bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isolation and preliminary characterization of 5‐fluoroindole‐resistant and IAA‐overproducer mutants of the ectomycorrhizal fungus Hebeloma cylindrosporum Romagnesi
Authors: DURAND N. , DEBAUD J. C. , CASSELTON L. A. , GAY G. 
Published: April 2006

summaryIAA‐overproducer mutants of the ectomycorrhizal basidiomycete Hebeloma cylindrosporum Romagnesi were isolated in an attempt to clarify the role of fungal IAA in ectomycorrhiza formation. By contrast to the wild type, mutants are able to metabolize endogenous Trp to IAA. They were isolated using a two‐step method. One hundred and forty‐four mutants with altered regulation of the Trp branch of the shikimate pathway were isolated from two compatible monokaryons by selecting for resistance to the indole analogue, 5‐fluoroindole. These mutants are Trp‐overproducers and most of them accumulate free Trp. Seventeen mutants able to synthesize IAA in the absence of exogenous precursor (tryptophan or intermediates of the tryptophan biosynthetic pathway) were identified by screening for the ability to metabolize endogenous Trp into IAA. By studying the activity of key enzymes of the Trp biosynthetic pathway (i.e. anthranilate synthase and Trp synthase), it was evident that different mechanisms led to IAA‐overproduction. A correlation was detected between the level of intracellular Trp accumulation and the ability of the mutants to metabolize endogenous Trp to IAA. This indicates that, irrespective of the mutation, intracellular Trp accumulation is a prerequisite for IAA overproduction. A positive correlation was also detected between, on the one hand, resistance to fluoroindole and, on the other hand, intracellular Trp accumulation and, subsequently, IAA‐overproduction. Thus, resistance to high fluoroindole concentrations appeared to provide a method for the direct selection of IAA‐overproducer mutants. In order to be able to compare these mutants with the wild parental dikaryon and to perform genetic analyses, the mutants were fused with a compatible wild monokaryon. The resulting dikaryons were able to form mycorrhizas with the normal host plant, Pinus pinaster, and to fruit under controlled culture conditions, thus allowing stabilization and purification of the mutations. IAA‐overproducer monokaryons were detected within the progeny of all the mutants. They are now being used to study the role of fungal IAA in ectomycorrhizas.
Uptake and accumulation of radiocaesium by mycorrhizal and non‐mycorrhizal heather plants
Authors: CLINT G. M. , DIGHTON J. 
Published: April 2006

summaryShort‐term uptake of 137Cs by heather (Calluna vulgaris L.) was measured using radiolabelled liquid media and plants grown from shoot cuttings. Uptake by mycorrhizal plants was compared with uptake by non‐mycorrhizal plants, and the effects of different external Cs and K concentrations were determined.At each time point during the 3 h experimental period the content (and hence also the apparent influx) of the mycorrhizal plants in each treatment was found to be lower than that of the non‐mycorrhizal plants.An increase of 100‐fold in the total external Cs concentration (from 5 to 500μM) gave between a 35‐fold and 96‐fold increase in initial influx of Cs. A similar change in external K concentration, however, had little effect on Cs influx. Root‐shoot transfer of Cs over the 3 h uptake period was slight; in most cases more than 90% of the radiocaesium remained in the root. The final shoot:root Cs ratio was higher in mycorrhizal than in non‐mycorrhizal plants, suggesting that in mycorrhizal plants, despite their lower overall accumulation during the first 3 h, a higher proportion of the Cs taken up is translocated to the shoot.
Occurrence of nodulation in legume species in the Amazon region of Brazil
Authors: DE SOUZA MOREIRA FATIMA MARIA , DA SILVA MARLENE FREITAS , DE SÉRGIO MIANA FARIA 
Published: April 2006

summaryThis paper reports the nodulation status of 172 legume species from different ecosystems within the Amazon region of Brazil. The nodulation ability of 98 species and eight genera was observed for the first time. Occurrence of nodulation is discussed in the context of the taxonomy of the family and the different ecosystems. The frequency of nodulation among tribes and genera was found to be higher in flooded (varzea and igapó) than in non‐flooded sites (terra firme); moreover, more plants had nodulated in nursery beds consisting of soil from flooded areas. The symbiosis may therefore be favoured in flooded areas.
Oriented degradation of the genome of cyanophage AN‐23 after exposure to NaCl
Authors: BANCROFT I. , SMITH R. J. 
Published: April 2006

