bluuebunny/crossref_metadata_2025 huggingface dataset:
In utero sensitization in Chagas' disease leads to altered lymphocyte phenotypic patterns in the newborn cord blood mononuclear cells
Authors: Neves Suzane Figueiredo , Elói‐Santos Silvana , Ramos Roger , Rigueirinho Simone , Gazzinelli Giovanni , Correa‐Oliveira Rodrigo
Published: March 2003

Neonates are sensitized in utero to maternal circulating antigens and idiotypes that eventually cross the placental barrier. We believe that children born of mothers under long lasting antigenic stimulation, as in a chronic infection, would be affected by these maternal influences and show differences in the phenotypic repertoire of lymphocytes. To test this hyphothesis, we evaluated flow cytometry studies in cord blood mononuclear cells (CBMC) from children born of chagasic mothers without congenital disease, with special attention to T and B cells and expression of activation markers. We have also evaluated the peripheral blood mononuclear cells (PBMC) of these children 6 months after delivery. We show that CBMC of children born of infected mothers have high proliferative responses to antigenic stimulation, significantly lower mean percentages of CD3+ T cells, CD4+ T cells and diminished expression of the costimulatory molecule CD28 in the CD8+ T cell subset. Interestingly, this subpopulation has an increased expression of the MHC class II gene product as evidenced by the expression of HLADR. It is noteworthy that the patterns observed in CBMC T lymphocyte populations of these children closely resemble earlier findings on lymphocytic profiles of chronic chagasic adult patients and those of their mothers. We also show that, 6 months after delivery, some alterations observed at birth are reversed to levels observed in noninfected individuals.
Human antibody responses to Wuchereria bancrofti infective larvae
Authors: Helmy Hanan , Weil Gary J. , Faris Rifky , Gad Adel M. , Chandrashekar Ramaswamy , Ashour Amin , Ramzy Reda M.R.
Published: March 2003

Human IgG antibody responses to Wuchereria bancrofti third stage infective larvae (L3) surface and somatic antigens were studied by indirect immunofluorescence (IFA) and immunoblot with endemic Egyptian sera (n = 115) with the aim of identifying targets of protective immunity. Human sera variably recognized 14 major bands in L3 by immunoblot. The statistical significance of group differences in antibody prevalence was assessed by the chi‐squared test. Children and young adults (aged 10–20 years) tended to have antibodies to more L3 somatic antigens than older adults, with significant differences for bands at 66, 60 and 5 kDa. Infected subjects had more consistent antibody responses to antigens at 55, 50 and 6 kDa than endemic normal subjects with negative serum filarial antigen tests, who are presumed to be uninfected. A 5 kDa antigen was preferentially recognized by the latter group. Antibodies to L3surface antigens were equally prevalent in uninfected children (75%) and adults (90%) but less prevalent in people with microfilaremia (38%) than in amicrofilaremic subjects with or without filarial antigenemia (81%) (P < 0.001). IFA‐positive sera showed significantly enhanced recognition of antigens at 66, 40 and 14 kDa in immunoblots relative to IFA‐negative sera. Additional studies are needed to further characterize antigens identified in this study and to establish whether they are indeed targets of protective immunity in humans.
Ascaris lumbricoides infection is associated with protection from cerebral malaria
Authors: Nacher Mathieu , Gay Frédérick , Singhasivanon Pratap , Krudsood Srivicha , Treeprasertsuk Sombat , Mazier Dominique , Vouldoukis Ioannis , Looareesuwan Sornchai
Published: March 2003

Following reports of increased IgE in severe malaria and hypothesizing that helminth coinfections could modify its outcome, we conducted a retrospective case–control study to establish whether helminths affect the evolution of Plasmodium falciparum malaria. Some 182 severe cases, 315 mild controls and 40 controls with circulating schizonts were examined for intestinal helminths. Comparing cerebral malaria with mild controls, Ascaris lumbricoides was associated with a protective adjusted odds ratio (OR) of 0.58 (0.32–1.03) P = 0.06, for coinfection with Ascaris and Necator americanus, OR = 0.39 (0.17–0.88) P = 0.02. Protection followed a dose–effect trend (P = 0.008). When comparing cerebral malaria cases and controls with circulating schizonts the OR was 0.25 (0.009–0.67) P = 0.006. We hypothesized that Ascaris infected patients may have had decreased cyto‐adherence, possibly through endothelial cell receptor downregulation and/or decreased splenic clearance leading to the absence of selection of virulent P. falciparum strains. IgE‐anti‐IgE immune complexes resulting from helminth preinfection may have an important role in influencing clinical presentation of severe malaria, and in establishing malaria tolerance, through the CD23/NO pathway.
Antigenic profile of Ixodes ricinus: effect of developmental stage, feeding time and the response of different host species
Authors: Lawrie Charles H. , Nuttall Patricia A.
Published: March 2003

