bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fructosyl transfer from sucrose and oligosaccharides during fructan synthesis in excised leaves of Lolium temulentum L.
Authors: HOUSLEY T. L. , GIBEAUT D. M. , CARPITA N. C. , SIMS I. , POLLOCK C. J. 
Published: April 2006

summaryFructan biosynthesis begins with the transfer of a fructosyl moiety from one sucrose molecule to another to yield a trisaccharide. Trisaccharides may also arise by the reversible transfer of a fructosyl moiety from higher oligomers to sucrose but in this case there is no net fructan synthesis. Short‐term and long‐term exposure of detached illuminated leaf blades of Lolium temulentum (L.I to 14CO2 was used to examine the mechanism of transfer of fructosyl residues to sucrose.Two trisaccharides, 1‐kestose and neokestose, were found to be radioactive when leaves excised and illuminated for 15 h ‐were exposed to NCO2 for 30 min. The label increased in neokestose during the chase period, while that in 1‐kestose increased for the first 2 h of the chase period then declined for the remaining 4h. With a longer exposure to 14CO2 during the first 6 h of the induction period, three trisaccharides, neokestose, 1‐kestose and 6‐kestose were radiolabelled. The label turned over in neokestose and 1‐kestose, but continued to accumulate in 6‐kestose during a subsequent 18 h chase period. The specific activities of glucose and fructose of the sucrosyl portion and the terminal fructosyl moiety of the various trisaccharides were compared. In the rapid pulse‐chase experiment the specific activity of the1 terminal fructosyl moiety was consistently less than that of the sucrosyl moiety. During the chase period, the specific activity of the terminal and internal fructose moieties became similar. These results indicate that in addition to trisaccharide formed by transfer of fructosyl units from sucrose, substantial amounts of both neokestose and 1‐kestose are made by transfer of fructosyl units from higher oligomers onto sucrose in reactions probably localized in the vacuole.
Fructan metabolism in leaves of Loliwn rigidum Gaudin
Authors: SMOUTER HENK , SIMPSON RICHARD J. 
Published: April 2006

summaryThis paper reports the conditions for the assay of sucrose–sucrose fructosyltransferase (SST); fructan–fructan fructosyltransferase (FFT), invertase and Fructan hydrolase (FH) in extracts of leaves of Loliutn rigidum Gaudin. Invertase had a temperature optimum between 30 and 35 °C and a pH optimum between 4.5 and 5.0 whereas the enzymes of fructan metabolism had temperature optima at 25 °C and pH optima at about 5.5. Analysis of the products of enzyme assays showed that crude SST activity produced mainly 1‐kestose from 100 mM sucrose and when incubated with 500 mvt sucrose, neokestose and possibly 6‐kestose were also formed in low concentrations. FFT produced two tetrasaccharides and neokestose after incubation with 100 mM 1‐kestose and FH produced fructose exclusively after incubation with high‐molecular‐weight fructan extracted from Loliutn rigidum and Jlclianthus tuberosus L. and with a commercial preparation of bacterial levan. Enzyme activities were also measured during a phase of fructan accumulation. FH activity declined by 50%, but SST and FFT activities increased about 2.5‐fold during this period. The data supported the proposed synthetic pathway of fructan accumulation from sucrose via 1 ‐kestose into high‐molecular‐weight fructan and indicated that fructan synthesis may occur at low substrate concentrations. Extracts from leaves which had not accumulated fructans contained measurable activities of SST and FFT.
Ammonium assimilation by spruce—Hebeloma sp. ectomycorrhizas
Authors: CHALOT M. , STEWART G. R. , BRUN A. , MARTIN F. , BOTTON B. 
Published: April 2006

summaryIn order to investigate the relative contribution of glutamine synthetase and NADP‐glutamate dehydrogenase to the assimilation of ammonium (NH4+) by spruce ectomycorrhizas, changes in free amino acid content and kinetics of 15N incorporation into free amino acids were measured together with the effect of specific enzyme inhibitors. Exposure of detached ectomycorrhizas to (15NH4) 2SO4 showed that the greatest flow of 15N enters into the amido group of glutamine. Label was also detected in glutamic acid, alanine and γ‐aminobutyric acid. Large amounts of alanine and glutamate accumulated in response to the addition of methionine sulfoximine (MSX) together with a decrease in 15N incorporation into both amido‐ and ammo‐nitrogen of glutamine. These results are consistent with a major role of glutamate dehydrogenase and glutamine synthetase in nitrogen assimilation in the symbiosis and do not suggest any significant role for glutamate synthase in the synthesis of glutamate. A large accumulation of unlabelled asparagine in response to MSX and albizziine inhibition suggests the occurrence of an unlabelled NH4+ pool in the host plant. The transfer of nitrogen compounds between the fungal cells and the host tissues is discussed.
Comparative water uptake by roots of different ages in seedlings of loblolly pine (Pinus taeda L.)
Authors: MACFALL J. S. , JOHNSON G. A. , KRAMER P. J. 
Published: April 2006

