A fructan:fructan 1-fructosyltransferase (1-FFT) was purified from edible burdock for the first t... more A fructan:fructan 1-fructosyltransferase (1-FFT) was purified from edible burdock for the first time, and a cDNA encoding 1-FFT was isolated from the plant. Two 1-FFTs named 1-FFTa and 1-FFTb were purified from extract of edible burdock by ammonium sulfate precipitation, followed by chromatographies on DEAE-Sepharose CL-6B, Toyopearl HW-55S and Sephadex G-100 columns. Inulin-type fructan such as nystose and fructooligosaccharides with higher DP were produced from 1-kestose by purified 1-FFTs. The general properties of both purified enzymes were very similar to each other. The purified 1-FFTa and 1-FFTb showed a single band by native PAGE and two bands, relative molecular masses of about 46,000 and 17,500 for 1-FFTa and 46,000 and 17,000 for 1-FFTb, by SDS-PAGE, respectively. The N-terminal sequences of the 46,000 peptides of both enzymes were the same, and those of the 17,500 and the 17,000 peptides were also identical. Based on the sequences, the 1-FFT cDNA named alft1 was cloned. The alft1 encoded a polypeptide of 617 amino acids. The relative molecular mass and pI of the mature protein region of deduced polypeptide were calculated to be 60,213 and 4.89, respectively. The characteristics of recombinant protein produced by Pichia pastoris closely resembled those of the native 1-FFTs purified from edible burdock. In this study, we demonstrated that alft1 encoding edible burdock 1-FFT was involved in the elongation of fructosyl chains of fructooligosaccharides in edible burdock.
We have recently identified two genes coding for inorganic phosphate transporters (Pht) in sorghu... more We have recently identified two genes coding for inorganic phosphate transporters (Pht) in sorghum (Sorghum bicolor) and flax (Linum usitatissimum) that were induced in roots colonized by arbuscular mycorrhizal (AM) fungi. Mycorrhizal acquisition of inorganic phosphorus (Pi) was strongly affected by the combination of plant and AM fungal species, but the expression level of these genes coding for AMinducible Pi transporters did not explain differences in plant phosphorus acquisition where flax and sorghum are sharing a common mycorrhizal network. In the present study, we investigated the possible role of fungal Pi transporters in the regulation of mycorrhizal Pi acquisition by measuring their expression in roots of flax and sorghum. One Pi transporter of Rhizophagus irregularis (RiPT5) showed a positive correlation with mycorrhizal Pi acquisition of sorghum. This indicates that a possible involvement in the regulation of mycorrhizal Pi acquisition. In general, expression of AMF Pi transporters was more related to mycorrhizal Pi acquisition of sorghum than of flax, indicating plant species-specific differences in the regulation of mycorrhizal Pi acquisition.
The effect of arbuscular mycorrhizas on fructan accumulation was studied in barley (Hordeum vulga... more The effect of arbuscular mycorrhizas on fructan accumulation was studied in barley (Hordeum vulgare) infected with Glomus mosseae. Treatments with and without fertilizer were included in order to distinguish between mere fertilizer effects and the effects of the symbiosis, and plants were harvested at two different time points, 35 and 50 d after planting. Fructan was the major storage carboyhdrate in both leaves and roots. The amounts of fructan were markedly altered in the mycorrhizal plants. In roots of non-fertilized mycorrhizal plants, fructan pools were significantly greater than in the corresponding non-mycorrhizal plants. By contrast, fertilization caused a general decrease in amounts of fructan in roots. The increase of fructan in mycorrhizal roots was correlated with a decrease of invertase activity. In leaves, fructan pools decreased or remained unchanged upon mycorrhizal infection ; fertilization had a similar effect. However, when individual leaves of a plant were compared, intriguing effects of the mycorrhizal symbiosis could be observed. Whereas in non-mycorrhizal plants, the youngest leaves had the highest fructan contents and the oldest leaves the lowest (as previously reported), this gradient was markedly altered in mycorrhizal plants, indicating systemic effects of mycorrhiza on assimilate partitioning in shoots.