Antigens recognized by host species in response to ectoparasite infestation have been widely reported. Although differences in the immune responses of different host species have been described, only a very few of these studies compare the range of antigens recognized by different host species in response to infestation. We used Western blot analysis to investigate antigenic responses of different host species that were repeatedly infested with Ixodes ricinus ticks. Antigenic profiles of larval and nymphal whole tick homogenates were compared with the respective salivary gland extract (SGE) samples using sera from rabbits repeatedly infested with either adults, nymphs or larvae. SGE samples were also analysed using sera from hamsters infested with adults, nymphs or larvae. Sera from BALB/C mice, Apodemus flavicollis (yellow‐necked mouse) or Clethrionomys glareolus (bank vole) repeatedly infested with larvae were used to compare the antigenic profiles of SGE and larval homogenate samples. We also investigated different sources of tick antigens, using rabbit sera, by comparing midgut extracts from female adult ticks and SGE from unfed ticks and from ticks throughout the 6‐day feeding period with whole tick homogenates of female and male adults, nymphs and larvae. The pattern of antigenic tick‐molecules recognized by infested host species varies with the period of feeding, developmental stage and the particular host species parasitized.
The influence of γδ T cells on the CD4+ T cell and antibody response during a primary Plasmodium chabaudi chabaudi infection in mice
Authors: Seixas Elsa , Fonseca Luis , Langhorne Jean
Published: March 2003

A primary infection with Plasmodium chabaudi chabaudi (AS) is characterized by an expansion ofγδcells after the acute phase of infection in mice. This is particularly marked during chronic infections in B cell‐deficient mice. Infections inγδT cell‐deficient mice suggest that, although these cells play some role in the control of parasitaemia and can produce interferon‐γ, they do not appear to be involved in the development of hypoglycaemia, loss of weight and temperature during a P. c. chabaudi infection. However,γδT cells do influence the nature of the CD4+T cell response during infection since, in their absence, Th2‐like responses, such as interleukin (IL)‐4 production and help for malaria‐specific antibody responses, are more pronounced. This alteration in CD4+T cells is reflected in a more rapid and greater immunoglobulin (Ig)G1 and IgG3 antibody response to the parasite. The largeγδT cell expansion normally observed in infected B cell‐deficient mice did not take place in the absence of IL‐2, and double‐knockout mice lacking both B cells and functional IL‐2 were highly susceptible to lethal infection with P. c. chabaudi. The majority of the single IL‐2 knockout mice, in contrast, were able to control and clear a primary infection, suggesting that for the CD4+T cell and antibody response, IL‐2 could be replaced by other cytokines.
Paraflagellar rod protein‐specific CD8+ cytotoxic T lymphocytes target Trypanosoma cruzi‐infected host cells
Authors: Wrightsman Ruth A. , Luhrs Keith A. , Fouts David , Manning Jerry E.
Published: March 2003

Our previous studies show that in mice immunized with the paraflagellar rod (PFR) proteins of Trypanosoma cruzi protective immunity against this protozoan parasite requires MHC class I‐restricted T cell function. To determine whether PFR‐specific CD8+ T cell subsets are generated during T. cruzi infection, potential CTL targets in the PFR proteins were identified by scanning the amino acid sequences of the four PFR proteins for regions of 8–10 amino acids that conform to predicted MHC class I H‐2b binding motifs. A subset of the peptide sequences identified were synthesized and tested as target antigen in 51Cr‐release assays with effector cells from chronically infected T. cruzi mice. Short‐term cytotoxic T lymphocyte (CTL) lines specific for two of the peptides, PFR‐1164–171 and PFR‐3123–130, showed high levels of lytic activity against peptide‐pulsed target cells, secreted interferon (IFN)‐γ in response to parasite‐infected target cells, and were found to be CD8+, CD4−, CD3+, TCRαβ+ cells of the Tc1 subset. Challenge of PFR immunized CD8−/− and perforin‐deficient (PKO) mice confirmed that while CD8+ cells are required for survival of T. cruzi challenge infection, perforin activity is not required. Furthermore, while lytic activity of PFR‐specific CD8+ T cell lines derived from PKO mice was severely impaired, the IFN‐γ levels secreted by CTLs from PKO mice were equivalent to that of normal mice, suggesting that the critical role played by CD8+ T cells in immunity to the parasite may be secretion of type 1 cytokines rather than lysis of parasite infected host cells.
Cold tolerance of a New Zealand alpine cockroach, Celatoblatta quinquemaculata (Dictyoptera, Blattidae)
Authors: BLOCK WILLIAM , WHARTON DAVID A. , SINCLAIR BRENT J.
Published: March 2003

Abstract. Ecophysiological features, including survival and recovery from freezing and determination of the freezable water content, are reported for a cold‐adapted cockroach Celatoblatta quinquemaculata Johns 1966 (Dictyoptera, Blattidae) inhabiting alpine communities at altitudes greater than 1300 m a.s.l. in mountains of Central Otago, New Zealand. Nymphs ranged from 15 to 51 mg live weight of which 67% was water. Cockroaches had a mean supercooling point temperature of −5.4 ± 0.1°C; with recovery from freezing close to this temperature being rapid, but no recovery was observed when frozen at −9 to −10°C. The duration of exposure to freezing conditions and the time allowed for recovery (24–96 h) both influenced individual recovery and subsequent survival. Comparison of supercooling point data and survival shows that this species possesses a few degrees of freeze tolerance, and individuals have been found frozen in the field when subzero temperatures occur. Differential scanning calorimetry showed ≈ 74% of body water froze during cooling and between 24 and 27% of total body water was osmotically inactive (unfreezable under the experimental conditions). Carbohydrates, other than glucose at 7.5μg/mg fresh weight, were in low concentrations in the body fluids, suggesting little cryoprotection. No thermal hysteresis from antifreeze protein activity was detected in haemolymph samples using calorimetric techniques. It is suggested that slow environmental cooling rates, together with high individual supercooling points, confer a small amount of freezing tolerance on this species enabling it to survive low winter temperatures. This has allowed it to colonize and maintain populations in alpine habitats > 1300 m a.s.1. in New Zealand.
Visualizing the postembryonic development ofSarcophaga peregrina(flesh fly) by NMR microscopy
Authors: Price William S. , Kobayashi Ayako , Ide Hiroyuki , Natori Shunji , Arata YojI.
Published: March 2003

