bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solute content and energy status of roots of barley plants cultivated at different pH on nitrate‐ or ammonium‐nitrogen
Authors: LANG BARBARA , KAISER WERNER M. 
Published: April 2006

summaryBarley seedlings (Hordeum vulgare cv. ‘Gaulois’) were precultured hydroponically for 4d on nutrient solutions with nitrate (3 mM) as N‐source at pH 4.7, and were then transferred to solutions with ammonium or nitrate as N‐source (3 mM), buffered and adjusted to different pH (4.0, 5.5, 6.8). Variations in shoot and root growth and solute contents were examined and grouped into pH‐effects, ammonium effects and interactions.Shoot biomass was not affected under all conditions. Root fresh weight was insensitive to the external pH when nitrate was the N‐source, but was drastically affected by a combination of ammonium and low pH. In contrast, root length was negatively affected by low pH per se.In nitrate‐grown plants, ammonium levels in roots and shoots were low (0.5 to 1 mM). After transfer of plants to ammonium solution, roots accumulated ammonium within 24 h about sixfold (18 mM) above the external concentration. At pH 5.5 or 6.8, but not at pH 4, root ammonium contents decreased afterwards to a lower steady state value (10 mM). Leaves also accumulated ammonium, especially at the most acidic pH.Concentrations of major inorganic cations in roots were markedly but differentially affected by acidic pH and ammonium. The magnesium content of roots was drastically decreased (from 18 to 2 mM) by ammonium nutrition, and this was independent of the external pH. In contrast, calcium levels in roots were decreased by low external pH, independent of the N‐source. Potassium levels in roots were rather insensitive to both low pH and ammonium.The pH of crude root homogenates was measured in order to obtain at least crude information about trends in possible cellular pH changes. At an external pH of 4.0 and 5.5, the pH of the homogenates was 5.8, and it increased to 6.3 when the external pH was 6.8. The pH of the homogenates was not affected by the N‐source.In spite of the drastic effects of the N‐source on the concentration of ammonium and magnesium in root tissues, ATP/ADP‐ratios were not affected. Also, sugar levels were unchanged or even increased. Thus, growth impairment could not be traced back to impaired carbohydrate or ATP‐supply, which might occur as a consequence of ammonium accumulation or Mg2+‐deficiency.
Root‐induced iron oxidation and pH changes in the lowland rice rhizosphere
Authors: BEGG C. B. M. , KIRK G. J. D. , MACKENZIE A. F. , NEUE H.‐U. 
Published: April 2006

summaryMeasurements of profiles of ferrous and ferric iron and pH in blocks of reduced soil in contact with planar layers of rice (Oryza sativa L.) roots are reported. Initially 11‐d‐old plants were kept in contact with the soil for up to 12 d. Over this period, substantial quantities of iron were transferred towards the root plane, producing a well‐defined zone of ferric hydroxide accumulation. The pH in this zone fell by more than two units. The profiles changed with time. The decrease in pH was in part due to protons generated in ferrous iron oxidation, and in part due to protons released from the roots to balance excess intake of cations over anions, N being taken up chiefly as NH4+. But the decrease in pH was less than expected from the net acid production in these two processes, possibly because of proton consumption in CO2 uptake by the roots. Because of the pH‐dependence of soil acidity diffusion, the two sources of acidity greatly reinforce each other. Some implications for nutrient and toxin dynamics are discussed.
Phosphate‐solubilizing bacteria associated with proteoid roots of seedlings of waratah [Telopea speciosissima(Sm.) R.Br.]
Authors: WENZEL C. L. , ASHFORD A. E. , SUMMERELL B. A. 
Published: April 2006

summaryBacteria isolated from proteoid roots and non‐proteoid lateral roots ofTelopea speciosissima(Sm.) R.Br. seedlings were able to acidify the medium and solubilize calcium phosphates when grown in culture in the presence of ammonium salts and an appropriate carbon source. In general this activity was not detected when NO3−was substituted for NH4+, and it is proposed that protons were secreted in exchange for ammonium ions. Cation exchange between these protons and calcium in the medium is a possible cause of the calcium phosphate solubilizing activity. The relevance of these data to phosphate‐solubilizing activity in natural environments is discussed.
Ozone effects on nitrogen incorporation and superoxide dismutase activity in spruce seedlings (Picea abies L.)
Authors: JUNG K. , ROLLE W. , SCHLEE D. , TINTEMANN H. , GNAUK T. , SCHÜÜRMANN G. 
Published: April 2006

