bluuebunny/crossref_metadata_2025 huggingface dataset:
Nitrate accumulation and growth of Aster tripolium L. with a continuous and intermittent nitrogen supply*
Authors: STIENSTRA A. W.
Published: April 2006

Abstract The ‘tidal salt marsh’ ecotype of the halophyte Aster tripolium L. was grown in a nutrient solution with either a continuous or an intermittent NO3− supply with either Cl− or SO42− as the alternative anion. With increasing periods of NO3− supply per week the rate of the dry weight increment increased. When NO3− was supplied for longer than 48 h per week, the dry weight and the organic‐N content in the shoots hardly increased, whereas the NO3− content in shoots and roots increased further. With alternated supply of a nutrient solution containing NO3− with one containing Cl−, the internal NO3− content in the shoot was lower than in shoots grown in solutions in which NO3− alternated with SO42−. It is concluded, that NO3− does not have a specific function in osmoregulation.
Stomatal conductance and transpirational responses of field‐grown cotton to ozone
Authors: TEMPLE P. J.
Published: April 2006

AbstractStomatal conductance and transpiration were measured on normally‐irrigated (NI) and water‐stressed (WS) field‐grown cotton (Gossypium hirsutumL.) exposed throughout the growing season to a gradient of ozone (O3) concentrations. Environmental conditions during the growing season strongly affected stomatal responses and yield reductions due to O3exposure. Maximum stomatal conductance and transpiration decreased with increased O3concentration both in NI and WS treatments. Maximum conductance in severely O3‐stressed plants averaged 30% lower than charcoal‐filtered (control) plants, but maximum transpiration was only 17% lower. Conductance in WS plots averaged 22% lower than in NI plots but transpiration rates were the same in both treatments. Yield reductions induced by O3were highly correlated (r2= 0.84) with daily transpiration. Stomata of O3‐stressed plants opened and closed at the same rate as control plants in response to changes in light intensity, suggesting that the mechanism of stomatal movement had not been impaired by exposure to O3. Reductions in conductance and transpiration in O3‐stressed plants were attributed to inhibition of photosynthesis by O3, leading to accumulation of CO2in intercellular spaces.
Changes in ion and water content of individual shoot organs in a salt‐tolerant and a salt‐sensitive clone of Agrostis stolonifera L. during and subsequent to treatment with sodium chloride
Authors: HODSON M. J. , ÖPIK H. , WAINWRIGHT S. J.
Published: April 2006

Abstract Individual leaves and stems were analysed for Na+, Cl−, K+ and water content in two clones of Agrostis stolonifera differing in salt resistance, during 14 d of treatment with NaCl, 100 and 200 mol m−3, and a further 7 d in a salt‐free medium. Great differences in ion and water content were revealed between individual organs, and organ‐by‐organ analysis also emphasized the differences between the clones better than whole shoot analysis. In both clones, Na+ and Cl− accumulated to the greatest degree in the older leaves, but for corresponding organs, the concentrations were lower in the more tolerant clone. In the sensitive clone, the lowest leaves dehydrated in 200 mol m−3 NaCl and failed to recover, while the plants of the more resistant clone maintained viable water content in all organs. In the resistant clone, K+ concentration decreased less in response to salt treatment than in the more sensitive clone. For a full appreciation of the plants' reactions, it was found necessary to express the analytical data on several bases, namely, per unit dry‐weight, unit water, and total ion‐content.
Arrhenius plots and the involvement of thermotropic phase transitions of the thylakoid membrane in chilling impairment of photosynthesis in thermophilic higher plants
Authors: MARTIN B.
Published: April 2006

Abstract Breaks and discontinuities in Arrhenius plots of physiological and physical properties of thylakoids are not diagnostic of thermotropic lipid phase transitions of the membrane. Bulk lipid transitions, as first inferred by the membrane phase transition hypothesis, do not occur in any higher plant at chilling temperatures. Solidification of some varying, but always minor, fraction of the total membrane lipid does take place. However, the presence of minor domains of solid thylakoid membrane lipid at chilling temperatures is not unique to chilling sensitive plants but is also found in tolerant species. Minor solidification may in some plants, or groups of plants, be controlled by the specific molecular species of phosphatidylglycerol only recently investigated. In plants containing little, or no, phosphatidylglycerol with this positional distribution of fatty acids, other yet unknown constituents of the membrane must fill a similar function, since DSC thermograms indicate minor solidification also in isolated, unperturbed thylakoids from chilling tolerant species. However, chilling induced phase transitions, or other perturbations, of the thylakoid membrane are not the reason for the chilling lability of net photosynthesis in the intact plant. This conclusion follows from detailed comparison between photosynthetic membranes isolated from prechilled plants and the effects of chilling exposure on CO2 fixation of the whole plant. Damage at the level of the thylakoid membrane does occur, although not to the extent where it can account for the proportionally much larger damage to CO2 fixation.
Loading and translocation of assimilate in the fine veins of sunflower leaves
Authors: WANG X.‐D. , CANNY M.J.
Published: April 2006

