bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of phosphorus nutrition on morphological characteristics of vesicular‐arbuscular mycorrhizal colonization of maize
Authors: BRAUNBERGER P. G. , Miller M. H. , PETERSON R. L.
Published: April 2006

summary

The morphology of the colonization of maize (Zea mays L.) by the vesicular arbuscular mycorrhizal fungus Glomus versiforme (Daniels and Trappe) Berch was determined quantitatively to establish the stage at which colonization was limited in response to increased P nutrition. Harvests were taken 14, 19, 24 and 29 d after planting maize in a calcined clay medium to which nutrient solution containing 0.16, 0.8 or 2.4 mM P was added daily. The fraction of the root length containing arbuscules (FAC) 19 d after planting was 0.4 with 0.16 mM P, 0.3, with 0.8 mM P and 0.17 with 2.4 mM P. Corresponding shoot P concentrations were 1.5, 2.0 and 3.2 mg g−l. Increased shoot P concentration reduced the number of appressoria per unit root length, but this accounted for only a part of the reduction in FAC. Increased root length did not account for the effect of shoot P concentration on FAC. The length of arbuscular colonized root length (total root length × FAC) per appressorium was strongly reduced in response to increased shoot P concentration. It was concluded that the reduction in FAC was mediated primarily through an inhibition of intra‐radical development.
Interactions between three alfalfa nodulation genotypes and two Glomus species
Authors: BRADBURY S. M. , PETERSON R. L. , BOWLEY S. R.
Published: April 2006

summary

Seedlings of a non‐nodulating alfalfa (Medicago sativa L.) genotype (nod−fix−) and an ineffectively nodulating alfalfa genotype (nod+fix−) exhibited resistance to vesiscular‐arbuscular mycorrhizal (VA mycorrhizal) colonization, when grown in pot cultures inoculated with either Glomus versiforme (Daniels and Trappe) Berth or Glomus intraradices Schenck and Smith. Appressoria, showing considerable variation in size and shape, developed on the root surface, but failed to form any internal structures such as arbuscules and vesicies. Wild‐type (nod+fix−) alfalfa seedlings developed normal colonization. This phenomenon will be extremely useful in studying the processes of recognition and compatibility between plant species and VA mycorrhizal fungal species.
The role of ascorbate in drought‐treated Cochlearia atlantica Pobed. and Armeria maritima (Mill.) Willd.
Authors: BUCKLAND SARAH M. , PRICE ADAM H. , HENDRY GEORGE A. F.
Published: April 2006

summary

Cochlearia atlantica is a species rich in ascorbic acid. After 4 days of intermittent drought treatment, there was a large decrease in the concentration of ascorbate and glutathione, functioning probably as radical scavengers (anti‐oxidants). Although there was no increase in lipid peroxidation (a marker of oxygen radical damage), drought treatment did result in the destruction of chlorophyll and a decrease in protein. This species showed little or no change in the activities of five enzymes usually associated with the processing of, and protection from, activated forms of oxygen. Armeria maritima showed similar decreases in relative water content and dry weight after droughting, but a quantitatively smaller decrease in ascorbate with no loss of glutathione. Instead a major response to drought, in this species, was the marked increases in the activities of superoxide dismutasc and peroxidase. Despite these increases in enzymic defences against oxygen radicals, drought treatment resulted in increased lipid peroxidation. in A. maritima. It is concluded that ascorbic acid and glutathione may play a significant role in the response to drought in C. atlantica but protection in A. maritima is largely through enzymic processing of activated farms of oxygen.
Variation in salinity tolerance and ion uptake in accessions of brown beetle grass [Diplachne fusca(L.) Beauv.]
Authors: WARWICK N. W. M. , HALLORAN G. M.
Published: April 2006

summary

Significant variation in tolerance was found in natural populations ofDiplachne fusca(L.) Beauv, grown under a range of NaCl concentrations, with greatest variation in accessions from different sites and a narrower range of tolerance from those within sites. Significant differences were found between accessions for Na, Cl and K uptake. Ma and Cl concentrations were found to be higher in sheaths than in leaf blades, indicating thatD. fuscahas the capacity to sequester high levels of Na and Cl in the sheath away from the leaf blade as well as maintaining a high selectivity for K. over Na. The salinity level of the site from which an accession was collected did not show any correlation with the salt‐tolerance of that accession. WhileD. fuscawas found generally to be highly tolerant of NaCl (with plants surviving at 400 mol m−3NaCl) there was variation in tolerance in its natural populations, indicating the potential for selecting to increase tolerance further.
Soil salinity modifies SO2 sensitivity in soybean
Authors: QIFU MA , MURRAY FRANK
Published: April 2006

summary

Soybean (Glycine max L. cv. Buchanan) growing in top‐covered chambers was exposed to a factorial combination of three concentrations of SO2, (2, 99 and 189 nl1−1) and three concentrations of soil salinity with electrical conductivities of 0.7, 4.9 and 7.0 dS m−1. Each combination was tested in duplicate chambers. SO2 exposure was for 4 h d−1 for 106 d from planting to final harvest.