summaryMagnetic resonance (MR) imaging was used to study water absorption from fine, moist sand by the taproot, first‐order lateral roots, and tine roots of 9‐month‐old loblolly pine seedlings. Magnetic resonance imaging provides the opportunity for repeated non‐destructive measurements of water uptake by roots growing in a solid medium such as sand. Root systems of container‐grown seedlings were pruned to a taproot, one or two first‐order laterals and attached fine roots, and were planted in small containers. Reference tubes filled with a mixture of CuSO4/D2O were placed in each container in the field of view. Roots of individual seedlings were repeatedly imaged at approximately 3 h intervals. Water uptake by individual roots was measured and uptake was calculated based on biomass, root length, and surface area. Based on weight and surface area, but not on root length, fine roots were more efficient than the lateral or taproots in water uptake.Measurement of water content in MR images of wet sand was confirmed by the imaging of Sand phantoms. These phantoms were tubes filled with fine sand at varied water contents (5–25%). Additional tubes of CuSO4 with D2O were also imaged. A linear relationship between signal intensity of moist sand (normalized against the CuSO4/D2O) and water conteni was demonstrated (R2= 0.97). Fitting the normalized signal intensity of the sand to the calculated linear regression allowed calculation of the water content of the sand.
Aspects of the genetic and botanical status of Neotropical Azolla species
Authors: ZIMMERMAN WILLIAM J. , WATANABE IWAO , VENTURA TERESITA , PAYAWAL PACIFICO , LUMPKIN THOMAS A. 
Published: April 2006

summaryVariation among neotropical and other species of the aquatic fern Azolla Lam, was examined using molecular and physiological parameters. The three neotropical species of Section Azolla, A. caroliniana Willd., A. mexicana Presl, and A. microphylla Kaulf., were very similar in their DNA fingerprints from hybridizations to heterologous and random homologous gene probes. These Azolla were also not separable by their symptomatic responses to phosphorus deficiency, although subgroups were observed that correlated to the +/− responses of cyanobionts to the monoclonal antibody McAb‐C16. The strong affinity among these taxa was also demonstrated in breeding trials between A. mexicana‐caroliniana and A. microphylla which yielded the first fertile Azolla hybrids, unlike previous Section Azolla crosses between A. filiculoides and A. mexicana or A. microphylla. Cumulative evidence indicates a need to reclassify Azolla of the New World.
Studies on the anhydrous fixation of dry seeds of lettuce (Lactuca saliva L.)
Authors: SMITH M. T. 
Published: April 2006

summaryA number of fixation techniques were used on cubes of dry cotyledonary tissue of lettuce seed to develop a satisfactory technique for the anhydrous fixation of dry seed material for electron microscopy. Fixation with formaldehyde or acrolein vapours in combination with Spurr's resin embedding produced satisfactory sections, while protocols involving the use of osmium tetroxide vapours resulted in brittle specimens that were difficult to section. The use of glycerol as a vehicle for anhydrous aldehyde fixation, followed by subsequent aqueous processing, introduced artifacts in membrane infrastructure. When model phospholipid systems, known to exist in the hexagonal phase, were prepared for electron microscopy and compared with anhydrously fixed cotyledonary tissue, the results suggested that dry seed membranes exist in a lamellar phase. It is proposed that leakage from imbibing seeds may be the result of physical/molecular changes in the membranes rather than of a phase change from the hexagonal to the lamellar state.
Response of old‐growth montane Picea abies (L.) Karst. forest to climatic variability in northern Sweden
Authors: HOFGAARD ANNIKA , KULLMAN LEIF , ALEXANDERSSON HANS 
Published: April 2006

