bluuebunny/crossref_metadata_2025_split huggingface dataset:
Which steps are essential for the formation of functional legume nodules?
Authors: SPRENT J. I. 
Published: April 2006

summaryNodulation is reviewed in terms of the phenotypes proposed by Vincent (1980).Individual legumes may be infectible by one or more of the three bacterial genera (collectively known as rhizobia)Rhizobium, Bradyrhizobium, orAzorhizobium.The type of infection process by which rhizobia gain entry is largely governed by the host genotype. In addition to the widely studied root‐hair pathway, infections may be associated with lateral root emergence or occur between root epidermal cells. The exact chemical and physical nature of the root hair/epidermal cell wall is likely to be a critical factor in determining whether infections can proceed. In addition to differing with species, wall composition may be influenced by soil chemical (e.g. Ca2+) and biotic factors (e.g. bacteria).Rhizobial features essential for infection include particular surface polysaccharides and the induction of nodulation genes by plant root exudates. Neither of these is likely to be a major barrier to the extension of nodulation to new hosts.Dissemination of rhizobia within developing nodules may be intercellular, via infection threads or by division of a small number of infected cells. All functional symbioses eventually have ‘intracellular’ bacteria, in the sense that rhizobia are geographically located within the boundary of the host cell walls. However, they remain extracellular in the sense that they are always confined by a membrane which is largely of host cell origin. In some genera they are also surrounded by infection thread walls, probably modified forms of ‘invasive’ infection thread walls, which allow differentiation of rhizobia into the nitrogen‐fixing form. Thus, natural, functional, symbioses may (a) never involve a stage in which bacteria are confined within tubular infection threads or (b) never release bacteria from infection threads. These features are determined by host genotype.The one feature of legume nodules so far found never to vary is the stem‐like character of a peripheral vascular system. This contrasts with the central vascular system of actinorhizas and the rhizobial‐induced nodules on the Ulmaceous genusParasponia.Although of great intrinsic interest, this character is unlikely to present an insurmountable barrier to the extension of nodulation to new species. Other features, such as the ability to produce haemoglobin are now known to the in the genetic makeup of many higher plants.The discovery of the wide range of nodule structures occurring in nature, together with work on mutant rhizobia which may bypass critical stages in the nodulation process, suggest various ways in which the extension of nodulation to non‐nodulated legumes and to other (initially at least, dicotyledonous) plants may be engineered.CONTENTSSummary129I.Introduction130II.The symbionts130III.Stages in nodulation132IV.Stems and nodules143V.Prospects for finding/making new symbioses144VI.Conclusions145Acknowledgements147References147
Nitrogen uptake and growth of wheat during O2 deficiency in root media containing NO3− only, or NO3− plus NH4+
Authors: BUWALDA F. , GREENWAY H. 
Published: April 2006

summaryThe effects of hypoxia at 0.003 mol O2 m−3 on growth and nitrogen uptake of wheat seedlings (Triticum aestivum L. ev. Gamenya) was compared between plants growing in nutrient solutions containing either NO3− only, or NO3− plus NH4+.Hypoxia reduced the uptake of N by the plants, however both at 0.28–0.31 mol O2 m−3 (aerated solutions) and 0.003 mol O2 m−3, rates of N uptake from solutions containing NO3− plus NH4+ were 34% higher than from solutions containing NO3− only. In aerated solutions, growth was faster when NO3− plus NH4+ was supplied. By contrast, at 0.003 mol O2 m−3 both N treatments had the same low growth rate (expressed on a dry weight basis) despite considerably higher internal N concentrations in the plants supplied with NO3− plus NH4+. It is concluded that N nutrition did not limit growth at 0.003 mol O2 m−3 in either N treatment. Other possible causes of the growth reduction and differences in uptake characteristics between NO3− and NH4+ are discussed.
Effects of cation leaching on mineral cycling and transpiration: investigations with beech seedlings, Fagus sylvatica L.
Authors: LEONARDI SILVIO , FLÜCKIGER WALTER 
Published: April 2006

summaryBeech seedlings (Fagus sylvatica L.) were sprayed with acidic or ammonium‐rich solutions of different concentrations, 10−3 or 10−5 mol l−1 H+ or NH4+. Whilst the leaching of Ca and Mg was increased by the more acid treatment, the K leaching was decreased. On the other hand, the concentrated NH4+ mist led to a substantial increase in the leaching of K. As a consequence of the greater uptake of cations due to their leaching, more protons were released to the nutrient solution and into the rhizosphere of potted plants. Increased transpiration was observed following the application of acidic mist to the plants in nutrient solution but decreased stomatal diffusive resistance of potted plants was detected only at night. Acid mist caused changes in stomatal behaviour that were responsible for a rapid and greater water loss of detached leaves.
Effects of drought and CO2 enrichment on competition between two old‐field perennials
Authors: MARKS SUSAN , STRAIN BOYD R. 
Published: April 2006

