transcribed when cells are grown in the standard culture media (Innes et al 1985; Mulligan et al 1985; Rossen et al 1985; Spaink et al, this volume). Recent data in several laboratories using the nod promoters fused to the E.coli lacZ gene show that the induction of these nod operons requires both a functional nodD gene product and a substance present in root exudate (Innes et al 1985; Mulligan et al 1985; Rossen et al 1985; Shearman et al 1986; Spaink et al, this volume). These inducible common or host-specific nod operons are preceeded by a very strongly conserved sequence of DNA, the nod box, which is located about 200 bp upstream the start codon of the first gene (Rostas et al 1986; Schofield et al 1986; Scott et al 1986; Shearman et al 1985; Spaink et al, this volume). The complete inducibility of a 114 bp clone of the nodA promoter of R. leguminosarum, which contains an intact nod box strongly suggest that these nod boxes are important elements of nod promoters (Spaink et al, this volume).
Biological Fixation of Nitrogen for Ecology and Sustainable Agriculture, 1997
The symbiotic interaction between rhizobia and legume plants, resulting in formation of nitrogen-... more The symbiotic interaction between rhizobia and legume plants, resulting in formation of nitrogen-fixing root nodules, is host-plant-specific. For example, Rhizobium leguminosarum biovar viciae nodulates pea and vetch, but not clover, soybean or alfalfa, whereas R. leguminosarum biovar trifolii preferably nodulates clover. Key factors in mutual recognition of the symbiotic partners are lipochitin oligosaccharides (LCOs), produced by the rhizobia. Expression of host-plant-specificity is a two-step process: host plant-derived flavonoids can specifically induce production of LCOs by rhizobia, and LCOs can specifically induce root nodule formation in host plant roots.
The interactions of leguminous plants and bacteria of the genera Rhizobium, Bradyrhizobium and Az... more The interactions of leguminous plants and bacteria of the genera Rhizobium, Bradyrhizobium and Azorhizobium -here collectively called rhizobia- result in the formation of root nodules, new organs in which the bacteria are able to fix atmospheric nitrogen into ammonia. The formation of root nodules involves a number of developmental steps (Newcomb, 1976; Newcomb, 1981). First the bacteria attach to the root hairs of the host plant and cause deformation and curling of root hairs. Then the bacteria enter the plant by newly formed tubular structures, the infection threads, starting from the curls of the root hairs. At the same time, cells in the cortex of the root become mitotically active and form a nodule primordium. The infection threads grow towards the nodule primordia, and after penetration of individual primordium cells the bacteria are released in the cytoplasm, by endocytosis. Then the nodule primordium differentiates into a nodule.
Expression ofnodgenes during symbiosis: The expression of inducible nod genes of Rhizobium requir... more Expression ofnodgenes during symbiosis: The expression of inducible nod genes of Rhizobium requires three components: (i) an inducible nod gene promoter, (ii) a functional nodD gene, whose product acts as a positive regulator when activated, and (iii) flavonoid compounds of the plant, which activate the nodD gene product. The chemical nature of the flavonoid inducers, either present in roots or seeds or exuded from theirs have been determined for host plants of several species of Rhizobium and Bradyrhizobium. In general, there are numerous inducers, which differ between plant species, and can contribute to host specificity (13,17). Also, there appear to be differences between different organs of the same plant species, as the seeds of alfalfa exude different inducers to the roots (10,11).
The mRNA population in pea root hairs was characterized by means of in vitro translation of total... more The mRNA population in pea root hairs was characterized by means of in vitro translation of total root hair RNA followed by 2-dimensional gel electrophoresis of the translation products. Root hairs contain several mRNAs not detectable in total RNA preparations from roots. Most of these root hair-specific mRNAs occur in elongating root hairs at higher levels than in mature root hairs. The expression of some genes in pea root hairs is typically affected by inoculation with Rhizobium leguminosarum. One gene, encoding RH-42, is specifically induced while the expression of another gene, encoding RH-44, is markedly enhanced. Using R. leguminosarum mutants it was shown that the nodC gene is required for the induction and enhancement of expression of the RH-42 and RH-44 genes, respectively, while the Rhizobium chromosomal gene pss1, involved in exopolysaccharide synthesis, is not essential. After induction of the nod genes with apigenin the bacteria excrete into the culture medium a factor that causes root hair deformation. This deformation factor stimulates the expression of the RH-44 gene but does not induce the expression of the gene encoding RH-42.