Alternative Farming Systems, Biotechnology, Drought Stress and Ecological Fertilisation, 2010
Abstract Soil microorganisms can be used to decrease the input of fertilizers, pesticides and oth... more Abstract Soil microorganisms can be used to decrease the input of fertilizers, pesticides and other chemicals. Among soil microorganisms, arbuscular mycor-rhizal (AM) fungi and Rhizobium spp. can promote plant growth and control plant fungal diseases. However these ...
A DNA fragment of Sa~~rh~lromj~ces cur-ei'isiae with high homology to the acetyl-coenzyme A (acet... more A DNA fragment of Sa~~rh~lromj~ces cur-ei'isiae with high homology to the acetyl-coenzyme A (acetyl-CoA) synthetase genes of Aspergillus nidulans and Neurospora crassa has been cloned, sequenced and mapped to chromosome I. It contains an open reading frame of 2139 nucleotides, encoding a predicted gene product of 79.2 kDa. In contrast to its ascomycete homologs, there are no introns in the coding sequence. The first ATG codon of the open reading frame is in an unusual context for a translational start site, while the next ATG. 24 codons downstream. is in a more conventional context. Possible implications of two alternative translational start sites for the cellular localization or the enzyme are discussed. A stable mutant of this gene. obtained by the gene disruption technique. had the same low basal activity of acetyl-CoA synthetase as wild-type cells when grown on glucose but completely lacked the strong increase in activity upon entering the stalionary phase, providing direct proof that the gene encodes an inducible acetyl-CoA synthetase ( A C S I ) of yeast. As expected, the mutant was unable to grow on acetate as sole carbon source. Nevertheless, it showed normal induction of isocitrate lyase on acetate media, indicating that activity ofacetyl-CuA synthetase is dispensable for induction or the glyoxylate cycle in S. cerevisirre. Surprisingly. disruption of the ACSI gene did not affect growth on media containing ethanol as the sole carbon source, demonstrating that there are alternative pathways leading to acetyl-CoA under these conditions.
Fructan (polyfructosylsucrose) is an important storage carbohydrate in many plant families. fruct... more Fructan (polyfructosylsucrose) is an important storage carbohydrate in many plant families. fructan:fructan 6G-fructosyltransferase (6G-FFT) is a key enzyme in the formation of the inulin neoseries, a type of fructan accumulated by members of the Liliales. We have cloned the 6G-FFT from onion by screening a cDNA library using barley sucrose:fructan 6-fructosyltransferase (6-SFT) as a probe. The deduced amino acid sequence showed a high homology with plant invertases and 6-SFT. Incubation of protein extracts from transgenic tobacco plants with the trisaccharide 1-kestose and sucrose resulted in the formation of neokestose and fructans of the inulin neoseries with a degree of polymerization up to six. Introduction of the onion 6G-FFT into chicory resulted in the synthesis of fructan of the inulin neoseries, in addition to the synthesis of linear inulin.
The scarcity of non-renewable resources such as soils and fertilizers and the consequences of cli... more The scarcity of non-renewable resources such as soils and fertilizers and the consequences of climate change can dramatically influence the food security of future generations. Mutualistic root microorganisms such as plant growth-promoting rhizobacteria (PGPR) ...
Trehalose (α-d-glucopyranosyl-1,1-α-d-glucopyranoside), a disaccharide widespread among microbes ... more Trehalose (α-d-glucopyranosyl-1,1-α-d-glucopyranoside), a disaccharide widespread among microbes and lower invertebrates, is generally believed to be nonexistent in higher plants. However, the recent discovery of Arabidopsis genes whose products are involved in trehalose synthesis has renewed interest in the possibility of a function of trehalose in higher plants. We previously showed that trehalase, the enzyme that degrades trehalose, is present in nodules of soybean (Glycine max [L.] Merr.), and we characterized the enzyme as an apoplastic glycoprotein. Here we describe the purification of this trehalase to homogeneity and the cloning of a full-length cDNA encoding this enzyme, named GMTRE1(G. maxtrehalase1). The amino acid sequence derived from the open reading frame of GMTRE1 shows strong homology to known trehalases from bacteria, fungi, and animals. GMTRE1 is a single-copy gene and is expressed at a low but constant level in many tissues.