summaryWe studied the effects of drought stress and CO2 enrichment on the competition between Aster pilosus Willd. (aster, C3) and Andropogon virginicus L. (broomsedge, C4) under two CO2 concentrations (350 and 650 μl l−1 CO2) and two water treatments (well‐watered and water‐limited). Although broomsedge is the more drought‐tolerant species, this did not increase its competitive ability against aster under drought conditions. With CO2 enrichment, aster was a stronger competitor than broomsedge and comprised 75% of above‐ground pot biomass in both water treatments. CO2 enrichment also increased aster survival when competing with broomsedge under extreme drought conditions. Although drought stress and CO2 enrichment interacted to affect the two species in different ways, there was no interaction of drought stress and competition; aster was a stronger competitor than broomsedge under CO2 enrichment in both well‐watered and water‐limited conditions. With future increases in the atmospheric CO2 concentration, aster may delay broomsedge dominance in old‐field communities.
Effects of low concentrations of ozone on the fine structure of radish leaves
Authors: MIYAKE H. , MATSUMURA H. , FUJINUMA Y. , TOTSUKA T. 
Published: April 2006

summaryRadish (Raphanus sativus L.) plants were fumigated with 0.1 or 0.05 μl l−l O3 for 8 or 24 h a day for 6 to 18 d and the leaf tissues examined by light and electron microscopy. Ultrastructural damage was apparent in the leaves fumigated with as low as 0.05 μl l−1 for 8 h a day for 6 d. Ozone induced an increase in both the number and size of the plastoglobules but a decrease in chloroplast dimensions. These changes in the chloroplasts developed further even after O3 fumigation had been discontinued. The plastoglobules were electron dense in the early stages of exposure to O3 but subsequently became electron translucent. Finally large plastoglobules were extruded into the vacuole, a phenomenon which may partly account for the reduction in chloroplast size. Ozone also caused disruption of the tonoplast and this was followed by collapse of the cells. Low concentrations of O3 appear to accelerate senescence of the chloroplasts.
Intercellular infection in the meristematic region of ‘Piceirhiza gelatinosa’ mycorrhizas
Authors: HAUG I. 
Published: April 2006

summary ‘Piceirhiza gelatinosa’ mycorrhizas from Schluchsee, but not from two other sites in the Black Forest, showed intercellular hyphae in the apical region of unbranched and finger‐like branched roots. The hyphae of the fungus were able to penetrate between the meristematic and immature cortical cells. In outer regions of the root, hyphae were arranged in layers one to two cells deep but towards the middle, single hyphae were most commonly encountered. The method of penetration and a possible relationship with abnormal growth are discussed.
Shoot: root interrelationships in leeks infected with the rust, Puccinia allii Rud.: Growth and nutrient relations
Authors: ROBERTS A. M. , WALTERS D. R. 
Published: April 2006

summaryGrowth and nutrient relations were examined in healthy leeks and in leeks inoculated with the rust, Puccinia allii, to give three different intensities of infection (i.e. 10, 20 and 30%). Experiments were conducted over an 8‐week experimental period, although only data from 5 weeks after inoculation are shown. The dry weights of rust‐infected plants were substantially reduced compared with controls over the entire experimental period. Although shoot: root (S: R) ratios were increased in rusted plants 2 weeks after inoculation, the trend was reversed thereafter and for the remainder of the experiment S:R ratio was reduced in comparison with healthy controls.The contents of nitrogen, phosphate, potassium and calcium were reduced in rusted plants compared to controls. On the other hand, with few exceptions, the concentrations and specific absorption rates of these minerals increased in rusted plants compared with healthy controls. The ability of infected plants to maintain a functional S:R equilibrium with respect to nutrient uptake was examined using an analysis based on comparing changes in incremental plant dry weight with incremental nutrient weight. Calculated values of functional equilibrium for control and rusted plants showed that rust infection altered functional equilibrium with respect to uptake of the four nutrients. The possible mechanisms underlying these changes in physiology and the analysis of such changes are discussed.
Histochemical localization of desoxyhemigossypol, a phytoalexin in Verticillium dahliae‐infected cotton stems
Authors: MACE M. E. , STIPANOVIC R. D. , BELL A. A. 
Published: April 2006

