bluuebunny/crossref_metadata_2025 huggingface dataset:
HLA‐A*0201 restricted CD8+ T‐lymphocyte responses to malaria: identification of new Plasmodium falciparum epitopes by IFN‐γ ELISPOT
Authors: González John Mario , Peter Katrin , Esposito Fulvio , Nebié Issa , Tiercy Jean‐Marie , Bonelo Anilza , Arévalo‐Herrera Myriam , Valmori Danila , Romero Pedro , Herrera Sócrates , Corradin Giampietro , López José Alejandro
Published: March 2003

The role of antigen specific CD8+ T‐lymphocytes in mediating protection against sporozoite‐induced malaria has been well established in murine models. In humans, indirect evidence has accumulated suggesting a similar protective role for antigen‐specific CD8+ T‐lymphocytes. Nevertheless, the low frequency of circulating specific cells together with the lack of sensitive methods to quantify them has hampered the direct assessment of their function. Using a combination of short‐term cell culture and IFN‐γ ELISPOT, we studied CD8+ T‐lymphocyte responses to a panel of HLA‐A*0201 binding peptides. In addition to confirming the response to already described epitopes, we also identified five new CD8+ T‐lymphocyte epitopes. These epitopes are presented in pre‐erythrocytic stages gene products of Plasmodium falciparum 7G8 strain and correspond to the following protein segments: circumsporozoite (CS) 64‐72, 104‐113, 299‐308 and 403‐411; liver stage antigen (LSA‐1) repeat region; sporozoite surface protein 2 or thrombospondin related anonymous protein (SSP2/TRAP) 78–88 and 504–513. Four of these peptides are conserved amongst all published sequences of P. falciparum strains. We conclude that the modified IFN‐γ ELISPOT assay is a sensitive technique to monitor antigen‐specific CD8+ T‐lymphocyte responses in human malaria which may help in the improvement and assessment of the efficacy of malaria subunit vaccines.
Infection induces antibodies against the cercarial secretions, but not against the cercarial elastases of Schistosoma mansoni, Schistosoma haematobium, Schistosoma japonicum and Trichobilharzia ocellata
Authors: Bahgat Mahmoud , Francklow Katherine , Doenhoff Michael J. , Li Yong‐Long , Ramzy Reda M.R. , Kirsten Christa , Ruppel Andreas
Published: March 2003

Cercarial secretions from different species of the parasite Schistosoma and from Trichobilharzia ocellata contain a proteolytic activity, cercarial elastase, which was demonstrated by a 30 kDa band in gelatin gels. Sera of patients infected with Schistosoma mansoni, Schistosoma haematobium or Schistosoma japonicum contain immunoglobulin G which react in ELISA with cercarial secretions from all schistosomes and cross‐react among the different parasite species. In Western blots, however, infection sera from patients, as well as heavily infected mice or rabbits, did not react with a 30‐kDa protein. Moreover, when sections from infected snails (Biomphalaria, Bulinus and Lymnaea) were analysed by immunofluorescence using the same infection sera, only the tegument of the developing cercariae was recognized, but not the acetabular glands. In contrast, when antisera against purified cercarial elastase from either S. mansoni or S. haematobium were tested with sections of infected Biomphalaria or Bulinus, fluorescence was strong in the preacetabular glands of the cercariae of either species, but undetectable with the tegument. Cross‐reactivity of both antisera extended to T. ocellata‐infected Lymnaea, but not to S. japonicum‐infected Oncomelania. In conclusion, although immunization with purified cercarial elastase results in antibody production, the enzyme does not induce an apparent antibody response following natural infection.
Seasonal morphometric variation in sexual and asexual, North American and Australian, populations of the aphid, Acyrthosiphon pisum
Authors: Smith M. A. H. , Mackay P. A. , Lamb R. J.
Published: March 2003

The lengths of the body and appendages of the aphid Acyrthosiphon pisum (Harris) (Homoptera: Aphididae) vary seasonally in sexual North American and asexual Australian populations. The first generation of spring aphids in North America and winter aphids in Australia have short appendages in relation to body length. Excluding this phenotype, North American and Australian aphids cannot be discriminated morphometrically. The short appendages in North America are associated with a specialized morph called a fundatrix; the short appendages of Australian aphids are caused by exposure to low temperatures during prenatal development. The same temperature‐sensitive mechanism operates in sexual and asexual North American aphids, but does not explain the short appendages of the fundatrix, which appear to arise through a separate mechanism. The short appendages are caused neither by a maternal effect from winged mothers, although such an effect exists, nor by seasonal changes in body length and allometry, nor by microevolutionary changes. The temperature‐induced shortening of appendages is a seasonal polymorphism, which mimics the short appendages seen in fundatrices. The two types of phenotypic plasticity have the same consequence in sexual and asexual populations of the same species and may be an example of convergent evolution.
Water loss in desert ants: caste variation and the effect of cuticle abrasion
Authors: Johnson Robert A.
Published: March 2003

