bluuebunny/crossref_metadata_2025 huggingface dataset:
Ontogeny of synthesized Picea abies (L.) Karst.–Hebeloma crustuliniforme (Bull. ex St Amans) Quél. ectomycorrhizas
Authors: BRUNNER I. , SCHEIDEGGER C.
Published: April 2006

summary

Ectomycorrhizas were synthesized between Picea abies (L.) Karst. and Hebeloma crustuliniforme (Bull. ex St Amans) Quél. in growth pouches containing activated charcoal filter paper. Immediately emanating hyphae from inoculated plugs contacted root hairs and root surfaces, hyphal morphology was altered. They became short‐celled with few clamp connections, highly branched, and lacked cell wall ornamentation. Then, hyphae on root surfaces formed an inner synenchymatous mantle and loose hyphae formed an outer prosenchymatous mantle. Simultaneously, root cap cells became invaded by fungal hyphae and their remnants were incorporated into the inner mantle. Further root elongation took place but root hair production was suppressed. Thirdly, a Hartig net began to form in basal portions of developing ectomycorrhizas and the fungal mantle became denser and thicker. Fourthly, growth of the root was reduced and the hyphae of the Hartig net penetrated between cortical cells moving toward the apex. Fifthly, metacutis occasionally surrounded the meristem. At this stage the formation of the ectomycorrhiza can be considered to be complete and the rootlet itself is temporarily in a dormant state.
Effects of low‐concentration sulphur dioxide fumigation and vesicular–arbuscular mycorrhizas on 14C‐partitioning in Phleum pratense L.
Authors: CLAPPERTON M. JILL , REID DAVID M.
Published: April 2006

summary

The effect of long‐term low‐concentration (0.04–0.065 μl l−1) exposure to sulphur dioxide (SO2) on assimilate partitioning in Phleum pratense colonized by vesicular‐arbuscular (VA) mycorrhizal fungi from field soil was examined by supplying leaves with 14CO2. Seedlings were grown and exposed to SO2 for six weeks and then pulsed with 4CO2 for 15 min. The distribution of the 14C was analysed after a 12 h chase. SO2 fumigation had little effect on plant dry matter production, however, it had significant effects on the assimilation of 14CO2.

Plants colonized by VA mycorrhizal fungi, both fumigated and controls, had a greater percentage of the total incorporated 14C in the roots, a significantly lower percentage of the total as 14C‐labelled soluble carbohydrates in the shoots, and a greater percentage of the total as 14C‐labelled amino‐ and organic acids in the shoots and roots than non‐mycorrhizal plants. SO2 exposure reduced root length, root length colonized by VA mycorrhizal fungi, and the length of root infected with arbuscules. It appeared that colonization by VA mycorrhizal fungi in field soil had an overriding effect on carbon assimilation, use, and translocation in the host, and these probably affect host sensitivity to SO2 exposure.
Timing of ozone stress and resulting status of ribulose bisphosphate carboxylase/oxygenase and associated net photosynthesis
Authors: PELL E. J. , ECKARDT N. , ENYEDI A. J.
Published: April 2006

summary

Experiments were conducted to determine how the timing of an exposure to ozone influenced the impact of the gas on ribulose‐ 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) throughout the life span of a designated leaf. Saplings of Populus maximowizii×trichocarpa NE 388 received 5‐d exposures to O3 in growth chambers during and at the termination of presumed synthesis of Rubisco in a designated leaf. Ozone had no detectable impact on Rubisco activity or quantity when the exposure occurred during the time of increasing concentration of the protein in the leaf. When the concentration of Rubisco was near its peak, O3 induced a reduction in quantity and activity of Rubisco, but after cessation of the O3 stress, levels converged with those of the untreated tissue. When O3exposure occurred after full leaf expansion, minimal effects of the gas could be detected. When plants of hybrid popular or Raphanus sativus L. cv. Cherry Belle received chronic O3 treatment throughout the lifespan of the leaf, Rubisco activity and quantity declined more rapidly and never converged with values of untreated tissue.