AbstractThe time course of loading and transport of assimilate in sunflower leaves was examined by pulse labelling with14CO2, followed by freeze drying or freeze substitution, and dry autoradiography at both low and high resolution. The five classes of veins, V1‐V5 (V5 being smallest), show a division of function: V5 and V4 are engaged in loading and short distance transport; V3 to V1, in long distance translocation. The first high concentration of14C is found in two or three phloem parenchyma cells (intermediary cells) of V5 and V4 veins. The sieve elements of V5 and V4 veins do not show comparable concentrations of14C at any time. Recently assimilated14C is transported by the intermediary cells for distances of about 0.5 mm to the V3 veins. In V3 to V1 veins translocation is in the sieve tubes. Transport in V5 and V4 veins is in two directions, that in V3 to V1, in one direction towards the petiole. The high concentration of14C formed in the intermediary cells does not increase further as the assimilate moves to the sieve tubes of the V3 veins, and so is probably the origin of the gradient that drives translocation.
Diurnal osmotic cycling in cotton leaves as an indicator of source–sink balance
Authors: RADIN J. W. , MAUNEY J. R. , GUINN G.
Published: April 2006

Abstract Diurnal cycling of osmotic potential was studied in leaves of cotton plants (Gossypium hirsutum L.) grown in the field. Osmotic potential was determined by a pressure‐volume procedure as the value coinciding with zero turgor. In plants grown under favourable conditions (no water stress or N stress), osmotic potential at zero‐turgor measured at midday was initially about 0.3 MPa lower than before dawn, but this cycling disappeared during the season as the number of fruits per plant increased. In water‐stressed or N‐deficient plants, osmotic cycling was decreased or even eliminated. Across treatments, cycling of osmotic potential occurred only when plants carried at least 560 cm2 of leaf area per fruit. The results are interpreted to mean that diurnal cycling of osmotic potential reveals a ‘sink‐limited’ condition within the plant.
Seasonal relationships between leaf nitrogen content (photosynthetic capacity) and leaf canopy light exposure in peach (Prunus persica)
Authors: DeJONG T. M. , DOYLE J. F.
Published: April 2006

Abstract Field gas exchange measurements on intact peach (Prunus persica (L.) Batsch) leaves indicate that leaf nitrogen content (NL) and leaf weight per unit leaf area (Wa) are highly correlated with CO2 assimilation rate (A) and mesophyll conductance (gm). Therefore, NL and Wa were used to study seasonal relationships between leaf carboxylation capacity and natural light exposure in tree canopies. From mid‐season onwards, NL and Wa were linearly correlated with light exposure expressed as the amount of time during a clear day that a leaf was exposed to a photosynthetic photon flux density (Q) of ≥ 100 μmol m−2 s−1. The data support the hypothesis that whole‐tree photosynthesis is optimized by partitioning of photosynthetic capacity among leaves in deciduous tree canopies with respect to natural light exposure.
Determination of orchid seed viability using fluorescein diacetate
Authors: PRITCHARD H. W.
Published: April 2006

Abstract Fluorescein diacetate (FDA) staining (0.25% FDA for 10 min) was found to be a suitable technique for the rapid determination of orchid seed viability. Penetration of the dye through the testa varies between species, thus the test is ideally performed on isolated embryos. Direct FDA application to isolated embryos of seeds taken from dry storage, but after the surface had been sterilized, elicits a poor staining reaction. Incubation of the surface sterilized seeds in distilled water for 16 h, either at 6°C or at room temperature, prior to applying the test was found to overcome this problem. In the range of species studied, FDA staining accurately indicates seed viability when compared with germination of seeds on sterile nutrient media. Storage of dry Dactylorhiza fuchsii (Druce) Soó seed at an elevated temperature of 62°C indicated that, under such conditions of accelerated ageing, the FDA test accurately describes the rate of seed viability loss.
C4 photosynthesis at low temperatures
Authors: LONG S. P.
Published: April 2006

Abstract. C4 plants grown in optimum conditions are, by comparison to C3, capable of higher maximum dry‐matter yields and greater efficiencies of water and nitrogen use, yet they are rare outside the subtropics. Both latitudinal and altitudinal limits of C4 distributions correlate most closely with a mean minimum temperature of 8‐10°C during the period of active growth. The possibility that the C4 process is inherently incapable of functioning at low temperatures is examined. The reversible effects of chilling on the quantum efficiency of C4 photosynthesis and the functioning of the individual steps in the C4 cycle are examined. Chilling also produces an irreversible loss of capacity to assimilate CO2 which is directly proportional to the light received during chilling. It is suggested that the reversible reduction in capacity to assimilate CO2 and the lack of an alternative pathway for the utilization of lightgenerated reducing power may make C4 species more prone to chilling‐dependent photoinhibition. Laboratory studies and limited field observations suggest that this damage would be most likely to occur during photosynthetic induction at the temperatures and light levels encountered on clear, cool mornings during the spring and early summer in cool climates. Even those C4 species occurring naturally in cool climates do not appear fully capable of tolerating these conditions; indeed their growth patterns suggest that they may be adapted by avoiding ‘rather than enduring’ such conditions.
Differential Na2SO4 tolerance in tobacco plants regenerated from Na2SO4‐grown callus
Authors: PUA ENG‐CHONG , TREVOR A.
Published: April 2006