SO2, increased leaf sulphur concentrations, while high salinity had the opposite effect. Stress interactions were observed late in the season, with leaf sulphur concentrations significantly decreased by simultaneous SO2, and salinity stress when compared with exposure to SO2, alone, SO2 or salinity stress both reduced leaf chlorophyll concentration, leaf area, plant dry weight and seed yields. Although SO2‐salinity interactions on the growth variables were not statistically significant, there were stress interactions on seed yield by affecting the number of pods produced. As SO2‐induced leaf injury developed is became more severe in the nonsaline plants than in the saline plants, indicating a protective function for salinity against SO2 injury. However, salinity‐induced leaf injury occurred earlier and was more severe in the high SO2 and saline‐treated plants than in the low SO2 and non‐fumigated saline‐treated plants.
The mechanisms of arsenate tolerance in Deschampsia cespitosa (L.) Beauv. and Agrostis capillaris L.
Authors: MEHARG ANDREW A. , MACNAIR MARK R.
Published: April 2006

summary

Arsenate influx isotherms in Deschampsia cespitosa (L.) Beauv. and Agrostis capillaris L. showed that tolerance to arsenate in these grasses is achieved at least in part by adaptation of the arsenate uptake system, which leads to reduced influx of arsenate in arsenate‐tolerant plants. In D. cespitosa, this reduction in arsenate ioflux was by suppression of the Vmax of the high‐affinity uptake system and by an increase in the Km of the low‐affinity uptake system. In A. capillaris the reduction in arsenate uptake in arsenate‐tolerant plants was by a decrease in the Vmax of both uptake systems and by an increase in the Km of the high‐affinity uptake system. The differences in the rates of arsenate influx between tolerant and non‐tolerant plants was much greater for D. cespitosa than for A. capillaris. The mechanism of arsenate tolerance in D. cespitosa and A. capillaris was the same mechanism of tolerance that had been demonstrated in arsenate‐tolerant Holcus lanatus L. Reduced arsenate influx by adaptation of the arsenate uptake mechanism is a mechanism of tolerance that has evolved in three separate species.
Are seedlings from small seeds always inferior to seedlings from large seeds? Effects of seed biomass on seedling growth in Pastinaca sativa L.
Authors: HENDRIX STEPHEN D. , NIELSEN ERIC , NIELSEN TODD , SCHUTT MARK
Published: April 2006

summary

Previous field studies of recruitment in Pastinaca sativa L. indicate that more seedlings from small seeds than from large seeds survive short‐term droughts. To explore this phenomenon, the effects of variation in seed biomass in Pastinaca sativa on embryo size and seedling characteristics 10, 20, 30 and 40 days after emergence were investigated. On the basis of most characteristics, seedlings from large seeds should be superior to seedlings from small seeds. Embryo length and cotyledon area were positively related to seed biomass, as were above ground biomass, total leaf area, and root biomass in all harvests. Total seedling biomass was positively related to seed biomass in the 10, 20, and 30 day harvests, but not the 40 day harvest. However, the ratio of maximum root length/total leaf area was negatively related to seed biomass in the 10 and 20 day harvests, suggesting that, under drought conditions, seedlings from small seeds may transpire less water than those from large seeds relative to their ability to reach water supplies. Although seedlings from larger seeds had greater root biomass, this may be of little advantage under drought conditions since approximately 90% of the root biomass is in the upper 10 cm of soil which dries out quickly. The advantage that seedlings from small seeds have under drought conditions is short‐lived, lasting about 20 days in the glasshouse and an estimated 60–90 days in the field. This advantage is short‐term because the relationship between seed biomass and resource allocation patterns changes during early seedling development.
Population structure and mating system in Marasmius androsaceus Fr.
Authors: HOLMER LILLIAN , STENLID JAN
Published: April 2006