summaryRepeat photography and tree ring analyses were used to investigate structural change, 1938–88, of an old growth and high elevation Picea abies (L.) Karst. forest in northern Sweden. The forest, initially moribund, senescent and top‐broken, regenerated broken tops and apparently gained in vigour. Up to the 1930s this progressive change was pre‐dated by an increase of annual increment growth, which subsequently declined until the 1980s, The tree‐ring response concurs with the general course of summer temperature while canopy processes appear to lag behind. The study stresses the importance of phenotypic plasticity for Long‐term behavior of marginal J spruce forest. It is also evident that canopy development is not a fully predictable ageing process, but to some extent dependent on climatic variability.
Which stage of nodule initiation in Lupinus angustifolius L. is sensitive to iron deficiency?
Authors: TANG CAIXIAN , ROBSON ALAN D. , DILWORTH MICHAEL J. 
Published: April 2006

summaryTransfer experiments in solution culture were conducted to establish the stage of nodulation in lupins (Lupinus angustifolius L. cv. Yandee) most sensitive to iron deficiency. In all experiments, iron deficiency had a much greater effect on nodule number than on host plant growth.Irrespective of the iron treatment of either the Bradyrhizobium or the lupin plant prior to inoculation, plants receiving 2.5 μM iron after inoculation successfully formed nodule initials and nodules while those receiving 0.05 μM iron almost completely failed to initiate nodules. Thus, the prevention of nodulation by iron deficiency is not a consequence of either an inadequate number of infective bradyrhizobia surviving in the solution or an alteration in the iron status of the host root.Supply of 2.5 μM iron for 4 d or more after inoculation produced a similar number of nodule initials and nodules as did continuous supply of 2.5 μMiron. Delaying supply of 2.5 μM iron for 3 d or less after inoculation did not delay or prevent nodule initiation and formation. One‐day exposure of plants to 2.5μM iron on day 4 after inoculation induced the highest number of nodules of any 1 d treatment although this short exposure was not enough to allow the full complement of nodules to form. Hence, the impairment of the nodulation process by iron deficiency can be attributed to the prevention of a step at day 4, the stage just before nodule initials are formed.A further study was conducted to examine the effect of iron on nodule formation by using a vertical split‐root technique in which Bradyrhizobium sp. (Lupinus) was added to the upper compartment. Compared to plants receiving 0.05 μM iron in both compartments, plants receiving 0.05 μM in the upper and 5 5 μM iron in the lower compartments had only a slightly higher concentration of iron in the cortex of the upper part of the root. Furthermore, supplying 5 μM iron to the lower part of a root did not permit nodulation on the upper part of the root receiving 0.05 μMiron. Low concentration of iron in the cortex of roots may limit nodule formation.
Fungal decomposition of attached angiosperm twigs
Authors: GRIFFITH G. S. , BODDY LYNNE 
Published: April 2006

summaryMany fungi commonly isolated (>5% isolation frequency) from dead attached ash (Fraxinus excelsior L.), beech (Fagus sylvatica L.) and oak (Quercus robur L.) twigs were capable of growth at water potentials below – 6 MPa, including Phomopsis spp., Cryptosporiopsis spp., Libertella fraxinea Oganova, Fusarium lateritium Nees. and Aureobasidium pullulans (De Bary) Arnaud. Several of these underwent morphological switches at low water potentials. Growth of almost all basidiomycetes common in dead twigs, including Peniophora spp. and Vuilleminia comedens (Nees.: Fr.) Maire, was inhibited at water potentials below –4 MPa.The ecology of fungi commonly isolated from dead ash twigs was studied in greater detail. All except Peniophora lycii (Pers.) V. Hohn & Litch and L. fraxinea, survived in wood for 1 yr at extremely low water potentials (below − 200 MPa). P. lycii was the only species that grew at low temperatures (<5 °C). Water potential was a major determinant of decay rate. Generally, even at high water potentials, decay by individual fungi over a 1 yr period was limited to 20–30 % dry weight losses. However, at −0.05 and −0.8 MPa P. lycii caused 70 % weight loss, and L. fraxinea caused 50% weight loss at −4.1 MPa (its optimal water potential for decay). At water potentials between −4 and −9 MPa L. fraxinea, Phomopsis platanoidis Died, and unidentified sp. 12 were capable of producing significant lignocellulose decay.
Ultrastructure of the Gliocladium‐like endophyte of perennial ryegrass (Lolium perenne L.)
Authors: PHILIPSON MELVA N. 
Published: April 2006

