bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differentiation of polyphosphate metabolism between the extra‐ and intraradical hyphae of arbuscular mycorrhizal fungi
Authors: Tatsuhiro Ezawa , Sally E. Smith , F. Andrew Smith 
Published: March 2003

Summary

• Regulation of polyphosphate metabolism is reported in arbuscular mycorrhizal symbiosis.

• Marigold (Tagetes patula) plants inoculated with Glomus coronatum or Glomus etunicatum were grown in mesh bags. Exopolyphosphatase activity in extra‐ and intraradical hyphae was measured and characterized. The hyphae were stained with Neutral red to show acidic vacuoles in which polyphosphate synthesis might occur.

• Exopolyphosphate activity was differently expressed between the extra‐ and intraradical hyphae, as indicated by different pH optima; high activity was observed at pH 5.0 in the intraradical hyphae of both fungal species. Km values were lower at neutral pH with long‐chain polyphosphate, whereas acidic activity showed lower Km with short‐chain polyphosphate. Both extra‐ and intradical hyphae had acidic vacuoles. Polyphosphate occurred in the hyphae of the high‐P, but not the low‐P treatment. By contrast, exopolyphosphatase activity and vacuolar acidity were relatively constant irrespective of polyphosphate status.

• The fungi have at least two different exopolyphosphatase‐type enzymes which are differently expressed between extra‐ and intraradical hyphae; polyphosphate accumulation might be a dynamic balance between synthesis and hydrolysis.
Photosynthesis might be limited by light, not inorganic carbon availability, in three intertidal Gelidiales species
Authors: Mercado Jesús M. , Xavier Niell F. , Candelaria Gil‐Rodríguez M. 
Published: March 2003

Summary

• The interaction between incident photon fluence density (PFD) and dissolved inorganic carbon (DIC) availability on photosynthesis is reported for three species of Gelidiales (Rhodophyta) from the Canary Islands.

• Photosynthetic O2 evolution in response to both DIC concentration and PFD, and external carbonic anhydrase activity were measured in thalli of Gelidium canariensis, Gelidium arbuscula and Pterocladiella capillacea maintained in a controlled‐environment room.

• No detectable external carbonic anhydrase activity, high sensitivity to alkaline pH and moderate values of photosynthetic conductance for DIC indicated that the three species had a low capacity for using the external pool of HCO3−; therefore photosynthetic rates were dependent on CO2 availability. The seawater concentration of DIC was insufficient to saturate photosynthesis at high PFD; photosynthesis vs PFD was not affected by DIC concentration at 0.07–0.04 mol O2 mol−1 photon. ANOVA revealed that incident PFD had a greater effect than DIC availability on photosynthesis rates in G. canariensis.

• Photosynthesis is probably limited by incident light rather than DIC concentration despite the apparent low affinity for HCO3− in G. canariensis, G. arbuscula and P. capillacea in their natural habitats.
Light and salinity affect growth of the salt marsh plantAster laurentianus
Authors: Reynolds Christina E. , Houle Gilles , Marquis Christophe 
Published: March 2003

Summary• The effects are reported of substrate salinity and light on the relative growth rate of the annualAster laurentianus, an endangered species of eastern Canadian salt marshes.• The independent and combined effects of photosynthetically active photon flux density and salinity on the relative growth rate (RGR) and overall plant performance were measured in glasshouse and growth‐chamber experiments on seedlings ofA. laurentianus.•  Low light availability decreased RGR through its negative effect on unit leaf rate. However, specific leaf area and leaf mass ratio varied inversely with changes in light, such that leaf area ratio did not differ greatly among light levels. High salinity decreased RGR by reducing unit leaf rate and leaf area ratio; a reduction in the latter was brought about by a lower leaf mass ratio rather than by a lower specific leaf area. Low light availability combined with high substrate salinity affectedA. laurentianusin a strictly additive manner; there was no significant interaction between the two factors on overall plant performance.• Light and salinity are important factors controlling growth ofA. laurentianus,and might explain the distribution pattern of the species in the field.
Symbiotic specificity of tropical tree rhizobia for host legumes
Authors: Bala Abdullahi , Giller Ken E. 
Published: March 2003

Summary

• The host range and specificity is reported of a genetically diverse group of rhizobia isolated from nodules of Calliandra calothyrsus, Gliricidia sepium, Leucaena leucocephala and Sesbania sesban.