Abstract The regenerated shoots from sodium sulphate (Na2SO4) grown callus of tobacco (Nicotiana tabacum L. cv. Wisconsin 38) were evaluated for Na2SO4 tolerance based on shoot proliferation and rooting in vitro, and seed germination in vivo in response to Na2SO4. An increase in Na2SO4 concentration resulted in significantly decreasing shoot fresh weight, number of shoots, shoot length and leaf size, and increasing per cent shoot dry weight of both control and Na2SO4‐grown cultures. In rooting, shoots of Na2SO4‐grown cultures exhibited the highest per cent rooting (85%) in the presence of 1% w/v Na2SO4. However, per cent rooting, root number per rooted cutting and root fresh weight decreased significantly with increasing Na2SO4 concentration when shoots were transferred to the medium in the absence of Na2SO4 for 4‐monthly passages. Following acclimatization of the rooted shoots of Na2SO4‐grown cultures, phenotypic variation was observed during growth and development. There were 13.2% sterile plants. Fertile plants were sorted into normal (N), tolerant (T), and sensitive (S) categories and the respective percentages of plants were 31.6, 44.7 and 10.5, based on per cent germination, germination velocity index and seedling survival to Na2SO4. The response of N, T and S types to Na2SO4 in subsequent shoot proliferation was similar to that of seed germination.
Restitution of polarity in statocytes from centrifuged roots*
Authors: WENDT M. , SIEVERS A.
Published: April 2006

Abstract The structural polarity of statocytes from cress roots is changed by centrifugation. Upon low‐ dose centrifugation (3000 g min), the extent of stratification depends on statocyte position, i.e., central statocytes are affected more than lateral ones. Upon higher doses of centrifugation (60,000 and 360,000 g min), a uniform density gradient is established in all statocytes. If, after centrifugation, the roots are exposed to gravity again, the endoplasmic reticulum (ER) cisternae are relocated parallel to the periclinal cell walls within a few minutes; this relocation is independent of the direction of gravity in relation to the root axis, and independent of the previously applied centrifugation dose. This supports the notion that polarity is determined genetically. Cytochalasin B treatment, before and during centrifugation, totally inhibits the relocation of ER. After removing the drug by rinsing the roots, the statocytes restore cell polarity and relocate ER. These results indicate that relocation of ER cisternae may be mediated by microfilaments. When centrifuged roots are exposed to 1 g in the horizontal position, the latent period of gravitropism increases by 8–10 min relative to controls, regardless of the previously applied centrifugation doses. The kinetics of curvature are virtually identical. Since the increase in the latent period coincides with the time needed for most statocytes to restore the distal cell pole, it is evident that perception of gravity is correlated to the integrity of the distal cell pole.
Photosynthesis and the influence of CO2‐enrichment on δ13C values in a C3 halophyte
Authors: GUY R. D. , REID D. M.
Published: April 2006

Abstract Shifts in †13C of the graminaceous C3 halophyte Puccinellia nuttalliana (Schultes) Hitch. can be induced by salinization. To investigate this phenomenon, three approaches were taken: assay of carboxylases, CO2‐enrichment studies, and gas exchange analysis. Although ribulose‐1,5‐bisphosphate carboxylase activity decreased with salinity, phosphoenolpyruvate carboxylase activity did not increase and its levels were not atypical of C3 plants. When plants were grown at four NaCl concentrations under atmospheres of 310 and 1300 cm3 m−3 CO2, the CO2‐enrichment enhanced the effects of salinity on †13C. This is consistent with a biophysical explanation for salt‐induced shifts in †13C, whereby there is a steepening of the CO2 diffusion gradient into the leaf. Gas exchange analysis indicated that intercellular CO2 concentrations were depressed in the leaves of salt‐affected plants. This resulted from a greatly decreased stomatal conductance coupled with only small effects on intrinsic photosynthetic capacity. Water‐use efficiency was enhanced.
Voltage transients elicited by sudden step‐up of auxin
Authors: PICKARD BARBARA G.
Published: April 2006

Abstract It is hypothesized (i) that the molecular mechanism for the reception of friction and flexure and the mechanism by which auxin enhances ethylene production have in common a release of free calcium into the cytosol, (ii) that elevated cytosolic calcium initiates vesicle exocytosis, and (iii) that the vesicles release a factor or set of factors which depolarizes the plasmalemma and promotes ethylene synthesis. One consequence of such exocytosis should be small, extracellularly observable voltage transients. Transients, ranging in size up to 600 μV and possessing risetimes (10–90%) of approximately 200 ms, are known to be elicited in etiolated stems of Pisum sativum L. by friction and are here shown to be elicited by sudden increase of auxin concentration and also by a Ca2+ ionophore.
The role of capacitance in the water balance of Andean giant rosette species
Authors: GOLDSTEIN GUILLERMO , MEINZER FREDERICK , MONASTERIO MAXIMINA
Published: April 2006

AbstractPith water storage capacity and its role in plant‐water relations were studied in seven giant rosette species of the genusEspeletiafrom the Venezuelan Andes. Readily available water from the pith was calculated to be capable of sustaining mean transpiration for up to 2.5 h. The relative importance of water stored in the pith, however, differed among species. The species that grow in the higher and colder environments tended to have a greater capacitance than the species that grow in the lower and less extreme environments. The pith volume per unit leaf area (PV/LA) was found to be a good indicator of the relative water storage capacity of the adult individuals of each species. Diurnal fluctuations in leaf water potential were not as pronounced in the species with higher PV/LA values. The species‐specific PV/LA was highly correlated with the leaf turgor loss point and with the total resistance to water flow from soil to leaves. These results suggested that species‐specific capacitance in the genusEspeletiais a response to temperature‐limited soil water availability and that cold tropical environments with frequent subfreezing temperatures tend to select for high water storage capacity in giant rosette plants.
Ethanol synthesis and loss from flooded roots of Medicago sativa L. and Lotus corniculatus L.
Authors: BARTA A. L.
Published: April 2006

Abstract Field flooding of established alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.) for up to 12 d resulted in a significant increase in alcohol dehydrogenase activity (ADH) and an increase in the Km of ADH in both species. Root concentration of ethanol increased throughout the flooding regime in alfalfa roots. No ethanol was detected in any trefoil root samples. Alfalfa plants which had shoots removed 5 d prior to flooding accumulated significantly higher levels of root ethanol and showed flooding injury sooner, indicating a significant effect of shoots on development of flooding injury.