summaryThe influence of low concentrations of ozone (100 ppb) on nitrogen incorporation and the specific activity of superoxide dismutase (SOD) in 3‐yr‐old cloned spruce seedlings was studied under controlled conditions (potted plants in fumigation chambers). For the determination of nitrogen uptake, 15N tracer experiments were performed using emission spectrometric isotope analysis. Superoxide dismutase (SOD) activity was determined by inhibition of formazan formation.Low doses of ozone led to a significant increase in both NO3‐N uptake from the soil and in specific SOD activity. The results show that stable isotope 15N tracer technique analysis is a suitable tool for the investigation of potential impacts of air pollutants on the nitrogen metabolism of plants.
Fitness constraints on flower number, seed number and seed size in the dimorphic species Primula farinosa L. and Armeria maritima (Miller) Willd.
Authors: BAKER KATHLEEN , RICHARDS A. J. , TREMAYNE MICHELLE 
Published: April 2006

summaryUsing two dimorphic species with diallelic incompatibility, Primula farinosa L. and Armeria maritima (Miller) Willd., we tested the hypothesis that an association of seedling performance with seed size, and an inverse association of seed size with seed number, might, contrary to most fitness models, select for plants which set relatively few seeds.In P. farinosa we discovered positive relationships between seed number per capsule and capsule number per inflorescence. As capsules are formed in most flowers, scapes with few flowers set the fewest seeds per capsule. This suggests that conspicuousness to pollinators and/or plant resource play an important role in reproductive success in this species. Seed size and seedling performance were also positively associated.For P. farinosa, which has multi‐seeded fruits, we discovered an inverse association between seed size and seed number for capsules containing more than 65 seeds. We suggest that stabilizing selection may occur for flower number per inflorescence in this species, as inflorescences with 8–11 capsules tend to set many seeds which may be inefficiently small. This tends to confirm our hypothesis.However, for A. maritima there is a positive association between seed size and seed number per inflorescence. For such plants with single‐seeded fruits there should be directional selection for large flower number pet‐inflorescence, a trend which may have led to the evolution of the capitulum.
The recent vegetational history of the Forest of Bowland, Lancashire, UK
Authors: MACKAY ANSON W. , TALLIS JOHN H. 
Published: April 2006

summaryThe results of 14C‐ and 210Pb‐dated pollen profiles from the Forest of Bowland, Lancashire are presented, covering the period from the late Iron Age up to the present day. Two notable features of the pollen profile are the apparent lack of a period of large‐scale forest destruction during the time of the Norse invasions and the substantial phase of tree clearance towards the end of the Iron Age period. The evidence suggests that the Viking invasions into Lancashire may not have been as destructive as once believed. The invasions were probably gradual, possibly localized (certainly as regards the Bowland area) and seem to have occurred alongside existing populations. Previous pollen‐analytical evidence regarding the Iron Age peoples of north‐west England has supposed them to have had little effect on their surrounding vegetation. It is now suggested that forest clearance previously assigned to the Romans in north‐west England is of Iron Age origin.The pollen profiles presented also reflect several changes of socio‐economic conditions that have affected rural populations in Lancashire during the last millennium. An important example is the decimation of populations during the fourteenth and seventeenth centuries. It is suggested that these were caused by the development of subsistence economies, leading each time to a Malthusian crisis. These population declines may also have been exacerbated by outbreaks of plague. The fall in population at both times, is clearly reflected by rising arboreal pollen values, indicative of slackening rates of forest clearance.
Tansley Review No. 62 The phytosociology of myxomycetes
Authors: ING BRUCE 
Published: April 2006

summaryThe factors influencing the distribution of myxomycetes are discussed and a detailed review of habitats, arranged according to major vegetation types, is offered. Some advances have been made in the past 25 years but it is only possible to claim the following: that temperature plays a significant role as a limiting factor in tropical, subtropical, Mediterranean and alpine species; that availability of water is of prime importance and water‐retaining substrates, whether they be bark, wood, litter, soil or humus are essential; that the distinction between corticolous, lignicolous and foliicolous species is reasonably consistent; that a few species are particularly associated with terrestrial bryophytes or are fungicolous; that, among the lignicoles, certain species are more or less confined to coniferous wood and others to angiospermous wood; that species are seasonal but the seasonally may vary for a given species in different climatic zones; that the occurrence of a myxomycete species is not governed, except perhaps in the corticolous species, by dispersal, which is efficient and effective, but by availability of suitable substrates; that there is a major ecological role for myxomonads in soil and probably within dead wood, and that there may be a limited association between the myxoflora and the vegetation.