• Nodule number and nitrogen content was measured in seedlings of herbaceous and woody legume species after inoculation with rhizobial strains isolated from tropical soils, to establish symbiotic effectiveness groups for rhizobial strains and their hosts.

• Specificity for nodulation and N2 fixation varied greatly among the legumes. Symbionts of all four legumes exhibited a wide range of promiscuity and symbiotic effectiveness with isolates of S. sesban having the narrowest host range. N2 fixation varied greatly; although some strains fixed large amounts of N2 with more than one host, none was effective with all hosts. Rhizobial isolates of C. calothyrsus, G. sepium and L. leucocephala were able to effectively cross‐nodulate each others’ hosts as well as a number of other species.

• The complex nature of cross‐nodulation relationships between diverse rhizobial strains and legume hosts is highlighted. Host plants inoculated with effective rhizobial strains showed better nitrogen use efficiency than plants supplied solely with mineral nitrogen.
Nutrients and pH regulate algicide accumulation in cultures of the cyanobacterium Oscillatoria laetevirens
Authors: Ray S. , Bagchi S. N. 
Published: March 2003

Summary

• The change in algicide synthesis in response to nutrients and pH in axenic cultures of the planktonic cyanobacterium, Oscillatoria laetevirens is reported.

• Analytical and bioassay techniques were used to determine the effects of nitrogen (N), sulpher (S), phosphorus (P), magnesium (Mg2+), calcium (Ca2+) and hydrogen (H+) on Oscillatoria laetevirens growth, secondary metabolite accumulation and minimum inhibitory concentration in culture filtrates.

• Growth and secondary metabolite production were affected by nutrient addition. High algicide production, which was not dependent on optimal growth, correlated with deficiences of magnesium and phosphate, and high pH. Algicidal activity in the culture medium was not detected following organic nitrogen addition while optimal growth was sustained; however, ammonia reduced biomass yield but did not affect algicide formation. The differential algicide concentration inside the cells and in the culture medium indicated secretion by an efflux mechanism rather than leakage from aging cells.

• Algicide production by Oscillatoria laetevirens was negatively regulated by both phosphate and magnesium, and by pH. The interactive influence of nutrients and allelopathy is discussed in species succession and dominance in the maintenance of freshwater blooms.
Developmental and induced responses of nickel‐based and organic defences of the nickel‐hyperaccumulating shrub, Psychotria douarrei
Authors: Davis Micheal A. , Pritchard Seth G. , Boyd Robert S. , Prior Stephen A. 
Published: March 2003

Summary

• Developmental and inducible changes in metal‐based (nickel (Ni)) and organic defences (phenolics) are compared in the Ni‐hyperaccumulating shrub, Psychotria douarrei.
• Young and old leaves of P. douarrei shrubs, subjected to different degrees of simulated herbivory, were analyzed for metals, tannins, macronutrients and total carbon, and compared with a co‐occuring nonhyperaccumulator shrub, Ficus webbiana.
• Leaf age affected both nickel Ni‐based and organic defences in P. douarrei; foliar metal concentrations were higher in mature leaves, whereas organic defences were higher in young leaves. Neither metal‐based nor organic defences were increased by simulated herbivore damage, implying noninducibility, although some organic defence compounds were significantly reduced. P. douarrei had a greater percentage of total phenolics, condensed tannins and protein precipitation ability than F. webbianai. Since total carbon content did not differ between species, Psychotria invests more of its leaf carbon budget in organic defences than does Ficus.
• Data suggest that P. douarrei foliage is well protected by Ni, but tannins have multiple functions. The high concentrations of tannins in Psychotria leaves might function as a detoxification mechanism for elevated cytoplasmic metal concentrations, in addition to providing defensive benefits.
Fructans and fructan‐metabolizing enzymes in leaves of Lolium perenne
Authors: Pavis N. , Boucaud J. , Prud’homme M. P. 
Published: March 2003