Water loss rates (WLRs) varied across castes (workers > alate males > alate females) for desert ants in the generaAphaenogaster, MessorandPogonomyrmex. Exposure to soil caused increased WLRs in workers and foundresses (mated, dealate females), apparently because of cuticular abrasion caused by nest excavation. Moreover, field‐collected workers and foundresses from incipient nests (those exposed to soil) had similar WLRs, as did unabraded workers and alate females (those unexposed to soil). These data call into question previous adaptive scenarios for differences in WLRs across ant species and castes. For live alate females, WLRs increased over two stages. The first increase occurred immediately after mating, and the second occurred for foundresses collected 2 days later from incipient nests. By contrast, WLRs of HCN‐killed females were unaffected by mating, but increased significantly for foundresses collected from 2‐day‐old nests.
Responses of male Helicoverpa zea to single pulses of sex pheromone and behavioural antagonist
Authors: Quero Carmen , Fadamiro Henry Y. , Baker Thomas C.
Published: March 2003

Male Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) flying in a pheromone plume respond to the loss of pheromone when they fly into a large pocket of clean air by going into crosswind casting flight in a mean of 0.48 s; 0.62 s after re‐contacting pheromone presented as a single pulse, they surge upwind in a kind of narrow zigzagging flight. After 0.36 s of surging, they lapse into casting flight once again in the clean air following the pulse. The addition of a known behavioural antagonist (Z)‐11‐hexadecenyl acetate (Z11–16:Ac), to the pheromone significantly increases the mean latency of the response to a single pulse to 0.85 s. No other aspects of the surge were significantly changed by the presence of antagonist in the single pulse of pheromone. Thus, unlike males of the related species, Heliothis virescens, which show significant changes in track and course angles when antagonist is present in single pulses, only an increased latency of response to a filament containing antagonist occurred in H. zea males. The increased latency could act cumulatively when the male is exposed rapidly and repeatedly to filaments in a natural plume and explain the profound arrestment effect of the antagonist in such plumes. The latencies to casting and surging in response to a pulse of pheromone blend are longer than those of the smaller species, H. virescens, and may be due to size‐related differences in manoeuverability of H. zea vs. H. virescens.
Repeated exposure to enhanced UV‐B radiation in successive generations increases developmental instability (leaf fluctuating asymmetry) in a desert annual
Authors: Midgley G. F. , Wand S. J. E. , Musil C. F.
Published: March 2003

Populations of the desert annual Dimorphotheca sinuata, derived from a common seed stock, were exposed concurrently over four successive generations to either ambient (representing no stratospheric ozone depletion) or elevated (representing 20% stratospheric ozone depletion) UV‐B levels during their complete life cycle. Leaf fluctuating asymmetry (FA) was measured in populations of plants grown from seeds of selected generations which had experienced different UV‐B exposure histories, and from seeds collected from a wild population of this species which grows in a naturally enhanced UV‐B environment. These measured plants had been grown in a greenhouse under essentially UV‐B‐free conditions. Leaf FA was significantly increased by greater numbers of enhanced UV‐B exposures in the parentage of the seed. There was a linear to exponential dose–response relationship between number of UV‐B exposure iterations in seed parentage and leaf FA, suggesting that damage to DNA caused by UV‐B exposure during plant development may not be fully repaired, and thus be inherited by offspring and accumulated over successive generations in this species. Leaf FA of plants grown from seed from the wild population was not significantly greater than that of control plants whose parentage experienced only ambient UV‐B exposures, although this negative result may have been due to low sampling intensity and measurement resolution, and the relatively low UV‐B enhancement experienced by the wild population. We conclude that leaf FA may constitute a relatively sensitive yet inexpensive means of quantifying UV‐B damage to plants.
Cold‐induced photoinhibition and growth of seedling snow gum (Eucalyptus pauciflora) under differing temperature and radiation regimes in fragmented forests
Authors: Blennow K. , Lang A. R. G. , Dunne P. , Ball M. C.
Published: March 2003

Fluorescence characteristics and growth of seedling snow gum (Eucalyptus pauciflora Sieb. ex Spreng.) during autumn and winter were related to variation in radiation and temperature regime in a fragmented forest. Seedlings were planted in four treatments along transects perpendicular to tree island edges to characterize plant responses to microclimates ranging from those of cleared areas to those beneath forest canopies. Three‐dimensional mapping of seedling leaf display, in combination with information retrieved from hemispherical photographs about shading from overstory canopies, were used to calculate the intercepted amounts of direct radiation energy for unit area of leaves on clear days (IDRE). IDRE was highest on the outside, most variable at the edges and lowest well inside the tree islands. Minimum temperature decreased with increasing view of the sky. Photoinhibition, measured as decrease in Fv/Fm, was correlated with spatial and seasonal differences in weekly minimum temperature and IDRE. Seedlings in the open and under the most canopy cover, with low variability in IDRE in a scale of weeks, exhibited less variability in photoinhibition than those growing along forest edges. Seedlings in the open tended to be most photoinhibited and grew the most. The combination of increased IDRE with reduced minimum temperatures resulted in persistent and strong photoinhibition as the season progressed. Results are discussed in relation to the potential for seedling establishment following forest fragmentation.
Fitting models predicting dates of flowering of temperate‐zone trees using simulated annealing
Authors: Chuine I. , Cour P. , Rousseau D. D.
Published: March 2003

