bluuebunny/crossref_metadata_2025 huggingface dataset:
Decomposition of 14C‐labelled substrates by ectomycorrhizal fungi in association with Douglas fir
Authors: DURALL D. M. , TODD A. W. , TRAPPE J. M.
Published: April 2006

Ectomycorrhizas of Pseudotsuga menziesii (Mirb.) Franco were synthesized in pure culture with Cenococcum geophilum Fr., Laccaria bicolor (Maire) Orton, Rhizopogon vinicolor Smith, or Suillus lakei (Murr.) Smith and Thiers. The mycorrhizal plants were grown in sterile vessels with peat/vermiculite plus 14C labelled hemicellulose, cellulose, Douglas fir needles, or humic polymers as an organic substrate. The sum of the 14C respired and that found in the seedling after 240 d of growth was used to quantify decomposition of the labelled substrates. All mycobionts released at least 20–30% of the 14C in hemicellulose and all were able to release 14C from cellulose and needles, escept L. buolttr, which failed to release 14C from needles. S. lakei released the largest amount of 14C from cellulose. C. geophilum, S. lakei and R. filticolor released similar amounts of 14C from needles. Generally, substrates could be ranked in terms of ease of breakdown by the ectomycorrhizal fungi as follows: humic polymers < needles < cellulose < hemicellulose.
Variation in mycorrhizal development and growth stimulation by 20 Pisolithus isolates inoculated on to Eucalyptus grandis W. Hill ex Maiden
Authors: BURGESS T. , DELL B. , MALAJCZUK N.
Published: April 2006

Twenty isolates of Pisolithus, covering u range of hosts, basidiocarp types and geographic locations were compared on their ability to form mycorrhiza in vitro with Eucalyptus grandis and to stimulate seedling growth in vivo. There was a large variation between isolates in the rate of mycorrhizal development and this was used to categorize isolates into six types. Mycorrhiza of seedlings inoculated with type I isolates were the most advanced with a dual‐layered mantle, a fully‐developed Harris net and radially elongated epidermal cells. Mycorrhiza of seedlings inoculated with types II V isolates were progressively less advanced so that mycorrhiza of type V isolates had a thin single‐layered mantle, the Hartig net was only partially developed and the epidermal cells were not elongated. Root lips of seedlings inoculated with type‐ VI isolates were non‐mycorrhizal. Inoculated seedlings were transplanted directly into undrained pots containing a yellow sand deficient in phosphorus. Growth stimulation of E. grandis seedlings in the glasshouse varied greatly between Pisolithus isolates, with dry weight increases ranging from two to 45 times that of the non‐inoculated control seedlings. Extent of mycorrhizal development was positively correlated to growth stimulation in the glasshouse and it is proposed that this could be used as an indicator of isolate aggressiveness and consequently the potential of an isolate to promote tree growth.
O3‐induced degradation of Rubisco protein and loss of Rubisco mRNA in relation to leaf age in Solanum tuberosum L.
Authors: ECKARDT N. A. , PELL E. J.
Published: April 2006

The effect of ozone (O3) on Rubisco degradation was investigated by dark incubation of potato plants (Solanum tuberosum L. cv. Norland) following exposure to charcoal‐filtered air or 0.30μl l−1 O3 for 6 h. Rubisco small subunit (rbcS) mRNA levels declined dramatically in control foliage within 10.16 h of dark incubation; thus declines in Rubisco protein following a 48‐h dark period were ascribed to proteolytic degradation. Foliage sampled from the 4th and 6th leaves from the apex, designated immature and mature, respectively, showed no effect of O3 on Rubisco protein content immediately following the exposure. However, the decline in Rubisco quantity during the dark incubation was significantly enhanced by prior treatment with O3 in the mature leaves. The immature leaves sustained a similar decline in Rubisco quantity in both O2 and control treatments. O3 had a significant effect on the relative quantity of rbcS mRNA in the immature leaves (sampled immediately following the O3 exposure). Levels of rbcS mRNA in mature leaves and Rubisco large subunit (rbcL) mRNA in both leaf ages were not significantly affected by O3, There was no effect of O3, on Rubisco quantity in immature or mature leave's of plants maintained in the greenhouse under a 16 h photoperiod far 48 h following the exposure. Thus the effect of short‐term O3 exposure on processes affecting Rubisco synthesis and degradation may have been transient, and a more prolonged exposure would he necessary to effect a decline in Rubisco protein quantity in plants grown under a 16 h photoperiod. We concluded that O3 caused enhanced degradation of Rubisco in mature leaves of plants induced to senesce by dark incubation following O3 exposures. The potential for O3‐induced reduction in synthesis of Rubisco also exists.
Cytokinins in the xylem sap of the dioecious fynbos shrub, Leucadendron rubrum Burm. f.: seasonal fluctuations and their possible interaction with morphological characteristics as expressed in the two sexes
Authors: DE KOCK MARIANNA , THERON KAREN I. , SWART PIETER , WEILER ELMAR W. , BELLSTEDT DIRK U.
Published: April 2006