Studies of gas exchange revealed that changes in Rubisco were associated with a decline in net photosynthesis (A) and that these effects preceded the observed reduction in foliar conductance. CO2 response curves were measured periodically, and the initial slope (linear portion) of the curve, reflecting carboxylation capacity, declined more rapidly with leaf age in O3‐treated than in untreated poplars. There was no effect of O3 on stomatal limitation to CO2, assimilation except for a slight increase during the last 2 wk of the 9‐wk experiment. This supported the hypothesis that O3 effects on A were associated with CO2‐fixing capability of the leaf.
Plastid development in distinctively coloured juvenile leaves
Authors: WHATLEY JEAN M.
Published: April 2006

summary

The juvenile leaves of many tropical and a few temperate plants are translucent and apparently colourless or are white, red or brown in colour rather than green. It is already known that the distinctive colours of the young leaves can result from a delayed increase in chlorophyll content and/or from the masking effects and changing levels of other pigments. The present study deals with the patterns of chloroplast development during leaf growth in Coffea arabica L., Durio zibethinus Murray, Mangifera indica L., Photinia×Fraseri Dress. Red Robin and Theobroma cacao L. Even in very young leaves the mesophyll cells contain chloroplasts, but these are small and few in number. Although conspicuous greening usually takes place only after the leaves are fully expanded, chloroplast development proceeds without interruption throughout leaf growth. The late increase in chlorophyll content is associated with a noticeable increase in the long axes of the chloroplasts and/or their numbers within each cell section. The way in which the overall increase in chloroplast volume per cell is achieved varies between species.
Visualization of the cytoskeleton in red algae using fluorescent labelling
Authors: GARBARY DAVID J. , McDONALD A. ROSA , DUCKETT JEFFREY G.
Published: April 2006

summary

Cytoskeletal components have been visualized for the first time in red algae using fluorescent labelling. Rhodamine‐phalloidin was used to stain actin in a variety of filamentous species: Griffithsia pacifica, Tiffaniella snyderae, Ceramium strictum, Antithamnion kylinii (Ceramiales) and Audouinella dasyae (Acrochaetiales). Immunofluorescent labelling of microtubules was obtained only in Griffithsia pacifica. In both procedures, successful labelling was achieved only after wall digestion with glucuronidase and protocols using cellulase resulted in no labelling. Both microfilaments and microtubules formed extensive arrays in the peripheral cytoplasm of Griffithsia. Microtubules were associated with nuclei in these highly multinucleate cells, suggesting that they maintain the extremely regular nuclear arrangement. Dense labelling of microfilaments occurred at rhizoid apices, however, this was not observed in apical cells, suggesting that two distinct mechanisms of tip growth may be present. Of the algae studied, only Griffithsia formed extensive peripheral arrays of microfilaments in all cells; the remaining genera showed actin labelling in a variety of different structures including, long and short ‘ropes’ of varying thicknesses, basket‐like structures and ‘spikes’. In Griffithsia extensive actin staining was often associated with the pit plugs between adjoining cells. Cytoskeletal components often showed a polar distribution with denser labelling towards the bases or apices of cells. In dividing apical cells of Griffithsia, a band of microfilaments was observed prior to deposition of the new cross wall. These preliminary results suggest that cytoskeletal studies will provide important insights into understanding development and cell function in red algae.
Ammonia and ammonium fluxes between photolithotrophs and the environment in relation to the global nitrogen cycle
Authors: RAVEN JOHN A. , LINDA BERND WOLLENWEBER , HANDLEY L.
Published: April 2006

summary

Ammonium (used here to signify NH4+ plus NH3) is the immediate inorganic precursor of organic nitrogen in photolithotrophs. In marine habitats ammonium is also the major exogenous nitrogen source, and the same is probably true of terrestrial habitats. In addition to this major role of ammonium as exogenous nitrogen source, it is also quantitatively very important as an endogenous nitrogen source with nitrate or N2 as exogenous nitrogen source, and as a recycled nitrogen compound in photorespiration and in phenylpropanoid synthesis. The shoots of terrestrial plants have higher NH3 compensation partial pressures than most natural soils, and especially higher than that of the sea. However, long‐distance transport of gaseous NH3 (e.g. from continents to oceans) is a negligible component of the ‘natural’ global nitrogen cycle. Current concepts of evolution of the atmosphere and biosphere do not involve high partial pressure of NH3 in the atmosphere: any ammonium produced in inorganic or biological processes is removed from the atmosphere by rain‐out, or, over larger time‐scales, by the action of ultraviolet radiation (especially before the ozone screen came into being) and of hydroxyl radicals (especially after oxygenation of the atmosphere). In addition to posing problems for the origin of life and arguing for an early rather than a late evolution of diazotrophy, a low NH3 partial pressure renders implausible arguments that phenylpropanoid synthesis was restricted early in evolution by the effect of high ammonia in reversing phenylalanine ammonia‐lyase.
A comparison of ammonium and nitrate as nitrogen sources for photolithotrophs
Authors: RAVEN JOHN A. , WOLLENWEBER BERND , HANDLEY LINDA L.
Published: April 2006