The aim of the present study was to test the four commonly used models to predict the dates of flowering of temperate‐zone trees, the spring warming, sequential, parallel and alternating models. Previous studies concerning the performance of these models have shown that they were unable to make accurate predictions based on external data. One of the reasons for such inaccuracy may be wrong estimations of the parameters of each model due to the non‐convergence of the optimization algorithm towards their maximum likelihood. We proposed to fit these four models using a simulated annealing method which is known to avoid local extrema of any kind of function, and thus is particularly well adapted to fit budburst models, as their likelihood function presents many local maxima. We tested this method using a phenological dataset deduced from aeropalynological data. Annual pollen spectra were used to estimate the dates of flowering of the populations around the sampling station. The results show that simulated annealing provides a better fit than traditional methods. Despite this improvement, classical models still failed to predict external data. We expect the simulated annealing method to allow reliable comparisons among models, leading to a selection of biologically relevant ones.
Photosynthesis and conductance of spring‐wheat leaves: field response to continuous free‐air atmospheric CO2 enrichment
Authors: Garcia R. L. , Long S. P. , Wall G. W. , Osborne C. P. , Kimball B. A. , Nie G. Y. , Pinter P. J. , Lamorte R. L. , Wechsung F.
Published: March 2003

Spring wheat was grown from emergence to grain maturity in two partial pressures of CO2 (pCO2): ambient air of nominally 37 Pa and air enriched with CO2 to 55 Pa using a free‐air CO2 enrichment (FACE) apparatus. This experiment was the first of its kind to be conducted within a cereal field without the modifications or disturbance of microclimate and rooting environment that accompanied previous studies. It provided a unique opportunity to examine the hypothesis that continuous exposure of wheat to elevated pCO2 will lead to acclimatory loss of photosynthetic capacity. The diurnal courses of photosynthesis and conductance for upper canopy leaves were followed throughout the development of the crop and compared to model‐predicted rates of photosynthesis. The seasonal average of midday photosynthesis rates was 28% greater in plants exposed to elevated pCO2 than in contols and the seasonal average of the daily integrals of photosynthesis was 21% greater in elevated pCO2 than in ambient air. The mean conductance at midday was reduced by 36%. The observed enhancement of photosynthesis in elevated pCO2 agreed closely with that predicted from a mechanistic biochemical model that assumed no acclimation of photosynthetic capacity. Measured values fell below predicted only in the flag leaves in the mid afternoon before the onset of grain‐filling and over the whole diurnal course at the end of grain‐filling. The loss of enhancement at this final stage was attributed to the earlier senescence of flag leaves in elevated pCO2. In contrast to some controlled‐environment and field‐enclosure studies, this field‐scale study of wheat using free‐air CO2 enrichment found little evidence of acclimatory loss of photosynthetic capacity with growth in elevated pCO2 and a significant and substantial increase in leaf photosynthesis throughout the life of the crop.
Simultaneous recording of xylem pressure and trans‐root potential in roots of intact glycophytes using a novel xylem pressure probe technique
Authors: Wegner L. H. , Zimmermann U.
Published: March 2003

The radial electrical potential difference between the root xylem and the bathing solution, i.e. the so‐called trans‐root potential, was measured in intact maize and wheat plants using a xylem pressure probe into which an Ag/AgCl electrode was incorporated. Besides other advantages (e.g. detection and removal of tip clogging; determination of the radial root resistance), the novel probe allowed placement of the electrode precisely in a single xylem vessel as indicated by the reading of sub‐atmospheric or negative pressure values upon penetration. The trans‐root potentials were of the order of 0 to – 70 mV and + 40 to – 20 mV for 2‐ to 3‐week‐old maize and wheat plants, respectively. Osmotic experiments performed on maize demonstrated that addition of 100 mM mannitol to the solution resulted in a decrease of xylem pressure associated with a slow, but continuous depolarization. The depolarization was reversible upon removal of the mannitol. For wheat plants it could be shown that the oscillations of the xylem pressure described recently by Schneider et al. (1997, Plant, Cell and Environment 20, 221–229) were accompanied by (rectangular, saw‐tooth and/or U‐shaped) oscillations in the trans‐root potential (but not by corresponding changes of the membrane potential of the cortical cells measured simultaneously with conventional microelectrodes). Increase of the light intensity (up to 550 μmol m–2 s–1) resulted in a drop of the xylem pressure in wheat, whereas the trans‐root potential showed a biphasic response: first hyperpolarization (by about 10 mV) was observed, followed by depolarization (by up to about + 40 mV). Similar light‐induced biphasic (but often less pronounced) changes in the trans‐root potential were also recorded for maize plants. Most interestingly, the response of the trans‐root potential was always faster (by about 1–3 min) than the response of the xylem pressure upon illumination, suggesting that changes in the transpiration rate are reflected very quickly in the electrical properties of the root tissue. The impact of this and other findings on long‐distance transport of solutes and water as well as on long‐distance signalling is discussed.
Intercellular separation forces generated by intracellular pressure
Authors: Jarvis M. C.
Published: March 2003

Turgor pressure tends to force plant cells towards a spherical form, thus separating them at the angles from adjacent cells. In cooked vegetables containing starch, the swelling pressure of starch gelatinization generates analogous cell separation forces. A theoretical analysis of the relationship between internal pressure and cell separation forces is presented. Apart from the effect of internal pressure, cell separation forces increase with the diameter of the cell and decrease with the number of cell sides. Cell separation forces are reduced by the introduction of intercellular spaces and decrease further as these expand. The relationship between intracellular pressure and cell separation forces provides a basis upon which the strength of intercellular adhesion can be measured by experiment.
‘Node counting’: an internal control of balanced vegetative and reproductive development
Authors: Sachs T.
Published: March 2003