Brandies of male and female plants of the dioecious Leucadendron rubrum Burm. f. were collected on the site of the Weikamp weather‐station in the Jonkershoek State Forest, Stellenbosch, from July 1990 to September 1991. Xylem sap was extracted from the branches by vacuum extraction. HPLC was employed to purify the xylem sap and to separate the cytokinins prior to quantitation by ELISA. The cytokinin levels in the purified plant samples were determined using rabbit antiserum‐based ELISAs for the determination of the levels of the cytokinins DHZR and IPA, and a trans‐ZR specific monoclonal antibody‐based ELISA for the determination of the levels of the cytokinin ZR.

It was observed that the levels of the cytokinins DHZR and ZR did not differ significantly between male and female plants but did correlate with the seasonal growth patterns. The levels of the cytokinin IPA, in male and female plants of L. rubrum, not only correlated specifically with the different seasonal growth patterns observed but differed significantly between male and female plants. Peaks in the levels of all three cytokinins. i.e. ZR, DHZR and IPA, occurred during the study period. These peaks corresponded with the phenological development of L. rubrum, specifically with vegetative bud break and inflorescence differentiation and appeared to be synchronized with the growth and development.

An attempt was also made to correlate cytokinin levels with the extreme differences in morphological characters exhibited by male and female plants, and possibly to explain to what extent these phytohormones influence sex expression in L. rubrum
Developmental anatomy of internal cavities of epidermal origin in leaves of Polygonum (Polygonaceae)
Authors: CURTIS J. D. , LERSTEN N. R.
Published: April 2006

Two types of internal oil cavity that develop from the epidermis occur in leaves of 15 species of Polygonum, sect. Persicaria. In one type, found in 10 species, epidermal cells develop directly into epidermal/epithelial (E/E) cells. In P. hydropiper, a single protoderm cell enlarges, grows into the mesophyll, and divides only anticlinically to form three, to seven (usually four) E/E cells. The enlarging E/E cells separate along the medial pan of their shared walls to form a central cavity. The protoplast of each E/E cell then retracts from the inner cell wall and deposits a new cell wall to form a peripheral lacuna between the original inner wall and the new wall. The original cell walls between central cavity and peripheral lacunae eventually disappear leaving an oil‐filled mature internal cavity but with each E/E tell tip still exposed at the surface. The second type, found m five species, involves both subepidermal and epidermal cells. In our examples. P. glabrum and P. densiflorum, the initial protoderm cell divides anticlinally to form 8–20 cells, most of which grow into the mesophyll, divide periclinally, and separate to become epithelial cells surrounding a cavity. The Outermost cells remain epidermal the deeper ones are secondarily subepidermal. Peripheral lacunae and a central cavity form as in the epidermal cavity, but they do not merge into a single mature cavity. Epithelial cells, peripheral lacunae, and central cavity collectively form a subepidermal cavity complex.
Stems of Allium cepa L. contain starch
Authors: ERNST M. , BUFLER G.
Published: April 2006

summary

Stems of Allium cepa L. were prepared for histochemical analysis and stained by periodic acid‐Schiff reaction and Lugol's iodine for detecting starch grains (amyloplasts). Starch was found in the root cap of the root initials, around the central cylinder vascular tissues of the stem and in the primary thickening meristem during sprouting but not during dormancy.
High soil carbon dioxide concentrations inhibit root respiration of Douglas fir
Authors: QI JINGEN , MARSHALL JOHN D. , MATTSON KIM G.
Published: April 2006