Summary

Longitudinal variability is reported in internal carbon partitioning as is the activity of enzymes involved in fructan synthesis during leaf development of Lolium perenne cv. Bravo.
Sink activity was reduced in L. perenne plants by cooling the roots while continuous illumination enhanced source activity, resulting in preferential accumulation of fructans at the leaf base. Fructan contents and enzymatic activity of two trisaccharides (SST (sucrose : sucrose fructosyltransferase) and 6G‐FT (fructan : fructan 6G‐fructosyltransferase)) were measured in segments of elongating leaves, both mature leaf blades and sheaths.
The complement of fructans accumulated was similar in both elongating leaves and mature leaf sheaths. 6G‐FT activity was found in L. perenne and characterized in a crude extract; this activity was greatest in the basal segment of elongating leaves and mature leaf sheaths. Throughout the leaf blade, however, SST and 6G‐FT activities remained low and constant, and did not increase under conditions of sucrose accumulation.
Differences are shown in fructan accumulation between leaf tissues; the significance of these findings and the putative pathway of fructan synthesis in L. perenne are discussed.
Nitrogen fertilization and developmental stage alter the response of Lolium perenne to elevated CO2
Authors: Daepp Markus , Nösberger Josef , Lüscher Andreas 
Published: March 2003

Summary

Plant response to elevated atmospheric CO2 may depend on the carbon sink strength, determined by the availability of resources other than CO2, and the developmental stage.
In a 2‐yr field experiment with model swards of Lolium perenne, the effect of CO2 enrichment (FACE) on yield and allocation of dry mass (DM) and N were examined under three N fertilization treatments during vegetative and reproductive growth.
During vegetative growth, in the highest N treatment, the greatest increase in DM yield occurred at elevated CO2; there was no change in DM allocation. By contrast, at low N, residual biomass, but not yield, increased under CO2 enrichment, and the tillers were shorter. During reproductive growth, under CO2 enrichment DM yield increased similarly across all N treatments; there was no change in DM and N partitioning. The mean weight and height of the reproductive tillers increased.
At high N availability, or during reproductive growth, L. perenne swards overcome carbon‐sink limitation and show a strong yield response to elevated CO2. Biomass allocation and the height of the plants, in response to elevated CO2, clearly depend on N fertilization and developmental stage.
Unravelling response‐specificity in Ca2+ signalling pathways in plant cells
Authors: Rudd Jason J. , Franklin‐Tong Vernonica E. 
Published: March 2003

SummaryConsiderable advances have been made, both in the technologies available to study changes in intracellular cytosolic free Ca2+ ([Ca2+]i), and in our understanding of Ca2+ signalling cascades in plant cells, but how specificity can be generated from such a ubiquitous component as Ca2+ is questionable. Recently the concept of ‘Ca2+ signatures’ has been formulated; tight control of the temporal and spatial characteristics of alterations in [Ca2+]i signals is thought to be responsible, at least in part, for the specificity of the response. However, the way in which Ca2+ signatures are decoded, which depends on the nature and location of the targets of the Ca2+ signals, has received little attention. In a few key systems, progress is being made on how diverse Ca2+ signatures might be transduced within cells in response to specific signals. Valuable pieces of the signal‐specificity puzzle are being put together and this is illustrated here using some key examples; these emphasize the global importance of Ca2+‐mediated signal‐transduction cascades in the responses of plants to a wide diversity of extracellular signals. However, the way in which signal specificity is encoded and transduced is still far from clear.