summaryVegetative hyphae of the Gliocladium‐like endophyte of Lolium perenne L. were characterized by apparently unstructured walls and high lipid content. Hyphae were intercellular during their active phase from late summer to winter, at which point they reached their highest density and became also intracellular in the tissues of the senescent outermost leaf. When numbers of hyphae in host tissue were greatest, a marked cytoplasmic change was noted in the endophyte present in blades of the outermost leaves of tillers. This involved depletion of lipid and deposition of electron‐opaque material within vacuoles. These modifications occurred shortly before the formation of reproductive structures and defined a pre‐sporulation phase. Aggregates of hyphae near the epidermis in senescent outer sheaths resembled sclerotia, but lacked indurated rinds. Concentric bodies were observed in pre‐sporulation hyphae. Conidiomata formed in the senescent outermost leaf blade and on its surface during winter. Conidiophores developed from pre‐sporulation hyphae and produced mucilage‐secreting, penicillate conidiomata bearing cylindrical phialides with enteroblastic conidia at their apices. Phialide cytoplasm contained many ribosomes, small vacuoles and enlarged vesicles. The envelope of the prominent nucleus showed connections with an extensive and variable system of dilated rough endoplasmic reticulum stacks close to the nucleus and, further removed, areas of smooth fenestrated cisternae. With formation of the first conidium, the outer mucilaginous wall of the phialide ruptured to form a recurved collarette. Conidia continued maturation after schizolytic secession, with enlargement, disappearance of reserve materials, and elongation and contortion of the nucleus. A layer of parallel‐lying short lengths of peg‐ or rod‐like structures lay within the inner membrane of the envelope and heterochromatin was excluded from this zone.
Ultrastructure of the Gliocladium‐like endophyte of perennial ryegrass (Lolium perenne L.)
Authors: PHILIPSON MELVA N. 
Published: April 2006

summaryConidiomata of the Gliocladium‐like endophyte of ryegrass (Lolium perenne L.) formed in air lacunae of senescent outermost leaf sheaths during winter. Each conidioma originated on a vegetative hypha as a swelling which enlarged to form a conidiophore that maintained connection with the parent hypha by a septal pore. The swelling was enclosed within the mucilaginous coating of the parent hypha and was also covered by a fibrillar cap which ruptured as the conidiophore elongated. Each conidiophore bore one or more conidiogenous cells (phialides) either laterally or subterminally and, in addition, bore a terminal or lateral conidium. The conidiogenous cells continued to produce conidia and further conidiogenous cells sympodially. A marked difference in ultrastructure and lipid content of the endophyte was evident between the vegetative hyphae and the cells of the conidioma. The site of initiation of the enteroblastic conidium was indicated by a fibrillar cap, which ruptured to form an upstanding collarette around the base of the conidium. A succession of conidia produced a thickening in the neck region at the apex of the conidiogenous cell. The principal features distinguishing these sheath conidiomata from those occurring in the leaf blade (Philipson, 1989) include conidiomata initiation, form of branching and shape of cells, the presence or absence of a fibrillar cap over the conidial locus, and, possibly, the mode of conidial secession.
Behaviour of zoospores and zoospore cysts in relation to root infection byPythium aphanidermatum
Authors: Jones S. W. , Donaldson S. P. , Deacon J. W. 
Published: April 2006

summaryThe Pre‐Penetration Sequence Involving Zoospore Taxis, encystment, Cyst Germination And Germ‐Tube Orientation Was Studied By Video Microscopy When Roots Of Wheat, Cress or Tomato Were Placed In Suspensions of Zoospores ofPythium aphanidermatum(Edson) Fitzp. The Sequence Was Also StudiedIn Vitro, to identify the responsible Factors.Several amino acids, sugars or volatile compounds elicited one of more stages of the sequence, but only glutamic acid and aspartic acid elicited all stages and thus could account for the observed behaviour on roots. Polyuronates of root surface slime also may be needed for encystment and orientation of Spores, because germ‐tubes emerged towards roots from a fixed point near the former position of the water‐expulsion vacuole. However, identical patterns of zoospore accumulation and encystment on untreated roots and roots encased in alginate gel indicated that neither polyuronates nor Specific sugar residues of root slime caused localized encystment on roots.Based on these results, a ‘simplest case’ model of the pre‐penetration sequence on roots is proposed.
Proteinase activity in mycorrhizal fungi III.
Authors: LEAKE J. R. , READ D. J. 
Published: April 2006