Alfalfa and trefoil plants grown in the greenhouse were flooded and ethanol in the transpiration effluent was trapped and measured. Alfalfa transpired measurable quantities of ethanol which peaked just prior to development of shoot injury symptoms. No ethanol was detected in the transpiration effluent from trefoil shoots. Flooded roots of both alfalfa and trefoil excreted ethanol but alfalfa roots synthesized more total ethanol and retained a larger proportion in the roots than did trefoil.

While the ethanol accumulation response in alfalfa and trefoil are consistent with the ethanol ‘self‐poisoning’ hypothesis of flooding injury, the very small quantities of ethanol found in these roots still raises questions as to its absolute effect in the plant.
Characterization of a proton pump from pea stem microsomes
Authors: VIANELLO A. , MACRÍ F.
Published: April 2006

Abstract The present work deals with the characterization of an ATP‐dependent proton translocation monitored by the ΔpH probe acridine orange.

The ATP‐dependent proton translocation has an optimum activity at pH 6.5 and is substrate specific for ATP. It is stimulated by Cl−, HCO3− and Br−, but is insensitive to several monovalent cations. Divalent cations (Mg2+ or Mn2+) are required for proton translocation, while in the presence of Ca2+ no uptake is observed. NO3−, NO2− and citrate strongly inhibit proton uptake. On the contrary, F−, SO42−, malate, pyruvate, succinate, oxalate and acetate have no inhibitory effect. Proton uptake is stimulated by valinomycin and unaffected by molybdate. Two thiols, dithioerythritol and dithiothreitol, are able partially to prevent the FCCP‐abolished proton uptake or partially restore the ATP‐dependent proton translocation in FCCP‐collapsed vesicles.

It is suggested that pea stem microsomes possess an electrogenic ATPase, acting as a proton pump, which, on the basis of its characteristics, can be tentatively associated with membranes of tonoplast origin.
Evidence contrary to the existence of storage lipid in leaves of plants inhabiting cold climates
Authors: HETHERINGTON ALISTAIR M. , HUNTER M. IAN S. , CRAWFORD ROBERT M. M.
Published: April 2006

Abstract In a study of the lipid composition of the upland Empetrum nigrum subspp. hermaphroditum and Empetrum nigrum subspp. nigrum with a lowland distribution, no evidence was found to support the suggestion that lipids (triacylglycerols) play a major energy storage role in the leaves of alpine species. On a quantitative basis the triacylglycerols constituted less than 5% of the total lipid in both species and the lowland species possessed the higher levels of total lipid, neutral lipid and triacylglycerols. It is suggested that the presence of a well‐developed waxy cuticle might account for the high total lipid levels encountered in dwarf evergreen shrubs.
Occurrence of unstable PEP carboxylase in C4 grasses in the genus Spartina Schreb.
Authors: SMITH ALISON M. , WOOLHOUSE HAROLD W.
Published: April 2006

Abstract The aims of this work were to discover the distribution within the C4 grass Spartina anglica of a PEP carboxylase which is very unstable during and after extraction, and to determine whether this unstable form occurs in other members of the genus. In S. anglica, only the leaf contains an unstable PEP carboxylase. Within the leaf only the major one of two isoenzymes is unstable, and this is located in the mesophyll cells. The unstable isoenzyme is inactivated during extraction and storage unless protected by bovine serum albumin or Triton X‐100, and is inactivated in assay mixtures at optimum pH in the absence of PEP. Evidence is presented that inactivation is not due to degradation or inhibition during extraction and storage. The enzyme from leaves of Spartina species taxonomically closely related to S. anglica is also very unstable during and after extraction, but that from less closely related species is much more stable.
Contrasting types of photoperiodic response in the control of dormancy
Authors: VINCE‐PRUE DAPHNE
Published: April 2006

Abstract The effect of night‐break or day‐extension treatments with red (R) and/or far‐red (FR) light were examined in the control of dormancy and extension growth in Weigela florida and Picea abies.

Dormancy in Weigela (as assessed by the continued production of new leaves) was completely prevented by a 30 min night‐break treatment with R: the effect of R was prevented by a subsequent exposure to 30 min FR. A day‐extension treatment for 8.25 h with R or with R+FR also completely prevented dormancy, irrespective of whether it was given before or after a short day (SD) in sunlight. There was no significant difference between any dayextension treatment, nor between day‐extension treatments and a night‐break with R.

Dormancy in Picea (as assessed by the maintenance of shoot growth) was also delayed by a night‐break with R but less effectively than the most effective day‐extension. A day‐extension treatment for 9 h with R light was more effective when it preceded than when it followed a SD in sunlight. The addition of FR in the second but not in the first 9 h of a 17 h photoperiod increased its effectiveness.

It is concluded that the mechanisms of the control of dormancy must differ in the two species.

