bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of sodium chloride on growth and nitrogenase activity in seedlings of Myrica cerifera L.
Authors: SANDE EVE , YOUNG DONALD R.
Published: April 2006

summary

The actinorhizal shrub, Myrica cerifera L., is widespread in coastal areas where it may be exposed to variable saline conditions. In growth chamber studies, 5‐month‐old seedlings remained viable during exposure to 150 mM NaCl for 35 d, though concentrations above 50 mM significantly depressed plant and root nodule growth. Concentrations of NaCl above 50 mM also depressed stomatal conductance to water vapour diffusion and net photosynthetic rates. Relative to control plants, nitrogenase activity per g dry weight of nodules decreased for 21 d in plants subjected to a range of NaCl concentrations. By day 35. plants exposed to 25 and 50 mM NaCl had recovered some nitrogenase activity relative to the controls, whereas plants receiving 100 and 150 mM had not. At 35 d, plants treated with 150 mM NaCl had a rate of N2 fixation per g dry weight of nodule tissue 26% of that in control plants. However, no mortality had occurred, and full recovery followed the conclusion of the experiment. Thus, although periodic natural increases in salinity from sea spray or storm overwash may not lead to plant mortality, growth and N2 fixation will be significantly decreased in M. cerifera.
External hyphae of vesicular‐arbuscular mycorrhizal fungi associated with Trifolium subterraneum L.
Authors: JAKOBSEN I. , ABBOTT L. K. , ROBSON A. D.
Published: April 2006

summary

Variation among VA mycorrhizal fungi in their ability to enhance phosphorus uptake and plant growth could be due to differences in the length, distribution and phosphorus uptake of external hyphae. Trifolium subterraneum L. was grown in a sandy soil in association with the VA mycorrhizal fungi Acaulospora laevis Gerdemann & Trappe, Glomus sp., Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders or left uninoculated. When mycorrhizas had become well established, plants were transferred to a two‐compartment system, where root growth into a hyphal compartment was restricted by a fine nylon mesh. Spread of hyphae into the hyphal compartment was monitored by sequential sampling of soil cores at different distances from the root compartment. Plants were harvested at three times.

The spread of hyphae differed between fungi. The length density of hyphae of S. calospora declined approximately exponentially with increasing distance from the roots, whereas A. laevis maintained a plateau of constant hyphal density up to 7 and 11 cm from the roots after 28 and 47 d, respectively. Glomus sp. had an intermediate pattern of spread with a plateau closest to the roots followed by an exponential decline. The average rate of hyphal spread (mm d−1) was 3.1 for A. laevis but only 0.7–0.8 for Glomus sp. and S. calospora. In addition to its more extensive hyphal spread, A. laevis produced the largest increases in phosphorus uptake and plant growth. All mycorrhizal plants had a larger phosphorus inflow than the non‐mycorrhizal controls, but the phosphorus inflow per unit mycorrhizal root length was 25.3 times as high with A. laevis as with the two other fungi. These differences between the fungi became even more pronounced when the phosphorus inflow was expressed on the basis of hyphal length.

This work indicates that the efficiency of phosphorus uptake by a VA mycorrhizal fungus is strongly affected by its spatial distribution of hyphae in the soil, and possibly also by differences in capacity for uptake by unit length of hypha.
Antagonistic effects of simultaneous exposure to sulphur dioxide gas and vapour of the herbicide 2, 4‐D iso‐octyl on the carbon dioxide exchange of tomato and field bean plants
Authors: BREEZE VICTOR G. , FOWLER ALISON T.
Published: April 2006

summary

Tomato and field bean plants were exposed simultaneously to SO2 gas (in the range 0.07–0.57 μg 1−1) and to vapour of the herbicide [14C]2, 4‐D iso‐octyl (0.8–2.7 ng 1−1), for periods of 6–24 h in an air‐flow system at a water vapour pressure deficit of >2 kPa. Greater response was shown by the plants to 2, 4‐D vapour than to SO2. Herbicide vapour alone decreased CO2 exchange during the 3 d experimental period in both species, but the combination of herbicide plus SO2 had less effect. The response by tomato was both greater and more rapid than by field bean (which showed an initial stimulation of CO2 exchange due to 2, 4‐D), and the two species differed in the effect on transpiration. SO2 did not affect the uptake and distribution of herbicide within the plants. It appeared that 2, 4‐D iso‐octyl vapour and SO2 were antagonistic in effect on the CO2 exchange of the two species under the experimental conditions, and that in tomato this was largely due to changes in stomatal conductance.
Foliar uptake and release of inorganic nitrogen compounds in Pinus sylvestris L. and Picea abies (L.) Karst.
Authors: WILSON E.J.
Published: April 2006

summary

Foliar uptake and release of inorganic nitrogen compounds were studied by immersing current‐year shoots of Scots pine (Pinus sylvestris L.) and Norway spruce [Pica abies (L.) Karst] in either NH4+‐ or NO3−‐rain solutions at different N concentrations. The effects of N form, N concentration and tree species on ion influx and efflux were investigated.

