bluuebunny/crossref_metadata_2025 huggingface dataset:
Positive responses to Zn and Cd by roots of the Zn and Cd hyperaccumulator Thlaspi caerulescens
Authors: WHITING STEVEN N. , LEAKE JONATHAN R. , McGRATH STEVE P. , BAKER ALAN J. M.
Published: March 2003

The effects of localized zinc (ZnO) and cadmium (CdS) enrichment on the allocation of root biomass, root length and partitioning of current assimilate within root systems of the Zn hyperaccumulator Thlaspi caerulescens were investigated using a rhizobox system. The rhizoboxes contained either homogeneous soil or juxtaposed control and metal‐enriched soil. In the heterogeneous treatments the Zn‐enriched soil contained 250, 500 or 1000 mg Zn kg−1. The plants consistently allocated c. 70% of their total root biomass and length into the metal‐enriched soil. Moreover, 70% of the current assimilate (14C) allocated to the roots was localized in the Zn‐enriched soil of the heterogeneous treatments. The concentration of Zn (250–1000 mg kg−1) in the enriched soil had no effect on these patterns of root allocation, nor were there significant effects of the Zn treatments on the total root or shoot biomass of the plants. The positive responses to the localized metal treatments were therefore characterized by a concomitant reduction in root allocation into the control soil. In contrast to T. caerulescens, when grown with juxtaposed control and Zn‐enriched soil the non‐accumulator Thlaspi arvense showed reduced root allocation into a patch enriched with 500 mg kg−1 Zn. In a further experiment, two populations of T. caerulescens that differ in their abilities to accumulate Cd were grown with juxtaposed control and Cd‐enriched soil. The plants from a population that accumulated Cd also showed increased root biomass and root length allocation into the Cd‐enriched soil. Plants from the population that did not accumulate Cd showed no such increase. The possibility that T. caerulescens forages for metals, and the precision of its root allocation with respect to localized metal enrichment is highlighted. The significance of these findings for the selection of hyperaccumulator plants for use in the phytoextraction of Zn and Cd from mine spoils (phytomining) and the phytoremediation of heterogeneous contaminated soils are discussed.
Nitrogen inhibition of nodulation and N2 fixation of a tropical N2‐fixing tree (Gliricidia sepium) grown in elevated atmospheric CO2
Authors: THOMAS R. B. , BASHKIN M. A. , RICHTER D. D.
Published: March 2003

Interactive effects of elevated atmospheric CO2 and soil N availability on N2 fixation and biomass production were examined using Gliricidia sepium, a tropical leguminous tree species. Our objective was to determine if elevated CO2 alters the inhibitory effects of soil N on N2 fixation, and whether the response of Gliricidia to elevated CO2 was a function of N source originating from either substrate N fertilizer or N2 fixation. We hypothesized that CO2 enrichment would ameliorate the inhibitory effects of N fertilization on seedling nodulation and N2 fixation through increased C partitioning to nodules. Seedlings were grown from seed for 100 d in growth chambers at either 350 or 700 μmol mol−1 CO2. Seedlings were inoculated with Rhizobium spp. and grown either with 0, 1 or 10 mM N fertilizer. The δ15N isotope‐dilution technique was used to determine N source partitioning between N2 fixation and inorganic N fertilizer uptake. The addition of 10 mM N fertilizer significantly reduced nodule number and mass, specific nitrogenase activity, the specific rate of N2 fixation, and the proportion of plant N derived from N2 fixation. Elevated CO2, however, strongly ameliorated the inhibitory effects of N fertilization, indicating that increased C availability for nodule activity may partially offset the inhibition of N2 fixation caused by substrate N, as nodule sugar concentrations were stimulated with CO2 enrichment. This study clearly shows that elevated CO2 enhanced plant productivity and net N content of Gliricidia tree seedlings by stimulating N2 fixation. In addition, seedling biomass production was greatly enhanced by elevated CO2, regardless of whether plant N was derived from the substrate or from the atmosphere. We conclude from this study that CO2 enrichment mitigates the inhibitory effects of substrate N on nodule initiation and development and specific N2 fixation, either
through increased C allocation to nodule production and activity, or through increased N demand by the plant for biomass production. This experiment with Gliricidia provides evidence for a positive feedback between increased atmospheric CO2 concentrations, C allocation to symbiotic N2‐fixing bacteria, and plant C and N accumulation that may occur when N2‐fixing plants are grown under conditions where substrate N may typically inhibit N2 fixation.
Sloughing of cap cells and carbon exudation from maize seedling roots in compacted sand
Authors: IIJIMA MORIO , GRIFFITHS BRYAN , BENGOUGH A. GLYN
Published: March 2003

Sloughing of root cap cells and exudation of mucilage plays an important role in the penetration of compacted soils by roots. For the first time we have quantified the rate of sloughing of root cap cells in an abrasive growth medium that was compacted to create mechanical impedance to root growth. The number of maize (Zea mays) root cap cells
sloughed into sand increased as a result of compaction, from 1930 to 3220 d−1 per primary root. This represented
a 12‐fold increase in the number of cells sloughed per mm root extension (from 60 to >700). We estimated that
the whole of the cap surface area was covered with detached cells in compacted sand, compared with c. 7% of the
surface area in loose sand. This lubricating layer of sloughed cells and mucilage probably decreases frictional
resistance to soil penetration. The total carbon deposited by the root was estimated at c. 110 μg g−1 sand d−1. Sloughed cells accounted for <10% of the total carbon, the vast majority of carbon being contained in mucilage exudates.
Correlations of stomatal conductance with hydraulic and chemical factors in several deciduous tree species in a natural habitat
Authors: AUGÉ ROBERT M. , GREEN CRAIG D. , STODOLA ANN J. W. , SAXTON ARNOLD M. , OLINICK JOSHUA B. , EVANS RICHARD M.
Published: March 2003