Contents

Summary
175

I.
Introduction
175

II.
The geography of myxomycetes
178

III.
The ecology of myxomycetes
178

IV.
Forest mjTtomycetes
180

V.
Heathland and grassland myxomycetes
189

VI.
Wetland myxomycetes
191

VII.
Desert myxomycetes
192

VIII.
Maritime myxomycetes
193

IX.
Myxomycetes and the man‐made landscape
194

X.
Effects of climatic and ecological changes
196

XI.
Concluding remarks
197

Acknowledgements
197

References
197
In situ studies of Crassulacean acid metabolism in several sympatric species of tropical trees of the genus Clusia
Authors: FRANCO AUGUSTO C. , OLIVARES ELIZABETH , BALL ERIKA , LÜTTGE ULRICH , HAAG‐KERWER ANGELA 
Published: April 2006

summaryThe genus Clusia is characterized by the presence of C3, C3,‐CAM and CAM species growing sympatrically in many areas of the neotropics, The aim of this study was to investigate the photosynthetic behaviour of such sympatric species, and the effect that differences in photosynthetic metabolism and light levels have on their leaf characteristics, nutritional status, carbon and water economy. In the two field sites in Northern Venezuela, the apparent C3C. multiflora had the lowest leaf water content, leaf dry weight, N and P levels, when compared with the four other Clusia species that showed CAM activity, as measured by dawn/dusk changes in malate levels. Respiratory CO2., recycling probably accounted for 19 to 76% of nocturnal malate accumulation in the species with CAM activity. The measured δ13C values of C. minor were similar to values of a C3 plant, although about half of the CO2 uptake from the atmosphere occurred during night‐time. Under these conditions, C. multiflora had larger carbon gain and lower night‐time respiration rates than C, minor in spite of a lower water use efficiency. Light levels affected leaf concentrations of nitrogen, phosphorus and chlorophyll, as well as leaf water content and leaf dry weight of both species. Sun‐exposed leaves of both species had higher night‐time respiration rates than shade leaves. Leaves of C. minor under full sun exposure had a higher proportion of their total net CO2 uptake during daytime compared with shaded or partly shaded leaves, although night‐time citrate and malate accumulation were depressed. However, even under these conditions, the daylight decarboxylation of both acids could potentially maintain substantial photosynthetic rates during the midday stomatal closure period that characterizes CAM plants. Soluble sugars and starch are apparently the precursors of night‐time citrate and malate synthesis. The predominant utilization of soluble sugars for the formation of both organic acids moderated large dawn/dusk changes in vacuolar osmotic pressure.
Invertase: understanding changes in the photosynthetic and carbohydrate metabolism of barley leaves infected with powdery mildew
Authors: SCHOLES J. D. , LEE P. J. , HORTON P. , LEWIS D. H. 
Published: April 2006

summaryInfection of barley leaves with powdery mildew results in an increase in the activity of acid invertase, concomitant with an accumulation of glucose, fructose and sucrose in the infected leaf; this increase is confined to the mesophyll cells. The rate of photosynthesis is controlled by different factors depending upon the experimental conditions under which it is measured. In saturating light and ambient CO2, photosynthesis is determined to a large extent by Rubisco whereas, in saturating light and saturating CO2. it is mainly determined by the rate of end‐product synthesis (Pi‐limitation). The rate of photosynthesis was measured under these conditions to reveal which of the partial processes was most affected in mildewed leaves. Under conditions of saturating light and ambient CO2, the rate of photosynthesis declined in mildewed leaves from 3 d after inoculation, suggesting that carboxylation had been affected. However, the maximum capacity for photosynthesis, measured at saturating CO2 and irradiance, increased in mildewed leaves for the first 3 d after infection and then decreased to below control values on days 5 and 7, suggesting that Pi was not limiting photosynthesis. This hypothesis was investigated by measuring changes in photosynthetic intermediates and in the activity and amount of key enzymes of the Calvin cycle as infection progressed. There was a decline in the activity of the stromal fru‐1, 6‐bisPase, Rubisco and NADP‐GAPDH in mildewed leaves. These decreases were consistent with changes in the ratio of metabolites. As infection progressed, there was an increase in the ratio of Rul,5P2: PGA and triose‐P: Rul,5P2, the first indicating a restriction in the carboxylation of CO2 and the second a restriction in the regeneration of Rul,5P2, The PGA: triose‐P ratio was similar in control and mildewed leaves until day 7 when it decreased, suggesting that the reduction of PGA to triose‐P was not affected by the disease. There was little evidence of Pi‐limitation in the mildewed leaves; the amount of Pi in infected leaves was similar to controls, infected leaves showed no secondary oscillations during a transition from dark to light and there was a reduction in the amount of PGA in infected leaves. We suggest that the high concentration of carbohydrates, resulting from the increase in invertase activity, causes directly or indirectly a gradual down‐regulation of the Calvin cycle leading to aft inhibition of photosynthesis.
Hereditary symbiosis in the grass genus Danthonia
Authors: Clay Keith 
Published: April 2006