The postembryonic development of the flesh fly was studied using high resolution nuclear magnetic resonance imaging. Because this development occurs in a puparium, this process cannot be observed directly using standard histological techniques. The remodelling of histolysing larval tissues to developing imaginal tissues including the yellow body, a transient alimentary structure, and the integration of the developed adult structure were revealed in the images. Most surprisingly it was found that a large gas space that forms in the central region of the prepupa moves to the dorso‐anterial region in less than 5 min due to the larval–pupal apolysis together with separation of the developing pupal epidermis from the puparium.
The structure and surface properties of the eggshell of Megaselia imitatrix Borgmeier (Diptera, Phoridae) in relation to the respiration of the embryo
Authors: Benton Forbes , Claugher Donald
Published: March 2003

The role of the chorion in the mechanism of respiration is examined for the egg of Megaselia imitatrix. An air layer in the chorion is not essential for respiration, and oxygen can be absorbed through a hydrophilic pathway in the chorion by diffusion from the surrounding water. A model based on the diffusion of oxygen through the surface layer of the water down to the depth of the egg is proposed and presented in detail.
Comparative study of the metabolic responses during food shortage and subsequent recovery at different temperatures in the adult lesser mealworm, Alphitobius diaperinus (Coleoptera: Tenebrionidae)
Authors: Renault D. , Hervant F. , Vernon P.
Published: March 2003

Metabolic responses to prolonged food shortage (35 days) and subsequent re‐feeding (14 days) were investigated in adults of an introduced beetle, Alphitobius diaperinus Panzer, as a function of temperature (12, 16, 20 and 24 °C). Various qualitative and quantitative changes that greatly vary according to the temperature experienced occurred in metabolite levels during prolonged starvation. Whereas levels of protein and ATP did not change significantly, triglycerides decreased markedly and glycogen changed little. Metabolite levels were differently affected by temperature, with triglycerides being less rapidly degraded at 20 than at 24 °C and almost completely depleted at 12 and 16 °C; in contrast to higher temperatures, glycerol is accumulated at 12 °C. Physiological adaptation to starvation and low temperatures are highly linked and energy allocation for starvation vs. temperature acclimation must be strictly regulated, both being essential for insect survival. Re‐synthesis rates during recovery are probably highly temperature‐dependent for all metabolites. The proteins retained during starvation and the preferential degradation of lipids allowed a rapid recovery. Above 16 °C, adult A. diaperinus regained locomotory activity rapidly and the triglyceride, glycerol and glycogen reserves were restored. This tropical species may be able to colonize other environments such as natural and/or artificial biotopes where conditions are close to those of its natural habitat.
Seasonal differences in foliar content of chlorogenic acid, a phenylpropanoid antioxidant, in Mahonia repens
Authors: Grace S. C. , Logan B. A. , Adams W. W.
Published: March 2003

To assess the possible physiological function of chlorogenic acid (CGA, 3‐O‐caffeoylquinic acid) in vivo, we characterized the free radical scavenging properties of pure phenylpropanoids and leaf extracts against two free radicals, superoxide and the 2,2’‐azinobis(3‐ethylbenzothiazoline‐6‐sulphonic acid) (ABTS) radical cation. CGA was found to be a highly efficient scavenger of these free radicals, surpassing the activity of all other phenylpropanoids tested, as well as the ‘classical’ antioxidant ascorbate. Seasonal differences in the leaf content of CGA were examined in field populations of the broadleaf evergreen Mahonia repens growing in different light environments. Leaves of fully sun‐exposed plants contained significantly more (74 ± 10 mmol m–2) CGA in winter than leaves from plants growing under deeply shaded conditions (17 ± 2 mmol m–2). Sun‐acclimated, but not shade‐acclimated, leaves also produced high levels of anthocyanins in winter, suggesting a simultaneous increase in carbon flow through the phenylpropanoid and flavonoid pathways in response to high light and seasonal low temperature stress. In summer, high light‐acclimated leaves contained ≈ 2‐fold less CGA than in winter, whereas CGA levels were similar between seasons in shaded leaves. Consistent with the strong scavenging capacity of CGA measured in vitro, a linear correlation was observed between CGA content and the antioxidant activity of leaf extracts in both scavenging assays. On the basis of these results, we propose that CGA is a powerful hydrogen‐donating antioxidant that may play an important role in mitigating the effects of oxidative stress in plants.
Limitation of plant water use by rhizosphere and xylem conductance: results from a model
Authors: Sperry J. S. , Adler F. R. , Campbell G. S. , Comstock J. P.
Published: March 2003