Recent research in whole‐plant stomatal physiology, conducted largely with potted plants in controlled environments, suggests that stomatal conductance (gs) might be more closely linked to plant chemical variables
than to hydraulic variables. To test this in a field situation, seasonal gs was examined in relation to a number of
plant and environmental variables in 11 temperate, deciduous forest tree species. Stomatal conductance was
generally better correlated with environmental variables (air temperature, vapor pressure deficit, PPFD) than with
plant variables, and slightly better correlated with plant hydraulic variables (shoot water and osmotic potentials)
than with plant chemical variables (xylem sap ABA concentration, xylem sap pH). We examined a model,
developed previously for maize, which describes regulation of gs by xylem sap ABA concentration with leaf water
status acting to modify stomatal sensitivity to the ABA signal. This model explained slightly more variation in
seasonal gs in the forest trees than did single plant variables but not more variation than most single environmental
variables. Response surface models, especially those incorporating environmental variables, were more consistently
successful at explaining gs across species.
Fungal species‐specific responses of ectomycorrhizal Scots pine (Pinus sylvestris) to elevated [CO2]
Authors: GORISSEN A. , KUYPER TH. W.
Published: March 2003

Ectomycorrhizal seedlings of Scots pine (Pinus sylvestris) inoculated with the nitrotolerant Laccaria bicolor and the nitrophobic Suillus bovinus were exposed to ambient (350 μl l−1) and elevated (700 μl l−1) [CO2]. After 79 d the seedlings were labelled for 28 d with 14CO2, after which they were harvested. 14C was determined in shoots, roots plus mycorrhizas, soil, and below‐ground respiration; nitrogen was determined in shoots and roots. Total net 14C uptake increased under elevated [CO2]. The extra carbon did not increase the shoot mass but was translocated to the roots and resulted in a decreased shoot‐to‐root ratio in the Suillus‐inoculated seedlings. Laccaria‐inoculated seedlings did not incorporate the additional carbon in root or fungal tissue but only increased below‐ground respiration. S. bovinus acquired or transferred nitrogen better than L. bicolor and enabled the seedlings to perform better with regard to net carbon uptake under elevated [CO2]. This resulted in nitrogen concentrations in shoots of Suillus‐inoculated seedlings that were twice as high as in Laccaria‐inoculated seedlings, irrespective of [CO2]. The higher nitrogen concentration in the shoots resulted in a doubling of the 14C uptake per unit shoot mass. Our results suggest that the ability of ectomycorrhizal Scots pine seedlings to respond positively to elevated atmospheric [CO2] is strongly fungal‐species specific.
Microsatellite high‐density mapping of the stripe rust resistance gene YrH52 region on chromosome 1B and evaluation of its marker‐assisted selection in the F2 generation in wild emmer wheat
Authors: PENG J. H. , FAHIMA T. , RÖDER M. S. , LI Y. C. , GRAMA A. , NEVO E.
Published: March 2003

A new stripe rust resistance gene, YrH52, derived from the unique Mount Hermon population of wild emmer wheat (Triticum dicoccoides) in Israel, was previously located on chromosome 1B. The main objectives of the present study were to increase marker density in the vicinity of the YrH52 gene using additional microsatellite markers, and to evaluate the accuracy and efficiency of marker‐assisted selection on this gene in the F2 generation. By means of 70 additional microsatellite primer pairs, 150 individuals of the F2 mapping population were genotyped. Among 202 marker loci, 20 were found to be linked to the YrH52 gene with log‐likelihood (LOD) scores ranging from 3.84 to 58.82, and linkage distances ranging from 0.33 to 41.39 cM. A genetic map was constructed of chromosome 1B, consisting of 23 markers and the YrH52 gene, with a total map length of 149.5 cM. Most of the markers were located in the region close to YrH52, which was flanked by Xgwm413 and Xgwm273a with map distances of 1.3 and 2.7 cM, respectively. The accuracy and efficiency of marker‐assisted selection were calculated as AMAS and EMAS, respectively, for homozygous resistant genotypes of YrH52 gene in the F2 generation. AMAS and EMAS for homozygous resistant genotypes of the YrH52 gene in the F2 generation showed linear and significant negative correlation with the map distance between marker and target gene or between the two bracketing markers. It was concluded that the YrH52 region on chromosome 1B is significantly more enriched by microsatellite markers than the previously published map; that a single microsatellite marker is efficient for marker‐assisted selection of homozygous resistant genotypes of YrH52 gene in the F2 generation when the map distance is <5.0 cM; and that when two markers are used AMAS can be dramatically improved and becomes relatively stable, whereas EMAS will not be obviously improved and will still vary linearly with map distance.
Kinetics of nutrient uptake by roots: responses to global change
Authors: BASSIRIRAD HORMOZ
Published: March 2003

