bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution of parasite stages in tissues of Toxoplasma gondii infected SCID mice and human peripheral blood lymphocyte‐transplanted SCID mice
Authors: Meyer Desiree J. , Allan Jane E. , Beaman Miles H.
Published: March 2003

The establishment of Toxoplasma gondii infection in the tissues of SCID mice and SCID mice transplanted with human peripheral blood lymphocytes (PBL) was investigated. The presence of bradyzoites and tachyzoites was analysed in hu‐PBL SCID mice using Southern blot of reverse transcriptase‐polymerase chain reaction products for the expression of B1, BAG1 and SAG1 of T. gondii. BAG1 was present by week 1 in brain, lung, liver and spleen of some animals; by week 3, BAG1 was present in all animals and in all of these tissues. In contrast, SAG1 was rarely detected until week 2 (mainly in the lung and brain) and by week 3, some animals still did not have detectable SAG1 in brain, lung, liver and spleen. SAG1 expression was increased in the lungs of animals transplanted with human PBL compared to nontransplanted SCID mice. Human PBL engraftment was demonstrated, initially in uninfected mice, by the presence of human CD3+ T cells in the spleen (3.1 × 105 positive cells) and peritoneal cavity (3.4 × 105 cells) 4 weeks after transplantation. The final outcome of infection was not influenced by the presence of human PBL, with similar mortality in human PBL transplanted and nontransplanted mice. These studies provide a detailed analysis of the kinetics and distribution of both the cyst and tachyzoite stage of T. gondii. This system has been established to allow evaluation of therapies against T. gondii immunodeficient mice in the presence of human immune cells.
Immunogenicity of synthetic peptides from the Sm31 antigen (cathepsin B) of the Schistosoma mansoni adult worms
Authors: Noya Oscar , De Noya Belkisyolé Alarcón , Ballen Diana E. , Bermúdez Henry , Bout Daniel , Hoebeke Johan
Published: March 2003

The chemical synthesis of peptides may simplify the production of molecules for diagnosis of Schistosoma mansoni. Seventeen polymeric, 20‐amino acids long, peptides comprising the entire Sm31 molecule of the adult worm, were synthesized under the t‐boc strategy and their immunogenicity was evaluated. Of these, 10 peptides were immunogenic in rabbits. The peptides containing the sequence Gly74‐Ser93 (peptide IMT‐172) and the sequence Val154–Ala173 (peptide IMT‐180) were responsible for the recognition of the Sm31 molecule by Western blot. This was confirmed by the specific inhibition of recognition of each molecule with the homologous peptide. Additionally, antibodies against these peptides strongly fixed to the adult worm gut. The present results, together with the strong immunogenicity shown for the adult worm 31 kDa antigen, establish the basis for the development of an immunodiagnostic method using synthetic peptides.
Host plant evaluation behaviour of Bemisia tabaci and its modification by external or internal uptake of imidacloprid
Authors: Isaacs Rufus , Cahill Matthew , Byrne David N.
Published: March 2003

The behaviour of adult Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) was observed on leaves of cotton, Gossypium hirsutum L., to study the process of host plant evaluation. Seven distinct behavioural elements were identified and recorded for a period of 20 min after initial contact with leaves. The behaviour of the whiteflies was observed on untreated leaves or on leaves treated with either foliar or systemically applied imidacloprid. Thus, contact with imidacloprid by whiteflies was either via the external cuticle or by ingestion, allowing determination of the effect of uptake route on host evaluation behaviour. Analysis of behavioural sequences and comparison of latencies, frequencies and durations of elements of behaviour between treatments revealed that host evaluation behaviour was similar on untreated and foliar treated leaves, but markedly different on those treated systemically. After their first probe, whiteflies on systemically treated leaves were much more active, spending significantly greater time walking and dabbing the labium tip onto the leaf surface. There was also a 50% reduction in the total time spent probing into systemically treated leaves, compared to the other treatments. This effect was the result of a shorter mean probe duration, and no effect of treatment was found on the frequency of probing. Pre‐oviposition behaviour was significantly more common on the systemically treated leaves, although the number of eggs laid was similar on all treatments. These results also show that the host evaluation phase of adult female B. tabaci was dominated by probing. The behavioural sequence that leads to probing was affected significantly by imidacloprid when ingested, but not by direct contact with this compound on the leaf surface. The wider implications for the mechanisms of whitefly–host plant interactions are discussed.
Response of female Lutzomyia longipalpis to host odour kairomones from human skin
Authors: Rebollar‐Tellez E. A. , Hamilton J. G. C. , Ward R. D.
Published: March 2003