A day‐extension for 16 h with light from tungstenfilament lamps increased stem elongation in Weigela when compared with an R night‐break. This resulted from an increase in internode length and there was no significant difference between the two treatments in their effect on leaf production.
Tropic responses of hypocotyls from normal tomato plants and the gravitropic mutant Lazy‐1
Authors: ROBERTS JEREMY A.
Published: April 2006

Abstract Etiolated hypocotyls from normal tomato plants show a negative gravitropic response within 20 min of stimulation. In contrast, etiolated hypocotyls from the gravitropic mutant Lazy‐l do not reorientate after gravistimulation. Etiolated hypocotyls from both types of plant are positively phototropic, however, Lazy‐l seedlings achieve a greater final angle of bending following phototropic stimulation compared to normal plants.

Anatomical studies reveal that etiolated hypocotyls from normal plants contain sedimenting amyloplasts located within the endodermal cells. Such sedimenting amyloplasts are absent in Lazy‐l tissue. It is hypothesized that the hypocotyl of Lazy‐l is agravitropic since it is unable to perceive a gravistimulus.
Seasonal changes of osmotic pressure, symplasmic water content and tissue elasticity in the blades of dune grasses growing in situ along the coast of Oregon
Authors: PAVLIK BRUCE MICHAEL
Published: April 2006

Abstract Midday water potentials of blades of the dune grasses Ammophila arenaria (L.) Link and Elymus mollis Trin. ex Spreng. growing in situ declined over the summer growing period, indicating a trend of increasing water stress. An analysis of the water relations characteristics of these blades using pressure‐volume techniques demonstrated that both species increased bulk osmotic pressure at full hydration () and, therefore, bulk turgor as an acclimation response. In A. arenaria, however, the increase of osmotic pressure (+ 0.35 MPa) was entirely the result of decreasing symplasmic water content. The increase of osmotic pressure (+ 0.54 MPa) observed in E. mollis blades was due to solute accumulation (72% of Δ) and to a lesser degree, decreased symplasmic water content (28% of Δ). Osmotic adjustment in E. mollis blades was accompanied by a significant decrease in tissue elasticity (max went from 12 to 19 MPa). The elastic properties of A. arenaria blades remained constant over the same period and had a maximum modulus (10 MPa) that was always less than that of E. mollis, As estimated from Höfler plots, these seasonal adjustments of osmotic pressure and differences in tissue elasticity enabled plants in situ to maintain turgor pressure in the range of 0.5–0.6 MPa at the lowest water potentials of mid‐August. Laboratorygrown plants exhibited the species‐specific differences in osmotic pressure, turgor pressure, and tissue elasticity observed in field plants. Although certain alterations of leaf structure were expected to coincide with the observed changes and species‐specific differences in symplasmic water content and tissue elasticity, these could not be detected by measurements of specific leaf weight or the ratio of dry matter to saturated water content.
Effects of hydration conditions on the stroma inclusion of some CAM chloroplasts
Authors: SANTOS ISABEL , SALEMA R.
Published: April 2006

Abstract The tubular protein inclusion of the chloroplasts of some CAM plants was found to maintain its normal pattern of accumulating by day and dissolving at night when the hydration state of the chloroplasts was reversed by promoting influx of water during the day and efflux of water during the night. Morphometric study of the chloroplast inclusion of Sedum telephium supports our suggestion that the behaviour of the aggregate of tubules is independent of the water content of the chloroplasts.
The partitioning of nitrate assimilation between root and shoot of higher plants
Authors: ANDREWS M.
Published: April 2006

Abstract The partitioning of nitrate assimilation between root and shoot of higher plant species is indicated by the relative proportions of total plant nitrate reductase activity (NRA) in the two plant parts and the relative concentrations of nitrate and reduced N in the xylem sap. These have been collated here from the literature and temperate and tropical species compared.

Both the distribution of NRA and xylem sap nitrate: reduced N indicate that the following four generalizations can be made.

Temperate, perennial species growing in low external nitrate concentrations (about 1 mol m−3) carry out most of their nitrate assimilation in the root. As external nitrate concentration increases (in the range found in agricultural soils, 1–20 mol m−3), shoot nitrate assimilation becomes increasingly important.

Temperate, annual legume species growing in low external nitrate concentrations carry out most of their nitrate assimilation in the root. Shoot nitrate assimilation increases in importance as external nitrate concentration is increased.

Temperate, annual non‐legume species vary greatly in their partitioning of nitrate assimilation between root and shoot when growing in low external nitrate concentrations. Regardless of the proportion carried out in the root at low external nitrate concentrations, nitrate assimilation in the shoot becomes increasingly important as external nitrate concentration is increased.

Tropical and subtropical species, annual and perennial, carry out a substantial proportion of their nitrate assimilation in the shoot when growing in low external nitrate concentrations. The partitioning of nitrate assimilation between root and shoot remains constant as external nitrate concentration increases.

It is proposed that a greater proportion of nitrate assimilation occurs in the shoot when an increase in the rate of nitrate uptake does not induce an increase in NR level in the root. Thus, a greater proportion of the nitrate taken up remains unassimilated and is passed into the xylem. A constant partitioning of nitrate assimilation between root and shoot is achieved by balancing NR levels in the root with rates of nitrate uptake.