Contents

Summary
7

I.
Introduction: Ca2+ as a signal transducer
8

II.
Alterations in intracellular [Ca2+]
8

1. Measuring alterations in [Ca2+]
8

Imaging [Ca2+]i using Ca2+‐sensitive dyes
8

Measuring [Ca2+]i using aequorin
9

Imaging [Ca2+]i using cameleon
10

2. The concept of the ‘Ca2+ signature
10

3. How might specific Ca2+ signatures be generated?
11

Control of intracellular Ca2+ release
11

Control of influx of extracellular Ca2+
12

4. Examples of Ca2+ signatures and cellular responses to increases in [Ca2+]
13

Ca2+ signatures in stomatal guard cells in response to abscisic acid signals
14

Ca2+ signals in response to abiotic stimuli1
8

Ca2+ signatures involved in plant‐pathogen responses
19

Ca2+signatures in control of plant reproduction
20

Ca2+signatures in root hairs in response to nodulation signals
23

III.
Decoding the [Ca2+]i signatures
24

1. Coupling Ca2+ signals to responses through CaM
26

2. Coupling Ca2+ signals to responses through CDPK
27

3. Novel Ca2+ binding proteins as primary Ca2+ sensors
28

Conclusions and Perspective
28

References
29
Morphological responses of plant roots to heterogeneity of soil resources
Authors: Šmilauerová Marie , Šmilauer Petr 
Published: March 2003

Summary• Root morphological response to experimentally induced soil heterogeneity is reported here on three grassland species (Luzula campestris, Poa angustifolia and Plantago lanceolata) under field conditions.• Nutrient application was combined with suppression of mycorrhizal infection and with substrate structure modification in experimental patches. For each isolated root, we determined five dimensional characteristics and two topological parameters, including a newly introduced topological index (dichotomous branching index).• Nonmycorrhizal L. campestris responded little to nutrient application, but strongly to benomyl application, in all characteristics measured. Mycorrhizal P. angustifolia produced the longest, most branched roots but exhibited limited sensitivity to nutrients and benomyl application. Strongly mycorrhizal P. lanceolata was the most sensitive to nutrient application, but showed little response to benomyl application. It was the only one among the species studied with root characteristics influenced (negatively) by increased production of total root biomass in the patches. Substrate structure influenced dimensional characteristics of Poa and Luzula roots, but not the topological indices.• Results indicate different exploitation of soil microsites by L. campestris, P. angustifolia and P. lanceolata. Root topology seems to play a limited role in this process.
Deriving a consistent δ13C signature from tree canopy leaf material for palaeoclimatic reconstruction
Authors: Turney Chris S. M. , Hunt John E. , Burrows Colin 
Published: March 2003

Summary

Contemporary studies of stable carbon isotope values (δ 13
C) from leaves in the canopies of mature forest indicate that reduced irradiance and respired CO
2
might bias palaeoenvironmental reconstructions developed using the
13 C content of unsorted plant material formed within comparable ancient environments.
Here, we investigated whether any simple morphological and/or chemical characteristics could identify the position of the leaf within a canopy of the evergreen mountain beech ( Nothofagus solandri
var.
cliffortiodes ).
Leaf mass per unit area, carbon content and δ 13 C values of both bulk and lignin components of the leaves increased exponentially from the ground up through the canopy. Nitrogen, remobilized before death, was unsuitable as an indicator of canopy position. Leaf mass per unit area on the forest floor indicated that leaves from the sunlit part comprised approximately 30% of the fallen leaves; leaves originating from the upper canopy made up the remaining litter.
Application of leaf mass per unit area to a 22 000‐yr‐old sequence dominated by mountain beech leaves from Mount George (New Zealand), demonstrated that this signal was preserved in the fossil record. Sunlit leaf material can be successfully differentiated from that originating deeper within the palaeo‐canopy, thereby allowing robust δ 13 C analyses for palaeoenvironmental reconstruction.
An oxidative burst of hydrogen peroxide during rehydration following desiccation in the moss Atrichum androgynum
Authors: Mayaba Nosisa , Minibayeva Farida , Beckett Richard Peter 
Published: March 2003

Summary

The Afromontane understorey moss Atrichum androgynum
is shown here to display an oxidative burst of hydrogen peroxide (H
2O2) during rehydration following desiccation.
Maximum rates of H 2O2 production, assayed spectrophotometrically using the xylenol orange assay, occurred during the first 15 min of rehydration. Although the production of H2O2 increased with increasing desiccation times, the moss produced significant amounts of H2O2 during rehydration after desiccation for times that did not inhibit photosynthesis or cause potassium (K+) leakage. Atrichum androgynum also produces H2O2 during desiccation; artificially induced desiccation, using polyethylene glycol, strongly stimulates H2O2 production.
Experiments involving inhibitors and exogenously supplied reductants indicated that peroxidases might be responsible for the production of H 2O2. Factors that influence the rate of H2O2 production during rehydration included light and the hormone abscisic acid. Patterns of H2O2 production in A. androgynum are discussed in terms of their possible role in defence against pathogenic fungi and bacteria.
Authentic British food products: a review of consumer perceptions
Authors: Groves Angela M. 
Published: March 2003