Spruce shoots absorbed NH4+ from the external solution. Uptake apparently occurred by diffusion rather than by H+ or base cation exchange as commonly accepted, and increased linearly with NH4+ concentration in the external solution. In contrast, pine shoots released NH4+to the external solution. The different reactions of spruce and pine may reflect species differences in physical and chemical properties or differences in tissue N concentration. If the latter is the case, a tree's N status may determine whether the canopy acts as a source or sink for NH4+ influencing deposition rates to the needle surface. The results show that where NH4+ concentration on the needle surface exceeds 4 mg 1−1, foliar uptake may make a significant contribution to N status. In the absence of NH4+‐base cation exchange, atmospheric inputs of NH4+to the canopy appear unlikely to be directly‐responsible for the nutrient deficiencies typical of Dutch forest decline.

Neither spruce or pine shoots were able to utilize NO3− in the external solution and generally released NO3−. Adverse effects resulting from foliar accumulation of wet‐deposited NO3− appear unlikely. However, higher NO3− concentrations and longer residence times than simulated in this experiment may result in foliar uptake of NO3− in the field.
Ultrastructural studies on differentiating chloroplasts in the ‘forma fuscoviridis’ of Ceratozamia mexicana Brongn.*
Authors: BONZI LAURA MORASSI , BONATTI PIERA MEDEGHINI , MARINI CECILIA , FORNASIERO ROBERTA BARONI , PAOLETTI CINZIA
Published: April 2006

summary

Chloroplast ontogenesis has been examined ultrastructurally in leaflets of ‘forma fuscorviridis’ of Ceratozamia mexicana Brongn., a cycad displaying a dark red‐brown colour in young developing leaves. In very young leaves the chloroplasts contain large paracrystalline prolamellar bodies (PLBs), widely extending thylakoid strips, starch, membrane‐bounded paracrystals (MbPs) and conspicuous electron‐dense plastoglobules (PGBs) densely packed around the PLBs. All these features progressively disappear as the development of the thylakoid system proceeds. In mature leaves the chloroplasts are characterized by randomly orientated grana stacks containing large numbers of thylakoids. The conspicuous presence of different membrane precursors during leaf ontogeny may be associated with the very low rate of leaf development in Ceratozamia.
The ecological status of grey alder (Alnus incana (L.) Moench) in the upper subalpine birch forest of the central Scandes
Authors: KULLMAN LEIF
Published: April 2006

summary

Elevational distribution, site characteristics and regeneration patterns of grey alder [Alnus incana (L.) Moench] have been studied in subalpine forest of the southern Swedish Scandes, mainly as a basis for paleoecological inferences. Alder occurs very sparsely in the mountain birch forest and is strictly confined to sites with fresh finegrained soils with an insignificant mor humus layer. It frequently grows in close association with moving water (inundation in the spring). The potential climatic tree‐limit is inferred to appear about 30 m below that of mountain birch. Within a more than 200 m broad vertical zone below the tree‐limit, sexual reproduction does not take place at the present. Conceivably, the alders here are old relicts from a warmer period in the past. In contrast to other tree species, the range‐limit did not advance altitudinally in response to the 20th century warming (up to the 1930s/1940s) and a non‐equilibrium relationship with climate is hypothesized to have developed after the maximum range extension in the early‐ or mid‐Holocene. The virtual extinction of alder in the upper subalpine forest during the late Holocene is understandable in terms of pronounced thermophily of generative life‐cycle stages and a narrow range of soil preference. Both these properties are acting regressively on reproductive success as a consequence of climatic cooling and long‐term soil deterioration.
A containerized staining system for mycorrhizal roots
Authors: Claassen V. P. , Zasoski R. J.
Published: April 2006

summary

A useful device for manipulating root segments during clearing and staining of VA mycorrhizal roots is described. The device is constructed by cutting the tip off of a disposable syringe and welding a polypropylene screen on to the barrel. With this system, the plunger is used to draw in or expel reagents rapidly with little or no loss of root material during the repeated changing of reagents. The system speeds the process of clearing and staining and reduces the potential for operator contact with reagents.
Amelioration of aluminium toxicity in wheat by fluoride
Authors: MacLEAN D. C. , HANSEN K. S. , SCHNEIDER R. E.
Published: April 2006

summary

The deleterious effects of aluminium in the rhizosphere on growth, root morphology, ion uptake, and stomatal conductance in wheat (Triticum aestivum L.) were prevented or attenuated by the inclusion of fluoride in the growth medium; the more fluoride present relative to the concentration of aluminium, the greater the alleviation. Results support the conclusion that the ameliorative effects of fluoride were due to reductions in the concentration of the rhizotoxic trivalent cation (Al3+) through the formation of aluminium–fluoride complexes that are neither phytotoxic nor readily translocated from roots to shoots.
The use of ion‐selective microelectrodes for measuring calcium and hydrogen ion transfer between foliar surfaces and simulated rain solutions
Authors: LAUVER T. L. , MCCUNE D. C. , SHAFF J. E. , KOCHIAN L. V.
Published: April 2006