There is a growing recognition that accurate predictions of plant and ecosystem responses to global change require a better understanding of the mechanisms that control acquisition of growth‐limiting resources. One such key mechanism is root physiological capacity to acquire nutrients. Changes in kinetics of root nitrogen (N) uptake might influence the extent to which terrestrial ecosystems will be able to sequester excesses in carbon (C) and N loads. Despite its significant role in determining plant and ecosystem cycling of C and N, there is little information on whether, or how, root nutrient uptake responds to global change. In this review various components of global change, namely increased CO2 concentration, increased soil temperature and increased atmospheric N deposition
and their effects on kinetics of root nutrient uptake are examined. The response of root nutrient uptake kinetics
to high CO2 is highly variable. Most of this variability might be attributable to differences in experimental
protocols, but more recent evidence suggests that kinetic responses to high CO2 are also species‐specific. This
raises the possibility that elevated CO2 might alter community composition by shifting the competitive interaction
of co‐occurring species. Uptake of NH4+ and NO3− seem to be differentially sensitive to high CO2, which could
influence ecosystem trajectory toward N saturation. Increased soil temperature might increase N and P uptake
capacity to a greater extent in species from warm and fluctuating soil habitats than in species from cold and stable
soil environments. The few available data also indicate that increased soil temperature elicits a differential effect
on uptake of NH4+ versus NO3−. Root uptake kinetics are generally down‐regulated in response to long‐term exposure to atmospheric N deposition. The extent of this down‐regulation might, however, vary among species, stages of succession, land‐use history and plant demand. Nonetheless, it is suggested that root N uptake kinetics might be an accurate biological indicator of the ecosystem capacity to retain N. The results reviewed here clearly highlight the scanty nature of the literature in the area of root nutrient absorption responses to global change. It is also clear that effects of one component of global change on root nutrient absorption capacity might be counterbalanced by another. Therefore, the generalizations offered here must be viewed with caution and more effort should be directed to rigorously test these initial observations in future research.
Dynamics of root systems in native grasslands: effects of elevated atmospheric CO2
Authors: ARNONE J. A. , ZALLER J. G. , SPEHN E. M. , NIKLAUS P. A. , WELLS C. E. , KÖRNER C.
Published: March 2003

The objectives of this paper were to review the literature on the responses of root systems to elevated CO2 in intact,
native grassland ecosystems, and to present the results from a 2‐yr study of root production and mortality in an
intact calcareous grassland in Switzerland. Previous work in intact native grassland systems has revealed that
significant stimulation of the size of root systems (biomass, length density or root number) is not a universal
response to elevated CO2. Of the 12 studies reviewed, seven showed little or no change in root‐system size under
elevated CO2, while five showed marked increases (average increase 38%). Insufficient data are available on the
effects of elevated CO2 on root production, mortality and life span to allow generalization about effects. The
diversity of experimental techniques employed in these native grassland studies also makes generalization difficult.
In the present study, root production and mortality were monitored in situ in a species‐rich calcareous grassland
community using minirhizotrons in order to test the hypothesis that an increase in these two measures would help
explain the increase in net ecosystem CO2 uptake (net ecosystem exchange) previously observed under elevated
CO2 at this site (600 vs 350 μl CO2 l−1; eight 1.2‐m2 experimental plots per CO2 level using the screen‐aided CO2
control method). However, results from the first 2 yr showed no difference in overall root production or mortality
in the top 18 cm of soil, where 80–90% of the roots occur. Elevated CO2 was associated with an upward shift in
root length density: under elevated CO2 a greater proportion of roots were found in the upper 0–6‐cm soil layer,
and a lower proportion of roots in the lower 12–18 cm, than under ambient CO2. Elevated CO2 was also associated
with an increase in root survival probability (RSP; e.g. for roots still alive 280 d after they were produced under
ambient CO2, RSP = 0.30; elevated CO2, RSP = 0.56) and an increase (48%) in median root life span in the
deepest (12–18 cm) soil layer. The factors driving changes in root distribution and longevity with depth under
elevated CO2 were not clear, but might have been related to increases in soil moisture under elevated CO2
interacting with vertical patterns in soil temperatures. Thus extra CO2 taken up in this grassland ecosystem during
the growing season under elevated CO2 could not be explained by changes in root production and mortality.
However, C and nutrient cycling might be shifted closer to the soil surface, which could potentially have a
substantial effect on the activities of soil heterotrophic organisms as CO2 levels rise.
Nitrogen fixation by Baltic cyanobacteria is adapted to the prevailing photon flux density
Authors: EVANS A. M. , GALLON J. R. , JONES A. , STAAL M. , STAL L. J. , VILLBRANDT M. , WALTON T. J.
Published: March 2003

N2 fixation, measured as acetylene reduction, was studied in laboratory cultures and in natural assemblages (both
as a mixed population and as individually picked colonies) of the heterocystous cyanobacteria Aphanizomenon sp.
and Nodularia spp. from the Baltic Sea. During a diurnal cycle of alternating light and darkness, these organisms
reduced acetylene predominantly during the period of illumination, although considerable activity was also
observed during the dark period. In both laboratory cultures and natural populations N2 fixation was saturated
below a photon flux density of 600 μm−2 s−1. In cyanobacterial blooms in the Baltic Sea, nitrogenase activity was
mostly confined to the surface layers. Samples collected from greater depths did not possess the same capacity for
acetylene reduction as samples from the surface itself, even when incubated at the photon flux density prevailing
in surface waters. This suggests that, with respect to N2 fixation, Baltic cyanobacteria are adapted to the intensity of illumination that they are currently experiencing.
Tansley Review No. 113
Authors: WHITE PHILIP J. , BROADLEY MARTIN R.
Published: March 2003