summary

Total and basal respiration (RtandRb, respectively) of intact and undisturbed roots of one‐year‐old Douglas fir seedlings,Pseudotsuga menziesiivar.glauca[Beissn] Franco, were measured at experimentally varied soil carbon dioxide concentrations ([CO2]). Use of specially designed root boxes and a CO2gas‐flow compensating system designed around an infrared gas analyzer (IRGA) allowed controlled delivery of CO2to roots and simultaneous measurements of CO2released by roots. Root respiration rate responded to each inlet [CO2], independent of whether the previous concentration had been higher or lower, within two to three hours (pairedttest = 0.041,P= 0.622, andn= 13). Total and basal respiration rates decreased exponentially as soil [CO2] rose from 130 ppm, well below atmospheric [CO2], to 7015 ppm, a concentration not uncommon in field soils. Analyses of variance (ANOVA) showed that the effects of soil [CO2] on rates of total and basal root respiration were statistically significant. Root respiration rates decreased by 4 to 5 nmol CO2g−1dry weight of roots s−1for every doubling of [CO2] according to the following equations: ln(R1) (nmol CO2g−1s−1) = 5.24–0.30*ln[CO2] withr= 0.78,P< 0.0001, andn= 70; and ln(Rb) (nmol CO2g−1s−1) = 6.29–0.52 * ln[CO2] withr= 0.82,P< 0.0001, andn= 35. The sensitivity of root respiration to [CO2] suggests that some previous laboratory measurements of root respiration at atmospheric [CO2], which is 3 to 10‐fold lower than [CO2] in field soils, overestimated root respiration in the field. Further, the potential importance of soil [CO2] indicates that it should be accounted for in models of below‐ground carbon budgets.
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

summary

Barley 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

summary

Measurements 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

summary

Bacteria 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

summary

The 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

summary

Using 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

summary

The 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

summary

The 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

summary

The 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

summary

Infection 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

summary

Hereditary 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

summary

Polyphosphate 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

summary

Previous 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

summary

Nitrogen 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

summary

Direct 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

summary

The 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.
Studies of the cellular localization of the phenolic pungent principle of ginger, Zingiber officinale Roscoe
Authors: ZARATE RAFAEL , YEOMAN MICHAEL M.
Published: April 2006

summary

Examination of cryo‐sections from mature rhizomes, immature rhizomes and adventitious roots of ginger, Zingiber officinale Roscoe, showed the presence of yellow‐pigmented cells. There is a correlation between the number of pigrnenteci cells and the amount of [6]‐gingerol, the main pungent principle in ginger, in these organs. It is also shown histochemically and microspectrophotometrically that the yellow cells contain, in addition to flavonoid‐like compounds, possibly cureumin derivatives, phenolics and large amounts of lipid material. Low‐temperature scanning electron microscopy also demonstrates the oil content of these cells. Therefore, it would appear that the site of accumulation of flavonoids, curcumin derivatives, phenolics including gingerol and the essential oils of this spice lies within the same cell type.
Effects of ambient air pollution in open‐top chambers on bean (Phaseolus vulgaris L.)
Authors: SCHENONE G. , FUMAGALLI I. , MIGNANEGO L. , MONTINARO F. , SOLDATINI G. F.
Published: April 2006

summary

Field‐grown bean plants (Phaseolus vulgaris L. ev. Taylor's Horticultural) were exposed to ambient air pollution in open‐top chambers (OTCs) at two sites (urban and rural) in Northern Italy. At each site three OTCs received charcoal/Purafil filtered air (F) and three ambient non‐filtered air(NF). Net photosynthesis, stomatal conductance and transpiration of selected leaves were measured from July to September 1989. The results showed that net photosynthesis of NF plants decreased progressively during the season in comparison with the F ones. The difference was greatest at September (−40% at urban site and −23% at rural she). The maximum impairment of photosynthesis occurred during the ripening of the pods. For about 2 wk in August stomatal conductance of NF plants was greater than that of F plants at both sites. Later in August and in September the situation was reversed and stomatal conductance of NF plants wan significantly lower than that of F ones. By this time a significant negative correlation between net photosynthesis and sub‐stomatal carbon dioxide concentration was found in NF plants at both sites, indicating an increased importance of non‐stomatal limitation of photosynthesis. The measured leaves did not show any visible symptom of damage at the time of the physiological measurements; however brown spots on the upper surface became evident later on 20% of total leaves of NF plants. Ambient ozone is suspected to be the major air contaminant involved in causing the observed physiological effects.
The influence of elevated ozone on freezing tolerance of red spruce seedlings
Authors: WAITE C. E. , De HAYES D. H. , REBBECK J. , SCHIER G. A. , H.JOHNSON A.
Published: April 2006