RATIONALE Isotopic analysis of archaeological charred plant remains offers useful archaeological ... more RATIONALE Isotopic analysis of archaeological charred plant remains offers useful archaeological information. However, adequate sample pre-treatment protocols may be necessary to provide a contamination-free isotopic signal while limiting sample loss and achieving a high throughput. Under these constraints, research was undertaken to compare the performance of different pre-treatment protocols. METHODS Charred archaeological plant material was selected for isotopic analysis (δ13 C and δ15 N values) by isotope ratio mass spectrometry from a variety of plant species, time periods and soil conditions. Preservation conditions and the effectiveness of cleaning protocols were assessed through Fourier transform infrared spectroscopy and X-ray fluorescence (XRF) spectrometry. An acid-base-acid protocol, successfully employed in radiocarbon dating, was used to define a contamination-free isotopic reference. Acid-base-acid isotopic measurements were compared with those obtained from untreated material and an acid-only protocol. RESULTS The isotopic signals of untreated material and the acid-only protocol typically did not differ more than 1‰ from those of the acid-base-acid reference. There were no significant isotopic offsets between acid-base-acid and acid-only or untreated samples. Sample losses in the acid-base-acid protocol were on average 50 ± 17% (maximum = 98.4%). Elemental XRF measurements showed promising results in the detection of more contaminated samples albeit with a high rate of false positives. CONCLUSIONS For the large range of preservation conditions described in the study, untreated charred plant samples, water cleaned of sediments, provide reliable stable isotope ratios of carbon and nitrogen. The use of pre-treatments may be necessary under different preservation conditions or more conservative measurement uncertainties should be reported.
Small bacteriocin was isolated from the culture broth of the gram-negative bacterium Rhizobium le... more Small bacteriocin was isolated from the culture broth of the gram-negative bacterium Rhizobium leguminosarum, which forms symbiotic nitrogen-fixing root nodules on a number of leguminous plants. The structure of the molecule was elucidated by spectroscopic methods and identified as N-(3R-hydroxy-7-cis-tetradecanoyl)-L-homoserine lactone. The absolute configuration of both asymmetric carbon atoms in the molecule was determined by the use of the chiral solvating agents S-(+)- and R-(-)-2,2,2-trifluoro-1-(9-anthryl)-ethanol. small bacteriocin is structurally related to the quorum sensing co-transcription factors for genes from other bacteria such as Vibrio fischeri, Pseudomonas aeruginosa, Erwinia carotovora, and Agrobacterium tumefaciens which are involved in animal-microbe or plant-microbe interactions. The mechanism of regulation of such interactions by this kind of co-transcription factors is still unknown in R. leguminosarum.
Current Plant Science and Biotechnology in Agriculture, 1995
One of the most fundamental aspects in biology is the regulation of biochemical pathways, which i... more One of the most fundamental aspects in biology is the regulation of biochemical pathways, which is brought about by an interplay between signals, genetic elements and transacting factors. Our knowledge of the signals involved in nodulation and nitrogen fixation is progressing rapidly but our understanding of their mechanisms of action is rather poor. In this overview we will deal with signals known or assumed to be involved in the various steps which lead to nodulation and nitrogen fixation. Rhizobium will be the leading microsymbiont but, when appropriate, other microbes will be dealt with. Because of severe space limitation many valuable references had to be omitted.
Current Plant Science and Biotechnology in Agriculture, 1993
Bradyrhizobium japonicum, a Gram negative soil bacterium, has the ability to establish a nitrogen... more Bradyrhizobium japonicum, a Gram negative soil bacterium, has the ability to establish a nitrogen-fixing symbiosis with soybean, siratro, cowpea, and a few other leguminous plants. This process is termed nodulation and the plant is induced to form a new nitrogen-fixing organ, the nodule. B. japonicum is a member of the family Rhizobiaceae which also includes Rhizobium, Azorhizobium, and Agrobacterium species. In Rhizobium, Azorhizobium, and Bradyrhizobium species the bacterial nodulation (nod or nol) genes are necessary for the establishment of the symbiosis with their respective host plant. The expression of the nodulation genes is controlled, in part, by the product of the nodD gene which encodes a positive transcriptional regulator. Induction of the nodulation genes also requires the presence of specific plant flavonoids. In the case of the association between B. japonicum and soybean, these nod gene-inducing flavonoids are isoflavones (e.g., genistein, daidzein, and their corresponding glycosides, Smit et al. 1992).