summary

A method is presented for the rapid and quantitative assessment of the transfer of calcium (Ca2+) and hydrogen (H+) ions between the surface of a leaf and simulated acidic rain. A small volume (144 μl) of pH 3.5 simulated rain solution was confined within a rigid, Teflon capillary on the foliar surface. A liquid membrane‐type, neutral carrier‐based, ion‐selective microelectrode either for Ca2+or for H* was placed within the capillary with the tip of the microelectrode at least 100μm from the foliar surface. This allowed spatial and temporal aspects of ion gradients generated by ion diffusion from the foliar surface to be studied. Results indicate that, throughout a 60–minute period after contact of simulated rain with the adaxial foliar surface of spinach (Spinacea oleracea L. cv. Marathon) or Japanese pachysandra (Pachysandra terminalis Siebold & Zucc)., negligible amounts of foliar‐derived calcium diffused into the simulated rain solution, and there was virtually no neutralization of the pH 35 rain simulant present in the capillary. A discussion of these results with respect to previous methods of investigation and theoretical possibilities of ion diffusion and cuticular permeability is presented.
Cellulase production by the vesicular–arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe
Authors: GARCIA‐GARRIDO J. M. , GARCIA‐ROMERA I. , OCAMPO J. A.
Published: April 2006

summary

Production of endoglucanase (EC 3.2.1.4) and exoglucanase (EC 3.2.1.91) enzymes was studied during penetration of the host and development of the vesicular‐arbuscular mycorrhizal (VAM) fungus, Glomus mosseae, in roots of lettuce (Lactuca sativa) and onion (Allium cepa). Endo‐ and exoglucanase activities increase in VAM plants at the beginning of entry‐point formation and arbuscule development. No relationship was found between the number of vesicles and endo‐ and exoglucanase activities. Extracts from spores and external mycelium of G. mosseae had endo‐ and exoglucanase activities. Some of the cellulase activities detected in VAM roots were attributed to the fungus, since endoglucanase activity found in the external mycelium of G. mosseae and in mycorrhizal root extracts showed the same electrophoretic mobility.
Genecological studies of groundsel (Senecio vulgar is L.)
Authors: THEAKER A. J. , BRIGGS D.
Published: April 2006

summary

In order to investigate population variation and its maintenance in groundsel (Senecio vulgaris L.) growing in the Cambridge University Botanic Garden, experiments have been carried out to study heritable differences in the rate of development of progenies of seed‐parents from sites of different history and land use in and round the Garden. There were significant differences between progenies of seed‐parents and between samples from different flowerbeds but the oldest beds did not have the quickest developing plants. Such a pattern of behaviour may be related to the fact that all the beds have been well maintained since the 1950s.

Since its establishment, two distinctive genetic variants have entered the Garden. On average, progenies from radiate and from simazine‐resistant seed‐parents in the study area were significantly slower to develop than non‐radiate simazine‐sensitive plants but, in both cases, we also found plants of intermediate rate of development, which might be the result of hybridization between the ‘immigrants’ and the precociously developing non‐radiate, herbicide‐sensitive plants. Progenies from seed‐parents collected at two sites just outside the boundaries of the Botanic Garden were slower in their rate of development than those from the intensively hand‐weeded flowerbeds of the Garden. Samples collected from the same area in different seasons, and grown at the same time, did not differ overall in rate of development, but there were significant differences within flowerbeds.

Subsets of progenies of a set of seed‐parents were grown both in summer and winter. The rank order of maturity was not the same in the two parts of the experiment, indicating that the progeny of different seed‐parents have different relative fitness in different times of year. This behaviour, in a species which is capable of reproducing at all seasons of the year, could be a major factor in the maintenance of population variation in the Garden proper.
A pollen diagram, radiocarbon ages and evidence of agriculture on Extwistle Moor, Lancashire
Authors: BARTLEY D. D. , CHAMBERS C.
Published: April 2006

summary

A pollen diagram is presented from an upland area (about 360 m a.s.l.) on the western slope of the Pennines above Burnley. Radiocarbon assays from the peat suggest that the diagram covers about the last 3000 yr. The recent practice of dating both the ‘humin’ and ‘humic’ fractions of a peat sample leads to problems of assigning dates, especially calibrated dates, to particular events. The evidence from the pollen curves is compared with known climatic, archaeological and historical evidence in an attempt to see whether a chronology based on the humin dates or one based on the ‘weighted mean dates’ is more reliable. The evidence suggests that for this site the humin dates are more realistic and indicate that although the site has been covered by peat from about 1000 BC there were clearance phases in the area in the Iron Age, the Roman Period and from the sixteenth century on.
Fructosyl transferase activity in the tissue‐macerating preparation, pectolyase Y‐23*: physiological role of fructosyl transfer in Aspergillus and significance for studies of fructan synthesis in grasses
Authors: WINTERS ANA. L. , SMEEKENS SJEF C. M. , CAIRNS ANDREW J.
Published: April 2006

summary

Pectolyase Y‐23 is a commercially available plant tissue‐macerating preparation derived from culture filtrates of Aspergillus japonicus. When incubated with 600 mol m−3 sucrose at pH 5.5 and 30 °C, pectolyase catalyzed the rapid synthesis of oligofructans. During a 5 h incubation, 53 % of the original mass of substrate was converted to oligofructan. Thin layer chromatography (TLC) indicated that the predominant products were the trisaccharide isokestose and the tetrasaccharide nystose, though fructans of up to degree of polymerization (DP) 6 were also detected. The synthesis of oligofructan was accompanied by the release of large amounts of free glucose, but free fructose was a minor product of the reaction, indicating a low activity of invertase in the preparation. The fructan products were stable during incubation periods of up to 24 h showing the absence of fructan hydrolase in the pectolyase preparation. The pectolyase fructosyl transferase reaction was similar to reactions catalyzed by enzymes from other Aspergillus spp. In particular, the reaction strongly resembled the industrial synthesis of the commercial sugar product, Neosugar.