The advantages and disadvantages of assimilating nitrate in either the root or shoot are discussed in relation to temperate and tropical habitats.
The effect of root temperature on the uptake of nitrogen and the relative size of the root system in Lolium perenne. I. Solutions containing both NH+4 and NO3−
Authors: CLARKSON D. T. , HOPPER M. J. , JONES L. H. P.
Published: April 2006

Abstract Lolium perenne L. cv. S23 was grown in flowing culture solution, pH 5, in which the concentrations of NH4+, NO3− and K+ were frequently monitored and adjusted to set values. In a pre‐experimental period, plants were acclimatized to a regime in which roots were treated at 5°C with shoots at 25°C. The root temperature was then changed to one of the following, 3, 7, 9, 11, 13, 17 or 25°C, while air temperature remained at 25°C.

When root temperature was increased from 5X, the relative growth rate of roots increased immediately while that of shoots changed much less for a period of approximately 9 d (phase 1). Thus, the root: shoot ratio increased, but eventually approached a new, temperature‐dependent, steady value (phase 2). The fresh: freeze‐dried weight ratio (i.e. water content) in shoots (and roots) increased during the first phase of morphological adjustment (phase 1).

In both growth phases and at all temperatures, plants absorbed more NH4+ than NO4+, the tendency being extreme at temperatures below 9° where more than 85% of the N absorbed was NH4+. Plants at different root temperatures, growing at markedly different rates, had very similar concentrations of total N in their tissues (cells) on a fresh weight basis, despite the fact that they derived their N with differing preference for NH4+. Specific absorption rates for NH4+, NOx−, K+ and H2PO4− showed very marked dependence on root temperature in phase 1, but ceased to show this dependence once a steady state root: shoot ratio had been established in phase 2.

The results indicate the importance of relative root size in determining ion fluxes at the root surface. At higher temperatures where the root system was relatively large, ‘demand’ per unit root was low, whereas at low temperatures roots were small relative to shoots and ‘demand’ was high enough to offset the inhibitory effects of low temperature on transport processes.
Effects of NaCl on ion relations and carbohydrate status of roots and on osmotic regulation of roots and shoots ofAtriplex amnicola
Authors: JESCHKE W. D. , ASLAM Z. , GREENWAY H.
Published: April 2006

AbstractAtriplex amnicolawas grown at 25, 200 or 400 mol m3NaCl. Root tissues at different stages of development were investigated for concentrations of K+, Na+and Mg2+, and in some cases for Cl−. Sugar and starch concentrations were measured for plants grown at 25 or 400 mol m3NaCl.

In the ‘slightly vaeuolated’ root tips, Na+was only 40 mol m−3at an external concentration of 400 mol m−3NaCl. The concentrations of K+were not affected substantially by external NaCl between 25 mol m−3and 400 mol m−3. The ‘highly vacuolated’ root tissues had substantially higher concentrations of K+, Na+and Cl−in plants grown at 200 and 400 mol m3NaCl than in plants grown at 25 mol m−3NaCl. Concentrations of Cr and of the sum of the cations in recently expanded tissue were similar to those in the bulk of the roots, consisting mainly of old cells. However, the K+: Na+decreased with age; at 400 mol m−3external NaCl with a K+: Na+of 0.012, the K+: Na+in recently expanded 12 mm root tips was as high as 1.6, compared with 0.7 for the bulk of the roots.

These ion data were used to estimate cytoplasmic and vacuolar concentrations of K+and Na+. Such calculations indicated that between 25 mol m3and 400 mol m−3external NaCl the concentration of the sum of (Na++K+) in the cytoplasm was maintained at about 180–200 mol m−3(cell water basis). In contrast, the (Na++ K+) concentration in the vacuole was 170 mol m−3for plants grown at 25 mol m−3NaCl and 420 mol 400 mol m−3NaCl.

The expanding root (issues exhibited greatly decreased soluble sugars and starch between dusk and dawn. Ai both times, sugar and starch concentrations in these tissues were 2.5–4.0 times greater in plants grown at 400 mol m−3NaCl compared with plants grown at 25 mol m−3NaCl. In contrast, carbohydrate concentrations in expanded root tissues were very similar at 25 and 400 mol m−3and showed little diurnal fluctuation.

This paper considers the causes for the slower growth ofA. amnicolaat 400 than at 25 mol m”3NaCl, using the data for the roots described here, and those for the shoots presented in the preceding paper (Aslamet al., 1986). There is no support for possible adverse effects by high internal ion concentrations. Instead, there may be deficiencies in supply of organic solutes for osmotic regulation; during part of the night a limited supply of such solutes may well restrict the rate of expansion of cells in plants growing at 400 mol m−3NaCl. There is insufficient evidence to decide whether this limitation in the expanding tissues is particularly prominent for the roots or for the shoots.
Effect of NaCl and polyethylene glycol on solute content and glycosidase activities during germination of lentil seeds
Authors: CORCHETE P. , GUERRA H.
Published: April 2006

Abstract Lentil seeds were sown in water and with different concentrations of polyethylene glycol (PEG) 4000 or NaCl. Radicle emergence and growth were delayed by these substances. In cotyledons under stress no variations in solutes occurred, whereas in embryonic axes an accumulation of soluble sugars was observed. The major constituents of the soluble carbohydrates were sucrose, galactose and mannose. Glycosidase activities were not significantly affected in PEG‐ or NaCl‐germinatcd seeds, except axis α‐galactosidase, whose activity during axis growth was higher under stress. Water and salt stress did not have a marked effect on carbohydrate metabolism in intact seedlings. The rate of release of 14C from [6‐14C]‐glucose was similar in the stressed seeds and in the control seeds.
Accumulation and subcellular distribution of cations in relation to the growth of potassium‐deficient barley
Authors: LEIGH R. A. , CHATER M. , STOREY R. , JOHNSTON A. E.
Published: April 2006

Abstract Growth of barley (Hordeum vulgare L., cv. Georgie) was insensitive to soil K content above about 150 mg kg−1, but at lower levels it declined. The reduction in yield was greater in soils containing approximately 10 mg Na kg−1 than in soils with about 90 mg kg−1 of Na. Growth was unaffected by changes in shoot K concentration above 75 mol m−3, but declined at lower concentrations, and the decrease was less in plants grown in soils with high Na. Growth responses were not simply related to tissue K concentrations because plants grown in soils with extra Na had higher yields but lower K concentrations.