The sym-plasmid pRLl can be transferred to Agrobacterium tumefaciens. Exconjugants of A.tumefacie... more The sym-plasmid pRLl can be transferred to Agrobacterium tumefaciens. Exconjugants of A.tumefaciens harbouring pRL1::Tn5 produce medium bacteriocin and are able to nodulate on Vicia sativa (Van Brussel et al., 1982). Transfer of the self-transmissable plasmid pRL1 to A. tumefaciens was much lower than to Rhizobium. Transfer of pRL1 only occurred when 1062 pRL1 was the donor strain and transfer frequencies were very low e.g. 10-6 (table 1, lines 1, 2). Using A. tumefaciens pRL1::Tn5 as a donor the plasmid could be retransferred to 1062 and 5039 with equal frequencies (10-4). When now these two strains, harbouring pRL1::Tn5-A (the A stands for the transfer via A. tumefaciens) were used as donors pRL1::Tn5-A was transferred to A. tumefaciens in both cases with a rather high frequency (10-4). The resulting transconjugants A. tumefaciens pRL1::Tn5-A produced medium bacteriocin and nodulated V. sativa. The extra plasmid in these exconjugants was larger than the original pRL1 viz. 180 Mdal in stead of 135 Mdal. This large plasmid appeared to be a cointegrate between pRL1::Tn5 and pRL8, a 100 Mdal plasmid of 1062 (Johnston et al., 1982), because it was incompatible with pRL8. So pRL1 can only be transferred to A. tumefaciens as a cointegrate. This explains the low transfer frequencies when 1062 pRL1 is the donorstrain and the normal transfer frequencies when the cointegrate has been established.
Biology and Molecular Biology of Plant-Pathogen Interactions, 1986
Agrobacterium tumefaciens is the causative agent of the plant tumour, crown gall. The molecular b... more Agrobacterium tumefaciens is the causative agent of the plant tumour, crown gall. The molecular basis of the tumour induction by A. tumefaciens is the transfer and subsequent expression of a defined part, the T-DNA, of the Ti-plasmid, a large plasmid, from the bacterium to the plant cell [1]. The processes occurring between the first bacterium-plant contact and the expression of the T-DNA in planta are almost unknown. At least eight virulence (Vir) operons are involved, whose functions are essential for tumour formation on all plants or which influence the host range. Many of the Vir genes are located on the Ti-plasmid [2] but some Vir genes are located on the chromosome [3].
Current Plant Science and Biotechnology in Agriculture, 1998
Over the last decades it has become evident that also in rice (Oryza saliva) biological nitrogen ... more Over the last decades it has become evident that also in rice (Oryza saliva) biological nitrogen fixation by bacteria, e. g. Azospirillum brasilense and Herbaspirillum seropedicae can make significant contributions to the nitrogen input of this plant (Boddey et al. 1995). In analogy to the root nodule symbiosis between Rhizobium bacteria and leguminous plants, interactions with signal molecules may take place between the associated partners. Our study aims to find these signals.
Introduction The root-nodule bacteria Rhizobium, Bradyrhizobium and Azorhizobium (collectively rh... more Introduction The root-nodule bacteria Rhizobium, Bradyrhizobium and Azorhizobium (collectively rhizobia) invade and nodulate the roots of their host plants via either wounds or root hairs. The choice is made by the host plant, e.g. the same rhizobial strain infects Vigna roots via root hairs and Arachis roots via wounds (Sen & Weaver, 1984), whereas another strain infects Parasponia via root epidermal cracks and Macroptilium via root hairs (Marvel et al ., 1985). Shortly before or during root invasion, rhizobia induce cell divisions in the root cortex, resulting in formation of a nodule primordium. Through infection threads (tip-growing tubular structures containing invading rhizobia) and/or between cortical cells the rhizobia migrate towards the growing primordium, are endocytosed by young nodule cells, and differentiate into dinitrogenfixing bacteroids (see also Brewin et al ., this volume). Rhizobial invasion of most agronomically important legumes such as pea ( Pisum sativum ), soybean ( Glycine max ) and bean ( Phaseolus vulgaris ) occurs through root hairs. Infection of a living plant cell is an unusual phenomenon in plant–bacteria interactions. Plants are open organisms. At many sites, the intercellular space of a plant is in direct contact with the environment, e.g. in stomata, hydathodes or wounds resulting from emergence of lateral roots. A plant is used to regular visits of (plant-associated) bacteria to its interior. Therefore, wound-infection by rhizobia is a normal phenomenon whereas root hair infection is special.