The substrate concentration kinetics of glucose release from sucrose by pectolyase were determined and the parameters Vmax and Km for fructosyl transfer were calculated as 218 nkat mg−1 of pectolyase and 67 mol m−3 sucrose respectively. The fructosyl transferase was partially purified by quaternary‐amine ion exchange chromatography.

Pectolyase Y‐23 has previously been used in the preparation of a fructosyl transferase derived from barley leaf protoplasts. The pectolyase fructosyl transferase exhibited similar properties to those reported for the barley enzyme.
The effect of infection by Erysiphe pisi DC on acid and alkaline invertase activities and aspects of starch biochemistry in leaves of Pisum sativum L.
Authors: STORR TREVOR , HALL J. L.
Published: April 2006

summary

The acid and alkaline invertases of mature leaves of Pisum sativum were partially purified and characterized prior to determining the effects of powdery mildew (Erysiphe pisi) infection on their activities. Seven days after inoculation, infection resulted in significant increases in the activities of both acid and alkaline invertases in whole leaves of cv. Onward, but a significant increase in the activity of only alkaline invertase in isolated mesophyll of cv. Argenteum. Activity of α‐glucosidase was determined in leaves and it was concluded that this enzyme could not be responsible for the increased sucrose hydrolase activity observed in host tissues. Seven days after inoculation, infection caused a significant decrease in leaf starch content, a decrease in the activity of ADP‐glucose pyrophosphorylase, and no significant change in the activity of α‐glucan phosphorylase or content of inorganic phosphate. It was proposed that the decreased content of starch is a result of decreased starch synthesis.
Leaf adaptations of some Shorea species to sun and shade
Authors: ASHTON P. M. S. , BERLYN G. P.
Published: April 2006

summary

Seedlings of four species of the genus Shorea section Doona were examined. All co‐exist in the moist evergreen rain forest of southwestern Sri Lanka. Experiments were designed to investigate some physiological and anatomical attributes of leaves under different light conditions. The attributes considered were net photosynthesis, transpiration, stomatal conductivity, blade and cuticle thickness, stomatal frequency, thickness of upper epidermis and palisade mesophyll, and number of palisade layers. Results demonstrate the close association between anatomical adaptation and efficiency in physiological processes. Results also elucidate some of the relationships between distribution patterns of species across the forest topography and their differences in light and drought tolerance. This indicates that an important period determining site specialization of a species occurs during regeneration establishment. These relationships are not as simple or as ecologically noticeable though as for those relationships documented in many previous studies between tree species of markedly different successional stages or taxonomy.
Leaf fracture toughness and sclerophylly: their correlations and ecological implications
Authors: CHOONG M. F. , LUCAS P. W. , ONG J. S. Y. , PEREIRA B. , TAN H. T. W. , TURNER I. M.
Published: April 2006

summary

The fracture toughness of sun‐leaves of 42 tropical tree species growing in Singapore was measured along a ‘least tough’ path using an instrumented cutting technique. Punch‐and‐die (penetrometer) tests were also conducted. Intercostal material was analyzed for crude fibre and crude protein (total nitrogen concentration × 6.25) and the ratio of the two, the index of sclerophylly, calculated for each species. Leaf anatomy was examined and specific leaf area was calculated. Thirty‐seven of the species were from three definable plant communities, namely mangroves, trema belukar (secondary forest on undegraded sites) and adinandra belukar (secondary forest on highly degraded soils).

There was a highly significant positive correlation between fracture toughness and index of sclerophylly for the 42 species (R2= 0.43, P < 0.001) brought about largely by a high correlation between toughness and crude fibre content. Fracture toughness was not correlated with lamina tissue dorsi‐ventral thickness but high toughness was clearly associated with the presence of sclerenchyma bundle sheaths and sheath extensions. Analysis of the fracture path for 26 leaves of ten mangrove species showed a high correlation between the area fraction occupied by veins and fracture toughness if one species, Avicennia rumphiana, was excluded. The regression equation for the other nine species gave estimates of the fracture toughness of vein tissue and lamina matrix of 6053 and 327 J m−2 respectively. Punch‐and‐die test results only correlated well with the cutting tests when values were divided by lamina thickness.

The ratio of protein to fibre in a leaf (the reciprocal of the index of sclerophylly) has been established as a good predictor of leaf palatability and digestibility to generalist chewing folivores. The high correlation between fracture toughness and the index of sclerophylly for a large sample suggests that leaf toughness could be the factor used as a proximate cue for determining food quality in herbivore foraging strategies.
Effects of a short ozone exposure given at different stages in the development of Plantago major L.
Authors: REILING K. , DAVISON A. W.
Published: April 2006

summary

This paper reports a comparison of the effects of the same ozone exposure given at different stages of growth on a population of Plantago major L., which is as sensitive to ozone as Bel‐W3 tobacco. Plants were grown from seed for eight weeks in controlled environment chambers and exposed to 70 μl O3 1−1 7 h d−1 for the whole period or for 2‐wk episodes during weeks 1 + 2, 3 + 4, 5 + 6 or 7 + 8. Controls had charcoal filtered air. Effects on leaf, flower, seed and dry matter production, and on relative growth rate of shoot and root are given.