summary

Laboratory cold‐tolerance assessments were conducted over two seasons on red spruce (Picea rubens Sarg.) seedlings fumigated with various concentrations of ozone (O3) for one or two growing seasons in three independent experiments at three locations. Ozone fumigations were performed at either Boyce Thompson Institute in Ithaca, NY (BTI), the University of Maine in Orono, ME (UMO), or the US Forest Service Research Laboratory in Delaware, OH (USFS). Acid mist treatments of either pH 3.0 or 4.2 were applied in combination with O2 treatments at USFS, Seedlings fumigated with moderate or high concentrations of O3 were never significantly less cold tolerant than seedlings exposed to charcoal‐filtered (CF) air or low O3 concentrations. In fact, there was a tendency for seedlings fumigated with low concentrations of O3 or CF air to be the least cold tolerant. USFS‐fumigated seedlings receiving the lowest O3 concentration (50/0 nl 1−1, day/night concentration) were least cold tolerant on six of the seven sampling dates and significantly less cold tolerant in October and January. In addition, UMO‐fumigated seedlings receiving CF‐air were significantly less cold tolerant in January than those receiving either ambient air (no chamber or non‐filtered treatments) or elevated O3. Acid mist treatments had little influence on the cold tolerance of red spruce seedlings in autumn and early winter, but in January 1990 seedlings exposed to pH 3.0 acid mist were approximately 6 °C less cold tolerant than those receiving pH 4.2. Following the 1988‐89 winter, freezing injury was evident on all seedlings fumigated at BTI, but differences between 3 x ambient O3 and CF treatments were not significant.
Single and interactive effects of root‐knot nematode and coal‐smoke on okra
Authors: KHAN MUJEEBUR RAHMAN , KHAN M. WAJID
Published: April 2006

summary

Effects of coal‐smoke pollutants and the root‐knot nematode Meloidogyne incognita race 1, singly and jointly, were investigated on okra, Abelmoschus esculentus in 1988 and 1989. Plants in clay pots were placed at two sites (Kl and K2), 1 and 2 km away from the stack of a coal‐fired thermal power plant, and also at the Department of Botany, AMU (control site). The mean concentrations of SO2, NO2 and suspended particulate matter (SPM) were 141, 76 and 309 μg m−3 at K1, and 184, 93 and 205 μg m−3 at K2, but the concentrations of the pollutants at the control site were very low. Okra plants at the K2 site showed browning of the leaves, whereas injury was mild at Kl, The intensity of the browning and the impact of nematode disease was appreciably higher in the infected plants at the polluted sites in both the years. The plants grown at the two sites exhibited suppressions in plant growth, yield and photosynthetic pigments, particularly at K2. M. incognita at the control site also caused significant reductions, but joint effects of the nematode and coal‐smoke were synergistic. Nematode reproduction was enhanced at K1, hut was unaffected at K2. Egg laying was reduced by 13 and 27% a1 Kl and K2, respectively. The response of stomata and trichomes to air pollutants was negative and positive at the two sites, respectively, and stomatal opening was directly correlated with the percent suppressions in dry matter production, yield etc.
Deciduous Quercus in the Mediterranean region: tree‐ring/climate relationships
Authors: TESSIER L. , NOLA P. , SERRE‐BACHET F.
Published: April 2006

summary

Comparisons are made between ring‐width response functions relating to precipitation and temperature in 72 Quercus populations (Q. afares Pomel, Q. canariensis Willd., Q. pubesrens Willd. and Q. robur L.) situated in the north and south of the western Mediterranean region. A multivariate procedure applied to the whole set of response functions allows a distinction to be made of three types of response function according to the species considered. Analogies and differences between coded response functions are revealed by the calculation of a mean response, firstly for each species and for the genus, secondly for the groups of response functions derived from the multivariate analysis. For all the populations, and hence for the entire Quercus genus, a direct response to summer precipitation and an inverse response to temperature, especially minimum temperature, are obtained for the summer period. For the other seasons, each species is characterized by a particular behaviour conditioned by the characteristics of the habitat.
Flandrian vegetational history of sout‐heastern England. Stratigraphy of the Brede valley and pollen data from Brede Bridge
Authors: WALLER M. P. , MARLOW A. D.
Published: April 2006