summary

Potential advantages of ammonium relative to nitrate assimilation (assuming equal nitrogen supply in the two forms), deduced from known biochemical pathways and the site of nitrate assimilation in vascular land plants, include (i) a greater maximum specific growth rate, (ii) lower costs of photons and (in transpiring plants) water per unit carbon assimilated, and (iii) lower costs of iron, manganese and molybdenum per unit carbon assimilated per unit time. Actual measurements show that the growth rate and photon cost predictions are often, but not invariably, borne out; while data on the water cost of growth almost invariably contradict the prediction by showing a lower water cost from nitrate‐supplied than ammonium‐supplied plants. Few data seem to be available that test the predictions as to metal costs of growth; some of the predictions are borne out. These possible or realised advantages to the photolithotroph of using ammonium must be considered in the context of the relative availability of the two sources of combined nitrogen. In the oceans nitrification of ammonium produced in mineralization does not compete well with photolithotrophic assimilation of ammonium in the euphotic zone, so ammonium is the major combined nitrogen source for ‘recycled’ primary production, while ‘new’ production largely uses nitrate produced in deep, dark water. When both nitrogen sources are available to phytoplankton organisms ammonium is almost invariably preferred, with complete suppression of nitrate use with as little as 1–2 mmol m−3ammonium. In terrestrial habitats the nitrification of ammonium produced in mineralization is not photoinhibited (as can occur in the surface water of the ocean) but is subject to inhibition by anoxia, low pH and (possibly) plant‐produced defence compounds. However, the lower diffusion coefficient for ammonium than for nitrate in soils means that nitrogen‐limited plant growth as a given rate needs a higher mean dissolved ammonium concentration in the soil than is the case for nitrate when the soil contains only one of these nitrogen sources and root distribution and morphology are unaffected by the nitrogen source. With equal mean ammonium and nitrate concentrations, a nitrogen‐limited plant supplied solely with ammonium would need a more extensive root/root hair/mycorrhiza system to attain the same nitrogen uptake rate on a per plant basis as would a nitrate‐supplied plant, with consequences for resource allocation by, and growth rate of, the ammonium‐grown plant. In addition to the larger mean area‐based ammonium assimilation rate by photolithotrophs in the oceans, consideration of the interactions among ammonium diffusion coefficient, ammonium diffusion distance, organism surface area per unit biomass and the organism maximum specific growth rate in the ocean relative to soils can plausibly account for the lower mean ammonium concentrations in the ocean than in soils.
Oxygen controls the development of Frankia vesicles in continuous culture
Authors: HARRIS S. L. , SILVESTER W. B.
Published: April 2006

summary

Daily addition of sterile media at a dilution rate of 0.100–0.125 d−1 allowed Frankia to be maintained in continuous, derepressed (N2‐fixing) culture for periods of more than 30 d. Continuous cultures yielded Frankia populations with stable levels of growth and nitrogenase activity as well as constant vesicle morphology. These were then used to investigate the influence of oxygen on vesicle development.

Timing of vesicle induction is independent of po2 although thickening of the vesicle envelope and stalk, a ‘normal’ developmental process, is specifically controlled by oxygen. At higher po2 levels vesicles are thicker‐walled and therefore offer greater resistance to oxygen diffusion. Oxygen also influences induction of nitrogenase. Greater delay in the onset of acetylene reduction activity at highpo2 is apparently due to the time taken for vesicles to reach a critical minimum wall thickness. Recovery of nitrogenase underwent a similar time lag when Frankia cultures were exposed to a sudden increase in po2.
Accumulation and excretion of sodium, potassium and chloride from leaves of two accessions of Diplachne fusca (L.) Beauv.
Authors: WARWICK N. W. M. , HALLORAN G. M.
Published: April 2006