At whatever time the ozone was given, it altered relative growth rate, dry matter partitioning and seed output. The experiment supports the view that assessment of the sensitivity of a herbaceous species can be indicated by a short‐term exposure of young plants, even though the nature of the response may change with development.

Comparison of the effect of ozone on dry matter partitioning at different stages of growth suggested that at each stage in development, ozone relatively strengthened the currently dominant sink, therefore reducing allocation to subsidiary sinks. As a plant develops, the relative strengths of sources and sinks change so the effects of an ozone episode on allocation will depend upon the timing. It is concluded that the commonly held view that ozone tends to reduce root growth more than shoot may be an over‐simplification. For native plants growing in the field, the timing of episodes in relation to development may be crucial to understanding ozone impact. On the ecosystem level we need knowledge of response and source‐sink relationships at times of the year when episodes occur.
Modern pollen rain studies of the Nile Delta, Egypt
Authors: AYYAD S. M. , MOORE P. D. , ZAHRAN M. A.
Published: April 2006

summary

Modern pollen studies are proving increasingly valuable in the interpretation of fossil pollen assemblages, but relatively little work has been conducted in the arid and semi‐arid parts of the world. In this study, surface samples from a range of vegetation types along the Mediterranean coastal lands of the north of Egypt were collected. The sites were arranged along three representative sea–landward transects at different points along the Nile Delta coast. Samples have been analyzed for their pollen content and the resulting data ordinated using multivariate techniques (detrended correspondence analysis – DECORANA). The groupings that emerge from this analysis are generally closely related to the vegetation from which they were derived, although it proved impossible to separate saline barren areas from salt marsh sites on the basis of their pollen rain.

In order to test the results against fossil material, two short profiles of alluvial sediment were excavated from two of the study areas, and the profiles analyzed for pollen. Ordination of the data from these soil sections provided information on the past history of the sites, mainly related to local successional processes in these maritime environments. The results illustrate the potential of surface studies as a basis for environmental reconstruction in the coastal region of the Nile delta.
A reconsideration of fructan biosynthesis in storage roots of Asparagus officinalis L.*
Authors: CAIRNS ANDREW JOHN
Published: April 2006

summary

Total soluble neutral carbohydrate (SNC) from storage roots of seven cultivars of Asparagus officinalis L. was analyzed by HPLC and TLC. Fructan accounted for roughly 90% of the total SNC and, of the fructan fraction, 81–98% was of degree of polymerization of five and larger (DP 5). Smaller oligosaccharides and sucrose represented a correspondingly small proportion of the total SNC. This observation differs from the generally accepted view of Asparagus fructan, which emphasizes the presence of small oligofructan in root tissue.

On the basis of chromatographic mobility, neokestose and isokestose were identified as the two components of the trisaccharide fraction. Kestose did not accumulate in any of the cultivars studied.

A crude enzyme extract of Asparagus roots was prepared using established methods involving dialysis for 5 d. Microbiological analysis of this preparation revealed heavy bacterial contamination. Oligofructan apparently persisted in this protein preparation despite the long period of dialysis. These observations have consequences for the interpretation of previous reports of in vitro fructosyl transferase data for Asparagus root enzymes. The validity of long‐term dialysis in the study of fructan enzymes is questioned.

Crude protein extracts of roots were also desalted using a rapid gel‐exclusion method. When incubated with sucrose under conditions similar to established techniques, both invertase and fructosyl transferase activities were detected in this preparation. The trisaccharide products of the fructosyl transferase reaction were identified on TLC as neokestose, isokestose and kestose; the last did not accumulate in vivo. Oligofructans of DP > 3 were also synthesized by this preparation and the pattern of products revealed by TLC was similar to previous reports. These oligofructan products of enzyme reactions were compared directly with the complete range of fructan structures accumulating in the tissue, using TLC. The enzyme products bore little resemblance to the native fructan pattern. Such enzyme activities are of doubtful physiological relevance and may be the result of artifactual or ancillary activities of other enzymes such as invertase.

These findings are discussed with respect to previous studies of Asparagus root carbohydrates and serve as a basis for a critical reassessment of the enzymology of fructan biosynthesis both in this and other plant tissues.
Use of nitrogen by the Nostoc—Gunnera tinctoria (Molina) Mirbel symbiosis
Authors: OSBORNE BRUCE A. , CULLEN ANN , JONES PETER W. , CAMPBELL GARRET J.
Published: April 2006

summary

Comparison of Gunnera tinctoria (Molina) Mirbel plants grown in the presence and absence of nitrogen showed that N2 fixed by the cyanobacterium (Nostoc punctiforme L.) can supply all of the requirements for vegetative growth. Estimates of the proportion of tissue occupied by Nostoc indicates that an actively‐fixing cyanobacterial component (the cyanobiont) of somewhat less than 1 % of the total (host + cyanobiont) biomass was sufficient to meet the demands of the host. On the basis of low nitrogen contents and high C: N ratios the cyanobiont was nitrogen‐limited.