Plants commonly live in a symbiotic association with arbuscular mycorrhizal fungi (AMF). They inv... more Plants commonly live in a symbiotic association with arbuscular mycorrhizal fungi (AMF). They invest photosynthetic products to feed their fungal partners, which, in return, provide mineral nutrients foraged in the soil by their intricate hyphal networks. Intriguingly, AMF can link neighboring plants, forming common mycorrhizal networks (CMNs). What are the terms of trade in such CMNs between plants and their shared fungal partners? To address this question, we set up microcosms containing a pair of test plants, interlinked by a CMN of Glomus intraradices or Glomus mosseae. The plants were flax (Linum usitatissimum; a C3 plant) and sorghum (Sorghum bicolor; a C4 plant), which display distinctly different 13C/12C isotope compositions. This allowed us to differentially assess the carbon investment of the two plants into the CMN through stable isotope tracing. In parallel, we determined the plants’ “return of investment” (i.e. the acquisition of nutrients via CMN) using 15N and 33P as ...
The activity of sucrose-sucrose-fructosyltransferase (SST), a vacuolar enzyme strongly induced by... more The activity of sucrose-sucrose-fructosyltransferase (SST), a vacuolar enzyme strongly induced by light in excised leaves of barley (Hordeum vulgare L.), rapidly declined even in continuous light upon feeding of cycloheximide (CHI). The rate of decline was similar to that observed in light-treated leaves that were placed into darkness, in the presence or absence of CHI. The protease inhibitor leupeptin totally stopped the decline in SST activity in the dark and caused a substantial increase in the rate of induction of SST activity by light. Feeding of sucrose prevented or even reversed the SST activity decay induced by darkness in the absence of CHI but did not stabilize SST activity in the presence of CHI. The results suggest that SST is continuously subjected to rapid, constant proteolytic degradation in the vac- uole, and that the enhancement of SST activity in the light or upon feeding sucrose in the dark is due exclusively to de novo protein synthesis. Fructans are polymers of fructose with a terminal glucose that function as major vacuolar storage carbohydrates in the vegetative organs of many important crop plants, most nota-
ABSTRACT The soil-borne fungus, Fusarium solani f. sp. phaseoli, attacks roots and hypocotyls of ... more ABSTRACT The soil-borne fungus, Fusarium solani f. sp. phaseoli, attacks roots and hypocotyls of bean (Phaseolus vulgaris) plants causing a devastating disease called root and foot rot. In a study of the host-pathogen relationship it was found that young bean roots, with the radicle just emerging, were highly tolerant to the pathogen, whereas older bean seedlings, with a fully developed root system, were completely susceptible. Investigations by low-temperature scanning electron microscopy demonstrated that significantly fewer spores and hyphae were present on the root surface of young bean seedlings as compared to older ones. A similar pattern of attachment was found when bean roots were inoculated with spores of F. solani f. sp. pisi, a related pathogen causing disease on peas but not on beans. Light microscopic studies showed that F. solani f. sp. pisi did not penetrate the root but rapidly formed thick-walled resting spores on the root surface. F. solani f. sp. phaseoli on the other hand quickly penetrated the root and formed an extensive network of fungal hyphae. These results demonstrate that the ability of fungal propagules to adhere to and to penetrate host tissues are two distinct processes. Furthermore, the data indicate that young bean roots lack a surface component necessary for attachment of fungal spores which may help explain their tolerance to Fusarium root rot.
To study the role of fructan in leaf development of barley seedlings, fructan contents and the ac... more To study the role of fructan in leaf development of barley seedlings, fructan contents and the activities of enzymes involved in fructan metabolism were measured in segments of the third leaf at the stage of maximal growth. Fructans amounted to more than 10 % of the d. wt in the growth zone at the base of the developing leaf and decreased sharply in the zone above. The specific activities of sucrose : sucrose 1-fructosyltransferase (1-SST) and sucrose : fructan 6-fructosyltransferase (6-SFT), two key enzymes in fructan synthesis, also peaked in the growth zone but decreased more slowly in the zone above. By contrast, the specific activities of invertase and fructan exohydrolase (FEH) were low in the growth zone at the leaf base and had their peak just above it. The specific activity of fructan : fructan 1-fructosyltransferase (1-FFT) was approx. constant over the whole leaf. These results indicate that transitory accumulation of fructans in the growth zone plays a key role in the development of barley leaves.