summary

When two accessions of brown beetle grass [Diplachne fusca (L.) Beauv. syn. Leptochloa fusca (L.) Kunth], differing in tolerance to salinity, were exposed to NaCl over 15 d, Na concentrations were constant in the shoot. However, there were differences in shoot Na concentration between the two accessions which were manifest after 5 d exposure to 100 mol m−3 NaCl. Na and Cl concentrations in the shoot were found to be controlled within a narrow range and did not increase any further after 5 d exposure to NaCl. Leaves of differing maturity and growth rate of both accessions did not differ in their Na concentrations. Na concentrations remained stable in leaves of differing ages after the first 6 d of exposure to NaCl whereas K declined with time, possibly due to remobilization to younger leaves. Avoidance of high concentrations of Na in younger leaves by its sequestration in older tissue does not appear to be a salt‐tolerance mechanism in D. fusca. The primary mechanism of exclusion of Na and Cl from the plant is in the root, with secondary control of leaf Na and Cl concentration by excretion of excess Na and Cl through leaf salt‐glands. Total Na uptake for the relatively salt‐tolerant accession of D. fusca. M1, was similar to that for the relatively intolerant accession F3, although M1 had a lower Na concentration in its leaves than F3 after 5d exposure to NaCl. This suggests a possible mechanism for the higher tolerance of M1 to NaCl. Leaf Na concentration was significantly higher in F3 than M1, but M1 had significantly higher Na excretion rates than F3. The leaf salt‐glands of both accessions of D. fusca were found to be capable of excreting approximately 50–80 % of the Na entering the leaf.
Selection of donors for salt‐tolerance in tomato using physiological traits
Authors: CUARTERO J. , YEO A. R. , FLOWERS T. J.
Published: April 2006

summary

Attempts to enhance the salt‐tolerance of the cultivated tomato using the tolerance of related wild species of Lycopersicon Mill, have been unsuccessful commercially. An alternative approach is to attempt to accumulate physiological characters that contribute to tolerance within a genotype. We have investigated the relationships between tolerance and certain physiological characteristics in accessions of L. esculentum Mill., L. cheesmanii (Hook) C. H. Mull., L. pennellii (Correll) D'Arcy, L. peruvianum (L.) Mill, and L. pimpinellifolium Mill, with this aim in view.

At a salinity equivalent to 40% of that in an artificial seawater, the growth of young plants was ranked both in absolute terms (fresh weight, dry weight or the growth in area of a leaf that developed during the salt treatment) and relative to growth in a salinity 2% of that of seawater. In absolute terms, two cultivars of L. esculentum (‘Moneymaker’ and ‘Edkawy’) performed about as well as L. pimpinellifolium and better than L. pennellii and L. cheesmanii: L. peruvianum showed the poorest tolerance. In relative terms, L. pimpinellifolium remained the most tolerant of the species, and L. peruvianum the most sensitive. L. cheesmanii was little more tolerant than L. peruvianum.

The five species differed in their succulence and the Na: K ratio in leaves that developed during the treatment with salinity. Succulence was higher at low salinity in L. pennellii and L. cheesmanii than in the other species, but increased less on salinization. L. pimpinellifolium showed the greatest increase in succulence on salinization, a consequence of its low water content in 2% seawater. Sodium concentrations increased dramatically in all five species on salinization: L. pimpinellifolium had the highest and L. esculentum the lowest values. L. peruvianum was notable for maintaining a Na: K ratio of less than 3 throughout the period of the experiment.
Effects of salinity on root growth and death dynamics of tomato, Lycopersicon esculentum Mill.
Authors: SNAPP S. S. , Shennan C.
Published: April 2006

summary

Numerous hydroponic studies have shown that root growth of tomato (Lycopersicon esculentum Mill.) is little affected by salinity. In contrast, data from soil‐grown plants show salinity may induce reductions of up to 50% in root length density. In this study, root growth of two tomato cultivars exposed to salinity (NaCl and CaCl2, 4:1) was examined in the field, in large soil‐filled containers, and in hydroponics. The two cultivars, UC82B and CX8303, differed in susceptibility to a common root rot organism (Phytophthora parasitica Dast.), and were hypothesized to differ in root growth response to environmental stress. In agreement with the literature, root weight of young, hydroponically‐grown plants (as determined by multiple, destructive harvests) was unaffected by salinity in both cultivars. In contrast, root length density of cv. UC82B was reduced 40% by salinity in the field, whereas root length density of root rot‐tolerant cv. CX8303 was unaffected. Similar responses to salinity were observed in the containers, with root counts from horizontal minirhizotron tubes reduced in cv. UC82B, but not in cv. CX8303. Observations from windows in the sides of the containers showed that reduction in net root growth in cv. UC82B was primarily due to an increased rate of root death at high salinity. Root turnover remained low in cv. CX8303 under both low and high salinity. Differential effects of salinity on root growth of the two cultivars in containers were not evident until about 60 d after transplanting. This suggests that the discrepancy between salinity responses of hydroponic and soil‐grown plants was primarily due to differences in phenology. Enhanced rates of root death during the reproductive growth stage may represent an important, previously undocumented carbon cost to some genotypes exposed to salinity.
Field studies on Norway spruce trees at high altitudes
Authors: POLLE ANDREA , MÖSSNANG MICHAEL , VON SCHÖNBORN ALEXANDER , SLADKOVIC RUDOLF , RENNENBERG HEINZ
Published: April 2006