summaryThe low tolerance of cyanophage AN‐23 to NaCl at more than 0·05 M has been investigated. When isolated from clarified lysates that had been exposed to NaCl in the presence of added DNAse I, the phage genomic DNA consisted of a series of discrete fragments. The fragments were recovered from low melting temperature agarose electrophoresis gels and used for restriction analysis. Comparison of the restriction cleavage products with a restriction map of the 46 kbp AN‐23 genome has shown that the fragments are generated by removal of DNA from one end of the linear genome in steps of about 3 kbp. The data are consistent with a model in which NaCl triggers the ejection of the phage genome from the capsid.
Quiescent centre ontogenesis during early germination of Allium cepa L.
Authors: BITONTI M. B. , CHIAPPETTA A. , INNOCENTI A. M. , LISO R. , ARRIGONI O. 
Published: April 2006

summaryQuiescent centre ontogenesis has been studied during germination of Allium cepa L. seeds, starting from the onset of DNA synthesis in the embryo root meristems. The resumption of cell cycling activity in the meristem occurs late during root protrusion and the quiescent centre becomes well defined when the root is 5 mm long. The establishment of the quiescent centre in growing roots is related to structural changes of embryo radicle during germination. These results are discussed in relation to the role of the quiescent centre in the root growth.
Vacuolar development in the root meristem of Festuca rubra L.
Authors: DAVIES K. L. , DAVIES M. S. , FRANCIS D. 
Published: April 2006

summaryRoot meristematic cells of 10‐d‐old Festuca rubra L. were examined by TEM. A range of vacuolar structures were observed ranging from provacuolar bodies associated with dictyosomes and sequestration vacuoles, through to autolytic vacuoles and residual bodies. Based on these TEM observations, we suggest a sequence of vacuolar development in root meristematic cells in relation to tissue differentiation in F. rubra.
Acidic mist and nitrogen fertilization effects on growth, nitrate reductase activity, gas exchange, and frost hardiness of red spruce seedlings
Authors: L'HIRONDELLE S. J. , JACOBSON J. S. , LASSOIE J. P. 
Published: April 2006

summaryAcidic deposition may contribute to the decline of red spruce (Picea rubensSarg.) in eastern North America; response to acidic mist may depend on mist content and plant nutrient status. We grew red spruce seedlings with high or low nitrogen fertilization to roots (other elements in constant proportion to N), exposed only shoots to pH 3.0, high sulphate (10:1, S:N) or high nitrate (1:10, S:N) mist for 5 wk, then moved seedlings outdoors for cold acclimation. Effects of mist content were found until the third week of cold acclimation. Foliar necrosis was higher after exposure to sulphate than to nitrate mist and greater in older than new needles. Sulphate‐misted seedlings had lower new‐shoot biomass, shoot water content, and nitrate reductase activity, and higher foliar sulphur levels than nitrate‐misted seedlings. They also had greater needle frost hardiness (estimated by electrolyte leakage) at the start of cold acclimation. Effects of fertilization were found throughout the experiment. High‐N fertilization increased biomass, tissue N level, and shoot water content, and decreased foliar necrosis from mist. During cold acclimation, high‐N seedlings had lower transpiration and photosynthetic rates and higher water use efficiency than low‐N seedlings. High‐N fertilization increased needle frost hardiness after 5 wk of acclimation and decreased visible needle injury after an outdoor frost. However, high‐N seedlings had fewer needle primordia in terminal buds and more bud frost‐damage than low‐N seedlings. Fertilization, mist content, and their interaction strongly affected seedlings, showing that nutrient status can influence the response of red spruce to acidic deposition and frost.
Effects of ozone on foliar nitrogen metabolism ofPinus taedaL. and implications for carbohydrate metabolism
Authors: MANDERSCHEID R. , JÄGER H.‐J. , KRESS L. W. 
Published: April 2006