The main objective of this study was to shed light on the previously unknown arbuscular mycorrhiz... more The main objective of this study was to shed light on the previously unknown arbuscular mycorrhizal fungal (AMF) communities in Southern Arabia. We explored AMF communities in two date palm (Phoenix dactylifera) plantations and the natural vegetation of their surrounding arid habitats. The plantations were managed traditionally in an oasis and according to conventional guidelines at an experimental station. Based on spore morphotyping, the AMF communities under the date palms appeared to be quite diverse at both plantations and more similar to each other than to the communities under the ruderal plant, Polygala erioptera, growing at the experimental station on the dry strip between the palm trees, and to the communities uncovered under the native vegetation (Zygophyllum hamiense, Salvadora persica, Prosopis cineraria, inter-plant area) of adjacent undisturbed arid habitat. AMF spore abundance and species richness were higher under date palms than under the ruderal and native plants. Sampling in a remote sand dune area under Heliotropium kotschyi yielded only two AMF morphospecies and only after trap culturing. Overall, 25 AMF morphospecies were detected encompassing all study habitats. Eighteen belonged to the genus Glomus including four undescribed species. Glomus sinuosum, a species typically found in undisturbed habitats, was the most frequently occurring morphospecies under the date palms. Using molecular tools, it was also found as a phylogenetic taxon associated with date palm roots. These roots were associated with nine phylogenetic taxa, among them eight from Glomus group A, but the majority could not be assigned to known morphospecies or to environmental sequences in public databases. Some phylogenetic taxa seemed to be site specific. Despite the use of group-specific primers and efficient trapping systems with a bait plant consortium, surprisingly, two of the globally most frequently found species, Glomus intraradices and Glomus mosseae, were not detected neither as phylogenetic taxa in the date palm roots nor as spores under the date palms, the intermediate ruderal plant, or the surrounding natural vegetation. The results highlight the uniqueness of AMF communities inhabiting these diverse habitats exposed to the harsh climatic conditions of Southern Arabia. M. N. Al-Yahya'ei (*) : F. Oehl : D. Redecker : A. Wiemken
The main storage compounds in Lolium perenne are fructans with prevailing β(2-6) linkages. A cDNA... more The main storage compounds in Lolium perenne are fructans with prevailing β(2-6) linkages. A cDNA library of L. perenne was screened using Poa secunda sucrose:fructan 6-fructosyltransferase (6-SFT) as a probe. A full-length Lp6-SFT clone was isolated as shown by heterologous expression in Pichia pastoris. High levels of Lp6-SFT transcription were found in the growth zone of elongating leaves and in mature leaf sheaths where fructans are synthesized. Upon fructan synthesis induction, Lp6-SFT transcription was high in mature leaf blades but with no concomitant accumulation of fructans. In vitro studies with the recombinant Lp6-SFT protein showed that both 1-kestotriose and 6G-kestotriose acted as fructosyl acceptors, producing 1- and 6-kestotetraose (bifurcose) and 6G,6-kestotetraose, respectively. Interestingly, bifurcose formation ceased and 6G,6-kestotetraose was formed instead, when recombinant fructan:fructan 6G-fructosyltransferase (6G-FFT) of L. perenne was introduced in the en...
The fission yeast Schizo~accharomyces pombe was found to accumulate large amounts of polyphosphat... more The fission yeast Schizo~accharomyces pombe was found to accumulate large amounts of polyphosphate, particularly when grown on arginine as the nitrogen source. Upon transfer to a medium without phosphate, polyphosphate was degraded and served as at~ endogenous phosphate reserve. When phosphate was added again after a prolonged period of phosphate starvation, fission yeast cells synthesized more polyphosphate than they had contained before starvation, a phenomenon known as over-compensation. Strains carrying mutated structural genes for three different phosphatases, phol, pho2 or pho3, degraded polyphosphate at the same rate as the wild-type strain during phosphate starvation and showed the same type of over-compensation when phosphate was added again.