summary

The present study was performed on mature Norway spruce trees (Picea abies L.) with needle losses in the range of 25–35 %. The trees were growing at three altitudes (870, 1270, and 1700 m above sea level) in a mountain forest in the Calcareous Alps of Bavaria. The objectives were to assess the role of climate and pollution in addition to nutrient disorders for damage to spruce trees. During the growing season the average temperature was up to 5 °C lower and the average ozone concentration was about twofold higher at the high altitude in comparison to the low altitude (13 and 18 °C, and 60 and 35 nl I−1 ozone, respectively); the average NOx and SO2 concentrations did not exceed 5 nl I−1. Foliar analysis of pollutants did not indicate critical levels of Pb, Cd, Cl, F and S. Biometrical parameters, foliar element composition, pigment and protein content of the needles were determined during four seasons. Average dry:fresh weight ratios, specific needle weights, projected needle areas, soluble protein and carotenoid contents were similar within the 20 % range for needles from all three altitudes. Foliar analysis of nutrients indicated a low nutrient status especially for nitrogen, and showed a phosphorus deficiency in needles from the three sites. The chlorophyll content of the needles decreased with increasing altitude. Since nutrient imbalances were greatest in needles from the lowest site, it was concluded that the greater damage to spruce trees and lower chlorophyll content of the needles at altitudes > 1000 m above sea level were not caused by nutrient disorders.
The late Quaternary vegetational history of northwest Greece
Authors: WILLIS K.J.
Published: April 2006

summary

Rezina marsh, a small basin at a height of 1800 m, in the Pindus mountain range, is both the smallest and highest site yet to be studied in Greece. Techniques of pollen and plant macrofossil analysis, sediment chemistry, mineral magnetics and radiocarbon dating have been employed to reconstruct both vegetational and sedimentary history of the basin. The sequence extending back to c. 10000 bp, provides the first evidence for the possible location of full glacial refugia for temperate tree taxa in Greece. In the early postglacial a dense mixed woodland containing at least sixteen different tree taxa was present around the Rezina basin. This woodland persisted throughout the early postglacial although dominance of tree types in the woodlands changed several times. These changes are thought to be closely related to climatic changes during the early postglacial. At c. 6000 bp both the density and diversity of the woodland became greatly reduced. Although there was some recovery of the woodland at c. 5000 BP, anthropogenic intervention at c. 4000 BP led to total destruction of this montane forest and the development of open grassland similar to the present day situation.
The response of spring wheat (Triticum aestivum L.) to ozone at higher elevations
Authors: GRANDJEAN GRIMM A. , FUHRER J.
Published: April 2006

summary

The flux of O3 was determined in open‐top chambers (OTC) used to investigate its effect on spring wheat (Triticum aestivum L., cv. Albis) in 1989 and 1990. The experimental site was located at 900 m above sea level at Zimmerwald, near Bern (Switzerland). The aims were to evaluate the use of OTCs for O3 flux measurements under field conditions, to assess the role of stomata in controlling the O3 fluxes, and to establish a quantitative relationship between radiation‐weighted O3 concentrations and O3 flux. Measurements were carried out from full expansion of flag leaves until the onset of senescence. Ozone flux was determined by mass balance using the concentrations of O3 measured at the inlet and outlet of the OTC. The CO2 exchange rate was corrected for soil‐borne COO and used as a reference. Measurements of temperature, photosynthetically active radiation (PAR), saturated water vapour pressure deficit (SVPD), and boundary layer conductance were used to describe the microclimate inside OTCs.

In the warmer microclimate in 1989, the plant canopy was characterized by a smaller leaf area index (LAI) than in 1990, while the fluxes of O3 and CO2 during daytime were generally larger in 1989. The diurnal patterns of fluxes of O2 and CO2, in OTCs supplied with unfiltered air were similar. It is estimated that O3 absorption via the stomata contributed 50–70% of its total flux. Identical relationships between leaf conductance for O2, measured by porometry and leaf conductance calculated from O3 flux were found in both years, but measured leaf conductance during daytime was generally smaller in 1990 than in 1989. The results indicate that stomatal conductance largely controlled O3 flux, and that the canopy structure has an influence on the overall conductance of the canopy.