In situ nitrate assimilation was limited by nitrate uptake and/or transport. Whole plants did not accumulate nitrate and had little capacity to assimilate nitrate, although nitrate reductase activity could be induced in intact leaves or leaf segments supplied directly with aqueous nitrate solutions. The possible significance of these results is discussed. Growth of G. tinctoria on ammonium was depressed at high concentrations and this species may only be able to use low ammonium concentrations. These results indicate that G. tinctoria is almost entirely dependent on N2 fixed by the cyanobacterium to meet its nitrogen demands and has little capacity to use alternative forms of nitrogen.
Restriction of nodulation by the broad host range Rhizobium tropici strain CIAT899 in wild accessions of Phaseolus vulgaris L.
Authors: KIPE‐NOLT J. A. , MONTEALEGRE M. C. M. , TOHME J.
Published: April 2006

summary

Common bean (Phaseolus vulgaris L.) is nodulated by a heterogeneous group of Rhizobium strains. In a search for host plant restriction of nodulation by some of these strains, 50 wild and cultivated bean accessions were evaluated for the length of time taken to form effective nodules with three diverse bean strains. As bean genotypes vary substantially for this character, preference or restriction was defined as a relative parameter between the three Rhizobium strains for a given bean genotype. Many of the bean genotypes evaluated showed no preference for particular strains of Rhizobium though Rhizobium strain CIAT8002 was often slowest to nodulate. Amongst the wild and landrace bean accessions, there was a tendency for materials of Mesoamerican origin to form active nodules more rapidly with CIAT632 (a Rhizobium leguminosarum bv. phaseoli strain isolated from Guatemala) than with CIAT899 (a broad host‐range, R. tropici from Colombia). In contrast, in those cases in which some preference was observed, wild and landrace bean genotypes from Peru and Argentina (Andean origin) nodulated more rapidly with Rhizobium strain CIAT899. There were exceptions to this pattern among bred lines. Three wild bean accessions: G10002 from Mexico, G23418 from Costa Rica and G21117 from Colombia showed strong resistance to nodulation with CIAT899. Formation of effective nodules took more than 10 d longer with CIAT899 than with CIAT632. This strain preference was not altered by changing the time of inoculation between 0 and 8 d after sowing. Within an accession, plant to plant variation was observed in the time taken to nodulate with a given strain of Rhizobium. However this variation persisted in the progenies of contrasting individual plants of G21117.
Effects of excess nitrogen and phosphorus starvation on the extramatrical mycelium of ectomycorrhizas of Pinus sylvestris L.
Authors: WALLANDER H. , NYLUND J.‐E.
Published: April 2006

summary

The effect of excess nitrogen alone, and in combination with phosphorus and magnesium starvation, on the production of extramatrical mycelium was studied in Scots pine seedlings ectomycorrhizal with Laccaria bicolor (R. Mre.) Orton, Hebeloma crustuliniforme (Bull, ex St‐Amans) Quel. and Suillus bovinus (L. ex Fr.) O. Kuntze. Seedlings were grown in a semi‐hydroponic cultivation system and the ergosterol assay was used to estimate fungal biomass. The mycelial biomass increased rapidly when N was kept low (10–20 mg l−1) and in balance with other nutrients, but no extramatrical mycelium was produced when the N concentration was raised to 200 mg l−1. The growth of the extramatrical mycelium resumed when the excess N treatment was terminated and the seedlings were returned to a low nutrient regime, Laccaria showing more complete resumption of growth than Suillus, while Hebeloma had a low production of extramatrical mycelium in all treatments. Compared with the external mycelium, the amount of fungal tissue on the mycorrhizal roots (mantle and Hartig net) was much less affected by the high N treatment. P starvation increased the production of extramatrical mycelium tenfold, with almost no difference between high and low N nutrient regimes, while Mg starvation had no effect on the fungal biomass. The high N treatment lowered P and particularly Mg concentration of the needles, regardless of the mycorrhizal status of the plant.

It is suggested that nitrogen deposition from the atmosphere may damage the function of mycorrhiza even before root tip studies reveal any decline in the symbiotic state. On the other hand, moderate nitrogen fertilization of forest land unaffected by nitrogen pollution is likely to have only passing effects on mycorrhizal development.
Long‐term exposure of Norway spruce,Picea abies(L.) Karst., to ozone in opentop chambers
Authors: WALLIN G. , SKÄRBY L. , SELLDÉN G.
Published: April 2006

Rates of photosynthesis at different photosynthetic photon flux densities (PPFD; 0–1530 μmol m−2s−1) were measured on three shoot age classes of one clone of Norway spruce,Picea abies(L.) Karst. exposed to three different concentrations of ozone for three seasons (1985–7) in open‐top chambers. The treatments were charcoal‐filtered air (CF), non‐filtered air (NF) and non‐filtered air + ozone (NF +). The rate of net photosynthesis was determined using an infrared gas analyzer (IRGA) connected to a small cuvette, equipped with an artificial light source. In 1‐ and 2‐yr‐old shoots the apparent quantum yield decreased with increasing shoot age and ozone concentration, while no effect was found in the current‐year shoots. The decrease could probably partly be attributed to a lower efficiency of light capture due to a lower content of chlorophyll. No effect was observed on the Kok‐effect or on the convexity of the light response curve in any of the treatments or age classes. The significantly higher light compensation point found in current year shoots from the NF+ treatment compared to that of shoots from the CF and NF treatments was suggested to be attributed to an increase in dark respiration. The effect of ozone was larger on photosynthesis at light saturation than on the apparent quantum yield. It is therefore suggested that ozone has a greater influence on the photosynthetic efficiency at high light conditions than at low light conditions.
The physiological importance of accumulation of cyclitols inViscum albumL.*
Authors: RICHTER ANDREAS , POPP MARIANNE
Published: April 2006