summaryDose‐response relationship of ozone effects on foliar nitrogen metabolism of two half‐sib families ofPinus taedaL. was studied. Trees were exposed to six ozone concentrations, ranging from 0.2 to 3 times the ambient, for two consecutive growing seasons (1988 and 1989) in open‐top chambers. Content of total chlorophyll, soluble protein and soluble amino acids, and activities of glutamine synthetase and glutamate dehydrogenase, were measured in second‐flush needles of 1989, harvested in November of 1989. Root collar diameter growth rate was also determined. Variation in depth to soil mottling, an indicator of changing redox conditions, significantly affected tree growth and nitrogen metabolism. Therefore depth to soil mottling was used as a covariate and dose‐response curves were provided with adjusted means. A decline of root collar diameter growth rate and foliar chlorophyll content was found at the highest ozone level. However, both these parameters were affected much more by soil conditions than by ozone. Glutamine synthetase, glutamate dehydrogenase and amino acids, especially glutamate and glutamine, increased by approx. 2‐fold and 3‐fold, respectively, at two and three times ambient ozone. However, soluble protein content was only affected at the highest ozone concentration, showing a 25‐fold increase. Nitrogen metabolism was more influenced by ozone than by the variation in edaphic conditions. No consistent ozone × family interaction on nitrogen metabolism could be found, but the two half‐sib families significantly differed in glutamate dehydrogenase activity and the contents of glutamate and glycine, indicating a regulatory function of this enzyme between nitrogen and carbon metabolism. The increase of amino‐N turnover and the following rise in soluble protein content are explained by the strategy of the plant to reallocate the nutrients from needles subjected to accelerated senescence by ozone. Possible implications of this process in carbohydrate metabolism and carbon partitioning are discussed.
Field studies on Norway spruce trees at high altitudes: II. Defence systems against oxidative stress in needles
Authors: POLLE ANDREA , RENNENBERG HEINZ 
Published: April 2006

summaryAntioxidants were characterized in needles from mature spruce trees [Picea abies (L.) Karst.] grown in a forest on the Wank mountain in the Bavarian Calcareous Alps at three altitudes (870 m, 1270 m, and 1700 m). The effect of elevation, season and needle age on the activities of superoxide dismutase, glutathione reductase, ascorbate peroxidase, and the content of ascorbate and glutathione was analyzed. Ascorbate peroxidase and superoxide dismutase activity were little affected by stress from higher altitudes. Superoxide dismutase activity decreased with increasing needle age at all three altitudes. Maximum levels of glutathione and glutathione reductase were found in needles from the highest altitude, but the increase was not linear with increasing elevation. At the middle altitude, levels of glutatione reductase and glutatione were as low as, or even lower than at the lowest site. The mean ascorbate content increased with increasing altitude by about 2 μmol g−1 fresh weight per site. The seasonal change of the ascorbate content in the needles was twofold higher at the upper than at the lower sampling site. These findings suggest that superoxide dismutase and ascorbate peroxidase activities were sufficient to cope with a higher production of toxic oxygen species which probably occurs at high altitudes, and that adaptation was necessary for the antioxidant substrates and their regeneration system.
Secondary homostyly in Primula L.; evidence for the model of the ‘S’ supergene
Authors: WEDDERBURN F. M. , RICHARDS A. J. 
Published: April 2006

summaryIn Primula, in which 9% of the species are homostyle, it is estimated that 54% are polyploid, while only 4% of the cytologically examined heterostyle species are polyploid.To investigate the supposed secondary and recombinational nature of homostyly in polyploid Primulas of section Aleuritia, crosses were made between three diploid heterostyle and five polyploid homostyle species. Patterns of pollen germination, pollen tube growth and seed set in interspecific illegitimate crosses were the same as those observed for intraspecific crosses. However, interspecific legitimate crosses showed a late‐acting incompatibility not seen in the intraspecific crosses. In all cases, homostyles acted as it they were of thrum mating type when male, but as if they were of pin mating type when female. We conclude that for all five homostyle species, homostyly has arisen secondarily by recombination within the ‘S’ complex linkage group. The relationship between secondary recombinational homostyly and polyploidy in Primula is discussed.Although the small quantities of seed produced in crosses between four species of different ploidy levels were shown to be viable, substantial crossability barriers were demonstrated between all eight species. Thus, evidence of crossability supports the maintenance of these closely similar taxa as distinct species of disjunct distribution.
Association of esterase isozymes with morphology in F2 progenies of two growth variants in Poa annua L.
Authors: DARMENCY H. , BERTI A. , GASQUEZ J. , MATEJICEK A. 
Published: April 2006