Caesium (Cs) is a Group I alkali metal with chemical properties similar to potassium (K). It is present in solution as the monovalent cation Cs+. Concentrations of the stable caesium isotope 133Cs in soils occur up to 25 μg g−1
dry soil. This corresponds to low micromolar Cs+ concentrations in soil solutions. There is no known role for Cs
in plant nutrition, but excessive Cs can be toxic to plants. Studies of the mechanism of Cs+ uptake are
important for understanding the implications arising from releases of radioisotopes of Cs, which are produced in
nuclear reactors and thermonuclear explosions. Two radioisotopes of Cs (134Cs and 137Cs) are of environmental
concern owing to their relatively long half‐lives, emissions of β and γ radiation during decay and rapid
incorporation into biological systems. The soil concentrations of these radioisotopes are six orders of magnitude
lower than those of 133Cs. Early physiological studies demonstrated that K+ and Cs+ competed for influx to excised
roots, suggesting that the influx of these cations to root cells is mediated by the same molecular mechanism(s). The
molecular identity and/or electrophysiological signature of many K+ transporters expressed in the plasma
membrane of root cells have been described. The inward‐rectifying K+ (KIR), outward‐rectifying K+ (KOR) and
voltage‐insensitive cation (VIC) channels are all permeable to Cs+ and, by analogy with their bacterial
counterparts, it is likely that ‘high‐affinity’ K+/H+ symporters (tentatively ascribed here to KUP genes) also
transport Cs+. By modelling cation fluxes through these transporters into a stereotypical root cell, it can be
predicted that VIC channels mediate most (30–90%) of the Cs+ influx under physiological conditions and that the
KUP transporters mediate the bulk of the remainder. Cation influx through KIR channels is likely to be blocked
by extracellular Cs+ under typical ionic conditions in the soil. Further simulations suggest that the combined Cs+
influxes through VIC channels and KUP transporters can produce the characteristic ‘dual isotherm’ relationship
between Cs+ influx to excised roots and external Cs+ concentrations below 200 μM. Thus, molecular targets for
modulating Cs+ influx to root cells have been identified. This information can be used to direct future genetic modification of plants, allowing them to accumulate more, or less, Cs and thereby to remediate contaminated sites.

contents

Summary
241

I.
introduction: caesium in the environment
242

II.
uptake of caesium by plant roots
243

III.
molecular mechanisms catalysing caesium uptake
245

IV.
modelling caesium influx to root cells
249

V.
perspective
253

Acknowledgements
254

References
254
The base of the leaf acts as a localized sink for photosynthate in mature barley leaves
Authors: SHAIKH NASIR UDDIN , QUICK W. PAUL , ROLFE STEPHEN A.
Published: March 2003

The gradients in photosynthetic and carbohydrate metabolism which persist within the fully expanded second leaf of barley (Hordeum vulgare) were examined. Although all regions of the leaf blade were green and
photosynthetically active, the basal 5 cm, representing approximately 20% of the leaf area, retained some
characteristics of sink tissue. The leaf blade distal from the leaf sheath exhibited characteristics typical of source
tissue; the activities of sucrolytic enzymes (invertase and sucrose synthase) were relatively low, whilst that of
sucrose phosphate synthase was high. These regions of the leaf accumulated sucrose throughout the photoperiod
and starch only in the second half of the photoperiod whilst hexose sugars remained low. By contrast the leaf blade
proximal to the leaf sheath retained relatively high activities of sucrolytic enzymes (especially soluble, acid
invertase) whilst sucrose phosphate synthase activity was low. Glucose, as well as sucrose, accumulated throughout
the photoperiod. Although starch accumulated in the second half of the photoperiod, a basal level of starch was
present throughout the photoperiod, by contrast with the rest of the leaf. The 14CO2 feeding experiments indicated that a constant amount of photosynthate was partitioned towards starch in this region of the leaf irrespective of irradiance. These findings are interpreted as the base of the leaf blade acting as a localized sink for carbohydrate as a result of sucrose hydrolysis by acid invertase.
In vitro germination of nonphotosynthetic, myco‐heterotrophic plants stimulated by fungi isolated from the adult plants
Authors: BRUNS THOMAS D. , READ DAVID J.
Published: March 2003

Sarcodes sanguinea and Pterospora andromedea (Ericaceae, Monotropoideae) are nonphotosynthetic myco‐heterotrophic plants. Recent studies have shown that the roots of the adult plants are always associated with closely
related but exclusive sets of Rhizopogon species (Basidiomycota, Boletales) from section Amylopogon. We have
isolated Rhizopogon species that were associated with the adult plants and used them to germinate seeds under
gnotobiotic conditions. All Rhizopogon species isolated from either plant species were capable of stimulating seed
germination in both Sarcodes and Pterospora. Under the primary conditions used, germination varied from 9 to
73% in the case of Sarcodes and 0 to 13% in that of Pterospora. The single Rhizopogon strain that failed to elicit
germination in Pterospora under these conditions did stimulate germination under slightly different conditions. By
contrast, seeds failed to germinate on all media which lacked these Rhizopogon species, or in the presence of six
other genera of basidiomycetes. Seed germination could be stimulated either through cellophane or at the edge of
fungal colonies without direct fungus–seed contact. These results suggest that a diffusible or volatile compound
that is unique to Rhizopogon stimulates germination of these plant seeds. Seed lots of Sarcodes from two successive
years had similar germination levels. Sarcodes seeds that had overwintered under natural conditions were also
stimulated to germinate. These results demonstrate the potential for long‐term dormancy. We suggest that
a combination of dormancy and the use of specific germination cues might increase the opportunities of these
plants for recruitment. In addition, the specific germination response explains at least a part of the specialized
associations observed in the adult plants. Nevertheless, the seeds respond to a slightly broader range of Rhizopogon species than has been observed to be associated with the adult plants; thus other factors must also be involved with specificity under natural conditions.
Pseudothecia of Swiss needle cast fungus, Phaeocryptopus gaeumannii, physically block stomata of Douglas fir, reducing CO2 assimilation
Authors: MANTER DANIEL K. , BOND BARBARA J. , KAVANAGH KATHLEEN L. , ROSSO PABLO H. , FILIP GREGORY M.
Published: March 2003