Lutzomyia longipalpis Lutz & Neiva (Diptera: Psychodidae) is the vector of Leishmania chagasi, the aetiologic agent of visceral leishmaniasis in the New World. In the present study, the response of female sandflies from Jacobina, Brazil, to human odours from six different volunteers was investigated. Glass Petri dishes were handled by different volunteers and then exposed to female sandflies. There was a significant difference between subjects in that some individuals were more attractive or less repellent to sandflies. Response of flies to handled Petri dishes was higher during the first minutes of observation, suggesting the presence of volatile compounds in hand odours. Extracts of glass Petri dishes that had been handled by the volunteers were made with organic solvents such as acetone, methanol, pentane and ether. These were then concentrated and tested for sandfly response. Only extracts carried out with non‐polar solvents such as pentane and ether were able to transfer odours from handled glass Petri dishes onto clean dishes. The attractivity of male and female human subjects was monitored for 80 days, and minor fluctuations in attractiveness were observed.
Dose‐related upwind anemotaxis and movement up odour gradients in still air in the presence of methyl eugenol by the wild tobacco fly, Bactrocera cacuminata
Authors: Meats A. , Osborne A.
Published: March 2003

The behaviour of Bactrocera cacuminata (Hering) in wind varied according to the concentration of methyl eugenol (0, 95, 327 and 500 μg m−3, respectively). General locomotor activity (as measured by mean distance moved in 5 min, regardless of direction) was not significantly different in the first two treatments but was significantly lower in the others. Most flies in the fourth treatment did not move more than one body length. In the first two treatments, the rate and pattern of movement of most flies was basically similar, with walking in tortuous paths interspersed with short flights and usually no obvious bias in direction. However, 32% of flies in the second treatment did move in a biased direction, achieving upwind anemotaxis of at least 400 mm, but only 2–8% did so in the other conditions. Flies moved up a concentration gradient to a source of methyl eugenol in still air when released at a distance of 100, 150 or 200 mm. With one exception, no more than 40% did this within 3 min of release (whether or not the olfactory stimulus was augmented by a visual one). However, 77% responded when released 100 mm from a combined olfactory and visual stimulus. Visual augmentation of an olfactory stimulus may also be responsible for far fewer flies flying out of the vicinity at distances up to 150 mm, but not 200 mm.
Phase polymorphism in Locusta migratoria: the relative effects of geographical strains and albinism on morphometrics
Authors: Yerushalmi Yoram , Tauber Eran , Pener Meir Paul
Published: March 2003

An albino strain, which had originated from Okinawa, Japan, and a normally coloured strain, which had originated from West Africa, have been used to study density‐dependent morphometric phase characteristics and their changes in adults of the migratory locust, Locusta migratoria (L.). By repeated crossings we also obtained congenic albinos and normal phenotypes and investigated their morphometrics with increasing West African genome, eventually reaching 99.6% West African and 0.4% Okinawa gene pool. The data were analysed by the classical morphometric ratios (F/C and E/F; F = length of the hind femur, C = maximum width of the head, E = length of the fore wings), as well as by canonical discriminant (multivariate) analysis. The latter was based on measurements of F, C and E (as above), as well as of M (minimum width of the pronotum) and H (maximum height of the pronontum). Okinawa albinos showed more solitarious morphometrics and a smaller amplitude of morphometric phase change than West African normal phenotypes. Both the morphometric ratios and the canonical discriminant analysis demonstrated clearly that these differences were caused primarily by the strain (Okinawa vs. West African). However, the pigmentation (albino vs. normal colouration) also affected morphometric phase differences; albinos showed more solitarious morphometrics and somewhat more restricted morphometric phase change than congenic normal phenotypes. The effect of the pigmentation was considerably smaller than that of the strain. The results refute Nolte's claim that albino locusts constitute an extreme solitarious phase, even under crowding. However, Nolte's less extreme claim, that albino locusts have more solitarious morphometrics than normally coloured locusts, is validated by the present results.
The response of the malaria mosquito, Anopheles gambiae, to two components of human sweat, ammonia and l‐lactic acid, in an olfactometer
Authors: Braks M. A. H. , Meijerink J. , Takken W.
Published: March 2003