Hydraulic conductivity (K) in the soil and xylem declines as water potential (Ψ) declines. This results in a maximum rate of steady‐state transpiration (Ecrit) and corresponding minimum leaf Ψ (Ψcrit) at which K has approached zero somewhere in the soil–leaf continuum. Exceeding these limits causes water transport to cease. A model determined whether the point of hydraulic failure (where K = 0) occurred in the rhizosphere or xylem components of the continuum. Below a threshold of root:leaf area (AR:AL), the loss of rhizosphere K limited Ecrit and Ψcrit. Above the threshold, loss of xylem K from cavitation was limiting. The AR:AL threshold ranged from > 40 for coarse soils and/or cavitation‐resistant xylem to < 0·20 in fine soils and/or cavitation‐susceptible xylem. Comparison of model results with drought experiments in sunflower and water birch indicated that stomatal regulation of E reflected the species’ hydraulic potential for extracting soil water, and that the more sensitive stomatal response of water birch to drought was necessary to avoid hydraulic failure. The results suggest that plants should be xylem‐limited and near their AR:AL threshold. Corollary predictions are (1) within a soil type the AR:AL should increase with increasing cavitation resistance and drought tolerance, and (2) across soil types from fine to coarse the AR:AL should increase and maximum cavitation resistance should decrease.
Regulation of growth, water use efficiency and δ13C by the nitrogen source in Casuarina equisetifolia Forst. & Forst.
Authors: Martínez‐Carrasco R. , Pérez P. , Handley L. L. , Scrimgeour C. M. , Igual M. , Martín Del Molino I. , Sánchez De La Puente L.
Published: March 2003

Carbon isotope composition (δ13C) was measured in a glasshouse experiment with N2‐fixing and NO3–‐ or NH4+‐fed Casuarina equisetifolia Forst. & Forst plants, both under well‐watered and drought conditions. The abundance of 13C was higher (more positive δ13C) for NH4+‐ than for NO3– ‐grown plants and was lowest for N2‐fixing plants. NH4+‐fed plants had more leaf area and dry weight and higher water use efficiency (on a biomass basis) than N2‐ and NO3–‐grown plants and had lower water consumption than plants supplied with NO3–, either with high or low water supply. Specific leaf areas and leaf area ratios were higher with NH4+ than with NO3– or N2 as the N source. The difference observed in δ13C between plants grown with different N sources was higher than that predicted by theory and was not in the right direction (NH4+‐grown plants with a more negative δ13C) to be explained by differences in plant composition and engagement of the various carboxylation reactions. The more positive δ13C in NH4+‐ than in NO3–‐grown plants is probably due to a decreased ratio of stomatal to carboxylation conductances, which accounts for the lower water cost of C assimilation in NH4+‐grown plants.
Oscillatory model of crassulacean acid metabolism: structural analysis and stability boundaries with a discrete hysteresis switch
Authors: Blasius B. , Beck F. , Lüttge U.
Published: March 2003

We propose a simple oscillatory model of crassulacean acid metabolism (CAM) describing the CO2 uptake and nocturnal acidification of CAM plants by a system of coupled non‐linear differential equations. Large differences in the content of metabolite pools are treated using a pseudo‐steady‐state approach. For the first time, simulations of the CAM cycle investigate its dependence on all three major control parameters simultaneously: temperature, photon flux density and external CO2 concentration. Under stationary conditions in time the model shows either endogenous rhythmicity or two distinct steady states. Stability boundaries are calculated in parameter space.
Accumulation rate of ABA in detached maize roots correlates with root water potential regardless of age and branching order
Authors: Simonneau T. , Barrieu P. , Tardieu F.
Published: March 2003

How much ABA can be supplied by the roots is a key issue for modelling the ABA‐mediated influence of drought on shoot physiology. We quantified accumulation rates of ABA (SABA) in maize roots that were detached from well‐watered plants and dehydrated to various extents by air‐drying. SABA was estimated from changes in ABA content in root segments incubated at constant relative water content (RWC). Categories of root segments, differing in age and branching order, were compared (root branches, and nodal roots subdivided into root tips, subapical unbranched sections, and mature sections). All categories of roots accumulated ABA, including turgid and mature tissues containing no apex. SABA measured in turgid roots changed with root age and among root categories. This variability was largely accounted for by differences in water content among different categories of turgid roots. The response of SABA to changes in root water potential (Ψroot) induced by dehydration was common to root tips, nodal roots and branches of several ages, while this was not the case if root dehydration was expressed in terms of RWC. Differences among root categories in the response of SABA to RWC were due to different RWC values among categories at a given Ψroot, and not to differences in the response of SABA to Ψroot.
The ABSCISIC ACID‐INSENSITIVE 3 (ABI3) gene is expressed during vegetative quiescence processes in Arabidopsis
Authors: ROHDE A. , VAN MONTAGU M. , BOERJAN W.
Published: March 2003

The ABSCISIC ACID‐INSENSITIVE 3 (ABI3) gene of Arabidopsis thaliana (L.) Heynh is known to play an important role during seed maturation and dormancy. Here, we present evidence suggesting an additional role for ABI3 during vegetative quiescence processes. During growth in the dark, ABI3 is expressed in the apex of the seedlings after cell division is arrested. The 2S seed storage protein gene, a target gene of ABI3 in seeds, is also induced in the arrested apex under similar darkness conditions. In addition, β‐glucuronidase expression under the control of the ABI3 promoter is abolished by treatments that provoke leaf development in the dark [sucrose and abscisic acid (ABA) biosynthesis inhibitors] and induced by treatments that prevent leaf development (darkness and ABA). Furthermore, ABI3 expression is absent in apices of dark‐grown de‐etiolated (det 1) and abi3 mutants, both known to develop leaves or leaf primordia in the dark. The fact that the expression of the ABI3 gene is only observed in a fraction of the analysed plants suggests that ABI3 is probably only one of the components of a molecular network underlying quiescence. In addition to the expression of ABI3 in apices of dark‐grown seedlings, the ABI3 promoter confers expression in other vegetative organs as well, such as the stipules and the abscission zones of the siliques. In conclusion, apart from its role in seed development, ABI3 might have additional functions.
Differential effects of nitric oxide on peroxidase and H2O2 production by the xylem of Zinnia elegans
Authors: Ferrer M. A. , Ros BarcelÓ A.
Published: March 2003