summary

Isolates of the rhizomorph‐forming fungus Marasmius androsaceus were obtained from four different sites in stands of either Norway spruce or Scots pine of different age. The mating system and the mycelial interactions within each site were studied. The fungus had a bifactorial mating system and genetically different dikaryons were strongly mutually antagonistic in culture. On the basis of such antagonism, up to 18 different individual genets could be found within an area of 2.8 m2. No differences between the four sites could be detected with respect to the size of the genets. Isolates belonging to the same genet were frequently found in close proximity in areas from which other types were excluded. However, the older plots contained genets with a discontinuous distribution in the plots. The likely origin of this distribution is discussed in relation to the pattern of dispersal, establishment and spread of this saprophytic fungus in different woodland habitats.
Experimental studies of lobe growth in the lichen Parmelia conspersa (Ehrh. ex Ach.) Ach.
Authors: ARMSTRONG R. A.
Published: April 2006

summary

The radial growth of individual lobes of the foliose lichen, Parmelia conspersa (Ehrh. ex Ach.) Ach., was studied to determine whether (1) adjacent lobes exchange carbohydrate and (2) marginal competition between lobes influences radial growth. In a survey of thalli of different size, the number of marginal lobes was linearly related to thallus circumference. However, the relationship between mean lobe width and thallus circumference was fitted by a second order polynomial. Hence, mean lobe width may reach a maximum in thalli approx. 3 cm in diameter. The interactions between marginal lobes were studied by either painting single lobes with acrylic paint or by removing lobes from the thallus. Painting the whole of a lobe virtually stopped its radial growth while partially painted lobes grew less than control lobes. The radial growth of a lobe was unaffected by either completely painting or removing its neighbour. Removal of both neighbouring lobes did not influence the radial growth of a lobe but severing the lobe from the thallus reduced its radial growth. In addition, lobe width increased significantly when both neighbouring lobes were removed. These results suggest that adjacent lobes have a considerable degree of independence and that there is little exchange of carbohydrate between them. In addition, marginal competition between adjacent lobes may restrict the lateral extension of a lobe and this may maintain a more constant mean lobe width in larger thalli. It is possible that the intensity of marginal competition between adjacent lobes may vary with thallus size and this could be a factor determining the growth curve of a foliose lichen throughout its life.
The control of sucrose synthesis in leaves of Lolium temulentum L., a fructan‐accumulating grass
Authors: COLLIS B. E. , POLLOCK C. J.
Published: April 2006

summary

The control of sucrose synthesis was studied in leaves of the fructan‐accumulating species Lolium temulentum L. The cytoplasm it fructose‐1,6‐bisphosphatase (Cyt'F‐1,6‐BPase) was partially purified and its kinetic properties compared with the reported values for the enzyme from spinach leaves. The enzymes from the two species were similar, particularly in their inhibition by fructose‐2,6‐bisphosphate (F‐2,6BP). Leaves were excised and illuminated or whole plants were chilled and illuminated in order to increase the accumulation of sucrose and low‐molecular‐weight fructan, Leaf glucose‐6‐phosphate (G‐6‐P) and fructose‐6‐phosphate (F‐6‐P) contents were estimated. The G‐6‐P/F‐6‐P ratio showed that most of the hexose phosphates were present in the cytoplasm. In excised leaves G‐6‐P concentrations were higher than controls after 4 h of illumination, probably reflecting the release of glucose by fructan synthesis. This extra source of substrate supply may disrupt the coordinated control of sucrose phosphate synthase (SPS) and Cyt'F‐1,6‐BPase. The calculated activity of Cyt'F‐1,6‐BPase in vivo is insufficient to catalyse the observed flux of photo assimilates to sucrose and fructan. The maximum catalytic activity of phosphofructophosphotransferase (PFP) was determined, and was found to be 12–14Ümol hexose g1 f. wt h1 in control leaves. It is proposed that, given suitable metabolite concentrations, PFP could supplement the inhibited Cyt'F‐1,6‐BPase activity and contribute to the flux of photo assimilates to sucrose and fructan.
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

summary

Fructan 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

summary

This 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

summary

In 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

summary

Magnetic 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

summary

Variation 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

summary

A 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

summary

Repeat 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

summary

Transfer 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

summary

Many 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

summary

Vegetative 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

summary

Conidiomata 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

summary

The 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

summary

A 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

summary

The 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

summary

Douglas 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.
Cataclysmic response to recent cooling of a natural boreal pine (Pinus sylvestris L.) forest in northern Sweden
Authors: KULLMAN LEIF
Published: April 2006