Different linear functions were obtained for the relationship between radiation‐weighted O3 concentration and O3 flux, using data from OTCs supplied with either charcoal‐filtered air, unfiltered air or unfiltered air enriched with O. (two levels). These relationships form the basis for the calculation of mean O3 fluxes which can be used as an exposure index in the exposure‐response analysis.
The response of spring wheat (Triticum aestivum L.) to ozone at higher elevations
Authors: FUHRER J. , GRIMM A. GRANDJEAN , TSCHANNEN W. , SHARIAT‐MADARI H.
Published: April 2006

summary

The effect of ozone on the yield, yield components and grain composition of spring wheat (Triticum aestivum L., cv. Albis) was investigated in 1989 and 1990 at 900 m above sea level. Plants were grown from the three‐leaf stage until harvest in open‐top chambers ventilated with charcoal‐filtered air (CF), unfiltered air (UF) or unfiltered air with one of two levels of O3., added when global radiation exceeded 400 J m−2s−1(O3– 1, O3– 2). Ambient plots (AA) without chambers were used as a reference. Mean 7‐h d−1(09.00–16.00 h) O3 concentrations in the CF, O3– 1 and O3– 2 treatment, respectively, was approximately 0.5, 1.4 and 1.8 times the concentration in the UF treatment, which was 70μgm−3in 1989 and 76μg m−3in 1990. The OTC environment was characterized by a warmer, more humid microclimate and reduced soil moisture, compared with the open field. In 1989, this effect of the chambers was more pronounced than in 1990. When compared with A A plots, chamber enclosure significantly reduced grain and straw yield in 1989, while in 1990 no difference was observed. Grain yield decreased with increasing seasonal mean O3 concentration as a result of reductions in the weight of individual grains and in the number of grains per head. A small decrease in the ratio between grain weight and total above‐ground biomass (harvest index) indicated a shift in biomass allocation. With increasing O3, small or no changes were observed in protein, starch and K concentrations, and in protein quality (Zeleny value) of the grain. Relationships between different measures of O3 exposure and relative grain yield were constructed with a quadratic model. With mean concentrations (7‐h d−1mean or radiation‐weighted mean) or with a cumulative index (SUMO6 = sum of concentrations above 60 μl1−1) to describe exposure, the response of grain yield to increasing O3 was smaller in 1990 than in 1989. Nearly identical exposure‐response functions were obtained for both seasons, with the mean O3 flux used to estimate the absorbed dose of O3. Quadratic exposure‐response functions suggest that ambient levels of O3, reduced grain yield by 9‐5% and 11.6% in 1989 and 1990, respectively. Using Weibull exposure‐response functions, a comparison with results from an earlier study at 485 m above sea level indicates reduced sensitivity at the higher elevation.
Effects of nitrogen source on growth, nutrition, photosynthetic rate and nitrogen metabolism of mycorrhizal and phosphorus‐fertilized plants of Lactuca sativa L.
Authors: AZCÓN R. , GOMEZ M. , TOBAR R.
Published: April 2006

summary

Plants of Lactuca sativa L. cv. Romana were inoculated with two vesicular‐arbuscular (VA) mycorrhizal fungi, Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe and Glomus fasciculatum (Thaxter sensu Gerd.) Gerd. & Trappe, or provided with phosphorus. These three treatments plus a control were supplemented with 3.0 mM nitrogen as nitrate or ammonium in 1 of 5 NO3−/NH4+ ratios. Leaf and root weights, N, P, K, Ca and Mg absorption, as well as the percentage of root length colonized, were evaluated. Physiological parameters such as leaf area, photosynthetic rate, glutamine synthetase (EC 6.3.1.2) and nitrate reductase (EC 1.6.6.1) activity and leaf proline accumulation were also determined. Mycorrhizal lettuce and P‐fertilized plants derived significantly more benefit from N fertilization regardless of the N‐source than did controls. Ammonium was a better N‐source for non‐mycorrhizal plants and nitrate for mycorrhizal plants. P‐fertilized lettuce reached maximum growth when N was supplied as 50% NO3−/ 50% NH4+ so that mycorrhizal status particularly affected the plant response to the form of N provided. Growth of mycorrhizal plants was comparable to non‐mycorrhizal P‐fertilized plants when N was provided as 100% NH4+ or 25 % NO3−/75 % NH4+. When N applications were as 50% NO3−7 50% NH4+ or 75% NO3−/25% NH4+, growth of P‐fertilized plants was greater than mycorrhizal ones. Lettuce colonized by G. mosseae grew fastest when fed nitrate only. Separation of NO3− and NH4+assimilation into shoot and root compartments may account for the differential effects of such ions into symbiotic and non‐symbiotic plants. Uptake or metabolism of nitrogenous forms was particularly affected in G. mosseae‐colonized plants, independent of P nutrition. P fertilization increased activities of nitrate reductase (NR) by 29 % and glutamine synthetase (GS) by 24% compared with activities in control plants. In the case of G. fasciculatum‐colonized plants, NR and GS were increased 54% and 117 %, respectively, over control activities. In general, concentration of minerals, except Ca, were increased in mycorrhizal and P‐fertilized plants compared with controls. Assimilation of CO2 and accumulation of proline were increased in G. fasciculatum‐colonized lettuce under all N regimes.
Genecological studies of groundsel (Senecio vulgaris L.)
Authors: BRIGGS D. , BLOCK M.
Published: April 2006