In an olfactometer study on the response of the anthropophilic malaria mosquito Anopheles gambiae s.s. (Diptera, Culicidae) to human sweat it was found that freshly collected sweat, mostly of eccrine origin, was attractive, but that incubated sweat was significantly more attractive than fresh sweat. The behavioural response to l‐lactic acid and ammonia, the main constituents of sweat, was investigated. l‐lactic acid was attractive at one concentration only (11.11 mm) and removal of the l‐lactic acid from the sweat by enzymatic decomposition did not affect the attractiveness of sweat. Ammonia caused attraction over a range of 0.1–13.4 m on glass slides and at 0.84–8.40 μmol/min in an air stream. It is concluded that: human sweat contains kairomones for host‐seeking An. gambiae; ammonia is an important kairomone for this mosquito; and that l‐lactic acid is not a prerequisite in the attraction of An. gambiae to sweat.
Physiology of diapause and cold hardiness in overwintering pupae of the apple leaf miner Phyllonorycter ringoniella in Japan
Authors: Li Yi‐Ping , Oguchi Sumiko , Goto Michiyo
Published: March 2003

Abstract The apple leaf miner Phyllonorycter ringoniella (Matsumura) (Lepidoptera: Gracillariidae) overwinters as a diapausing pupa. The diapause rate reaches 100% in early October. Diapause intensity decreases gradually from early October and diapause terminates in early February. The fresh body weight of diapausing pupae is 1.6 times that of non‐diapausing pupae. The main cryoprotectant in P. ringoniella pupae is trehalose. Three stages are distinguishable as indicated by the correlations between diapause intensity, levels of cold hardiness and the trehalose content: diapause induction occurred in October, diapause development from November to December, and post‐diapause quiescence from January to April. During diapause induction, the pupae accumulate low levels of trehalose and do not survive exposure to −15 °C. During diapause development, the pupae gradually accumulate more trehalose and show some ability to survive exposure to −15 °C, but not to −20 °C. During post‐diapause quiescence, the pupae accumulate relatively more trehalose and cold hardiness fully develops, but decreases quickly in April. The trehalose content in pupae sampled in December is unaffected by acclimation temperatures in the range 0–30 °C, but decreases in pupae sampled in March after acclimation at temperatures from 5 to 15 °C. These results suggest that overwintering pupae of P. ringoniella have the ability to accumulate trehalose and develop a high level of cold hardiness during diapause development.
Photosynthetic capacity in relation to nitrogen content and its partitioning in lichens with different photobionts
Authors: Palmqvist K. , Campbell D. , Ekblad A. , Johansson H.
Published: March 2003

We tested the hypothesis that lichen species with a photosynthetic CO2‐concentrating mechanism (CCM) use nitrogen more efficiently in photosynthesis than species without this mechanism. Total ribulose bisphosphate carboxylase‐oxygenase (Rubisco; EC 4.1.1.39) and chitin (the nitrogenous component of fungal cell walls), were quantified and related to photosynthetic capacity in eight lichens. The species represented three modes of CO2 acquisition and two modes of nitrogen acquisition, and included one cyanobacterial (Nostoc) lichen with a CCM and N2 fixation, four green algal (Trebouxia) lichens with a CCM but without N2 fixation and three lichens with green algal primary photobionts (Coccomyxa or Dictyochloropsis) lacking a CCM. The latter have N2‐fixing Nostoc in cephalodia. When related to thallus dry weight, total thallus nitrogen varied 20‐fold, chitin 40‐fold, Chl a 5‐fold and Rubisco 4‐fold among the species. Total nitrogen was lowest in three of the four Trebouxia lichens and highest in the bipartite cyanobacterial lichen. Lichens with the lowest nitrogen invested a larger proportion of this into photosynthetic components, while the species with high nitrogen made relatively more chitin. As a result, the potential photosynthetic nitrogen use efficiency was negatively correlated to total thallus nitrogen for this range of species. The cyanobacterial lichen had a higher photosynthetic capacity in relation to both Chl a and Rubisco compared with the green algal lichens. For the range of green algal lichens both Chl a and Rubisco contents were linearly related to photosynthetic capacity, so the data did not support the hypothesis of an enhanced photosynthetic nitrogen use efficiency in green‐algal lichens with a CCM.
Inorganic ions modulate the path of phloem loading of sucrose in Ricinus communis L. seedlings
Authors: Schobert C. , Zhong WEN‐JUN , Komor E.
Published: March 2003