summaryHereditary symbiosis between the systemic, clavicipitaceous fungus Atkinsonella hypoxylon (Pk.) Diehl and five taxa of eastern North American Danthonia (Poaceae) was investigated by cultural and histological techniques. Many species of Danthonia, including D. alleni (or D. spicata var. alleni), D. compressa, D. epilis, D. serirea, and D, spicata produce both terminal panicles of wind‐pollinated florets and obligately self‐pollinated cleistogamous florets in the lower leaf axils, unlike most grasses. Terminal florets are aborted by infection while the basal florets produce viable, infected seeds (caryopses). The fungus grew out of surface‐sterilized cleistogamous seeds and seedlings at high frequency in progenies from infected plants but not from uninfected plants. Infection of seeds from terminal panicles from apparently healthy plants was lacking in 11 of 13 population samples from all taxa and was infrequent in two other populations. Growth chamber tests indicated that germination rates of infected and uninfected seeds of D. epilis were similar. Microscopic observations of sections of seeds and seedlings revealed that the fungus occurred epiphytically on meristems, in leaf axils, and on leaf primordia. Because infected plants are partially fertile, the fungus may be repeatedly transmitted for many generations via self‐fertilized cleistogamous seeds. The basal, and often subterranean, location of cleistogamous seeds may facilitate high infection frequencies in those Danthomia populations where cleistogamous seedling establishment predominates.
Demonstration of a short chain polyphosphate in Pisolithus tinctorius and the implications for phosphorus transport
Authors: ASHFORD A. E. , RYDE S. , BARROW K. D. 
Published: April 2006

summaryPolyphosphate was extracted from an Australian isolate of Pisolithus tinctorius (Pers.) Coker & Couch, known to be mycorrhizal with Eucalyptus pilularis. It was separated from RNA and characterized by PAGE and 31P NMR spectroscopy. A broad pink band, which showed y‐metachromasy with toluidine blue, ran faster on acrylamide gels than a number of purple‐blue bands (various RNA fractions) and did not stain with ethidium bromide, was identified as polyphosphate. The major pink band co‐migrated with a synthetic polyphosphate standard of a chain length of about 15 phosphate (P1) subunits, and analysis by 31P nuclear magnetic resonance (NMR) spectroscopy confirmed that polyphosphate was a major fraction in the extract. Polyphosphate was extracted from mycelium grown at both high and low levels of P1 but the amount extracted from cultures grown with 10 mM P1 (added as ammonium phosphate) was significantly greater. Polyphosphate was a substantial fraction of the phosphorus present in the hyphae and it is proposed that polyphosphate is transported along the hyphae by the motile tubule and vacuole system present in this fungus.
Expression of glutamate dehydrogenase and aspartate aminotransferase in eucalypt ectomycorrhizas
Authors: BOTTON B. , DELL B. 
Published: April 2006