The following study investigates the timing and mechanism of impact of Swiss needle cast on Douglas‐fir (Pseudotsuga menziesii) needle physiology (i.e. gas exchange). Swiss needle cast is a foliar disease caused by the fungus Phaeocryptopus gaeumannii, which occurs throughout the range of Douglas fir and until recently has been considered unimportant. However, recent surveys show the Swiss needle cast currently affects > 52611 ha of forested lands in western Oregon, USA, causing a reduction in growth of c. 23% or an implied growth loss of c. 3.2 m3 ha−1 yr−1 for 1996 alone. Gas exchange of artificially inoculated 2‐yr‐old Douglas‐fir seedlings was monitored on a monthly basis using A/Ci curve analysis. No effect of fungal presence on gas exchange was noted until the emergence of fungal fruiting structures (pseudothecia) from needle stomata. However, once present, maximum stomatal conductance and CO2 assimilation rates were inversely proportional to the presence of pseudothecia. A/Ci curve analysis showed that declines in CO2 assimilation appeared to be due to both stomatal and nonstomatal limitations. Stomatal limitations to CO2 assimilation were the direct result of reduced CO2 diffusion through blocked stomata. Nonstomatal limitations arose, in part, from an indirect effect of pseudothecia development on Rubisco activation. For example, in both Swiss needle cast‐infected foliage and foliage with artificially blocked stomata (by external application of petroleum jelly), the amount of Rubisco activation showed a strong, positive relationship with daily maximum stomatal conductance. A mechanism is proposed that outlines the impact of pseudothecia development on stomatal conductance and CO2 assimilation rates.
Sap velocity and canopy transpiration in a sweetgum stand exposed to free‐air CO2 enrichment (FACE)
Authors: Wullschleger Stan D. , Norby Richard J.
Published: March 2003

Canopy transpiration rates, as a major component of forest hydrologic budgets, are reported for 12‐yr‐old sweetgum (Liquidambar styraciflua) trees growing in a free‐air CO2 enrichment (FACE) study in eastern Tennessee, USA.

 The compensated heat‐pulse technique was used to measure rates of sap velocity, and stand transpiration was estimated as a function of measured sap velocity, total stand sapwood area and the fraction of sapwood functional in water transport.

 Sap velocity averaged 13% less for trees in elevated compared with ambient CO2 concentration. Stand transpiration reached 5.6 and 4.4 mm d−1 for the ambient and elevated CO2 treatments, respectively. Stratification of the data showed that significant differences in stand transpiration were observed between ambient and elevated CO2 only at mean daily radiation levels > 400 J m−2 s−1 and at vapor pressure deficits > 1.0 kPa.

 These data illustrate that while elevated CO2 may reduce canopy transpiration, the apparent dependency of such an effect on prevailing weather makes detecting a CO2‐induced impact on forest water use difficult.
Modelling the response of wheat canopy assimilation to atmospheric CO2 concentrations
Authors: Rodriguez D. , Ewert F. , Goudriaan J. , Manderscheid R. , Burkart S. , Weigel H. J.
Published: March 2003

•  The predictive capacity of two simulation models with different degrees of complexity for the calculation of assimilate production, was tested at different time scales, using a data set of wheat grown in an open‐top‐chamber experiment at two CO2 concentrations.

•  Observed values of net canopy assimilation (Pn) were obtained from wheat plants grown at ambient (410 µmol mol−1) and elevated (680 µmol mol−1) CO2 mole fractions. Pn was simulated by using either simple multiple regression equations (AFRCWHEAT2) or by highly detailed calculations of leaf energy balances and the coupling of photosynthesis with stomatal conductance (LINTULCC2).

•  Irrespective of the developmental stage of the crop or variation in weather, the models accurately simulated canopy assimilation and growth. We conclude that the response of aboveground‐biomass production to elevated CO2 concentrations was explained primarily by the effects of CO2 on radiation‐use efficiency and assimilate production.

•  The models explained satisfactorily the daily course of Pn, its integrated daily totals, and the seasonally produced aboveground biomass, both at ambient and elevated CO2 concentrations. Specific problems in the simulations were identified and discussed.
Interpretation of bioassays in the study of interactions between soil organisms and plants: involvement of nutrient factors
Authors: Troelstra S. R. , Wagenaar R. , Smant W. , Peters B. A. M.
Published: March 2003

Increased plant growth in sterilized soil is usually ascribed to the elimination of (often unidentified) soil‐borne pathogens. Plant–soil bioassays are reported here for three dune soils and two plant species (Ammophila arenariaandCarex arenaria).