A fructan:fructan 1-fructosyltransferase (1-FFT) was purified from edible burdock for the first t... more A fructan:fructan 1-fructosyltransferase (1-FFT) was purified from edible burdock for the first time, and a cDNA encoding 1-FFT was isolated from the plant. Two 1-FFTs named 1-FFTa and 1-FFTb were purified from extract of edible burdock by ammonium sulfate precipitation, followed by chromatographies on DEAE-Sepharose CL-6B, Toyopearl HW-55S and Sephadex G-100 columns. Inulin-type fructan such as nystose and fructooligosaccharides with higher DP were produced from 1-kestose by purified 1-FFTs. The general properties of both purified enzymes were very similar to each other. The purified 1-FFTa and 1-FFTb showed a single band by native PAGE and two bands, relative molecular masses of about 46,000 and 17,500 for 1-FFTa and 46,000 and 17,000 for 1-FFTb, by SDS-PAGE, respectively. The N-terminal sequences of the 46,000 peptides of both enzymes were the same, and those of the 17,500 and the 17,000 peptides were also identical. Based on the sequences, the 1-FFT cDNA named alft1 was cloned. The alft1 encoded a polypeptide of 617 amino acids. The relative molecular mass and pI of the mature protein region of deduced polypeptide were calculated to be 60,213 and 4.89, respectively. The characteristics of recombinant protein produced by Pichia pastoris closely resembled those of the native 1-FFTs purified from edible burdock. In this study, we demonstrated that alft1 encoding edible burdock 1-FFT was involved in the elongation of fructosyl chains of fructooligosaccharides in edible burdock.
We have recently identified two genes coding for inorganic phosphate transporters (Pht) in sorghu... more We have recently identified two genes coding for inorganic phosphate transporters (Pht) in sorghum (Sorghum bicolor) and flax (Linum usitatissimum) that were induced in roots colonized by arbuscular mycorrhizal (AM) fungi. Mycorrhizal acquisition of inorganic phosphorus (Pi) was strongly affected by the combination of plant and AM fungal species, but the expression level of these genes coding for AMinducible Pi transporters did not explain differences in plant phosphorus acquisition where flax and sorghum are sharing a common mycorrhizal network. In the present study, we investigated the possible role of fungal Pi transporters in the regulation of mycorrhizal Pi acquisition by measuring their expression in roots of flax and sorghum. One Pi transporter of Rhizophagus irregularis (RiPT5) showed a positive correlation with mycorrhizal Pi acquisition of sorghum. This indicates that a possible involvement in the regulation of mycorrhizal Pi acquisition. In general, expression of AMF Pi transporters was more related to mycorrhizal Pi acquisition of sorghum than of flax, indicating plant species-specific differences in the regulation of mycorrhizal Pi acquisition.
The effect of arbuscular mycorrhizas on fructan accumulation was studied in barley (Hordeum vulga... more The effect of arbuscular mycorrhizas on fructan accumulation was studied in barley (Hordeum vulgare) infected with Glomus mosseae. Treatments with and without fertilizer were included in order to distinguish between mere fertilizer effects and the effects of the symbiosis, and plants were harvested at two different time points, 35 and 50 d after planting. Fructan was the major storage carboyhdrate in both leaves and roots. The amounts of fructan were markedly altered in the mycorrhizal plants. In roots of non-fertilized mycorrhizal plants, fructan pools were significantly greater than in the corresponding non-mycorrhizal plants. By contrast, fertilization caused a general decrease in amounts of fructan in roots. The increase of fructan in mycorrhizal roots was correlated with a decrease of invertase activity. In leaves, fructan pools decreased or remained unchanged upon mycorrhizal infection ; fertilization had a similar effect. However, when individual leaves of a plant were compared, intriguing effects of the mycorrhizal symbiosis could be observed. Whereas in non-mycorrhizal plants, the youngest leaves had the highest fructan contents and the oldest leaves the lowest (as previously reported), this gradient was markedly altered in mycorrhizal plants, indicating systemic effects of mycorrhiza on assimilate partitioning in shoots.