When soil Na was low, plants accumulated Ca as tissue K declined, but when Na was provided this ion was accumulated. Plant Mg concentrations were generally low but increased as K decreased. The Ca and Mg were osmotically active. There were highly significant inverse linear relationships between yield and either the Ca or Mg concentrations in the shoots.

X‐ray microanalysis was used to examine the compartmentation of cations in leaves from barley plants (cv. Clipper) grown in nutrient solutions with high and low K concentrations. In plants grown with 2.5 mol m−3 K, this was the major cation in both the cytoplasm and vacuole of mesophyll cells. However, in plants grown with 0.02 mol m−3 K it declined to undetectable levels in the vacuole, although it was still detectable in the cytoplasm. In all plants, Ca was mainly located in epidermal cells. The implication of the results for explaining responses to K. in terms of compartmentation of solutes is discussed.
Nitrate and reduced‐N concentrations in the xylem sap of Stellaria media, Xanthium strumarium and six legume species
Authors: ANDREWS M.
Published: April 2006

Abstract At an applied nitrate concentration of 1 mol m−3, the proportion of xylem sap nitrogen as nitrate was < 15% for Cajanus cajan, Lupinus albus and Trifolium repens, 33% for Pisum sativum and within the range 57–62% for Glycine max, Phaseolus vulgar is, Stellaria media and Xanthium strumarium. At an applied nitrate concentration of 10 mol m∼3 the value had increased to 66% for T. repens while at 20 mol m−3 nitrate values had increased to 46, 51 and 49% for C. cajan, L. albus and Pisum sativum, respectively, and 89% and 85% for 5. media and X. strumarium, respectively. Glycine max and Phaseolus vulgaris differed from the other species in that the proportion of their xylem sap nitrogen as nitrate remained constant (∼ 60%) as applied nitrate concentration increased from 1 to 20 mol m−3.

The proportion of total plant nitrate reductase activity in the shoot of C. cajan, S. media and X. strumarium increased as applied nitrate concentration increased from 1 to 20 mol m−3. Values at the lower and upper concentrations were, respectively, 26 and 72% for C. cajan. 48 and 80% for X. strumarium and 68 and 87% for S. media. The partitioning of nitrate assimilation between root and shoot in these species is discussed.
The development of allergy in high‐risk children
Authors: BURR M. L. , MERRETT T. G. , DUNSTAN F. D. J. , MAGUIRE M. J.
Published: April 2006

Background
It is uncertain as to what extent the development of allergic disease in childhood is predictable during early infancy. A number of environmental factors have been suspected of increasing the risk of acquiring allergy, but the evidence is conflicting.

Objective
To observe the development of atopy and allergic disease in a cohort of high‐risk children so as to determine the importance of certain environmental factors and to study the relationship between early and later manifestations.

Methods
A cohort of infants, all at high risk of allergy, was followed up from birth to the age of 7 years. In half, selected at random, cow's milk protein was avoided for 4 months. Skin‐prick tests were performed and serum IgE measured in infancy and at 7 years, when an AlaTOP test was also performed.

Results
Skin sensitivity to egg in the first year of life was strongly associated with eczema, asthma, mite sensitivity and serum IgE at the age of 7 years, when mother's atopic history was associated with AlaTOP status, father's atopic history with skin sensitivity, and male sex with both. Maternal smoking during pregnancy was associated positively with IgE at 3 months and negatively with skin sensitivity at 7 years. The development of allergy was unrelated to infant feeding method or number of older siblings.

Conclusion
Allergic disease in childhood is to a large degree determined before birth or during infancy.
Interleukin‐4, interferon‐gamma and interleukin‐5 in peripheral blood of children with moderate atopic asthma
Authors: HOEKSTRA M. O. , HOEKSTRA Y. , DE REUS D. , RUTGERS B. , GERRITSE J. , KAUFFMAN H. F.
Published: April 2006

Background
In asthmatic inflammation, TH2 cells play an important role. TH2 cells specifically secrete cytokines like IL‐4 and IL‐5. IL‐4 stimulates IgE production and IL‐5 is involved in hemopoiesis, chemotaxis, priming and activation of eosinophils. IFNγ, produced by TH1 cells, has an inhibitory action on IgE production.

Objectives
To investigate the TH1/TH2‐cell pattern in the cytokine production of peripheral blood of asthmatic children. We determined IL‐4, IFNγ and IL‐5 in serum and in supematants of unstimulated and stimulated (24 h with Concanavaline A) cultures of peripheral blood mononuclear cells (PBMCs) in 22 children with moderate asthma (mean age 9.3 years) and in 17 healthy controls (mean age 10.3 years). All children visited the outpatient department (OPD) where history taking, physical examination and blood sampling took place. Children younger than 8 years of age performed symptom and peak flow registration during 1 week after the visit to the OPD.