Plants can complete an entire life cycle in uniform environments. This is evidence that while shoot apices reiterate leaf formation they also change as a function of their own development. These changes occur in individual apices rather than the plant as a whole, and they are most closely correlated with the number of nodes an apex has formed. Evidence about the mechanism of ‘node counting’ suggests a working hypothesis: apical transitions depend on cumulative information about the distances of an apex from the roots, rather than on any single, critical state. Studies of the ecological roles of plant size and age have neglected the physiological information about ‘node counting’. Yet it is evident in field conditions, especially in the morphological location of flowers on branches situated at different heights along the main axis. ‘Node counting’ affects flower formation, but as a component rather than sole determinant of apical differentiation it displays pronounced phenotypic plasticity. The ecological advantages of ‘node counting’ could include its being a basis for concurrent vegetative and reproductive development on the same plant. It also allows for environmental responses that are a function of the state of plant sectors without constraining the sizes of leaves and other organs.
NaCl and CuSO4 treatments trigger distinct oxidative defence mechanisms in Nicotiana plumbaginifolia L.
Authors: SAVOURÉ A. , THORIN D. , DAVEY M. , HUA XUE‐JUN , MAURO S. , VAN MONTAGU M. , INZÉ D. , VERBRUGGEN N.
Published: March 2003

To gain better insights into the generation of oxidative stress by NaCl stress, we compared the effects of toxic, sublethal concentrations of NaCl (150 mM) with those of CuSO4 (100 μM) on the antioxidant defence responses of Nicotiana plumbaginifolia L. plants grown in hydroponic culture. Short‐ and long‐term adaptive responses were investigated as well as the effects of root cutting to allow rapid absorption of ions. Our results show that photosynthesis is already affected after 12 h of both treatments and that photoinhibition is induced. Furthermore, the two treatments showed distinct patterns of induction of the genes of the antioxidant systems. Principally, NaCl stimulated catalase activity through activation of the Cat2 and Cat3 genes, whereas with CuSO4, transcript levels, protein levels, and enzymatic activities of glutathione peroxidase, ascorbate peroxidase, and superoxide dismutase were differentially induced. The antioxidants ascorbate and glutathione were found to be largely oxidized after 12 h, suggesting an inability of the recycling process to cope with the stress. In addition, both NaCl and CuSO4 treatments stimulated the accumulation of the osmolyte proline. Therefore, we conclude that the uptake and accumulation of different types of ions lead to the generation of distinct antioxidant responses in N. plumbaginifolia.
Relationships between shoot to root ratio, growth and leaf soluble protein concentration of Pisum sativum, Phaseolus vulgaris and Triticum aestivum under different nutrient deficiencies
Authors: Andrews  , Sprent  , Raven  , Eady
Published: March 2003

Relations between shoot to root dry weight ratio (S : R), total plant dry weight (DW), shoot and plant N concentration and leaf soluble protein concentration were examined for pea (Pisum sativum L.), common bean (Phaseolus vulgaris L.) and wheat (Triticum aestivum L.) under different nutrient deficiencies. A regression model incorporating leaf soluble protein concentration and plant DW could explain greater than 80% of the variation in S : R within and between treatments for pea supplied different concentrations of NO3– or NH4+ in solid substrate; pea and bean supplied different concentrations of N, P, K and Mg in liquid culture; and wheat supplied different concentrations of N, P, K, Mg, Ca and S in liquid culture. Addition of shoot or plant N concentration to the model explained little more of the variation in S : R. It is concluded that results are consistent with the proposal that macronutrient effects on S : R are primarily mediated through their effects on protein synthesis and growth.
Solute fluxes from tobacco to the parasitic angiosperm Orobanche cernua and the influence of infection on host carbon and nitrogen relations
Authors: Hibberd J. M. , Quick W. P. , Press M. C. , Scholes J. D. , Jeschke W. D.
Published: March 2003

Orobanche species are holoparasites which are very efficient sinks for host‐derived solutes. Here, we report the use of direct measurements of xylem sap solute concentrations and water fluxes, together with a modelling procedure to calculate element fluxes within an association between Orobanche cernua and its tobacco host. Infection of tobacco by the parasite markedly influenced carbon acquisition and partitioning; net fixation of carbon was 20% higher in infected tobacco compared with controls. Orobanche cernua caused a 84% increase in net carbon flux moving downward from the tobacco shoot and 73% of this carbon was intercepted by the parasite, almost entirely through the phloem (>99%). Further, the parasite also exerted a large impact on the nitrogen relations of the plant, notably nitrate uptake was stimulated and the amino acid content of xylem sap was lower. The parasite also relied heavily on host phloem for the supply of other resources, with only 5 to 15% of N, and 16% of K, 23% of Na, 63% of Mg and 13% of S being derived from the xylem. Thus, we provide quantitative information on the phloem dependency of the parasite and show that host carbon and nitrogen metabolism is stimulated as a consequence of infection.
Developmental changes in enzymes involved in the conversion of hexose phosphate and its subsequent metabolites during early tuberization of potato
Authors: Appeldoorn N. J. G. , De Bruijn S. M. , Koot‐Gronsveld E. A. M. , Visser R. G. F. , Vreugdenhil D. , Plas L. H. W. Van Der
Published: March 2003