 Dynamics of plant growth, availability and uptake of nutrients were compared in sterilized (25 kGy gamma‐irradiation) vs control soils.

 Plant growth, availability and acquisition of nutrients, for example P, even when provided in apparent excess, were significantly enhanced in gamma‐irradiated calcareous dune sands. WithA. arenaria, the positive sterilization effect occurred independently of initial plant dry mass. The addition of extracts of planted soils toA. arenariagrowing in unsterilized sand caused an increase in root growth that could not be related to either nutrients or pathogens.

 Increased availability and acquisition of nutrients in sterilized soil may contribute to nonsterile : sterile ratios of plant growth that are < 1. Any ecological speculation involving the role of soil‐borne biological factors should be based on fully validated plant–soil bioassays, which account for nutritional or other nonpathogen‐related side‐effects induced by soil sterilization.
Species‐specific responses of a root‐ and shoot‐feeding insect to arbuscular mycorrhizal colonization of its host plant
Authors: Gange Alan C.
Published: March 2003

The responses of root‐feeding black vine weevil (Otiorhynchus sulcatus) larvae and leaf‐feeding adults to colonization of strawberry (Fragaria x ananassa) plants by one or two species of arbuscular mycorrhizal fungi are reported here.

 Glomus mosseae and Glomus fasciculatum were isolated from a commercial field and used to colonize strawberry plants, singly and in combination. Vine weevil larvae were reared on roots of colonized and uncolonized plants. When the larvae were mature, leaves from all plants, with and without larvae, were fed to adult weevils.

 Colonization by either fungus reduced larval survival and biomass. However, colonization by both fungi had no effect on the larvae. These effects were manifested in changes in plant performance; weevil feeding decreased plant foliar and root biomass as well as runner production, but only when mycorrhizas were absent or inoculated together. Mycorrhizas also mitigated the effects of larval feeding on adult weevils.

 The response of root‐feeding insects to arbuscular mycorrhizal colonization depends on which fungi are present in the root system. Furthermore, arbuscular mycorrhizal fungi might play a critical role in mitigating interactions between phytophagous insects.
Receptor serine/threonine protein kinases in signalling: analysis of the erecta receptor‐like kinase of Arabidopsis thaliana
Authors: Lease Kevin A. , Lau Nelson Y. , Schuster Robert A. , Torii Keiko U. , Walker John C.
Published: March 2003

The Arabidopsis ERECTA (ER) gene regulates elongation of above‐ground organs. ER encodes a member of the leucine‐rich repeats–receptor‐like protein kinases (LRR–RLK) gene family, with the predicted protein containing a signal peptide, 20 leucine‐rich repeats in the extracellular domain, a transmembrane domain, and a cytoplasmic serine/threonine protein kinase domain. The structural features of the predicted ER protein suggest its role in cell–cell signalling is through phosphorylating serine/threonine residues. Consistent with this hypothesis, in vitro protein kinase analysis indicates that ER is a functional serine/threonine protein kinase. Furthermore, a large‐scale genetic screen was conducted to analyse new mutations in the erecta gene; 16 new er alleles were isolated, all of which were recessive. Here we present the identification of molecular lesions of seven alleles of er, which suggests the hypothesis that ERECTA might employ a mode of action distinct from other RLKs such as Xa21 or CLAVATA1, which function in disease resistance and developmental pathways, respectively.
Calmodulin as a versatile calcium signal transducer in plants
Authors: Snedden Wayne A. , Fromm Hillel
Published: March 2003

The complexity of Ca2+ patterns observed in eukaryotic cells, including plants, has led to the hypothesis that specific patterns of Ca2+ propagation, termed Ca2+ signatures, encode information and relay it to downstream elements (effectors) for translation into appropriate cellular responses. Ca2+‐binding proteins (sensors) play a key role in decoding Ca2+ signatures and transducing signals by activating specific targets and pathways. Calmodulin is a Ca2+ sensor known to modulate the activity of many mammalian proteins, whose targets in plants are now being actively characterized. Plants possess an interesting and rapidly growing list of calmodulin targets with a variety of cellular roles. Nevertheless, many targets appear to be unique to plants and remain uncharacterized, calling for a concerted effort to elucidate their functions. Moreover, the extended family of calmodulin‐related proteins in plants consists of evolutionarily divergent members, mostly of unknown function, although some have recently been implicated in stress responses. It is hoped that advances in functional genomics, and the research tools it generates, will help to explain themultiplicity of calmodulin genes in plants, and to identify their downstream effectors. This review summarizes current knowledge of the Ca2+–calmodulin messenger system in plants and presents suggestions for future areas of research.

Contents

I.
Introduction
36

II.
CaM isoforms and CaM‐like proteins
37

III.
CaM‐target proteins
42

IV.
CaM and nuclear functions
46

V.
Regulation of ion transport
49

VI.
CaM and plant responses to environmental stimuli
52

VII.
Conclusions and future studies
58

Acknowledgements
59

References
59
O3uptake and drought stress effects on carbon acquisition of ponderosa pine in natural stands
Authors: Grulke NE , Preisler HK , Rose C , Kirsch J , Balduman L
Published: March 2003

• The effect of O3exposure or uptake on carbon acquisition (net assimilation (A) or gross photosynthesis (Pg)), with and without drought stress, is reported here in 40‐yr‐old‐ponderosa pine (Pinus ponderosa) trees.