summaryThe terpenoid phytoalexin desoxyhemigossypol (dHG) was detected histochemically in the stem xyiem of Verticillium dahliae Kleb‐infected, wilt‐resistant Seabrook Sea Island cotton as a green product on V. dahliae mycelium within vessel lumens and in specialized, often solitary, paravascular parenchyma cells. The SbCl3‐HClO4 histochemical reagent yielded a green‐coloured Sb‐dHG product specific for dHG when used as a spray on chromatograms of extracts from Verticillium‐infected stele tissue. Both dHG and related terpenoid aldehyde derivatives occurred together in parenchyma cells and on V. dahliae mycelium. The presence of dHG on Verticillium mycelium reinforces previous studies that identified dHG as the most toxic and possibly most important phytoalexin in the resistance of cotton to V. dahliae.
Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela
Authors: LÜTTGE U. , MEDINA E. , CRAM W. J. , LEE H. S. J. , POPP M. , SMITH J. A. C. 
Published: April 2006

summaryIn an ecophysiological field investigation of plant communities of vegetation islands of an alluvial plain in northern Venezuela the members of the Cactaceae, Pereskia guamacho, and a columnar ceroid cactus, Subpilosocereus ottonis, were studied. The alluvial plain was flooded by fresh water in the rainy season in November/December 1985 and was dry and saline in the dry season in March/April 1986. The highly succulent leaves of P. guamacho were shed in the dry season. They performed C3 photosynthesis in the wet season and did not show signs of considerable salt accumulation. P. guamacho avoids stress due to drought and salinity by leaf‐shedding. The columnar stem succulent ceroids are salt‐excluding plants with crassulacean acid metabolism (CAM). Rapid die back and regeneration of absorptive roots, water parenchyma and CAM, with the possibility of nocturnal stomatal closure and CO2 recycling, are traits of adaptive value under fluctuating conditions between rainy and dry seasons on the alluvial plain.
Ecophysiology of xerophytic and halophytic vegetation of a coastal alluvial plain in northern Venezuela
Authors: LÜTTGE U. , POPP M. , MEDINA E. , CRAM W. J. , DIAZ M. , GRIFFITHS H. , LEE H. S. J. , SCHÄFER C. , SMITH J. A. C. , STIMMEL K.‐H. 
Published: April 2006

summaryThe perennial halophytes, Batis maritima L., Sesuvium portulacastrum L., and Portulaca rubricaulis H.B.K. which inhabit the extreme environment on parts of the salt plain and at the edges of the vegetation islands of Ciénega el Ostional were examined to determine their strategies for growth and survival in the rainy and dry seasons.All of the three species are leaf‐succulents. High leaf‐sap osmotic pressures, xylem tensions and Na+ and Cl− levels indicated that S. portulacastrum and B. maritima are salt‐accumulating halophytes. Succulence, leaf‐sap osmolalities and Na+ and Cl− levels increased in the dry season in B. maritima by a factor of 1.5‐2.0 and in S. Portulacastrum by a factor of 1.9–2.7. B. maritima also accumulated sulphate with a two‐fold increase of concentrations in the dry season. In S. portulacastrum Na+ accumulation much exceeded Cl− accumulation and oxalate synthesis was found to serve charge balance. In this species the compatible solutes, proline and pinitol, were clearly detectable in both seasons; their levels increased by a factor of about 6 in the dry season.Exchange of water vapour and CO2 was measured with a portable steady‐state porometer. Photosynthesis in B. maritima showed little response to the transition from the rainy to the dry season while S. portulacastrum was severely impaired in the dry season, showing pronounced midday depressions of gas exchange and about 40% inhibition of light‐saturated rates of CO2 uptake. P. rubricaulis shed its leaves in the dry season.According to carbon isotope ratios (δ13C), B. maritima (δ13C =−26.4‰) and S. portulacastrum (δ13C =−25.8 ‰) are C3 plants while P. rubricaulis (δ13C =−12.3‰) performed C4 photosynthesis.
Iron plaque on roots of Aster tripolium L.: interaction with zinc uptake
Authors: OTTE M. L. , ROZEMA J. , KOSTER L. , HAARSMA M. S. , BROEKMAN R. A. 
Published: April 2006