AbstractHistorically, soil, land, climatic constraints and individuals’ skills all contributed to the characteristics of regional food. Food, however, is also subject to the influences of colonialism, immigration, cultural exchange, international trade, improved distribution and technology. British food is constantly evolving in order to fulfil the demands of each generation. Thus, the concept of an authentic British food product is becoming increasingly unclear. This paper therefore addresses what today British consumers actually perceive to be authentic British foods. Results of an exploratory qualitative study are reviewed. Five focus groups were conducted with individuals responsible for half or more of their household’s shopping. The groups incorporated consumers with a range of demographic and economic characteristics. The data gathered from the focus groups revealed that British perceptions of authenticity relate to both artisan as well mass‐produced, branded products. In addition, five dimensions affecting consumer perceptions of an authentic British food product were identified, including: uniqueness to Britain, a cultural or traditional association with Britain, characteristics of the production process, the presence of an authority and specific extrinsic characteristics of the product. The findings have implications for product differentiation and communication, for producers and retailers and also for independent trade associations.
Swedish preschool children's experience of food
Authors: Wesslén Annika , Sepp Hanna , Fjellström Christina 
Published: March 2003

AbstractFocus group interviews were carried out at 12 preschools. The aim was to investigate children's perceptions and experiences of food, and the possibility of using focus group techniques with children aged 3–5 years. A total of 103 children participated. The children associated food and eating with rules and norms. Most children described these rules and norms as well as what they were and were not allowed to do. They knew very well the difference between acceptable and non‐acceptable mealtime behaviour, and were especially aware of what they were not allowed to do. When children were asked to rate foods they ‘disliked’, they spoke instead about their favourite foods. They did not categorize food as good or bad, as adults often do, but as ‘food’ and ‘non‐food’, for example, sweets were not food. The method used in this study, the focus group interview, was judged to be a useful tool for exploring how children think about and jointly reflect upon food.
Extracellular ATP stimulates an inhibitory pathway towards growth factor‐induced cRaf‐1 and MEKK activation in astrocyte cultures
Authors: Lenz Guido , Gonçalves Daniela , Luo Zhijun , Avruch Joseph , Rodnight Richard , Neary Joseph T. 
Published: March 2003

ATP, acting via P2Y, G protein‐coupled receptors (GPCRs), is a mitogenic signal and also synergistically enhances fibroblast growth factor‐2 (FGF‐2)‐induced proliferation in astrocytes. Here, we have examined the effects of ATP and FGF‐2 cotreatment on the main components of the extracellular‐signal regulated protein kinase (ERK) cascade, cRaf‐1, MAPK/ERK kinase (MEK) and ERK, key regulators of cellular proliferation. Surprisingly, ATP inhibited activation of cRaf‐1 by FGF‐2 in primary cultures of rat cortical astrocytes. The inhibitory effect did not diminish MEK and ERK activation; indeed, cotreatment resulted in a greater initial activation of ERK. ATP inhibition of cRaf‐1 activation was not mediated by an increase in cyclic AMP levels or by protein kinase C activation. ATP also inhibited the activation of cRaf‐1 by other growth factors, epidermal growth factor and platelet‐derived growth factor, as well as other MEK1 activators stimulated by FGF‐2, MEK kinase 1 (MEKK1) and MEKK2. Serotonin, an agonist of another GPCR coupled to ERK, did not inhibit FGF‐2‐induced cRaf‐1 activation, thereby indicating specificity in the ATP‐induced inhibitory cross‐talk. These findings suggest that ATP stimulates an inhibitory activity that lays upstream of MEK activators and inhibits growth factor‐induced activation of cRaf‐1 and MEKKs. Such a mechanism might serve to integrate the actions of receptor tyrosine kinases and P2Y‐GPCRs.