summary

In a well‐weeded site, selection is likely to favour quick‐maturing variants of annual weeds. Variation in rate of development ‐ from sowing, with synchronous germination, to first flowering and fruiting‐was studied in experiments with Senecio vulgaris L. from the Botanic Garden of Cambridge University, England. Experiments revealed that the number of nodes on the main axis could not be used a ‘genetic marker’ for rate of development.

From a large random sample of seed‐parents, progenies were raised from open‐pollinated capitula. Family lines differed significantly in rate of development, with markedly different degrees of variation within families. Twenty family lines, representing the extremes of variation, were chosen for further study. In cultivated selfed derivatives, the majority of the seed‐parents appeared to be behaving as inbred lines for rate of development. Evidence of genetic segregation was detected in only two out of 20 cases. Using the radiate locus as a marker, there was also evidence for a very small amount of outcrossing, with greater values for radiate than non‐radiate seed‐parents. In an experiment in which six inbred lines, derived from the original seed‐parents, were grown out‐of‐doors on fertile and infertile soils and on fertile soil in a glasshouse, there was considerable developmental flexibility in a number of heritable traits including rate of development.

Although the methods of weed control in the Botanic Garden would seem to exert a powerful directional selective force favouring only the quickest‐maturing variants of groundsel, a certain amount of variation was nevertheless detected. Many factors are likely to be important in the maintenance of population variation in rate of development in groundsels in the Garden. Several statistically significant lines x soils and lines x places of cultivation were discovered. Thus, the lines did not all behave in the same way in the inside and outside treatments and the rank order of date of maturity of the different lines was not the same in the two soils. This suggests that, in the Garden proper, relative fitness, in the face of weeding pressures, is not fixed but may vary seasonally and in soils of different fertility. This behaviour, in a species which is able to reproduce at all seasons of the year, could be a major factor in the maintenance of population variation. Other contributory factors are of great importance, namely, spatial and seasonal variation in the intensity of weeding, developmental flexibility and the effects of predators, pests and diseases.
Genecological studies of groundsel (Senecio vulgar is L.)
Authors: BRIGGS D. , BLOCK M. , FULTON E. , VINSON S.
Published: April 2006

summary

Plants of groundsel (Senecio vulgaris L.) in the very well‐kept University Botanic Garden, Cambridge are quicker in their rate of development than those from sites subject to less regular or no weeding pressure. However, the directional selection pressure favouring precocity has not resulted in population uniformity. In order to generate hypotheses about the development and maintenance of population variation in this annual weed, we have studied the origin and patterns of migration of two genetic variants. Also, we have investigated the history of the oldest established flowerbeds in the Garden, with particular reference to continuity of use and garden practices.

The Systematic Beds have been in existence for more than 140 years and, despite periods of difficulty, have been subject to regular and frequent weeding.

Evidence suggests that the radiate variant of groundsel was most likely introduced into the Garden in the late 1890s from plants collected at Bandon Station, County Cork, Ireland. Subsequently, this plant ‐ var. hibernicus Syme ‐ spread to many parts of the Garden but it did not establish itself on the Systematic Beds until 1985. Using the radiate capitulum locus as a marker, our results reveal a consistently very low level of outcrossing in non‐radiate plants and a more variable and seasonally higher frequency in radiate plants. In 1987, simazine resistant plants were detected in the Systematic Beds, an area which has never been treated with triazine herbicides. It seems likely that these resistant plants originated from a population of resistant plants on treated ground just outside the western border of the Garden.