Results
The number of eosinophils were significantly higher in children with asthma, compared with healthy controls. The concentration of IFNγ in supematants of cultures of stimulated PBMCs was significantly lower and the ratio of IL‐4/IFNγ was significantly higher in children with asthma compared with healthy controls. The FEV1 was directly and IgE was inversely related to the concentration of IFNγ in supematants of cultures of stimulated PBMCs.

Conclusion
IFNγ may play an important role in the pathophysiology of childhood atopic asthma.
Asthma among secondary schoolchildren in relation to the school environment
Authors: SMEDJE G. , NORBÄCK D. , EDLING C.
Published: April 2006

Background
Poor indoor air quality has been suggested to be related to the increase in the prevalence of asthma that has occurred in the western world, especially among children and young persons. Apart from the home, school is the most important indoor environment for children.

Objectives
The aims were to study the prevalence of current asthma among secondary pupils and its relationship to the school environment, but also to personal factors and domestic exposures.

Methods
Data on asthmatic symptoms, other health aspects, and domestic exposures were gathered using a questionnaire which was sent to 762 pupils in the seventh form (13–14 years old) in 11 randomly chosen schools in the county of Uppsala in Sweden. Pupils answering‘yes’ to having had asthma diagnosed by a physician, and having had recent asthma attacks, or who used asthma medication were defined as having current asthma. Data on exposures at school were gathered by measurements in 28 classrooms. The relationship between asthma and exposures was analysed by multiple logistic regression.

Results
The questionnaire was completed by 627 (82%). Current asthma was found among 40 pupils (6.4%). Current asthma was more common in those who had an atopic disposition, or food allergy, or who had attended a day care centre for several years. Controlling for these factors, current asthma was related to several factors in the school environment. There were more pupils with current asthma in schools that were larger, had more open shelves, lower room temperature, higher relative air humidity, higher concentrations of formaldehyde or other volatile organic compounds, viable moulds or bacteria or more cat allergen in the settled dust.

Conclusions
Although the pupils attended school for a minor part of their time, our study indicates that the quality of the school environment is of importance and may affect asthmatic symptoms.
Immunotherapy vs inhaled budesonide in bronchial asthma: an open, parallel, comparative trial
Authors: SHAIKH W. A.
Published: April 2006

Background
Budesonide, an inhaled corticosteroid and specific immunotherapy, are both routinely used in the treatment of bronchial asthma. However, there are as yet, no studies comparing the effects of budesonide vs immunotherapy.

Objective
The aim of this study is to compare the effects of budesonide with immunotherapy in patients having perennial asthma.

Methods
This study is an open, parallel, comparative trial, in which 51 young patients were administered either immunotherapy or budesonide for 1 year and their global symptom scores and FEV1, values assessed. Both treatments were abruptly discontinued after 12 months and the effects of cessation analysed.

Results
The use of budesonide resulted in a faster and more striking improvement during the first few months as compared to immunotherapy, with an even more rapid decline in benefits on cessation of budesonide. Immunotherapy on the other hand, resulted in slow but steady improvement which did not decline as rapidly as budesonide on cessation.

Conclusion
Although this was an open trial, it could be concluded that relief with inhaled corticosteroids in bronchial asthma is more rapid than immunotherapy; however the decline in benefit on cessation of inhaled cortieosteroid is even more rapid, a phenomenon not seen with immunotherapy.
Characterization of allergens in Apiaceae spices: anise, fennel, coriander and cumin
Authors: JENSEN‐JAROLIM E. , LEITNER A. , HIRSCHWEHR R. , KRAET D. , WÜTHRICH B. , SCHEINER O. , GRAF J. , EBNER C.
Published: April 2006

Background
Symptoms elicited by IgEmediated food allergy range from mild local to severe systemic reactions. Allergens in spices are particularly dangerous due to their hidden presence in many dishes.

Objectives and Methods
According to clinical observations, mugwort and birch pollen allergy, and hypersensitivity to spices are frequently associated, but the crossreacting compounds were not defined so far. We tested sera of 15 patients who experienced adverse reactions to spiced food and characterized their IgE‐binding patterns on anise, fennel, coriander and cumin extracts through immunoblot and inhibition experiments.

Results
The use of anti‐Bet v 1 (MoAb) and anti‐profilin (rabbit) antibodies revealed the presence of crossreacting allergens in the tested spice extracts. Inhibition experiments showed that IgE‐binding to allergens in Apiaceae spices could be blocked by preincubation of sera with rBet v I or rBet v 2 (birch profilin). Moreover, we detected crossreacting allergenic molecules in the molecular weight range of 60kDa. IgE‐binding to spice allergens occurred only with sera of 10/15 (66%) patients with allergy to pollen (birch, niugwort) and/or celeriac. In five out of 15 (33%) patients with a history of adverse reaction to spices, but without pollen and celeriac allergy, no IgE‐binding to any spice protein could be demonstrated. It is possible that these clinical reactions could bo elicited by other types of hypersensitivity (Type II. IIII, IV), however, as spices contain highly reactive substances, the symptoms may most likely be classified as food‐intolerant.

Conclusions
Bet v 1‐ and profilin‐related allergens may, besides higher molecular weight allergenic molecules, be responsible for Type I allergy to anise, fennel, coriander or cumin, members of the Apiaceae.