A highly synchronized in vitro tuberization system, based on single‐node cuttings containing an axillary bud, was used to investigate the activity patterns of enzymes involved in the conversion of hexose phosphates and related products during stolon‐to‐tuber transition of potato (Solanum tuberosum L.). At tuberization the activity of enzymes involved in glycolysis and the oxidative pentose phosphate pathway (OPPP) showed a small but clear increase. This increase reflects a higher capacity of respiratory(‐related) metabolism, presumably due to the onset of rapid cell division in the apical part of the tuberizing stolon. During the phase of successive tuber growth these enzymes decreased in activity, suggesting that the concomitant massive starch accumulation is not accompanied by a large increase in respiration. A high degree of positive correlation between the activities of these enzymes could be observed, implying that the level of respiratory metabolism‐related enzymes is co‐ordinately regulated by the same mechanism of coarse control. The activity pattern of pyrophosphate:fructose‐6‐phosphate phosphotransferase (PFP) showed no developmental change and does not resemble the activity pattern of the enzymes participating in respiratory(‐related) metabolism. Instead, its level of activity is very likely the result of metabolic regulation. The level of the content of the metabolites UDP‐glucose (UDPGlc) and glucose‐6‐phosphate (Glc6P) decreased after the onset of tuberization. This decline indicates that tuber induction is not accompanied by an appreciable increase in the level of the cytosolic hexose phosphate (hexose‐P) content but that it rather remains on a low level, which might be a prerequisite in order to maintain a high net rate of sucrose degradation during tuber development. In contrast to UDPGlc and Glc6P, the content of fructose‐1,6‐bisphosphate (Fru1,6bisP) showed an increase after tuber induction. The overall activities of ADP‐glucose pyrophosphorylase (AGPase) and starch phosphorylase (STP) both showed a large increase after tuber initiation, which is consistent with their presumed role in the process of starch synthesis and accumulation during rapid tuber growth.
Shoot structure, canopy openness, and light interception in Norway spruce
Authors: Stenberg P. , Kangas T. , Smolander H. , Linder S.
Published: March 2003

We analysed changes in shoot structure with canopy openness in control (C) and irrigated–fertilized (IL) Picea abies trees. Canopy openness, which was used to characterize light availability, varied between 0·23 and 0·90 for C shoots and 0·07 to 0·75 for IL shoots. Needle width and thickness increased with canopy openness, but were similar for C and IL needles. The ratio of needle thickness to width remained fairly close to one throughout the canopy. This resulted in large values (3·0–4·0) of the ratio of total to projected needle area. The ratio of total to projected needle area did not correlate with canopy openness. Shoot silhouette to total needle area ratio (STAR) and specific needle area decreased with canopy openness. As a result, shoot silhouette area per unit needle mass was up to three times larger in shade shoots than in sun shoots. STAR and specific needle area were similar for C and IL shoots and needles. Needle nitrogen concentration varied between 0·7 and 1·1% (C), and between 1·0 and 1·6% (IL). On both plots, nitrogen content was linearly related to estimated relative light interceptance (RLI) (both expressed per needle area), but the ratio of nitrogen content to RLI increased with decreasing canopy openness.
Ethylene production and ACC‐accumulation in Agrobacterium tumefaciens‐induced plant tumours and their impact on tumour and host stem structure and function
Authors: Wächter R. , Fischer K. , Gäbler R. , Kühnemann F. , Urban W. , Bögemann G. M. , Voesenek L. A. C. J. , Blom C. W. P. M. , Ullrich C. I.
Published: March 2003

Ethylene emission from wild‐type Agrobacterium tumefaciens (C58)‐induced stem tumours of Ricinus communis was continuously measured with two different methods, process gas chromatography and photo‐acoustic spectrometry. Ethylene production was as high as 700 pmol g FW–1 h–1, namely 140 times greater than emitted by non‐tumourized control stems. It was highest in 5‐week‐old tumours, independent of light, depressed by anoxia and, during water deficit it was stimulated by rewatering. A remarkable concomitant CO‐production was discovered. Accumulation of 1‐aminocyclopropane‐1‐carboxylic acid (ACC), the substrate of ACC‐oxidase, preceded ethylene emission with a maximum 2 weeks after tumour induction. Simultaneously, the xylem in the tumour‐adjacent host stem underwent drastic changes: it increased two to three times in thickness, vessel diameters decreased, the rays remained unlignified and became multiseriate. With increasing emission of ethylene aerenchyma developed in the non‐transformed, tumour‐surrounding tissue that formerly was stem cortex. Cotyledons reacted with epinastic symptoms indicating induction of senescence. The present results reveal an important role of ethylene, in addition to cytokinin and auxin, for the differentiation and physiology of A. tumefaciens‐induced tumours.
Leaf expansion and cell division are affected by reducing absorbed light before but not after the decline in cell division rate in the sunflower leaf
Authors: Granier C. , Tardieu F.
Published: March 2003