summaryPrevious studies of nitrogen‐assimilating enzymes in ectomycorrhizal associations of the Pinaceae (Norway spruce, Douglas fir) and the Fagaceae (beech) have suggested that the host plant may regulate the expression of some fungal enzymes. To improve our understanding of the regulation of nitrogen‐assimilating enzymes in ectomycorrhizal plants, we have extended this work to a third plant family, the Myrtaceae.Glutamate dehydrogenases, specific either for NAD (NAD‐GDH) or NADP (NADP‐GDH), and aspartate amminotransferase (AAT) were investigated by enzyme assays and electrophoretic patterns on polyacrylamide gels. Non‐mycorrhizal roots of four species of Eucalyptus (E. diversicolor, E. globulus, E. nitens and E. regnans) were characterized by a high activity of NAD‐GDH, while only NADP‐GDH was found in Hebeloma westraliense in pure culture. In associations of these eucalyptus with Hebeloma westratiense, both NAD‐ and NADP‐GDHs were detected. By contrast, NAD‐ and NADP‐GDHs found in the free‐living mycelium of Lacrayia lacrata were not detected in the associated ectomycorrhizas.In ectomycorrhizas of five species of eucalypts (E. diversicolor, E. globulus, E. grandis, E. regnans and E. urophylla) associated with either Laccaria laccata, Scleroderma verrucosum or Pisolithus tinctorius, fungal AAT. which was very active in free‐living mycelia, was not detected in the symbiotic tissues. In contrast, the two root AAT isoenzymes remained active in the mycorrhizas and were even stimulated.These results suggest that fungal gene expression is moderated by the host plant but also depends on the fungal associate. Factors which may contribute to the observed differences in enzyme activity between Hebeloma and Laccaria are discussed.
Phloem transport of recently‐fixed nitrogen in the Gunnera–Nostoc symbiosis
Authors: STOCK PAUL A. , SILVESTER WARWICK B. 
Published: April 2006

summaryNitrogen fixation and translocation were examined in the symbiosis between the angiosperm Gunnera monoica and the cyanobacterium Nostoc. Nitrogenase activity was higher in mature than in apical regions of G. monoica plants. Ten and 12 h pulse‐chase labelling experiments with 15N2 showed that nitrogen fixed in mature regions was rapidly translocated throughout the plant, particularly to the apex. Pulse‐chase labelling coupled with steam‐girdling demonstrated the importance of phloem in the transport of recently fixed nitrogen from mature to apical regions. Steam‐gird ling of a length of stolon between a 15N2 labelled mature node and apical region inhibited 15N movement past the point of treatment. This provided evidence that recently fixed nitrogen was translated along the stolon primarily by the phloem. Further steam‐girdling experiments showed that phloem also had a major role in translocating recently fixed nitrogen to the leaves. Such primary translocation is exceptional within symbiotic systems but is not inconsistent with the vascular arrangement and location of the symbiosis. As carbon is also imported into the symbiosis the export of nitrogen implies bidirectional phloem transport.
O2‐induced inactivation of nitrogenase as a mechanism for the toxic action of Cd2+ on Nostoc UAM 208
Authors: MATEO P. , FERNANDEZ‐PIÑAS F. , BONILLA I. 
Published: April 2006

summaryDirect involvement of Cd2+ in the inhibition of N, fixation in Nostoc UAM 208 has been investigated. Significant inhibition of nitrogenase activity was detected 2 h after addition of Cd2+ to the culture medium. Under anaerobic conditions the inhibitory effect of Cd2+ was largely prevented, suggesting that this ion induced inactivation of nitrogenase by O2 Addition of Ca2+ to Cd2+‐treated cultures markedly decreased the inhibition of nitrogenase activity, and this amelioration of Cd2+ toxicity was dose‐dependent, indicating an antagonistic interaction between the two ions. Ultrastructural examination of cultures treated with Cd2+ showed heterocyst deterioration and a decrease in the cohesiveness of the polysaccharide layer of the heterocyst envelope. A possible antagonistic relationship between Ca2+ and Cd24 in terms of the O2 mediated inhibition of N2 fixation is discussed.
The plant oncogene rolB stimulates the formation of flower and root meristemoids in tobacco thin cell layers
Authors: ALTAMURA M. M. , CAPITANI F. , GAZZA L. , CAPONE I. , COSTANTINO P. 
Published: April 2006

summaryThe expression and effects of the plant oncogene rolB during in vitro flower and root morphogenesis were investigated. Thin cell layers (TCL) were excised from floral pedicels and from stems of transgenic tobacco plants containing either rolB and the promoter of rolB fused to the GUS reporter gene (BpB–GUS plants) or only this latter construct (pB‐GUS plants). Organogenesis and GUS activity were monitored in pedicel and stem TCLs for 30 days under conditions of floral or root neoformation. Both flowering and rhizogenesis are substantially enhanced and more precocious in rolB‐transformed explants than in TCLs from pB‐GUS and control plants. Most interestingly, both in flower arid in root neoformation, meristemoids are much more numerous and appear sooner in rolB‐transformed tissues. Thus, the effect of rolB does not seem to be specifically the induction of rooting, but, rather, the promotion of meristem formation, regardless of subsequent differentiation. In addition, we provide evidence that the presence of the gene product of rolB does not alter the pattern and timing of expression of the gene.