IWF, intercellular washing fluid  pCMB, p‐chloromercuribenzoic acid  SNAP, S‐nitroso‐N‐acetyl‐penicillamine SNP, sodium nitroprusside  TMB, 3,3’,5,5’‐ tetramethylbenzidine   Sodium nitroprusside (SNP) and S‐nitroso‐N‐acetyl‐penicillamine (SNAP) are two nitric oxide (NO)‐releasing compounds that, when used at 5·0 mol m–3 concentrations, are capable of releasing NO in the aqueous phase at a rate of 35 ± 4 and 47 ± 5 μmol m–3 s–1, respectively. For this reason, the effect of SNP and SNAP on coniferyl alcohol peroxidase and on H2O2 production by the lignifying xylem of Zinnia elegans (L.) has been studied in order to ascertain whether NO, which is a synchronizing chemical messenger in animals and an air pollutant, has any effect on these plant‐specific metabolic aspects. The results showed that both SNP and SNAP provoke an inhibition in the mol m–3 concentration range of the coniferyl alcohol peroxidase activity of a basic peroxidase isoenzyme present in the intercellular washing fluid of Z. elegans. The effect of these NO‐releasing compounds on peroxidase was confirmed through histochemical studies, which showed that xylem peroxidase was totally inhibited by treatment with these NO donors at 5·0 mol m–3, and by NO at a concentration change rate of 55 ± 5 and 110 ± 9 μmol m–3 s–1. However, SNP, at 5·0 mol m–3, does not have any effect on H2O2 production by the xylem of Z. elegans. The fact that SNP and SNAP are two structurally dissimilar compounds which only share the common ability to release NO in aqueous buffer, and that similar results were obtained when using NO itself, suggest that NO could be considered as an inhibitor of coniferyl alcohol peroxidase which does not affect H2O2 production in the xylem of Z. elegans.
Root porosity and oxygen movement in waterlogging‐tolerant Trifolium tomentosum and ‐intolerant Trifolium glomeratum
Authors: Gibberd M. R. , Colmer T. D. , Cocks P. S.
Published: March 2003

Trifolium tomentosum and T. glomeratum are small (< 0·5 mg) seeded pasture legumes which are considered to be waterlogging tolerant and intolerant, respectively. The root porosity of the two species was compared for plants raised for 10 d in aerated nutrient solution and then transferred to either aerated (0·25 mol O2 m–3) or ‘hypoxic’ (0·031–0·069 mol O2 m–3) solutions for a further 7 and 21 d. After 21 d, T. tomentosum developed a root porosity of 11·2% in ‘hypoxic’ solution, which was significantly higher than the 6·1% developed by T. glomeratum. When grown in aerated solution, T. tomentosum also had a larger constitutive porosity (6·7%) than T. glomeratum (3·9%). Cylindrical root‐sleeving O2 electrodes were used to measure the rates of radial O2 loss (ROL) from roots of the two species when in an O2‐free medium. In general, roots previously grown in ‘hypoxic’ solution had higher rates of ROL than roots grown in aerated solution. Moreover, the rates of ROL along the main root of T. tomentosum were ≈ 5‐fold faster than from equivalent locations along roots of T. glomeratum. Manipulations of the shoot O2 concentration resulted in rapid changes in ROL near the root tip of T. tomentosum plants raised in aerated or ‘hypoxic’ solutions, whereas for T. glomeratum ROL only increased for roots of plants raised in ‘hypoxic’ solution. Thus, the cortical air spaces in roots of both species raised in ‘hypoxic’ solution formed a continuous, low resistance pathway for O2 diffusion from the shoots to the roots. ROL from the lateral roots was also evaluated and it was 3‐fold faster from T. tomentosum than from T. glomeratum. Moreover, ROL from lateral roots of T. tomentosum was 10–20‐fold higher than from a position on the primary root axis the same distance from the root/shoot junction. Relatively, high rates of ROL were also recorded for young (40 mm in length) lateral roots of T. glomeratum which were previously grown in ‘hypoxic’ solution, but the ROL was low for the older lateral roots of this species. The substantial amounts of ROL from the lateral roots may limit O2 supply to the lower parts of the primary root axis, so that the laterals probably become the main functional root system in waterlogged soils.
Carbohydrate partitioning into starch in leaves of Ricinus communis L. grown under elevated CO2 is controlled by sucrose
Authors: Grimmer Claudia , Bachfischer Tanja , Komor Ewald
Published: March 2003