Alternative Farming Systems, Biotechnology, Drought Stress and Ecological Fertilisation, 2010
Abstract Soil microorganisms can be used to decrease the input of fertilizers, pesticides and oth... more Abstract Soil microorganisms can be used to decrease the input of fertilizers, pesticides and other chemicals. Among soil microorganisms, arbuscular mycor-rhizal (AM) fungi and Rhizobium spp. can promote plant growth and control plant fungal diseases. However these ...
A DNA fragment of Sa~~rh~lromj~ces cur-ei'isiae with high homology to the acetyl-coenzyme A (acet... more A DNA fragment of Sa~~rh~lromj~ces cur-ei'isiae with high homology to the acetyl-coenzyme A (acetyl-CoA) synthetase genes of Aspergillus nidulans and Neurospora crassa has been cloned, sequenced and mapped to chromosome I. It contains an open reading frame of 2139 nucleotides, encoding a predicted gene product of 79.2 kDa. In contrast to its ascomycete homologs, there are no introns in the coding sequence. The first ATG codon of the open reading frame is in an unusual context for a translational start site, while the next ATG. 24 codons downstream. is in a more conventional context. Possible implications of two alternative translational start sites for the cellular localization or the enzyme are discussed. A stable mutant of this gene. obtained by the gene disruption technique. had the same low basal activity of acetyl-CoA synthetase as wild-type cells when grown on glucose but completely lacked the strong increase in activity upon entering the stalionary phase, providing direct proof that the gene encodes an inducible acetyl-CoA synthetase ( A C S I ) of yeast. As expected, the mutant was unable to grow on acetate as sole carbon source. Nevertheless, it showed normal induction of isocitrate lyase on acetate media, indicating that activity ofacetyl-CuA synthetase is dispensable for induction or the glyoxylate cycle in S. cerevisirre. Surprisingly. disruption of the ACSI gene did not affect growth on media containing ethanol as the sole carbon source, demonstrating that there are alternative pathways leading to acetyl-CoA under these conditions.
Fructan (polyfructosylsucrose) is an important storage carbohydrate in many plant families. fruct... more Fructan (polyfructosylsucrose) is an important storage carbohydrate in many plant families. fructan:fructan 6G-fructosyltransferase (6G-FFT) is a key enzyme in the formation of the inulin neoseries, a type of fructan accumulated by members of the Liliales. We have cloned the 6G-FFT from onion by screening a cDNA library using barley sucrose:fructan 6-fructosyltransferase (6-SFT) as a probe. The deduced amino acid sequence showed a high homology with plant invertases and 6-SFT. Incubation of protein extracts from transgenic tobacco plants with the trisaccharide 1-kestose and sucrose resulted in the formation of neokestose and fructans of the inulin neoseries with a degree of polymerization up to six. Introduction of the onion 6G-FFT into chicory resulted in the synthesis of fructan of the inulin neoseries, in addition to the synthesis of linear inulin.
The scarcity of non-renewable resources such as soils and fertilizers and the consequences of cli... more The scarcity of non-renewable resources such as soils and fertilizers and the consequences of climate change can dramatically influence the food security of future generations. Mutualistic root microorganisms such as plant growth-promoting rhizobacteria (PGPR) ...
Trehalose (α-d-glucopyranosyl-1,1-α-d-glucopyranoside), a disaccharide widespread among microbes ... more Trehalose (α-d-glucopyranosyl-1,1-α-d-glucopyranoside), a disaccharide widespread among microbes and lower invertebrates, is generally believed to be nonexistent in higher plants. However, the recent discovery of Arabidopsis genes whose products are involved in trehalose synthesis has renewed interest in the possibility of a function of trehalose in higher plants. We previously showed that trehalase, the enzyme that degrades trehalose, is present in nodules of soybean (Glycine max [L.] Merr.), and we characterized the enzyme as an apoplastic glycoprotein. Here we describe the purification of this trehalase to homogeneity and the cloning of a full-length cDNA encoding this enzyme, named GMTRE1(G. maxtrehalase1). The amino acid sequence derived from the open reading frame of GMTRE1 shows strong homology to known trehalases from bacteria, fungi, and animals. GMTRE1 is a single-copy gene and is expressed at a low but constant level in many tissues.