summaryThe morphology, flowering behaviour and esterase genotype was examined for six F2 progenies of hybrids between the two main variants of Poa annua L. (namely, annual‐erect and perennial‐prostrate). The association of flowering time with leaf and tiller morphology and Est 1 allozyme genotype, previously described for the two variants in populations from Burgundy, was fully broken in the F2 generation, indicating that no linkage blocks were involved. Whether selection maintains the association of isozyme genotype and growth form is discussed.
Adventitious root formation in hypocotyl cuttings of Picea sitchensis (Bong.) Carr. — the influence of plant growth regulators
Authors: SELBY C. , KENNEDY S. J. , HARVEY B. M. R. 
Published: April 2006

summaryA simple method for the study of adventitious root initiation on Sitka spruce [Picea sitchensis (Bong.) Carr.] hypocotyl cuttings is described and was used to examine the effects of plant growth regulators. Twenty‐one‐day‐old seedlings, grown at a low light intensity (15–20 μmol m−2 s−1) to stimulate hypocotyl elongation, provided easy to handle tissues which were responsive to root inducing treatments. Spontaneous rooting only occurred at a low frequency on untreated cuttings and reliable rooting depended upon auxin treatment. When continuous auxin treatment was used, indole‐3‐butyric acid (IBA) was more effective than either indole‐3‐acetic acid (IAA) or 1‐naphthaleneacetic acid (NAA), and was optimal between 10−6 and 10−5 M. Pulse treatments with 10−3 M IBA for as little as 10 min were sufficient to stimulate rooting. All other growth regulators examined were inhibitory to IBA induced rooting. 6‐benzylaminopurine (BA) was the most active being inhibitory down to a concentration of 3 × 10−7 M when it was applied in a mixture with IBA. Pre‐treatment of hypocotyl cuttings with BA prior to auxin treatment demonstrated strong cytokinin ‘carry‐over’ inhibitory effects on rooting. Gibberellic acid A3 (GA3), abscisic acid (ABA) and 2‐chloroethyl‐phosphoric acid (ethrel) were less potent inhibitors of rooting.
Sucrose‐metabolizing enzymes from leaves of barley infected with brown rust (Puccinia hordei Otth.)
Authors: TETLOW I. J. , FARRAR J. F. 
Published: April 2006

summaryThe capacity for sucrose synthesis in primary leaves of barley (Hordeum vulgare L.) infected with brown rust (Puccinia hordei Otth.) was assessed by measuring the activity of sucrose phosphate synthase (SPS). SPS activity gradually declined during rust infection to 32% of uninfected controls by the sporulation stage. Extractable SPS activity was constant in the light period in both uninfected and infected (sporulating) leaves; activity then declined in the first hour of darkness by 30% in uninfected and 60% in sporulating leaves until returning to the original activity at the start of the following light period. The activity of acid invertase (AI) increased more than four‐fold in rust‐infected (sporulating) primary leaves compared with controls. Extracellular AI activity in rusted tissue was two‐fold greater than in healthy. The consequences of the changes in enzyme activities in the diseased plant are discussed in relation to export from the diseased leaf.
Influence of intergeneric grafts between host and non‐host legumes on formation of vesicular–arbuscular mycorrhiza
Authors: GIANINAZZI‐PEARSON V. , GIANINAZZI S. 
Published: April 2006

summaryStem grafts were carried out between different varieties of vesicular‐arbuscular (VA) mycorrhizal host (pea, soybean) and non‐host (lupin) legumes. Only grafts on host rootstock were successful. Self‐grafts of three pea varieties (Amino, Solara, Frisson), and interspecific grafts between soybean (var. Amsoy 71) and pea (var. Frisson), did not generally affect development of, or arbuscule formation by, Glomus intraradices Schenck & Smith or G. mosseae Nicol. & Gerd. within the rootstock. In contrast, lupin (var. Alban and Lucky) scions greatly reduced colonization of the root cortex and completely inhibited arbuscule formation by both fungi in grafted pea rootstock. The possible role of mobile shoot factors in non‐host resistance to VA mycorrhizal fungi in lupins is discussed.
External hyphae of vesicular—arbuscular mycorrhizal fungi associated with Trifolium subterraneum L.
Authors: JAKOBSEN I. , ABBOTT L. K. , ROBSON A. D. 
Published: April 2006