summaryThe iron plaque on roots of Aster tripolium L. growing in waterlogged salt marsh soil adsorbed appreciable amounts of Zn and Cu, with maximum Zn/Fe and Cu/Fe ratios of 0.1 When concentrations of Zn or Cu adsorbed in the iron plaque are expressed as mg metal kg−1 FeOOH (assuming that iron plaque consists mainly of FeOOH), the Zn and Cu concentrations of the iron plaque was up to 680 and up to 2000 times higher than in the surrounding sediment, respectively. The Zn concentration in red roots (with iron plaque) was higher than in white roots (without iron plaque). Zn concentrations in field sampled roots were correlated with the amount of Zn on the roots and the Zn concentration in the soil, whereas Cu concentrations in the roots were only significantly correlated to the Cu concentration in the soil. In vitro experiments showed that red roots take up more Zn than white roots. Measurement of Zn uptake by excised roots showed that the uptake of Zn into the xylem fluid was significantly higher in roots with 500–2000 nmol Fe cm−2 on the root surface compared to roots with less than 500 or more than 2000 nmol Fe cm−2 on the root surface. The results indicate that iron plaque enhances uptake of Zn by the roots but may act as a barrier when large amounts of Fe are deposited on the root surface. The role of the iron plaque on roots of salt marsh plants growing in soil contaminated with heavy metals is discussed.
Sugar unloading in roots of Ricinus communis L.
Authors: CHAPLEO S. , HALL J. L. 
Published: April 2006

summaryThe accumulation of exogenous D‐fructose, D‐glucose and sucrose into root tips of Ricinus communis was studied. Accumulation of sucrose is biphasic with respect to substrate concentration, both saturable and non‐saturable Phases being discerned. Accumulation is sensitive to pH, the exogenous solute potential, PCMBS, and other sugars. Sap representative of the apoplast was collected by centrifugation and contains approximately 40 mol m−3 hexose equivalents. Plants were labelled to the steady state with respect to cotyledonary sucrose derivatives; whole roots were then analysed by compartmental analysis and the results indicated similar apoplastic hexose concentrations. The vacuoles of roots grown in low salt solution contain most of the root soluble sugars, at a concentration of about 70 mol m−3 hexose equivalents. The sugar content of such roots decreases with availability of KCl to an extent which indicates that this involves a replacement of vacuolar hexose by alternative osmotica, supporting the results from compartmental analysis.
Sugar unloading in roots of Ricinus communis L.
Authors: CHAPLEO S. , HALL J. L. 
Published: April 2006

summaryThe intercellular pathway of sugar transport within tissues of Ricinus communis roots, which are available to exogenous solutions, was investigated to identify the route of phloem unloading. Less than 3%, of soluble translocate within the root system accumulates in root bathing media designed to influence the apoplastic movement of soluble sugars. Sucrose and hexoses make up 80% of the leaked translocate. The influence of plant growth regulator substances and of amino acid analogues upon the accumulation of translocate into the primary root has been evaluated and is discussed in relation to the symplastic transport of carbohydrate.
A 13C NMR study of photosynthate transport and metabolism in the lichen Xanthoria calcicola Oxner
Authors: LINES C. E. M. , RATCLIFFE R. G. , REES T. A. V. , SOUTHON T. E. 
Published: April 2006

summary 13C nuclear magnetic resonance (NMR) spectroscopy was applied to the lichen Xanthoria calcicola Oxner. The in vivo spectra were poorly resolved and although the line‐broadening effect of variations in the bulk magnetic susceptibility could be eliminated by spinning the sample at the magic angle, the spectra were still relatively Uninformative in comparison with the spectra of methanol extracts of the tissue. The synthesis of ribitol by the algal symbiont and its subsequent metabolism to mannitol by the fungus was followed using pulse‐chase experiments. The fine structure in the spectra provided support for the role of the pentose phosphate pathway in the conversion of ribitol to mannitol. Preliminary experiments, in which the conditions of the pulse‐chase experiment were altered, showed that the incorporation of 13C into mannitol was reduced at a lower temperature, and in thalli of low moisture content, and was abolished by darkness.
Effects of the bisulphite ion on growth and photosynthesis in Sphagnum cuspidatum Hoffm.
Authors: BAXTER R. , EMES M. J. , LEE J. A. 
Published: April 2006