Investigations ofViscum albumon 16 different host species revealed an endogenous cyclitol pattern with pinitol, 1‐O‐methyl‐muco‐inositol, quebrachitol,chiro‐inositol, an unidentifiedO‐methyl‐inositol and traces of ononitol. Host‐specific cyclitols including bornesitol, quercitol, viburnitol,scyllo‐inositol and the hexitol, sorbitol, were also stored in the mistletoe. The endogenous cyclitols were accumulated to such high concentrations that they made a large contribution to the osmotic potential. It was estimated that 22.6–43 % of mistletoe carbon is derived from the host.
Differential attachment by conidia of the endophyte, Discula umbrinella (Berk. & Br.) Morelet, to host and non‐host surfaces
Authors: TOTI L. , VIRET O. , CHAPELA I. H. , PETRINI O.
Published: April 2006

Differential attachment of conidia to leaves of different species (host and non‐host) has been observed in the endophytic fungus, Discula umbrinella (Berk. & Br.) Morelet, a deuteromycete known to cause occasional epidemics of anthracnose in beech stands. On beech leaves, attachment gradually increased over 24 h and reached a maximum after 16–24 h; there were small differences in attachment between conidia suspended in water and those in HEPES buffer. The range of variation of results obtained with conidia suspended in HEPES was smaller but the adhesion was clearly enhanced. The adhesion of conidia to the host surface was highest at pH 5, and decreased with increasing pH. Heat and chemical treatments significantly reduced attachment. Two factors (or groups of factors) are likely to be involved in the recognition process. The first is heat‐labile, the second one could be a non‐protein molecule present on the conidial surface and actively recognized by the host. The physiological similarity between endophytes and other symbionts is briefly discussed.
Fructan biosynthesis in excised leaves of Lolium temulentum L.
Authors: CAIRNS ANDREW JOHN
Published: April 2006

Leaves of Lolium temulentum L. were induced to accumulate fructan by excision and continuous illumination. Enzyme extracts were prepared and protein was concentrated by precipitation with ammonium sulphate at 100% saturation. The preparation was incubated at a protein concentration equivalent to 3‐4 g f.wt of tissue cm‐3 with sucrose at an initial concentration of 400 mol‐3. The preparation catalyzed the synthesis of large fructans of apparent degree of polymerization (DP) ⩽20, based upon comparison with the chromatographic mobilities of oligoinulins on thin‐layer chromatography (TLC). The products were formed at a rate approximating to rates of fructan accumulation in leaf tissue. The overall pattern of in vitro products, when separated on TLC, resembled that of the native leaf fructans though the relative abundances of some of the products differed from the in vivo pattern. The reaction did not catalyze the formation of the high molecular weight fructans (Mr > 3 kDa; DP > 20) characteristic of this tissue. Equivalent protein preparations derived from uninduced leaves exhibited negligible rates of fructan synthesis. Feeding cycloheximide to leaves prevented fructan synthesis both by the tissue and by protein extracts. Cycloheximide did not directly inhibit in vitro fructan synthesis, suggesting that its in vivo effect was at the translational level. The characteristics of the in vitro reaction are compared with the properties of in vivo fructan synthesis and are discussed with respect to its possible physiological relevance.
Hyphal transport of15N‐labelled nitrogen by a vesicular—arbuscular mycorrhizal fungus and its effect on depletion of inorganic soil N
Authors: JOHANSEN A. , JAKOBSEN I. , JENSEN E. S.
Published: April 2006

Hyphal transport of nitrogen from a15N‐labelled ammonium source by a VA‐mycorrhizal fungus was studied under controlled experimental conditions.Cucumis sativusL. cv. Aminex (F1 hybrid) was grown alone or together withGlomus intraradicesSchenck and Smith in containers with a hyphal compartment separated from the rooting medium by a fine nylon mesh. Lateral movement of the applied15N towards the roots was minimized by using a nitrification inhibitor (N‐serve) and a hyphal buffer compartment. Recovery of15N by mycorrhizal and non‐mycorrhizal plants was 6 and 0%, respectively, after a labelling period of 23 days. The corresponding figures, without N‐serve added, were 4 and 7%. A prolongation of the labelling period by 8 days (N‐serve applied) resulted in an increase in the15N recovery by mycorrhizal plants to 30% of the applied15N. Non‐mycorrhizal plants contained only traces of15N. The external hyphae depleted the soil in the hyphal compartment efficiently for inorganic N. In contrast, hyphal compartments of control containers still contained considerable amounts of inorganic N. The15N assimilated by the external hyphae in one hyphal compartment was not translocated in significant amounts to the external hyphae in another hyphal compartment. The possible implication of this for inter‐plant N transfer by VA hyphal connections is discussed.
Dose—response relationships for SO2 fumigations in the lichens Evernia prunastri (L.) Ach. and Ramalina fraxinea (L.) Ach.
Authors: SANZ M. J. , GRIES C. , III NASH T. H.
Published: April 2006