The effect of absorbed photosynthetic photon flux density (PPFD) on leaf expansion is a key issue for analysing the phenotypic variability between plants and for modelling feedback loops. Expansion and epidermal cell division in leaf 8 of sunflower were analysed in a series of five experiments where absorbed photosynthetic photon flux density (PPFD) was reduced either by shading or by covering part of the leaf area. These treatments were imposed at different times during leaf development. Expansion and cell division were affected by a reduction in absorbed PPFD only in the first part of leaf development, while the leaf area was less than 2% of its final value and while absolute expansion rate was slow. In contrast, it was not affected if imposed later when the leaf was visible and absolute expansion rate was at maximum. A reduction in absorbed PPFD caused the same reduction in expansion and in cell division whether it was due to a reduction in incident PPFD or to a reduction in photosynthetic leaf area, suggesting that carbon metabolism was involved. Relative expansion rate recovered to control levels when relative division rate began to decline, in all experiments and in all zones of a leaf. This was probably linked to the source–sink transition, after which the leaf had such a high priority in carbon allocation that it was largely insensitive to changes in absorbed PPFD. The final leaf area was therefore closely related to the cumulated PPFD absorbed by the plant from leaf initiation to the end of exponential cell division.
Novel approaches for examining the effects of differential soil compaction on xylem sap abscisic acid concentration, stomatal conductance and growth in barley (Hordeum vulgare L.)
Authors: Hussain A. , Black C. R. , Taylor I. B. , Mulholland B. J. , Roberts J. A.
Published: March 2003

Novel techniques were devised to explore the mechanisms mediating the adverse effects of compacted soil on plants. These included growing plants in: (i) profiles containing horizons differing in their degree of compaction and; (ii) split‐pots in which the roots were divided between compartments containing moderately (1·4 g cm−3) and severely compacted (1·7 g cm−3) soil. Wild‐type and ABA‐deficient genotypes of barley were used to examine the role of abscisic acid (ABA) as a root‐to‐shoot signal. Shoot dry weight and leaf area were reduced and root : shoot ratio was increased relative to 1·4 g cm−3 control plants whenever plants of both genotypes encountered severely compacted horizons. In bartey cultivar Steptoe, stomatal conductance decreased within 4 d of the first roots encountering 1·7 g cm−3 soil and increased over a similar period when roots penetrated from 1·7 g cm−3 into 1·4 g cm−3 soil. Conductance was again reduced by a second 1·7 g cm−3 horizon. These responses were inversely correlated with xylem sap ABA concentration. No equivalent stomatal responses occurred in Az34 (ABA deficient genotype), in which the changes in xylem sap ABA were much smaller. When plants were grown in 1·7 : 1·4 g cm−3 split‐pots, shoot growth was unaffected relative to 1·4 g cm−3 control plants in Steptoe, but was significantly reduced in Az34. Excision of the roots in compacted soil restored growth to the 1·4 g cm−3 control level in Az34. Stomatal conductance was reduced in the split‐pot treatment of Steptoe, but returned to the 1·4 g cm−3 control level when the roots in compacted soil were excised. Xylem sap ABA concentration was initially higher than in 1·4 g cm−3 control plants but subsequently returned to the control level; no recovery occurred if the roots in compacted soil were left intact. Xylem sap ABA concentration in the split‐pot treatment of Az34 was initially similar to plants grown in uniform 1·7 g cm−3 soil, but returned to the 1·4 g cm−3 control level when the roots in the compacted compartment were excised. These results clearly demonstrate the involvement of a root‐sourced signal in mediating responses to compacted soil; the role of ABA in providing this signal and future applications of the compaction procedures reported here are discussed.
An accurate method to quantify ribulose bisphosphate carboxylase content in plant tissue
Authors: Ferreira R. B. , Esquível M. G.
Published: March 2003

A method is described to accurately measure the content of ribulose bisphosphate carboxylase (RuBP carboxylase, EC 4·1.1·39) in plant tissues. This procedure, termed the internal standard method, involves extraction of the plant tissue (containing an unknown amount of 1H‐RuBP carboxylase) in a buffer containing a known amount of previously purified 3H‐RuBP carboxylase (internal standard). The rapid and efficient, single step copurification of 1H‐ and 3H‐RuBP carboxylases on the Mono Q column of the Fast Protein Liquid Chromatography System (FPLC), or by sucrose density gradient ultracentrifugation, allows the accurate estimation of the purification yield (3H in purified enzyme/3H in the extraction buffer). Knowing the amount of 1H‐RuBP carboxylase in the purified enzyme and the purification yield, one can calculate the concentration of 1H‐enzyme present in the plant tissue. This procedure overcomes some of the main constraints associated with the methods described in the literature: it takes into account the enzyme that is lost during the clarification of the protein extracts or during the isolation and purification processes; it is independent of the proteolysis that occurs in vitro by the action of cell proteases; it is not affected by the presence of RuBP carboxylase breakdown products; it is not influenced by any of the factors that control the catalytic activity or the activation state of the enzyme; and, it does not depend on the specificity of antigen‐antibody reactions.
Influence of temperature and soil drying on respiration of individual roots in citrus: integrating greenhouse observations into a predictive model for the field
Authors: Bryla D. R. , Bouma T. J. , Hartmond U. , Eissenstat D. M.
Published: March 2003