summaryA study was made of the potential of low molecular weight sources of nitrogen (N) and carbon (C), of the kind that can occur in the rhizosphere of ericoid roots, to influence the production of extracellular acid proteinase by Hymenoscyphus ericae (Read) Korf & Kernan. The fungus was grown in liquid culture with either pure protein or with protein hydrolysate as sole source of N and C and the effect of supplementation with ammonium and glucose was investigated.Proteinase production was induced as effectively by protein hydrolysate as by pure protein but in each case was enhanced in the presence of a low concentration (10 μg ml−1) of ammonium. Maximum enzyme production was found in those cultures that were supplied with protein or hydrolysate as sole sources of carbon, a feature which was associated with release of additional ammonium. This ammonification coincided with an increase of pH to a final value of 645, at which point the enzyme appeared to be inactivated.Glucose strongly repressed proteinase production when the endophyte was grown with protein, but not when grown with hydrolysate. These contrasting responses suggest that conditions leading to induction exert a stronger influence over enzyme production than do conditions leading to repression. In addition, hydrolysis products of protein must be present before full enzyme production is induced.The interacting effects of C and organic or inorganic N on proteinase production by the mycorrhizal fungus are discussed in relation to conditions prevailing in heathland soil.
Effects of phosphorus fertilization and mycorrhizal development on phosphorus nutrition and carbon balance of loblolly pine
Authors: ROUSSEAU J. V. D. , REID C. P. P. 
Published: April 2006

summaryThe influence of ectomycorrhizal (ECM) development on the physiology of loblolly pine (Pinus taeda L.) seedlings was examined during seedling recovery from phosphorus (P) deficiency and for several weeks after seedlings had become P‐sufficient. Seedlings inoculated with Pisolithus tinctorius (Pers.) Coker and Couch and non‐inoculated seedlings responded similarly to an increase in P fertilization, except that nearly twice as much of the absorbed P in ECM seedlings remained in the fine‐root system compared to the non‐inoculated seedlings. Presumably, most of this P was associated with the ECM fungal hyphae. The presence of mycorrhizas initially caused a 1‐ to 2‐wk delay in the growth response of seedlings to P fertilization, possibly due to a restrictively slow rate of P transfer from the ECM fungus to the root. However, once seedlings had sufficient P for maximum growth, even high levels of mycorrhizal development (greater than 85%) did not reduce the growth rate of ECM seedlings compared to non‐mycorrhizal seedlings grown under the same high‐nutrient conditions. Possible explanations are discussed as to why a growth reduction due to ECM development is found in some studies but not in others.
Role for the photosynthate demand of ectomycorrhizas in the response of Douglas fir seedlings to drying soil
Authors: DOSSKEY M. G. , BOERSMA L. , LINDERMAN R. G. 
Published: April 2006

summaryDouglas fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings were inoculated with different species of ectomycorrhizal fungi, Rhizopogon vinicolor FSL788‐5, Laccaria laccata S238‐A, or Hebeloma crustuliniforme HeCr2, to determine how different fungi affect the response of photosynthesis and water relations of seedlings to drying soil. Potted seedlings were grown in a greenhouse for 6 months under well‐watered conditions, then transferred to a growth chamber where measurements were made as the soil dried. Rhizopogon enhanced both net photosynthesis rate and stomatal conductance compared to non‐mycorrhizal controls (P < 0.01) over the soil water potential range of −0.05 to −0.50 MPa, despite 0.2 to 0.3 MPa lower leaf water potential. Hebeloma tended to enhance, while Laccaria decreased net photosynthesis rate and stomatal conductance of host seedlings over this range of soil water potential, but neither fungus affected leaf potential. Our observations for Rhizopogon and Laccaria could not be explained by existing hypotheses based on mycorrhizal effects on plant size, nutrition, osmotic adjustment, or water uptake characteristics. Nutrition may have been a factor for Hebeloma.We propose that in the absence of nutritional and water uptake effects, net photosynthesis rate and stomatal conductance are correlated with rate of export of photosynthate to the mycorrhizal fungus. Strong mycorrhizal demand for photosynthate stimulates photosynthesis, to which stomata respond by opening, notwithstanding water stress. Our results for Rhizopogon are consistent with this hypothesis.