Ricinus communis plants were grown under normal (350 ppm) and elevated (700 ppm) CO2 atmosphere and the growth and carbohydrate status of leaf 2 (first leaf above the pair of primary leaves) was studied. Elevated carbon dioxide stimulated the growth of leaves 1·7‐fold. The glucose and fructose concentrations exhibited the same diurnal rhythm under both growth conditions. The sucrose concentrations stayed relatively constant and at 700 ppm were one‐third higher than at 350 ppm. The starch content increased steadily during the day and disappeared overnight at 350 ppm CO2, but remained partially in plants at 700 ppm CO2. Consequently at 700 ppm CO2, the leaves accumulated starch continuously over their life time. The rate of starch synthesis was correlated to the activity of ADP‐glucose pyrophosphorylase, which was related to the sucrose concentration in the leaf. It is concluded that sucrose controls the expression of ADP‐glucose pyrophosphorylase, leading to a shift of carbohydrate partitioning into starch when more sucrose is produced than consumed or exported, a situation which is especially pertinent at elevated CO2. These results show that the previously experimentally observed transscriptional regulation of starch synthesis by sucrose occurs in vivo in the daily life of a leaf.
Quantifying the response of photosynthesis to changes in leaf nitrogen content and leaf mass per area in plants grown under atmospheric CO2 enrichment
Authors: Peterson A. G. , Ball J. T. , Luo Y. , Field C. B. , Curtis P. S. , Griffin K. L. , Gunderson C. A. , Norby R. J. , Tissue D. T. , Forstreuter M. , Rey A. , Vogel C. S. , Participants Cmeal
Published: March 2003

Previous modelling exercises and conceptual arguments have predicted that a reduction in biochemical capacity for photosynthesis (Aarea) at elevated CO2 may be compensated by an increase in mesophyll tissue growth if the total amount of photosynthetic machinery per unit leaf area is maintained (i.e. morphological upregulation). The model prediction was based on modelling photosynthesis as a function of leaf N per unit leaf area (Narea), where Narea = Nmass×LMA. Here, Nmass is percentage leaf N and is used to estimate biochemical capacity and LMA is leaf mass per unit leaf area and is an index of leaf morphology. To assess the relative importance of changes in biochemical capacity versus leaf morphology we need to control for multiple correlations that are known, or that are likely to exist between CO2 concentration, Narea, Nmass, LMA and Aarea. Although this is impractical experimentally, we can control for these correlations statistically using systems of linear multiple‐regression equations. We developed a linear model to partition the response of Aarea to elevated CO2 into components representing the independent and interactive effects of changes in indexes of biochemical capacity, leaf morphology and CO2 limitation of photosynthesis. The model was fitted to data from three pine and seven deciduous tree species grown in separate chamber‐based field experiments. Photosynthetic enhancement at elevated CO2 due to morphological upregulation was negligible for most species. The response of Aarea in these species was dominated by the reduction in CO2 limitation occurring at higher CO2 concentration. However, some species displayed a significant reduction in potential photosynthesis at elevated CO2 due to an increase in LMA that was independent of any changes in Narea. This morphologically based inhibition of Aarea combined additively with a reduction in biochemical capacity to significantly offset the direct enhancement of Aarea caused by reduced CO2 limitation in two species. This offset was 100% for Acer rubrum, resulting in no net effect of elevated CO2 on Aarea for this species, and 44% for Betula pendula. This analysis shows that interactions between biochemical and morphological responses to elevated CO2 can have important effects on photosynthesis.
Individuation in Sorghum bicolor: a self‐organized process involved in physiological adaptation to salinity
Authors: Amzallag G. N.
Published: March 2003

In Sorghum bicolor, salt‐adaptation was defined as the capacity of plants to grow at 300 m
M NaCl (a lethal concentration) following a 3‐week pre‐treatment with 150 m
M NaCl (a sublethal concentration). Large populations induced for salt‐adaptation were analysed. Two modes of osmotic regulation (Na‐includer and Na‐excluder) were differentiated during induction of salt‐adaptation, in spite of the genetic and environmental homogeneity. This variability was not related to any incapacity of the Na‐includers to control accumulation of Na+ ions in the shoot, because most of the pre‐treated plants displayed a similar capacity of growth and control of Na+ uptake after transfer to 300 m
M NaCl. This unsuspected complexity of initially homogeneous populations points on the inadequacy of physiological studies focused on the ‘average individual’. Further analyses showed that variability was not directly related to micro‐environmental variations. It is concluded that a process of individuation is caused by a third source of variability, which is the expression of a self‐organizing process normally occurring during the transition phases in development. In constraining environments, this phenomenon of individuation includes adaptive modifications.
Trans‐root potential, xylem pressure, and root cortical membrane potential of ‘low‐salt’ maize plants as influenced by nitrate and ammonium
Authors: Wegner L. H. , Sattelmacher B. , Läuchli A. , Zimmermann U.
Published: March 2003

Upon addition of nitrate and ammonium, respectively, to the bath of intact ‘low salt’ maize plants, the cortical membrane potential and the trans‐root potential changed in a similar and synchronous way as revealed by applying conventional microelectrode techniques and the xylem pressure‐potential probe ( Wegner & Zimmermann 1998). Upon addition of nitrate, a hyperpolarization response was observed which was frequently preceded by a short depolarization phase. In contrast, addition of ammonium resulted in an overall depolarization response both of the cortical membrane potential and the trans‐root potential. The nitrate‐induced hyperpolarization response and the depolarization following the addition of ammonium were concentration‐dependent.