• Maximum daily gas exchange was measured monthly for 12 trees at four sites differing in pollutant exposure over two growing seasons with above‐ and below‐average annual precipitation. Gas exchange measures were estimated between sampling periods using a generalized additive regression model.

• Both A andPggenerally declined with cumulative O3exposure or uptake at all sites. As a response variable,Pgwas slightly more sensitive thanAto cumulative O3exposure. As a metric, O3uptake vs exposure permitted slightly better statistical resolution of seasonal response between sites.

• The effect of late summer drought stress was statistically significant only at the moderate pollution site, and combined synergistically with O3exposure or uptake to reducePg. The general additive model allows the user to define a deleterious level of cumulative O3exposure or uptake, and to quantitatively assess biological response.
Phospho‐imaging as a tool for visualization and noninvasive measurement of P transport dynamics in arbuscular mycorrhizas
Authors: Nielsen J. S. , Joner E. J. , Declerck S. , Olsson S. , Jakobsen I.
Published: March 2003

• A new method is described for monitoring hyphal 32P transport in compartmented, monoxenic mycorrhizal root cultures. Nondestructive time‐course measurements of P transport in hyphae were obtained by capturing digital autoradiograms on P‐imaging screens, and comparing with growth observed by optical scanning. 32P distribution measured by densitometry on the day of harvest closely agreed with values obtained by liquid scintillation counting after destructive harvest.

• Virtually all labeled PO4 was absorbed by arbuscular mycorrhizal (AM) hyphae, but transfer to the roots appeared to be incomplete. P transport was not unidirectional towards the roots, as 32P was also transported from the root compartment to the hyphal compartment. Net P flux rates were calculated for hyphae crossing between compartments, taking bidirectional flow into account.

• Amounts of transported P were poorly correlated with extra‐radical hyphal length and root d. wt, but highly correlated with the number of hyphae crossing the barrier separating the two compartments. Such correlations were highest when only hyphae with detectable protoplasmic streaming were considered.

• The method was tested using radiolabeled P sources, H2PO4− and cytidine triphosphate (CTP), and the AM fungi, Glomus intraradices and G. proliferum. Fungal transport of 32P from CTP was much slower than from PO4 for both fungi.
Nitrogen uptake by the floating macrophyte Lemna minor
Authors: Cedergreen Nina , Madsen Tom Vindbæk
Published: March 2003

Both roots and leaves of free‐floating plants can potentially take up nutrients. In this study, the ability and relative contribution of roots and fronds for N uptake by the floating macrophyte Lemna minor was investigated.

The NH 4
+
and NO
3
−
uptake kinetics of roots and fronds were measured on plants acclimated to three different NH
4NO3 concentrations.

Lemna
had the capacity to take up NH
4
+
and NO
3
− through both roots and fronds; uptake kinetics for the two tissue types were comparable on an area basis. The overall contribution of root and frond to whole‐plant uptake, estimated from measured kinetic characteristics, varied depending on plant N status (the root contribution increased from 32 to 73% for N‐satiated and N‐depleted plants, respectively).

The shift in the balance between root and frond contribution to whole‐plant uptake resulted from a 1.5–38 times greater increase in the area‐specific uptake capacity and affinity of roots relative to fronds, combined with a larger decrease in the minimum concentration for uptake ( C
min ) for roots than fronds. At the morphological level, root–frond surface area increased with declining N supply, which might be beneficial to the plants since the area return per unit biomass invested was nine times greater for roots than for fronds.
Needle dark respiration in relation to within‐crown position in Scots pine trees grown in long‐term elevation of CO2 concentration and temperature
Authors: Zha Tianshan , Wang Kai‐Yun , Ryyppö Aija , Kellomäki Seppo
Published: March 2003

The spatial distribution of leaf respiration in relation to specific needle area (SLA) and nitrogen concentration was studied in Scots pines ( Pinus sylvestris
) grown in environment‐controlled chambers for 4 yr under ambient conditions (CON), elevated CO
2 concentration (ambient + 350 µmol; EC), elevated temperature (ambient + 2–3°C; ET) or a combination of EC and ET (EC + ET).

Dark respiration rates within the crown were measured on attached needles using a portable photosynthesis analyzer.

Respiration rates decreased with increasing within‐crown depth and were linearly related to within‐crown positions, regardless of the treatments. The needles in the different depths in the crown had relatively similar responses of respiration to EC, ET and EC + ET. Respiration rates were reduced by EC relative to CON at any given within‐crown position, but were increased by ET and EC + ET. Respiration positively correlated with N concentration and negatively with SLA on an area basis.

It is assumed that respiratory acclimation to a change in light environment can occur irrespective of treatment. We suggested that SLA is a key determinant of respiration.
Horizontal gene transfer in the phytosphere
Authors: Van Elsas Jan Dirk , Turner Sarah , Bailey Mark J.
Published: March 2003

Here, the ecological aspects of gene transfer processes between bacteria in the phytosphere are examined in the context of emerging evidence for the dominant role that horizontal gene transfer (HGT) has played in the evolutionary shaping of bacterial communities. Moreover, the impact of the putative capture of genetic material by bacteria from plants is discussed. Examples are provided that illustrate how mobile genetic elements (MGEs) influence the behaviour of bacteria in their natural habitat, especially in structured communities such as biofilms on plant surfaces. This community behaviour is used as a framework to pose questions on the evolutionary role and significance of gene transfer processes in plant‐associated habitats. Selection within the highly structured phytosphere is likely to represent a dominant force shaping the genetic make‐up of plant‐associated bacterial communities. Current understanding of the triggering and impact of horizontal gene transfer, however, remains limited by our lack of understanding of the nature of the selective forces that act on bacteria in situ. The individual, colony, population and community level selection benefits imposed by the ability to use specific carbon sources or survive selective compounds are clear, but it is not always possible to assess what drives gene transfer and persistence. The role of HGT in the adaptation of host bacteria to their environmental niche is still not fully understood.
Determination of cholesterol in dairy products by infrared techniques: 2. FT‐NIR method
Authors: Paradkar Manish M , Irudayaraj Joseph
Published: March 2003