summaryShoots of Sphagnum cuspidatum Hoffm. were collected from two sites: one, a relatively unpolluted site in N. Wales, remote from pollution sources and the other, a grossly polluted site in the South Pennines.* Material from both sites was grown in the laboratory and exposed to artificial rainwater solution with and without bisulphite (HSO3) amendment (0.1 mM). Effects of exposure to HSO3 for up to 21 days on growth, photosynthesis, chlorophyll a fluorescence and chlorophyll concentrations were studied in the two Sphagnum populations.Application of HSO3 produced significantly less than maximum growth in Sphagnum from both sites. This effect was far greater, however, in the material from the unpolluted Welsh site.Photosynthesis in the Welsh material treated with HSO3 decreased steadily with time; after 21 days of exposure, photosynthetic oxygen evolution had ceased. This decrease was accompanied by a decrease in fluorescence quenching (as [(P – T)/P]), suggesting a gradual loss of water‐splitting activity.In contrast, HSO3 initially stimulated photosynthesis in Sphagnum from the polluted site. Chlorophyll concentration was decreased in Spliagmtm from both sites in the presence of HSO3Possible mechanisms of tolerance to HSO3 are discussed.
The relationship between extracellular metal accumulation and bisulphite tolerance in Sphagnum cuspidatum Hoffm.
Authors: BAXTER R. , EMES M. J. , LEE J. A. 
Published: April 2006

summary Sphagnum cuspidatum Hoffm. was collected from a remote site in N. Wales, and a polluted site in the S. Pennines. When added to artificial rainwater solution, HSO3− was oxidized to SO42−. The rate at which this oxidation occurred was modified differentially by the mosses from the two sites. S. cuspidatum from the S. Pennines promoted a rapid oxidation rate and disappearance of HSO3− was complete in 6 h. S. cuspidatum from N. Wales, on the other hand, achieved a very slow oxidation rate and HSO3− persisted in solution for more than 24 h. Prolonged exposure to HSO3− in the Welsh material caused damage to, and eventual death of, this material but not of the S. Pennine moss.The rates of HSO3− oxidation promoted by the mosses from the two sites appear to be related to the concentration of the transition metal ions, Fe(III), Mn(II), and Cu(II), present on the cell‐wall cation‐exchange sites. These metals, particularly Fe, present on the surface of the S. Pennine material catalysed a rapid chemical oxidation of HSO3− to SO42−. The increased levels of transition metals associated with the S. Pennine moss originate in the peat as a legacy of past pollution events at this site.Levels of Fe were approximately 100 times greater than those for Mn or Cu and 5–10 times higher on the S. Pennine moss than on that from N. Wales. Removal of these metal ions (using EDTA) from the surface of the S. Pennine material removed the HSO3− oxidizing ability of the moss, leading eventually to cell death.The ability to withstand high levels of HSO3− was conferred upon the Welsh moss by supplying Fe(m) in artificial rainwater solution under laboratory conditions. Transplanting Sphagnum from the Welsh to the S. Pennine site gave rise to a similar response. Nomenclature of mosses follows Smith (1978).
The effects of oxides of nitrogen and carbon dioxide enrichment on photosynthesis and growth of lettuce (Lactuca sativa L.)
Authors: CAPORN SIMON J. M. 
Published: April 2006

summaryThe response of glasshouse crops to the nitrogen oxide pollutants which may be generated during enrichment with O2 has been studied in controlled environments. Lettuce (Lactuca sativa L. cv. Ambassador) was grown in air containing either low CO2, (380μmol mol−1), high CO2, (1200 μmol mol −1), or high CO2 plus oxides of nitrogen? (NOx)‐ Carbondioxide enrichment increased the rate of emergence and expansion of leaves and the growth of Young plants. Addition of NOx (2μmol mol−1 NO and c. 0.5 μmol mol−1 NO2) to CO2‐enriched air significantly reduced the yield, compared with the ‘clean, high CO2 treatment, without producing visible symptoms of toxicity. Fumigation of single plants in high CO2, with NOx rapidly inhibited photosynthesis per unit leaf area. This did not appear to be due to a reduction in stomatal conductance. Removal of NOx from the atmosphere caused a rapid and complete recovery in the rate of photosynthesis. Studies were made of the effects of growing Plants for long periods in atmospheres containing high CO2 and NOx on the photosynthetic capacity of single leaves when measured in NOx‐free air. The decrease in photosynthetic rate as the fourth leaf aged occurred earlier in plants grown in CO2‐enriched air than in those from the low CO2 treatment. Leaves which developed in the CO2‐enriched air containing NOx did not suffer any long‐term damage to photosynthetic activity in comparison with those of the ‘clean’ high CO2. In mature leaves the principal long‐term effect of enrichment (with or without NOx was to reduce the rate of photosynthesis in saturating CO2. In contrast, there was less effect on the rate of Photosynthesis in low CO2. The absence of a long‐term effect of NOx, on the photosynthetic capacity suggested that photosynthesis by the lettuce crop will be inhibited only during the transient periods of NOx accumulation in the glasshouse.