The data suggest that a tight electrical coupling exists between the cellular and tissue level in the root of the intact plant and that the resistance of the cellular (symplastic) space is much less than the resistance of the apoplast.
The effects of UV‐B radiation on epidermal anatomy in loblolly pine (Pinus taeda L.) and Scots pine (Pinus sylvestris L.)
Authors: Laakso K. , Sullivan J. H. , Huttunen S.
Published: March 2003

The effects of enhanced UV‐B radiation on the needle anatomy of loblolly pine (Pinus taeda L.) and Scots pine (Pinus sylvestris L.) were studied in the field under supplemental UV‐B radiation supplied by a modulated irradiation system. The supplemental UV‐B levels were designed to simulate either a 16 or 25% loss of stratospheric ozone over College Park, Maryland. Enhanced UV‐B radiation caused different responses in these two species. The needles of loblolly pine had larger amounts of tannin in the lumen of epidermal cells and more wall‐bound phenolics in the outer epidermal walls of UV‐B‐treated needles, whereas the most pronounced effect on Scots pine needles was increased cutinization. In both species, the outer epidermal cell walls thickened and the needle cross‐sectional and mesophyll areas decreased (statistically significantly only in Scots pine). This suggests that more carbon may have been allocated to the protection mechanisms at the expense of photosynthetic area. The difference in response between these species suggests that the response to UV‐B radiation is not mediated by a single mechanism and that no generalization with regard to the effects of UV‐B on conifers can be made.
Process‐based modelling of isoprene emission by oak leaves
Authors: Zimmer W. , Brüggemann N. , Emeis S. , Giersch C. , Lehning A. , Steinbrecher R. , Schnitzler J‐P.
Published: March 2003

The emission rate of the volatile reactive compound isoprene, emitted predominantly by trees, must be known before the level of photo‐oxidants produced during summer smog can be predicted reliably. The emission is dependent on plant species and local conditions, and these dependencies must be quantified to be included in any empirical algorithm for the calculation of isoprene production. Experimental measurements of isoprene emission rates are expensive, however, and existing data are scarce and fragmentary. To overcome these difficulties, it is promising to develop a numerical model capable of precisely calculating the isoprene emission by trees for diverse ecosystems, even under changing environmental conditions. A basic process‐based biochemical isoprene emission model (BIM) has therefore been developed, which describes the enzymatic reactions in leaf chloroplasts leading to the formation of isoprene under varying environmental conditions (e.g. light intensity, temperature). Concentrations of the precursors of isoprene formation, 3‐phosphoglyceric acid and glyceraldehyde 3‐phosphate, are provided by a published light fleck photosynthesis model. Specific leaf and enzyme parameters were determined for the pedunculate oak (Quercus robur L.), so that the BIM is capable of calculating oak‐specific isoprene emission rates as influenced by the leaf temperature and light intensity. High correlation was observed between isoprene emission rates calculated by the BIM and the diurnal isoprene emission rates of leaves measured under controlled environmental conditions. The BIM was even capable of describing changes in isoprene emission caused by midday depression of net photosynthesis.
Stomatal responsiveness to leaf water status in common bean (Phaseolus vulgaris L.) is a function of time of day
Authors: Mencuccini M. , Mambelli S. , Comstock J.
Published: March 2003

Stomatal response to leaf water status was experimentally manipulated by pressurizing the soil and roots of potted common bean plants enclosed in a custom‐built root pressure chamber. Gas exchange was monitored using a whole‐plant cuvette and plant water status using in situ leaf psychrometry. Bean plants re‐opened their stomata upon pressurization, but the extent of re‐opening was strongly dependent on the time of day when the soil was pressurized, with maximum re‐opening in the morning hours and limited re‐opening in the afternoon. Neither leaf nor xylem abscisic acid concentrations could explain the reduced response to pressurization in the afternoon. The significance of this phenomenon is discussed in the context of circadian rhythms and of other recent findings on the ‘apparent feed‐forward response’ of the stomata of some species to vapour pressure deficit.
Modelling of reserve carbohydrate dynamics, regrowth and nodulation in a N2‐fixing tree managed by periodic prunings
Authors: Berninger F. , Nikinmaa E. , Sievänen R. , Nygren P.
Published: March 2003

We used a modified transport resistance approach to model legume tree growth, nodulation and dynamics of reserve carbohydrates after pruning. The model distributes growth between roots and shoots applying the transport resistance approach. Within shoots, growth is divided into leaves, branches and stems applying the pipe model theory. The model also accounts for the metabolic differences of principal N sources, nitrate, ammonium and atmospheric dinitrogen, in a mechanistic way. We compared the simulation results with measured biomass dynamics of Gliricidia sepium (Jacq.) Walp. (Papilionaceae: Robinieae) under humid and subhumid tropical conditions. Comparison showed that the biomass production predicted by the model is close to measured values. Total N2 fixation is also similar to measured values. Qualitatively the model increases the proportion of N2 fixation if roots acquire less mineral N. In the present study, the general form of the model is discussed and compared with similar models. The results encourage the use of this approach for studying biomass dynamics of legume trees under the scheme of periodic prunings. Also, it shows that process‐based models have potential in the simulation of trees disturbed by prunings, herbivory or similar factors.
Extracellular complexation of Cd in the Hartig net and cytosolic Zn sequestration in the fungal mantle of Picea abies – Hebeloma crustuliniforme ectomycorrhizas
Authors: Frey B. , Zierold K. , Brunner I.
Published: March 2003