Plants commonly live in a symbiotic association with arbuscular mycorrhizal fungi (AMF). They inv... more Plants commonly live in a symbiotic association with arbuscular mycorrhizal fungi (AMF). They invest photosynthetic products to feed their fungal partners, which, in return, provide mineral nutrients foraged in the soil by their intricate hyphal networks. Intriguingly, AMF can link neighboring plants, forming common mycorrhizal networks (CMNs). What are the terms of trade in such CMNs between plants and their shared fungal partners? To address this question, we set up microcosms containing a pair of test plants, interlinked by a CMN of Glomus intraradices or Glomus mosseae. The plants were flax (Linum usitatissimum; a C3 plant) and sorghum (Sorghum bicolor; a C4 plant), which display distinctly different 13C/12C isotope compositions. This allowed us to differentially assess the carbon investment of the two plants into the CMN through stable isotope tracing. In parallel, we determined the plants’ “return of investment” (i.e. the acquisition of nutrients via CMN) using 15N and 33P as ...
The activity of sucrose-sucrose-fructosyltransferase (SST), a vacuolar enzyme strongly induced by... more The activity of sucrose-sucrose-fructosyltransferase (SST), a vacuolar enzyme strongly induced by light in excised leaves of barley (Hordeum vulgare L.), rapidly declined even in continuous light upon feeding of cycloheximide (CHI). The rate of decline was similar to that observed in light-treated leaves that were placed into darkness, in the presence or absence of CHI. The protease inhibitor leupeptin totally stopped the decline in SST activity in the dark and caused a substantial increase in the rate of induction of SST activity by light. Feeding of sucrose prevented or even reversed the SST activity decay induced by darkness in the absence of CHI but did not stabilize SST activity in the presence of CHI. The results suggest that SST is continuously subjected to rapid, constant proteolytic degradation in the vac- uole, and that the enhancement of SST activity in the light or upon feeding sucrose in the dark is due exclusively to de novo protein synthesis. Fructans are polymers of fructose with a terminal glucose that function as major vacuolar storage carbohydrates in the vegetative organs of many important crop plants, most nota-
ABSTRACT The soil-borne fungus, Fusarium solani f. sp. phaseoli, attacks roots and hypocotyls of ... more ABSTRACT The soil-borne fungus, Fusarium solani f. sp. phaseoli, attacks roots and hypocotyls of bean (Phaseolus vulgaris) plants causing a devastating disease called root and foot rot. In a study of the host-pathogen relationship it was found that young bean roots, with the radicle just emerging, were highly tolerant to the pathogen, whereas older bean seedlings, with a fully developed root system, were completely susceptible. Investigations by low-temperature scanning electron microscopy demonstrated that significantly fewer spores and hyphae were present on the root surface of young bean seedlings as compared to older ones. A similar pattern of attachment was found when bean roots were inoculated with spores of F. solani f. sp. pisi, a related pathogen causing disease on peas but not on beans. Light microscopic studies showed that F. solani f. sp. pisi did not penetrate the root but rapidly formed thick-walled resting spores on the root surface. F. solani f. sp. phaseoli on the other hand quickly penetrated the root and formed an extensive network of fungal hyphae. These results demonstrate that the ability of fungal propagules to adhere to and to penetrate host tissues are two distinct processes. Furthermore, the data indicate that young bean roots lack a surface component necessary for attachment of fungal spores which may help explain their tolerance to Fusarium root rot.
To study the role of fructan in leaf development of barley seedlings, fructan contents and the ac... more To study the role of fructan in leaf development of barley seedlings, fructan contents and the activities of enzymes involved in fructan metabolism were measured in segments of the third leaf at the stage of maximal growth. Fructans amounted to more than 10 % of the d. wt in the growth zone at the base of the developing leaf and decreased sharply in the zone above. The specific activities of sucrose : sucrose 1-fructosyltransferase (1-SST) and sucrose : fructan 6-fructosyltransferase (6-SFT), two key enzymes in fructan synthesis, also peaked in the growth zone but decreased more slowly in the zone above. By contrast, the specific activities of invertase and fructan exohydrolase (FEH) were low in the growth zone at the leaf base and had their peak just above it. The specific activity of fructan : fructan 1-fructosyltransferase (1-FFT) was approx. constant over the whole leaf. These results indicate that transitory accumulation of fructans in the growth zone plays a key role in the development of barley leaves.