In citrus, the majority of fine roots are distributed near the soil surface – a region where conditions are frequently dry and temperatures fluctuate considerably. To develop a better understanding of the relationship between changes in soil conditions and a plant’s below‐ground respiratory costs, the effects of temperature and soil drying on citrus root respiration were quantified in controlled greenhouse experiments. Chambers designed for measuring the respiration of individual roots were used. Under moist soil conditions, root respiration in citrus increased exponentially with changes in soil temperature (Q10 = 1·8–2·0), provided that the changes in temperature were short‐term. However, when temperatures were held constant, root respiration did not increase exponentially with increasing temperatures. Instead, the roots acclimated to controlled temperatures above 23 °C, thereby reducing their metabolism in warmer soils. Under drying soil conditions, root respiration decreased gradually beginning at 6% soil water content and reached a minimum at <2% soil water content in sandy soil. A model was constructed from greenhouse data to predict diurnal patterns of fine root respiration based on temperature and soil water content. The model was then validated in the field using data obtained by CO2 trapping on root systems of mature citrus trees. The trees were grown at a site where the soil temperature and water content were manipulated. Respiration predicted by the model was in general agreement with observed rates, which indicates the model may be used to estimate entire root system respiration for citrus.
Screening of cadmium‐responsive genes in Arabidopsis thaliana
Authors: Suzuki N. , Koizumi N. , Sano H.
Published: March 2003

Seedlings of Arabidopsis thaliana were treated with Cd, and transcript populations that changed their levels were screened by a fluorescent differential display method. Among the 170 cDNAs initially identified, 31 were further characterized for their identity, expression profile and response to other stresses. Sequencing revealed 10, 12 and 15 to be related to signal transduction, protein denaturing stress and responses to active oxygen species, respectively. Many of these genes responded not only to Cd, but also to oxidative stress, Cu ions and a protein denaturation agent. Upon introduction into yeast cells, two genes, encoding ATMEKK1 and a putative farnesylated protein that has two metal binding motifs, endowed marked toleration of Cd toxicity. These results suggest that oxidative stress and protein denaturation are important components of Cd toxicity, and that to cope with such stresses, plants activate a set of genes involved in metal detoxification, protein refolding and wound healing. The results also suggested temporarily and spatially well‐regulated protein phosphorylation and activation of transcription factors, accompanied by their transcription.
Leaf ontogenetic dependence of light acclimation in invasive and native subtropical trees of different successional status
Authors: Yamashita N. , Koike N. , Ishida A.
Published: March 2003

In the Bonin Islands of the western Pacific where the light environment is characterized by high fluctuations due to frequent typhoon disturbance, we hypothesized that the invasive success of Bischofia javanica Blume (invasive tree, mid‐successional) may be attributable to a high acclimation capacity under fluctuating light availability. The physiological and morphological responses of B. javanica to both simulated canopy opening and closure were compared against three native species of different successional status: Trema orientalis Blume (pioneer), Schima mertensiana (Sieb. et Zucc.) Koidz (mid‐successional) and Elaeocarpus photiniaefolius Hook.et Arn (late‐successional). The results revealed significant species‐specific differences in the timing of physiological maturity and phenotypic plasticity in leaves developed under constant high and low light levels. For example, the photosynthetic capacity of T. orientalis reached a maximum in leaves that had just fully expanded when grown under constant high light (50% of full sun) whereas that of E. photiniaefolius leaves continued to increase until 50 d after full expansion. For leaves that had just reached full expansion, T. orientalis, having high photosynthetic plasticity between high and low light, exhibited low acclimation capacity under the changing light (from high to low or low to high light). In comparison with native species, B. javanica showed a higher degree of physiological and morphological acclimation following transfer to a new light condition in leaves of all age classes (i.e. before and after reaching full expansion). The high acclimation ability of B. javanica in response to changes in light availability may be a part of its pre‐adaptations for invasiveness in the fluctuating environment of the Bonin Islands.
Hydraulic architecture of leaf venation in Laurus nobilis L.
Authors: Zwieniecki M. A. , Melcher P. J. , Boyce C. K. , Sack L. , Holbrook N. M.
Published: March 2003

Veins are the main irrigation system of the leaf lamina and an understanding of the hydraulic architecture of the vein networks is essential for understanding leaf function. However, determination of leaf hydraulic parameters is challenging, because for most leaves the vein system is reticulate, contains a hierarchy of different vein sizes, and consists of leaky conduits. We present a new approach that allows for measurements of pressure differences between the petiole and any vein within the leaf. Measurements of Laurus nobilis leaves indicate that first‐ and second‐order veins have high axial conductance and relatively small radial permeability, thus allowing water to reach distal areas of the leaf with only a small loss of water potential. Higher order veins tend to be more hydraulically resistant and permit greater radial leakage. This design allows for a relatively equitable distribution of water potential and thus reflects the capacity of the venation to provide a relatively homogeneous water supply across the leaf lamina, with only the leaf margins being hydraulically disadvantaged relative to the rest of the leaf.
Life‐long growth of Quercus ilex L. at natural CO2 springs acclimates sulphur, nitrogen and carbohydrate metabolism of the progeny to elevated pCO2
Authors: SCHULTE M. , VON BALLMOOS P. , RENNENBERG H. , HERSCHBACH C.
Published: March 2003