Compartmentation of heavy metals on or within mycorrhizal fungi may serve as a protective function for the roots of forest trees growing in soils containing elevated concentrations of metals such as Cd and Zn. In this paper we present the first quantitative measurements by X‐ray microanalysis of heavy metals in high‐pressure frozen and cryosectioned ectomycorrhizal fungal hyphae. We used this technique to analyse the main sites of Cd and Zn in fungal cells of mantle and Hartig net hyphae and in cortical root cells of symbiotic Picea abies – Hebeloma crustuliniforme associations to gain new insights into the mechanisms of detoxification of these two metals in Norway spruce seedlings. The mycorrhizal seedlings were exposed in growth pouches to either 1 mM Cd or 2 mM Zn for 5 weeks. The microanalytical data revealed that two distinct Cd‐ and Zn‐binding mechanisms are involved in cellular compartmentation of Cd and Zn in the mycobiont. Whereas extracellular complexation of Cd occurred predominantly in the Hartig net hyphae, both extracellular complexation and cytosolic sequestration of Zn occurred in the fungal tissue. The vacuoles were presumed not to be a significant pool for Cd and Zn storage. Cadmium was almost exclusively localized in the cell walls of the Hartig net (up to 161 mmol kg−1 DW) compared with significantly lower concentrations in the cell walls of mantle hyphae (22 mmol kg−1 DW) and in the cell walls of cortical cells (15 mmol kg−1 DW). This suggests that the apoplast of the Hartig net is a primary accumulation site for Cd. Zinc accumulated mainly in the cell walls of the mantle hyphae (111 mmol kg−1 DW), the Hartig net hyphae (130 mmol kg−1 DW) and the cortical cells (152 mmol kg−1 DW). In addition, Zn occurred in high concentrations in the cytoplasm of the fungal mantle hyphae (up to 164 mmol kg−1 DW) suggesting that both the cell walls and the cytoplasm of fungal tissue are the main accumulation sites for Zn in P. abies resulting in decreased Zn transfer from the fungus to the root.
Modelling assimilation and intercellular CO2 from measured conductance: a synthesis of approaches
Authors: Katul G. G. , Ellsworth D. S. , Lai C.‐T.
Published: March 2003

A spectrum of models that estimate assimilation rate A from intercellular carbon dioxide concentration (Ci) and measured stomatal conductance to CO2 (gc) were investigated using leaf‐level gas exchange measurements. The gas exchange measurements were performed in a uniform loblolly pine stand (Pinus taeda L.) using the Free Air CO2 Enrichment (FACE) facility under ambient and elevated atmospheric CO2 for 3 years. These measurements were also used to test a newly proposed framework that combines basic properties of the A–Ci curve with a Fickian diffusion transport model to predict the relationship between Ci/Ca and gc, where Ca is atmospheric carbon dioxide concentration. The widely used Ball–Berry model and five other models as well as the biochemical model proposed by Farquhar et al. (1980) were also reformulated to express variations in Ci/Ca as a function of their corresponding driving mechanisms. To assess the predictive capabilities of these approaches, their respective parameters were estimated from independent measurements of long‐term stable carbon isotope determinations (δ13C), meteorological variables, and ensemble A–Ci curves. All eight approaches reproduced the measured A reasonably well, in an ensemble sense, from measured water vapour conductance and modeled Ci/Ca. However, the scatter in the instantaneous A estimates was sufficiently large for both ambient and elevated Ca to suggest that other transient processes were not explicitly resolved by all eight parameterizations. An important finding from our analysis is that added physiological complexity in modeling Ci/Ca (when gc is known) need not always translate to increased accuracy in predicting A. Finally, the broader utility of these approaches to estimate assimilation and net ecosystem exchange is discussed in relation to elevated atmospheric CO2.
Diurnal changes in the photochemical efficiency of the symbiotic dinoflagellates (Dinophyceae) of corals: photoprotection, photoinactivation and the relationship to coral bleaching
Authors: Jones R. J. , Hoegh‐Guldberg O.
Published: March 2003

The photochemical efficiency of symbiotic dinoflagellates within the tissues of two reef‐building corals in response to normal and excess irradiance at water temperatures < 30 °C were investigated using pulse amplitude modulated (PAM) chlorophyll fluorescence techniques. Dark‐adapted Fv/Fm showed clear diurnal changes, decreasing to a low at solar noon and increasing in the afternoon. However, Fv/Fm also drifted downwards at night or in prolonged darkness, and increased rapidly during the early morning twilight. This parameter also increased when the oxygen concentration of the water holding the corals was increased. Such changes have not been described previously, and most probably reflect state transitions associated with PQ pool reduction via chlororespiration. These unusual characteristics may be a feature of an endosymbiotic environment, reflective of the well‐documented night‐time tissue hypoxia that occurs in corals. Fv/Fm decreased to 0·25 in response to full sunlight in shade‐acclimated (shade) colonies of Stylophora pistillata, which is considerably lower than in light‐acclimated (sun) colonies. In sun colonies, the reversible decrease in Fv/Fm was caused by a lowering of Fm and Fo suggesting photoprotection and no lasting damage. The decrease in Fv/Fm, however, was caused by a decrease in Fm and an increase in Fo in shade colonies suggesting photoinactivation and long‐term cumulative photoinhibition. Shade colonies rapidly lost their symbiotic algae (bleached) during exposure to full sunlight. This study is consistent with the hypothesis that excess light leads to chronic damage of symbiotic dinoflagellates and their eventual removal from reef‐building corals. It is significant that this can occur with high light conditions alone.