summaryPhosphorus transport by hyphae of the three VA mycorrhizal fungi, Acaulospora laevis Gerdemann & Trappe, Glomus sp. and Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders, associated with Trifolium subterraneum L. was investigated by means of radiotracer techniques. Plants with roots heavily colonized by each mycorrhizal fungus were transplanted to two‐compartment systems, where a hyphal compartment was separated from the main compartment by a fine mesh preventing root penetration. The hyphal compartment contained layers of 32P‐labelled soil, which were placed at 0, 1, 2.5, 4.5 or 7 cm from the root compartment.A time‐course study over 37 d showed that Glomus sp. transported most 32P to shoots over soil‐root distances shorter than 1 cm. In contrast, A. laevis transported most 32P to shoots over soil–root distances longer than 1 cm. This ability of A. laevis to transport phosphorus over longer distances than Glomus sp. parallels previous observations that hyphae of A. laevis spread faster and further in soil than hyphae of the Glomus sp. Scutellospora calospora transported much less 32P to plants, but accumulated more 32P in its hyphae, than the two other fungi. The higher specific radioactivity in the hyphae of S. calospora than of A. laevis and Glomus sp. indicated a retarded translocation of 32P in its hyphae or retarded transfer of 32P across its interface with the host. However, the poor phosphorus transport by S. calospora might also have resulted from its reaction to root trimming at transplanting; percentage root colonization by S. calospora decreased markedly after transplanting to the labelling system.
The ecology and functioning of vesicular—arbuscular mycorrhizas in co‐existing grassland species
Authors: SANDERS I. R. , FITTER A. H. 
Published: April 2006

summaryVesicular–arbuscular mycorrhizal infection and morphology was measured in six co‐existing plant species of a semi‐natural grassland during a two year period, in order (1) to measure within‐year variation in mycorrhizal infection, (2) to determine whether seasonal trends in mycorrhizal infection were the same in both years, and (3) to quantify and interspecific differences in this variation. Seasonal trends in total mycorrhizal infection in the six plant species grouped together were very different in the two years. When the plant species were considered individually distinct patterns emerged. Mycorrhizal infection in Plantago lanceolata L. and Rumex acetosa L. varied greatly both within and between years. In contrast, Festuca rubra L., Holcus lanatus L., Lathyrus pratensis L. and Trifolium pratense L. all exhibited more constant levels of infection within one year and between successive years. However, interspecific differences in infection occurred between these four species. Although there was temporal variation in hyphal density, arbuscule and vesicle density varied very little with time and thus could not be used to indicate whether there are predictable periods of host cost or benefit. Vesicle width varied significantly between the plant species; this might represent infection by different fungal species.
The ecology and functioning of vesicular–arbuscular mycorrhizas in co‐existing grassland species
Authors: SANDERS I. R. , FITTER A. H. 
Published: April 2006

summaryAlthough vesicular–arbuscular mycorrhizas (VAM) are abundant in natural ecosystems, the evidence for the mutualistic effect of this association under field conditions is conflicting. VAM infection and inflow of phosphorus, copper, zinc and manganese was measured in six co‐existing plant species of a semi‐natural grassland, during a 2‐yr period, in order to establish whether patterns of nutrient uptake and plant growth in co‐existing species can be related to levels of mycorrhizal infection. There was no relationship between VAM infection and shoot concentrations of P, Cu, Zn or Mn, or plant biomass, and only in a few cases was nutrient inflow related to infection.Although the results do not support the hypothesis that VAM infection is beneficial for plant nutrition, high levels of P inflow do occur at certain periods during the growth season, suggesting that mycorrhizas may promote plant nutrient uptake at these times. Owing to the abundance of VAM, the lack of speciation and high P inflows which can occur in the field, these mycorrhizal associations are likely to be mutualistic.