summary

Instant stand‐level dieback occurred in boreal coniferous forests of northern Sweden in 1987. A population of pine (Pinus sylvestris L.) and subdominant spruce (Picea abies (L.) Karst.) was analysed with respect to defoliation, age structure, radial increment and soil conditions. Defoliation and mortality were due to frost and drought in response to an early winter with abnormal cold and a thin snow cover. A thick mor humus layer preconditioned ground frost preservation. Annual radial increment had declined steadily over c. 40 years, in variance with climatic cooling and local exposure. Possibly, the growth decline depleted energy reserves and lowered the tolerance to climatic stress during extreme conditions. It is obvious that the structure of northern boreal forests responds perceivably to short‐term thermal decline. The outlined mechanism of dieback may prevent the evolution of climax in the absence of other exogenous disturbances. The present event may be a small‐scale analogue of forest responses to rapid cooling during, for example, the Younger Dryas period and the Little Ice Age.
Localization of sucrose synthase in soybean root nodules
Authors: GORDON A. J. , THOMAS B. J. , REYNOLDS P. H. S.
Published: April 2006

summary

Immunogold labelling studies using polyclonal antibodies to sucrose synthase suggest that this enzyme is exclusively located in the cytoplasm of soybean nodule cells. A significantly greater intensity of labelling was found in the cytosol of uninfected interstitial cells of the central nodule region compared with the cytosol of the infected cells. Labelling was low in the bulk of the cortical cells but was found to be high in the vascular endodermis and in the cortical cells between the bundle and the infected region. The results are discussed in relation to carbohydrate supply and metabolism and in the context of nodule structure.
The physiological role of old stolon material in white clover (Trifolium repens L.)
Authors: CHAPMAN D. F. , ROBSON M. J.
Published: April 2006

summary

Clonal plants of white clover (Trifolium repens L.), consisting of a single stolon plus roots and either three fully unfolded leaves or one fully unfolded leaf at the stolon apex, were grown in a controlled environment and sampled three times (after 7, 49 and 85 d growth) to examine the effects of increasing respiratory demand imposed by an increasing mass of old stolon material upon carbon allocation patterns and plant morphology.

Where the total pool of available carbohydrate remained more‐or‐less constant over time, greater C allocation to stolon tissue was associated with reduced allocation to new leaf growth between d 7 and d 49. Rapid death of old stolon material began about d 70, perhaps as the result of withdrawal of C previously supplied to stolon tissue by leaves at the apex. Current assimilate no longer needed to maintain this old stolon material was, in part, reallocated to the apex region.

Stolon death was greater when stolons were covered rather than fully illuminated, reflecting the elimination of direct CO2 assimilation by stolon tissue (estimated to be 12–22% as efficient as leaves in assimilating CO2, on a surface area basis) and accentuation of the carbohydrate deficit. Respiration accounted for an estimated 32% of C fixed by leaves on d 85 when stolons were covered, compared to 25 % when stolons were fully illuminated. The relevance of these results to the seasonal changes in plant morphology in pastures, and the effects of stolon burial, are discussed.
Effects of dry‐deposited sulphur dioxide on fungal decomposition of angiosperm tree leaf litter II. Chemical content of leaf litters
Authors: NEWSHAM K. K. , INESON P. , BODDY LYNNE , FRANKLAND JULIET C.
Published: April 2006

summary

Ash (Fraxinus excelsior L.), birch (Betula spp.), hazel (Corylus avellana L.), sessile oak [Quercus petraea (Mattuschka) Liebl.] and sycamore (Acer pseudoplatanus L.) leaf litters from a non‐polluted and a heavily sulphur dioxide (SO2)‐polluted woodland were fumigated with environmentally‐realistic concentrations (0.010–0.030 μl l−1) of SO2 for 16–68 wk in an open‐air field‐fumigation experiment. Fumigation markedly increased sulphate and protons in leachates from the litters and decreased calcium and magnesium contents of the leaves. However, there were few differences in the responses between leaf litters from the two woodlands. This was attributed to rapid sulphate wash‐out from the litters from the heavily polluted woodland, so that the litters from the two sites quickly reached the same sulphate status.
A study of ageing of spruce [Picea sitchensis (Bong.) Carr.] ectomycorrhizas. I. Morphological and cellular changes in mycorrhizas formed by Tylospora fibrillosa (Burt.) Donk and Paxillus involutus (Batsch. ex Fr.) Fr.
Authors: DOWNES G. M. , ALEXANDER I. J. , CAIRNEY J. W. G.
Published: April 2006

summary

An age sequence of mycorrhizas formed by Paxillus involutus (Batsch. ex Fr.) Fr. and Tylospora fibrillosa (Burt.) Donk was sampled from 6–9‐month‐old seedlings of Picea sitchensis (Bong.) Carr. grown on peat in root observation chambers. Information about the ageing process was obtained from co‐ordinated studies of mycorrhizal morphology, anatomy, ultrastructure and cell vitality (indicated by FDA‐staining).