Sulphur dioxide fumigation of the lichens Evernia prunastri (L.) Ach and Ramalina fraxinea (L.) Ach, whose thallus water content was held at 100‐120%, throughout each experiment, resulted in changes in net photosynthesis, dark respiration and chlorophyll content in relation to both concentration and duration of exposure. Net photosynthesis was the most sensitive response variable. Significant reduction in chlorophyll content was found when no recovery in net photosynthesis occurred after two weeks. A reduction in dark respiration was only found at high SO2 concentrations. Evernia prunastri was affected by lower concentrations and shorter exposure times than Ramalina fraxinea and the data for both species showed dose‐response relationships.
Deposition of H15NO3 vapour to white oak, red maple and loblolly pine foliage: experimental observations and a generalized model
Authors: HANSON PAUL J. , GARTEN CHARLES T.
Published: April 2006

Nitric acid vapour enriched with 15N (H15NO3) was volatilized into the cuvette of an open‐flow gas exchange system containing red maple (Acer rubrum L.), white oak (Quercus alba L.), or loblolly pine (Pinus taeda L.) seedling shoots to facilitate direct measurements of total foliar deposition, and subsequent assessments of the rate of HNO3 movement across the cuticle (transcuticular uptake). Total H15NO3 vapour deposition to foliar surfaces ranged from <5 to 27 nmol m‐2 s‐1 the variability being largely accounted for by differences in HNO3 concentrations and leaf conductance. Mean whole‐leaf conductance to HNO3 ranged between 0.9 and 3.4 mm s‐1 for hardwoods and between 6 and 34 mm s‐1 for loblolly pine. Of the total H15NO3 vapour deposited to leaves, an average of 39 to 48 % was immediately‘bound’into hardwood foliage whereas only 3 % was bound to loblolly pine needles. This implies that rain events might extract greater amounts of HNO3‐derived nitrate in throughfall from conifer canopies as compared to hardwood canopies. Post‐exposure H15NO3 uptake rates across the leaf cuticle increased with surface nitrate concentrations, but were 1 to 2 orders of magnitude lower (O06 to 0.24 nmol m‐2 s‐1) than total HNO3, deposition during exposures.

A generalized leaf‐level model of HNO3 deposition to foliage capable of simulating deposition pathways to sorption sites on the leaf surface, and to the metabolically active leaf interior via transcuticular or stomatal pathways is formulated and suggested for use in planning future work on HNO3 deposition.
Phragmites australis: Venturi‐ and humidity‐induced pressure flows enhance rhizome aeration and rhizosphere oxidation
Authors: ARMSTRONG JEAN , ARMSTRONG WILLIAM , BECKETT PETER M.
Published: April 2006

A Venturi‐induced convection of gases through the Phragmites rhizome system is reported and the effects of this, and a humidity‐induced convection previously described, are quantified. The Venturi‐convection is driven by a pressure differential created by wind blowing across tall dead culms which sucks air into the underground system via culms snapped off close to ground level. The results demonstrate how wind, by increasing Venturi‐induced convection, and how radiant energy, by increasing humidity‐induced convection, raise the oxygen concentrations in the rhizome system, thereby causing much greater fluxes of oxygen into root and rhizosphere than are achieved if rhizome aeration is by diffusion alone. In laboratory experiments convective flow rates of as low as 0·7‐1·4 × 10−8 m3 s−1 (approx. 20‐40 mm min−1 in the rhizome) were sufficient to raise rhizome oxygen concentrations to 90% of atmospheric. The significance of this is discussed in connexion with pollution control by constructed wetlands, and photographic evidence is provided of the rhizosphere oxidizing activities in soil and anaerobic solution. A mathematical model is derived to help to evaluate the contributions of convection and diffusion in rhizome aeration, and to assess the likely effects of root and rhizosphere oxygen demands.
A relationship between plant growth and increasing VA mycorrhizal inoculum density
Authors: Clapperton M. Jill , Reid David M.
Published: April 2006

The relationship was examined between the density of vesicular‐arbuscular (VA) mycorrhizal inoculum and the growth of Phleum pratense L. and Agropyron trachycaulum (Link) Malte. The most probable number method (MPN) was used with combinations of host, VA mycorrhizal inoculum and a series of dilutions of field soil. There was a positive correlation between the proportion of field soil and the amount of mycorrhizal colonization. The numbers of tillers and leaves, shoot and root dry weights, and root:shoot ratios were negatively affected by increasing proportions of field soil inoculum. The addition of fertilizer alleviated the effects of increasing proportions of field soil on plant growth and reduced the amount of colonisation by mycorrhizal fungi. The relationship between increasing proportions of field soil and plant growth was not species‐specific. We conclude that there was an interaction between the inoculum density of VA mycorrhizal fungi and soil nutrient availability which affected plant growth.
Morphological and physiological properties of symbiotic cyanobacteria
Authors: VAGNOLI L. , MARGHERI M. C. , And G. ALLOTTA , MATERASSI R.
Published: April 2006

The main morphological and physiological characters of several symbiotic cyanobacterial strains, isolated from different plant—cyanobacteria associations (Anthoceros, Azolla, cycads and Gunnera) were investigated. All the strains showed heterocystous immotile filaments and motile hormogonia, typical of the genus Nostoc. In accordance with their symbiotic origin, all were found capable of photoheterotrophic growth. On the basis of the morphological and physiological properties and the phycobiliprotein content, the isolates from Azolla appeared very close to each other and quite distinct from the other cyanobionts. The latter showed many characteristics in common, such as marked tendency to produce hormogonia, synthesis of C‐phycoerythrin and rather small dimensions of the akinetes. With regard to the cycad cyanobionts, there was no correlation between the properties of the isolates and the host plants.