The aim of the present study was to analyse whether offspring of mature Quercus ilex trees grown under life‐long elevated pCO2 show alterations in the physiological response to elevated pCO2 in comparison with those originating from mature trees grown at current ambient pCO2. To investigate changes in C‐ (for changes in photosynthesis, biomass and lignin see Polle, McKee & Blaschke Plant, Cell and Environment 24, 1075–1083, 2001), N‐, and S‐metabolism soluble sugar, soluble non‐proteinogenic nitrogen compounds (TSNN), nitrate reductase (NR), thiols, adenosine 5′‐phosphosulphate (APS) reductase, and anions were analysed. For this purpose Q. ilex seedlings were grown from acorns of mother tree stands at a natural spring site (elevated pCO2) and a control site (ambient pCO2) of the Laiatico spring, Central Italy. Short‐term elevated pCO2 exposure of the offspring of control oaks lead to higher sugar contents in stem tissues, to a reduced TSNN content in leaves, and basipetal stem tissues, to diminished thiol contents in all tissues analysed, and to reduced APS reductase activity in both, leaves and roots. Most of the components of C‐, N‐ and S‐metabolism including APS reductase activity which were reduced due to short‐term elevated pCO2 exposure were recovered by life‐long growth under elevated pCO2 in the offspring of spring oaks. Still TSNN contents in phloem exudates increased, nitrate contents in lateral roots and glutathione in leaves and phloem exudates remained reduced in these plants. The present results demonstrated that metabolic adaptations of Q. ilex mother trees to elevated pCO2 can be passed to the next generation. Short‐ and long‐term effects on source‐to‐sink relation and physiological and genetic acclimation to elevated pCO2 are discussed.
Interaction between powdery mildew and barley with mlo5 mildew resistance
Authors: Lyngkjær M. F. , Oslash;stergård H.
Published: March 2003

Powdery mildew infection of barley with the mlo5 barley powdery mildew resistance gene was examined, using near‐isogenic barley lines, with and without mlo5 resistance, and two near‐isogenic powdery mildew isolates, HL3/5 and GE3 with high (virulent) or low (avirulent) penetration efficiency on the resistant barley line. In all isolate–host combinations (except GE3 on the resistant barley line), frequency of haustorium formation increased significantly from zero at 11 h after inoculation to a maximum by 13 h, and there was no subsequent increase up to 24 h. In the susceptible barley line, 27% of appressoria from both isolates formed haustoria. Although this was significantly higher than the frequency of haustorium formation (18%) of HL3/5 on the resistant barley line, HL3/5 was much more successful than GE3 (frequency of haustorium formation less than 1%). The fact that HL3/5 did not possess a generally higher ability to penetrate successfully to form haustoria on the susceptible barley line, indicates that HL3/5 did not overcome the mlo5 resistance by being generally more vigorous. In the resistant barley line, papillae were larger than in the susceptible line; however, both isolates were associated with papillae of the same diameter at the time of penetration. We suggest that the mlo5 resistant barley line confers two different forms of resistance: isolate‐specific and isolate‐nonspecific.
Control of soilborne clubroot disease of cruciferous plants by epoxydon from Phoma glomerata
Authors: Arie  , Kobayashi  , Okada  , Kono  , Yamaguchi
Published: March 2003

Culture broth from an isolate of Phoma glomerata (no. 324, = JCM 9972) from the leaves of Viola sp., controlled the soilborne pathogen Plasmodiophora brassicae which causes clubroot disease of cruciferous plants. This effect was caused by epoxydon (5‐hydroxy‐3‐(hydroxymethyl)‐7‐oxabicyclo[4.1.0]hept‐3‐en‐2‐one). Although this substance was known to have antitumour activity, phytotoxicity and antiauxin activity, no plant disease reduction had been reported previously. Epoxydon possessed neither strong antimicrobial activity nor did it induce acquired resistance. It protected crucifers from clubroot disease at 250 μg mL−1 following addition to the soil. Several antiauxins were tested for similar properties resulting in the suppression of clubroot disease and one, 2,3,5‐triiodobenzoic acid, was effective at 10 μg mL−1. Clubroot reduction by epoxydon may result from antiauxin activity. This opens opportunities for a new group of agrochemicals.
Endophytic bacterial communities in the periderm of potato tubers and their potential to improve resistance to soil‐borne plant pathogens
Authors: Sturz  , Christie  , Matheson  , Arsenault  , Buchanan
Published: March 2003

To evaluate whether the location of bacterial endophyte communities contributes to disease resistance in potato tubers (Solanum tuberosum), the population density, biodiversity and antibiotic activity of endophytic bacteria was examined from the tuber peel (periderm plus top 3 mm of tissue) of four cultivars (Russet Burbank, Kennebec, Butte and Shepody). There were no significant differences for population density of bacteria among the layers of peel examined and no cultivar × peel layer interaction. Endophytic bacteria from several layers of peel were challenged in in vitro bioassays to the soil‐borne plant pathogens Fusarium sambucinum, Fusarium avenaceum, Fusarium oxysporum and Phytophthora infestans (mating types A1 and A2). In general, antibiosis of bacterial endophytes against these pathogens was significantly higher (P = 0.01) in isolates recovered from the outermost layer of tuber peel and decreased progressively toward the centre of the tuber. Antibiosis against P. infestans was variable, with a progressive decrease in antibiotic activity from outer to inner layers of peel occurring in cvs Russet Burbank and Kennebec only. For antibiosis there were significant cultivar × peel, and cultivar × pathogen interactions (P = 0.01). In all cases the inhibitory activity of endophytic bacteria was significantly greater (P = 0.01) against the A1 than the A2 mating type of P. infestans. In four of seven cases, where the same species of bacteria were recovered from all three peel layers, antibiosis to pathogens decreased significantly (P = 0.01) with depth of recovery (from the periderm to inside the tuber), indicating that in certain communities of endophytic bacteria, defence against pathogens may be related to bacterial adaptation to location within a host and may be tissue‐type and tissue‐site specific.