Newly produced mycorrhizas were pale and turgid over most of their length with obvious extramatrical mycelium. Most mycorrhizas over 50 d old had a light turgid apical portion and a darkened wrinkled proximal portion: extramatrical mycelium was less obvious. Many remained in this state until the sampling stopped at day 142, but some were completely darkened before day 50. The morphological appearance of a mycorrhiza was not a good indicator of its chronological age. Most mycorrhizas displayed periodic busts of growth which added portions of young turgid cortex to an ageing axis.

The percentage of cortical cells showing nuclei in 1 μm sections of the apical 1 mm declined from 40–50 % in mycorrhizas < 25 d old to 5–15 % in mycorrhizas 110–140 d old. Cortical cells became more vacuolate as they aged and the number of organelles appeared to decline. Senescence proceeded from the outer to the inner cortex and from proximal to distal regions. Degenerate cortical cells were present in the Hartig net zone of mycorrhizas over 25 days old. Cortical cell degeneration preceded, but was closely followed by, degeneration of adjacent Hartig net.

The FDA study supported the general pattern and timing of cell death interpreted from the morphological and ultrastructural study. Cortical/Hartig net fluorescence declined markedly in mycorrhizas over 70–85 d old. The stele was the last tissue in the mycorrhiza to degenerate.

It is suggested that a mycorrhiza ceases to function in nutrient and water uptake when no living cortical/Hartig net interface remains. In this study a few mycorrhizas became non‐functional by day 31. For most mycorrhizas the major decline in function took place after 85 days. This estimate is in broad agreement with the estimates of mycorrhizal life span obtained from biomass studies in the field.
A study of ageing of spruce [Picea sitchensis (Bong.) Carr.] ectomycorrhizas. II. Carbohydrate allocation in ageing Picea sitchensis/Tylospora fibrillosa (Burt.) Donk ectomycorrhizas
Authors: CAIRNEY J. W. G. , ALEXANDER I. J.
Published: April 2006

summary

Translocation of 14C‐labelled photosynthate was studied in seedlings of Picea sitchensis (Bong.) Carr. ectomycorrhizal with Tylospora fibrillosa (Burt.) Donk grown in Perspex observation chambers. Although translocation to young and older mycorrhizas was observed, accumulation of current 14C‐labelled photosynthate was reduced in older compared with young mycorrhizas in the same root system.

Non‐structural carbohydrate components of P. sitchensis/T. fibrillosa and undefined beech ectomycorrhizas collected from the field were quantified by gas‐liquid chromatography. Relative differences in accumulated carbohydrates were identified between P. sitchensis/T. fibrillosa and beech mycorrhizas. Levels of total soluble and insoluble carbohydrate were lower in older compared with young P. sitchensis/T. fibrillosa mycorrhizas. The soluble sugars arabitol, glucose and mannitol were detected in significantly lower quantities in older mycorrhizas whilst fructose and trehalose content was similar to that of young mycorrhizas. These results are discussed in relation to the physiology of the ageing mycorrhiza.
A study of ageing of spruce [Picea sitchensis (Bong.) Carr.] ectomycorrhizas. III. Phosphate absorption and transfer in ageing Picea sitchensis/Tylospora fibrillosa (Burt.) Donk ectomycorrhizas
Authors: CAIRNEY J. W. G. , ALEXANDER I. J.
Published: April 2006

summary

Phosphate absorption and transfer to the host was studied in seedlings of Picea sitchensis (Bong.) Carr. ectomycorrhizal with Tylospora fibrillosa (Burt.) Donk grown in Perspex root observation chambers. Phosphate absorption into excised mycorrhizas was reduced in older compared with young mycorrhizas, kinetic analysis indicating physiological differences in phosphate absorption between the two age classes over a range of external concentrations up to 1000μM.

Individual young mycorrhizas labelled directly with 32P transferred more 32P to the host than older mycorrhizas in the same intact root system. There was variation in the ratio (young:older) suggesting a progressive reduction in nutrient transfer to the host as the mycorrhiza ages. The results are discussed in relation to nutrient accumulation in the field.