Recognition in Microbe-Plant Symbiotic and Pathogenic Interactions, 1986
The nodulation of leguminous plants by the soil bacterium Rhizobium is a multi-step process in wh... more The nodulation of leguminous plants by the soil bacterium Rhizobium is a multi-step process in which both plant genes and bacterial genes are involved (Vincent 1980). Many bacterial genes involved in the nodulation process have been shown to reside on plasmids, which are generally called Sym plasmids (Hooykaas et al 1981). These nod genes can be divided in common and host-specific genes, depending on whether they can be complemented by the corresponding genes of other fast-growing Rhizobia (Djordjevic et al 1985a; Fisher et al 1985; Wijffelman et al 1985). The genetic organization and the function of the common nod genes A, B, C, D, I, J of R. leguminosarum, R. trifolii and R. meliloti is very homologous, whereas the organization of the host-specific nodulation functions is more different (Djordjevic et al 1985b; Egelhoff et al 1985; Rossen et al 1984; Schofield et al 1986; Spaink et al, this volume; Torok et al 1984). The nodD gene of all three species is the only nod gene which is transcribed constitutively, whereas the other nod operons are not transcribed when cells are grown in the standard culture media (Innes et al 1985; Mulligan et al 1985; Rossen et al 1985; Spaink et al, this volume). Recent data in several laboratories using the nod promoters fused to the E.coli lacZ gene show that the induction of these nod operons requires both a functional nodD gene product and a substance present in root exudate (Innes et al 1985; Mulligan et al 1985; Rossen et al 1985; Shearman et al 1986; Spaink et al, this volume). These inducible common or host-specific nod operons are preceeded by a very strongly conserved sequence of DNA, the nod box, which is located about 200 bp upstream the start codon of the first gene (Rostas et al 1986; Schofield et al 1986; Scott et al 1986; Shearman et al 1985; Spaink et al, this volume). The complete inducibility of a 114 bp clone of the nodA promoter of R. leguminosarum, which contains an intact nod box strongly suggest that these nod boxes are important elements of nod promoters (Spaink et al, this volume).
Biological Fixation of Nitrogen for Ecology and Sustainable Agriculture, 1997
The symbiotic interaction between rhizobia and legume plants, resulting in formation of nitrogen-... more The symbiotic interaction between rhizobia and legume plants, resulting in formation of nitrogen-fixing root nodules, is host-plant-specific. For example, Rhizobium leguminosarum biovar viciae nodulates pea and vetch, but not clover, soybean or alfalfa, whereas R. leguminosarum biovar trifolii preferably nodulates clover. Key factors in mutual recognition of the symbiotic partners are lipochitin oligosaccharides (LCOs), produced by the rhizobia. Expression of host-plant-specificity is a two-step process: host plant-derived flavonoids can specifically induce production of LCOs by rhizobia, and LCOs can specifically induce root nodule formation in host plant roots.
The interactions of leguminous plants and bacteria of the genera Rhizobium, Bradyrhizobium and Az... more The interactions of leguminous plants and bacteria of the genera Rhizobium, Bradyrhizobium and Azorhizobium -here collectively called rhizobia- result in the formation of root nodules, new organs in which the bacteria are able to fix atmospheric nitrogen into ammonia. The formation of root nodules involves a number of developmental steps (Newcomb, 1976; Newcomb, 1981). First the bacteria attach to the root hairs of the host plant and cause deformation and curling of root hairs. Then the bacteria enter the plant by newly formed tubular structures, the infection threads, starting from the curls of the root hairs. At the same time, cells in the cortex of the root become mitotically active and form a nodule primordium. The infection threads grow towards the nodule primordia, and after penetration of individual primordium cells the bacteria are released in the cytoplasm, by endocytosis. Then the nodule primordium differentiates into a nodule.