The main objective of this study was to shed light on the previously unknown arbuscular mycorrhiz... more The main objective of this study was to shed light on the previously unknown arbuscular mycorrhizal fungal (AMF) communities in Southern Arabia. We explored AMF communities in two date palm (Phoenix dactylifera) plantations and the natural vegetation of their surrounding arid habitats. The plantations were managed traditionally in an oasis and according to conventional guidelines at an experimental station. Based on spore morphotyping, the AMF communities under the date palms appeared to be quite diverse at both plantations and more similar to each other than to the communities under the ruderal plant, Polygala erioptera, growing at the experimental station on the dry strip between the palm trees, and to the communities uncovered under the native vegetation (Zygophyllum hamiense, Salvadora persica, Prosopis cineraria, inter-plant area) of adjacent undisturbed arid habitat. AMF spore abundance and species richness were higher under date palms than under the ruderal and native plants. Sampling in a remote sand dune area under Heliotropium kotschyi yielded only two AMF morphospecies and only after trap culturing. Overall, 25 AMF morphospecies were detected encompassing all study habitats. Eighteen belonged to the genus Glomus including four undescribed species. Glomus sinuosum, a species typically found in undisturbed habitats, was the most frequently occurring morphospecies under the date palms. Using molecular tools, it was also found as a phylogenetic taxon associated with date palm roots. These roots were associated with nine phylogenetic taxa, among them eight from Glomus group A, but the majority could not be assigned to known morphospecies or to environmental sequences in public databases. Some phylogenetic taxa seemed to be site specific. Despite the use of group-specific primers and efficient trapping systems with a bait plant consortium, surprisingly, two of the globally most frequently found species, Glomus intraradices and Glomus mosseae, were not detected neither as phylogenetic taxa in the date palm roots nor as spores under the date palms, the intermediate ruderal plant, or the surrounding natural vegetation. The results highlight the uniqueness of AMF communities inhabiting these diverse habitats exposed to the harsh climatic conditions of Southern Arabia. M. N. Al-Yahya'ei (*) : F. Oehl : D. Redecker : A. Wiemken
The main storage compounds in Lolium perenne are fructans with prevailing β(2-6) linkages. A cDNA... more The main storage compounds in Lolium perenne are fructans with prevailing β(2-6) linkages. A cDNA library of L. perenne was screened using Poa secunda sucrose:fructan 6-fructosyltransferase (6-SFT) as a probe. A full-length Lp6-SFT clone was isolated as shown by heterologous expression in Pichia pastoris. High levels of Lp6-SFT transcription were found in the growth zone of elongating leaves and in mature leaf sheaths where fructans are synthesized. Upon fructan synthesis induction, Lp6-SFT transcription was high in mature leaf blades but with no concomitant accumulation of fructans. In vitro studies with the recombinant Lp6-SFT protein showed that both 1-kestotriose and 6G-kestotriose acted as fructosyl acceptors, producing 1- and 6-kestotetraose (bifurcose) and 6G,6-kestotetraose, respectively. Interestingly, bifurcose formation ceased and 6G,6-kestotetraose was formed instead, when recombinant fructan:fructan 6G-fructosyltransferase (6G-FFT) of L. perenne was introduced in the en...
The fission yeast Schizo~accharomyces pombe was found to accumulate large amounts of polyphosphat... more The fission yeast Schizo~accharomyces pombe was found to accumulate large amounts of polyphosphate, particularly when grown on arginine as the nitrogen source. Upon transfer to a medium without phosphate, polyphosphate was degraded and served as at~ endogenous phosphate reserve. When phosphate was added again after a prolonged period of phosphate starvation, fission yeast cells synthesized more polyphosphate than they had contained before starvation, a phenomenon known as over-compensation. Strains carrying mutated structural genes for three different phosphatases, phol, pho2 or pho3, degraded polyphosphate at the same rate as the wild-type strain during phosphate starvation and showed the same type of over-compensation when phosphate was added again.
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