A Fourier transformed near‐infrared (FT‐NIR) method for rapid determination of cholesterol in dairy products was demonstrated. FT‐NIR spectrum of pure cholesterol was characterized and the region between 3550 and 3650 cm−1 was found to be the most significant in cholesterol content determination. The FT‐NIR method was found to accurately predict the cholesterol content in a variety of dairy products with r2 value greater than 0.98 and SEP estimates of less than 1.70. The FT‐NIR procedure with suitable multivariate statistical model was further validated by recovery studies and compared with a conventional method. Results indicate that FT‐NIR has the potential for rapid estimation of cholesterol.
Comparison of different bacterial culture systems for the production of reduced‐fat Cheddar cheese
Authors: Fenelon M A , Beresford T P , Guinee T P
Published: March 2003

Six different culture systems, two controls (A and B) containing mesophilic starter lactococci and four experimental systems (C, D, E and F) containing mesophilic lactococci plus adjunct cultures (all of which contained
Lactobacillus helveticus
), were compared for their effects on the quality of reduced‐fat Cheddar cheese (175 g/kg fat). Adjunct cultures (i.e. C, D and F) resulted in cheeses having significantly higher concentrations of low molecular mass peptides (i.e. < 0.5 kDa) and free amino acids than the control cheeses. The adjunct cultures D and F resulted in cheeses that received higher flavour scores and were more acceptable than the control cheeses at 90 and 180 days.
Swiss‐type and Swiss–Cheddar hybrid‐type cheeses: effects of manufacture on sensory character and relationships between the sensory attributes and volatile compounds and gross compositional constituents
Authors: Ben Lawlor J , Delahunty Conor M , Wilkinson Martin G , Sheehan Jerimiah
Published: March 2003

The effects of manufacturing steps, including rate of acidification in the vat, hot room step, curd wash and ripening temperature, on the sensory character of Swiss‐type and Swiss–Cheddar hybrid‐type cheeses were determined. In addition, relationships were determined between sensory attributes of cheeses and their gross compositional constituents and volatile compounds. Ten assessors described the sensory characteristics using 12 odour, 19 flavour, four appearance and nine texture attributes. Gross compositional constituents were determined using standard methods. Volatile compounds were isolated using a model mouth apparatus that included a mastication device. Statistical methods were used to reduce the original sensory vocabulary to four odour, eight flavour, three appearance and five texture attributes. Results of a principal component analysis on the sensory data showed clear differences in sensory character between cheese types. For example, the Swiss‐type with a low rate of acid production in the vat and a hot room step had a more ‘nutty’ and ‘sweet’ flavour than the modified Swiss‐type with higher acid production and no hot room step. However, the modified Swiss–Cheddar hybrid with a curd wash step, a higher acid production and no hot room step also had a ‘nutty’ and ‘sweet’ flavour. Ripening temperature also has an effect on sensory character. Relationships between sensory character and volatile compounds and/or gross compositional constituents were determined by using partial least squares regression. One odour and one flavour attribute were shown to be correlated with subsets of volatile compounds and gross compositional constituents. Four texture attributes were correlated with subsets of gross compositional constituents. The availability of information on the manufacturing process increased the interpretability of the models.
Coexpression of Glucagon‐Like Peptide‐1 (GLP‐1) Receptor, Vasopressin, and Oxytocin mRNAs in Neurons of the Rat Hypothalamic Supraoptic and Paraventricular Nuclei
Authors: Zueco José A. , Esquifino Ana I. , Chowen Julie A. , Alvarez Elvira , Castrillón Patricia O. , Blázquez Enrique
Published: March 2003

Abstract : This study was designed to gain better insight into the relationship between glucagon‐like peptide‐1 (GLP‐1) (7‐36) amide and vasopressin (AVP) and oxytocin (OX). In situ hybridization histochemistry revealed colocalization of the mRNAs for GLP‐1 receptor, AVP, and OX in neurons of the hypothalamic supraoptic and paraventricular nuclei. To determine whether GLP‐1(7‐36)amide alters AVP and/or OX release, both in vivo and in vitro experimental study designs were used. In vivo, intravenous administration of 1 μg of GLP‐1(7‐36)amide into the jugular vein significantly decreased plasma AVP and OX concentrations. In vitro incubation of the neurohypophysis with either 0.1 or 1 μg of GLP‐1(7‐36)amide did not modify the release of AVP. However, addition of 1 μg of GLP‐1(7‐36)amide to the incubation medium increased slightly the secretion of OX. The coexpression of GLP‐1 receptor and AVP mRNAs in hypothalamic supraoptic and paraventricular nuclei gives further support to the already reported central effects of GLP‐1(7‐36)amide on AVP. Our findings also suggest a dual secretory response of AVP and OX to the effect of GLP‐1(7‐36)amide, which most likely is related to the amount and/or the route of peptide administration.