summary

The results of palaeoecological analyses and lithostratigraphic investigations are used to reconstruct the Flandrian evolution of a valley in the East Sussex Weald, the Brede. Particular emphasis is placed upon mid‐Flandrian vegetational history. Palynological data collected from one site, Brede Bridge, include detailed resolution of declines in Ulmus and Tilia pollen. Predominantly inorganic sediments were deposited in the valley during the early Flandrian. Marine conditions penetrated the lower valley under the general influence of sea level rise. After c, 6000 BP, peat formation became widespread and Alnus‐dominated communities occupied the valley floor. Despite forest clearance on the adjacent slopes, relatively little sediment was deposited in the period c. 3700 to c. 1800 BP. The lower valley again came under a marine influence after c. 1800 BP. The dryland forests of the valley were, during the mid‐Flandrian, dominated by Tilia. A general upward decline in Tilia pollen through the sequence is attributed to the valley floor widening and the Brede Bridge site becoming more distant from dryland areas. The first signs of human activity accompany the Ulmus decline, though major forest clearance is not evident until the Tilia decline c. 3700 BP. Comparison of the latter event with sires across south‐eastern and southern England offers support for a phase of human expansion in the late Neolithic/early Bronze Age involving the preferential exploitation of areas of lime forest.
CO2 enrichment responses of wheat: interactions with temperature, nitrate and phosphate
Authors: McKEE I. F. , WOODWARD F. I.
Published: April 2006

summary

Rising levels of atmospheric CO2, climate change, and fertilizer pollution provide the ecological imperative for investigating the interaction between plant responses to atmospheric CO2 concentration, temperature and nutrient supply. In this study spring wheat (Triticum aestivum L. cv. Wembley) was grown at 40, 50, 60 and 70 Pa atmospheric CO2, pressure and three experiments were conducted to investigate interactions between growth responses to the CO2 treatment and: (i) temperature (24/16 °C vs. 18/10 °C ‐ day/night), (ii) nutrient solution nitrate concentration (2.5, 5, 10 and 15 mM Ca(NO3)2.4H2O). and (iii) phosphate concentration (0.025 and 0.5 mM KH2PO4), Dry mass and root/shoot ratio increased with CO2 level at the higher temperature. These responses were reversed at the lower temperature. The increase in yield with CO2 enhancement was limited by low rates of nutrient supply in both absolute and relative terms. In the elevated CO2 treatments, the shoot nitrogen concentration was reduced, as was the proportional allocation to the uppermost leaves. These results are discussed with respect to possible physiological mechanisms and potential for improved crop performance in a future, elevated CO2 world.
Carbon balance of tropical tree seedlings: a comparison of two species
Authors: LEHTO TARJA , GRACE JOHN
Published: April 2006

summary

Seedlings of contrasting tropical tree species were grown at two levels of photon flux, and two levels of nutrient supply. The CO2 exchanges of plant organs were measured, in an attempt to account for the overall carbon balance of the plants in terms of the photosynthesis and respiration of their constituent parts (buds, stems, roots and leaves that were recently fully expanded, mature and senescing). On a per plant basis the buds and leaves dominated the carbon balance. High photon flux and high nutrient supply increased the respiration rate. The relative importance of leaves of different age in whole plant photosynthetic production and respiration was different in the two species and was affected by the light regime. Maintenance respiration of both species was about the same (0.036‐0.050 g CO2 g−1 d−1) but the pioneer species Trema displayed a much higher rate of growth respiration than did Milicia.
A postulated role for calcium oxalate in the regulation of calcium ions in the vicinity of stomatal guard cells
Authors: RUIZ L. P. , MANSFIELD T. A.
Published: April 2006

summary

Calcium ions are known to play an important part in signal transduction in stomatal guard cells. In Cummelina communis L., stomatal opening in isolated epidermis is strongly inhibited if the calcium concentration in the incubation medium is 0.1 mol mol m−3 or greater, It can be assumed that in the intact leaf, the apoplastic concentration of free calcium in the vicinity of the guard cells must be kept below this level if interference with stomatal functioning is to be avoided.

When C. communis was grown with 15 mol m−3 calcium in the rhizosphere, the concentration of free calcium in the xylem sap in the shoot was found to be 3.76 mol m−3. A mechanism is clearly needed for reducing this concentration as the sap traverses the apoplast between the xylem and the stomatal guard cells. Evidence is presented here that the deposition of calcium oxalate in cells of the leaf achieves the necessary regulation. The protective role of the six specialized subsidiary cells in this species appears to be specially important.

It is suggested that the regulation of apoplastic free calcium may take an important contribution to the effective stomatal control of gas exchange.