Expression ofnodgenes during symbiosis: The expression of inducible nod genes of Rhizobium requir... more Expression ofnodgenes during symbiosis: The expression of inducible nod genes of Rhizobium requires three components: (i) an inducible nod gene promoter, (ii) a functional nodD gene, whose product acts as a positive regulator when activated, and (iii) flavonoid compounds of the plant, which activate the nodD gene product. The chemical nature of the flavonoid inducers, either present in roots or seeds or exuded from theirs have been determined for host plants of several species of Rhizobium and Bradyrhizobium. In general, there are numerous inducers, which differ between plant species, and can contribute to host specificity (13,17). Also, there appear to be differences between different organs of the same plant species, as the seeds of alfalfa exude different inducers to the roots (10,11).
The mRNA population in pea root hairs was characterized by means of in vitro translation of total... more The mRNA population in pea root hairs was characterized by means of in vitro translation of total root hair RNA followed by 2-dimensional gel electrophoresis of the translation products. Root hairs contain several mRNAs not detectable in total RNA preparations from roots. Most of these root hair-specific mRNAs occur in elongating root hairs at higher levels than in mature root hairs. The expression of some genes in pea root hairs is typically affected by inoculation with Rhizobium leguminosarum. One gene, encoding RH-42, is specifically induced while the expression of another gene, encoding RH-44, is markedly enhanced. Using R. leguminosarum mutants it was shown that the nodC gene is required for the induction and enhancement of expression of the RH-42 and RH-44 genes, respectively, while the Rhizobium chromosomal gene pss1, involved in exopolysaccharide synthesis, is not essential. After induction of the nod genes with apigenin the bacteria excrete into the culture medium a factor that causes root hair deformation. This deformation factor stimulates the expression of the RH-44 gene but does not induce the expression of the gene encoding RH-42.
RATIONALE Isotopic analysis of archaeological charred plant remains offers useful archaeological ... more RATIONALE Isotopic analysis of archaeological charred plant remains offers useful archaeological information. However, adequate sample pre-treatment protocols may be necessary to provide a contamination-free isotopic signal while limiting sample loss and achieving a high throughput. Under these constraints, research was undertaken to compare the performance of different pre-treatment protocols. METHODS Charred archaeological plant material was selected for isotopic analysis (δ13 C and δ15 N values) by isotope ratio mass spectrometry from a variety of plant species, time periods and soil conditions. Preservation conditions and the effectiveness of cleaning protocols were assessed through Fourier transform infrared spectroscopy and X-ray fluorescence (XRF) spectrometry. An acid-base-acid protocol, successfully employed in radiocarbon dating, was used to define a contamination-free isotopic reference. Acid-base-acid isotopic measurements were compared with those obtained from untreated material and an acid-only protocol. RESULTS The isotopic signals of untreated material and the acid-only protocol typically did not differ more than 1‰ from those of the acid-base-acid reference. There were no significant isotopic offsets between acid-base-acid and acid-only or untreated samples. Sample losses in the acid-base-acid protocol were on average 50 ± 17% (maximum = 98.4%). Elemental XRF measurements showed promising results in the detection of more contaminated samples albeit with a high rate of false positives. CONCLUSIONS For the large range of preservation conditions described in the study, untreated charred plant samples, water cleaned of sediments, provide reliable stable isotope ratios of carbon and nitrogen. The use of pre-treatments may be necessary under different preservation conditions or more conservative measurement uncertainties should be reported.
Small bacteriocin was isolated from the culture broth of the gram-negative bacterium Rhizobium le... more Small bacteriocin was isolated from the culture broth of the gram-negative bacterium Rhizobium leguminosarum, which forms symbiotic nitrogen-fixing root nodules on a number of leguminous plants. The structure of the molecule was elucidated by spectroscopic methods and identified as N-(3R-hydroxy-7-cis-tetradecanoyl)-L-homoserine lactone. The absolute configuration of both asymmetric carbon atoms in the molecule was determined by the use of the chiral solvating agents S-(+)- and R-(-)-2,2,2-trifluoro-1-(9-anthryl)-ethanol. small bacteriocin is structurally related to the quorum sensing co-transcription factors for genes from other bacteria such as Vibrio fischeri, Pseudomonas aeruginosa, Erwinia carotovora, and Agrobacterium tumefaciens which are involved in animal-microbe or plant-microbe interactions. The mechanism of regulation of such interactions by this kind of co-transcription factors is still unknown in R. leguminosarum.
Uploads
Papers by A. Van Brussel