Two models have been devised to explain our findings. The first model postulates that weeding has been too efficient on the Systematic Beds to permit the slower developing radiate plant to establish itself there. A second model, which appears to fit the facts more closely than the first, postulates that the migration of the radiate variant has been restricted by gene flow.
Ecological segregation between closely related species in the flooded forests of the upper Rhine plain
Authors: SCHNITZLER ANNIK , CARBIENER ROLAND , TRÉMOLIÈRES MICHÈLE
Published: April 2006

summary

In the large European river floodplains, closely related species segregate between habitats within numerous forest communities whose structure and dynamics are shaped by the river and its tributaries. Factors of segregation are mainly geochemistry (lime content and texture), water stress and fluvial dynamics. When sympatric, the closely related species coexist by niche differentiation (life‐form, place in the successional stages, phenology and abundance).

We have made a comparative study of the niches of 70 species belonging to 24 genera in the alluvial forest communities of the upper Rhine valley (France), using a descriptive and qualitative approach. Results were compared with the literature on European biogeography. Particular attention was paid to seven woody genera (Populus, Salix, Ulmus, AInus, Acer, Crataegus and Primus) and to the behaviour of hybrids along the environmental gradients of the study area.
Palynological variation in primula L. subgenus Sphondylia (Duby) Rupr., and the relationship of this group to Dionysia Fenzl.
Authors: WADI HUSSEN AL , RICHARDS A. J.
Published: April 2006

summary

Primula subgenus Sphondylia is composed of eight localized and probably relictual taxa distributed from Ethiopia to the west Himalaya. It is considered to occupy an ancestral position in the genus, and to demonstrate stages in the evolution of dimorphic heterostyly. Previous authors have suggested that the heterostylous genus Dionysia evolved from forerunners of this group.

It has previously been reported that, in five of the species, only prolate 3‐colporoidate pollen is found, dimorphic in size for heterostylous species. However, the pollen of the heterostylous species P. edelbergii, P. gauheana and P. darisii is dimorphic for shape and colpus number, as well as for size. Thus, our study reports for the first time, a major morphological pollen dimorphism, and 1‐ and 2‐colpor(oid)ate pollen in the Primulaceae.

We found that three distinct trends in the development of pollen dimorphism can be traced in this group, two of which appear to have no major phyletic implication. However, it is possible that P. floribunda represents phyletic links between subgenus Sphondylia and later heterostylous developments in Primula.

Pollen in Dionysia is said to be weakly dimorphic for shape and colpus number, and our findings agree with this. We suggest that Dionysia is not closely related to Primula subgenus Sphondylia and that strong superficial resemblances between certain taxa in these groups may have resulted from parallel evolution.
Isolation and preliminary characterization of 5‐fluoroindole‐resistant and IAA‐overproducer mutants of the ectomycorrhizal fungus Hebeloma cylindrosporum Romagnesi
Authors: DURAND N. , DEBAUD J. C. , CASSELTON L. A. , GAY G.
Published: April 2006

summary

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

summary

Short‐term uptake of 137Cs by heather (Calluna vulgaris L.) was measured using radiolabelled liquid media and plants grown from shoot cuttings. Uptake by mycorrhizal plants was compared with uptake by non‐mycorrhizal plants, and the effects of different external Cs and K concentrations were determined.

At each time point during the 3 h experimental period the content (and hence also the apparent influx) of the mycorrhizal plants in each treatment was found to be lower than that of the non‐mycorrhizal plants.

An increase of 100‐fold in the total external Cs concentration (from 5 to 500μM) gave between a 35‐fold and 96‐fold increase in initial influx of Cs. A similar change in external K concentration, however, had little effect on Cs influx. Root‐shoot transfer of Cs over the 3 h uptake period was slight; in most cases more than 90% of the radiocaesium remained in the root. The final shoot:root Cs ratio was higher in mycorrhizal than in non‐mycorrhizal plants, suggesting that in mycorrhizal plants, despite their lower overall accumulation during the first 3 h, a higher proportion of the Cs taken up is translocated to the shoot.
Occurrence of nodulation in legume species in the Amazon region of Brazil
Authors: DE SOUZA MOREIRA FATIMA MARIA , DA SILVA MARLENE FREITAS , DE SÉRGIO MIANA FARIA
Published: April 2006

summary

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

summary

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

summary

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

summary

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

summary

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