The impact of inorganic ions on sucrose fluxes in the cotyledons and on the pathway of phloem loading was studied in Ricinus communis L. seedlings. The cotyledons were incubated in defined solutions which contained either potassium, sodium, magnesium or calcium as chloride salts, or the sodium salts of sulphate or phosphate. Sucrose uptake from the medium into the cotyledons was only slightly affected by the salts. Sucrose efflux to the medium was increased by phosphate and sulphate and to a lesser extent by sodium and potassium. Phloem loading from the apoplasm and the symplasm was analysed by addition of labelled sucrose to the medium, determination of the specific radioactivity of sucrose in sieve‐tube exudate and quantification of export into the seedling axis. Potassium and sodium stimulated the apoplasmic route of phloem loading of sucrose, mostly at the expense of loading from cotyledon sucrose pools. In contrast, sulphate and phosphate strongly inhibited the apoplasmic route whereas the (small) symplasmic flux from the cotyledon sucrose pools was less affected. Magnesium ions inhibited phloem loading by both pathways. The potential of ions in modulating the pathways of sucrose export in day to day operation of plants is discussed.
Altered night‐time CO2 concentration affects the growth, physiology and biochemistry of soybean
Authors: GRIFFIN K. L. , SIMS D. A. , SEEMANN J. R.
Published: March 2003

Soybean plants (Glycine max (L.) Merr. c.v. Williams) were grown in CO2 controlled, natural‐light growth chambers under one of four atmospheric CO2 concentrations ([CO2]): (1) 250 μmol mol–1 24 h d–1[250/250]; (2) 1000 μmol mol–1 24 h d–1[1000/1000]; (3) 250 μmol mol–1 during daylight hours and 1000 μmol mol–1 during night‐time hours [250/1000] or (4) 1000 μmol mol–1 during daylight hours and 250 μmol mol–1 during night‐time hours [1000/250]. During the vegetative growth phase few physiological differences were observed between plants exposed to a constant 24 h [CO2] (250/250 and 1000/1000) and those that were switched to a higher or lower [CO2] at night (250/1000 and 1000/250), suggesting that the primary physiological responses of plants to growth in elevated [CO2] is apparently a response to daytime [CO2] only. However, by the end of the reproductive growth phase, major differences were observed. Plants grown in the 1000/250 regime, when compared with those in the 1000/1000 regime, had significantly more leaf area and leaf mass, 27% more total plant dry mass, but only 18% of the fruit mass. After 12 weeks of growth these plants also had 19% higher respiration rates and 32% lower photosynthetic rates than the 1000/1000 plants. As a result the ratio of carbon gain to carbon loss was reduced significantly in the plants exposed to the reduced night‐time [CO2]. Plants grown in the opposite switching environment, 250/1000 versus 250/250, showed no major differences in biomass accumulation or allocation with the exception of a significant increase in the amount of leaf mass per unit area. Physiologically, those plants exposed to elevated night‐time [CO2] had 21% lower respiration rates, 14% lower photosynthetic rates and a significant increase in the ratio of carbon gain to carbon loss, again when compared with the 250/250 plants. Biochemical differences also were found. Ribulose‐1,5‐bisphosphate carboxylase/ oxygenase concentrations decreased in the 250/ 1000 treatment compared with the 250/250 plants, and phosphoenolpyruvate carboxylase activity decreased in the 1000/250 compared with the 1000/1000 plants. Glucose, fructose and to a lesser extent sucrose concentrations also were reduced in the 1000/250 treatment compared with the 1000/1000 plants. These results indicate that experimental protocols that do not maintain elevated CO2 levels 24 h d–1 can have significant effects on plant biomass, carbon allocation and physiology, at least for fast‐growing annual crop plants. Furthermore, the results suggest some plant processes other than photosynthesis are sensitive to [CO2] and under ecologically relevant conditions, such as high night‐time [CO2], whole plant carbon balance can be affected.
Ecophysiology of the hypotonic response in the salt‐tolerant charophyte alga Lamprothamnium papulosum
Authors: SHEPHERD V. A. , BEILBY M. J. , HESLOP D. J.
Published: March 2003

The ecophysiology of the hypotonic response was studied in the charophyte alga, Lamprothamnium papulosum, which was grown in a marine (SW; 1072 mosmol kg–1) and a brackish (1/2 SW; 536 mosmol kg–1) environment. The cells produced an extracellular mucilage identified by histochemical staining as a mixture of sulphated and carboxylated polysaccharides. The thickness and chemical composition of the mucilage layer was a function of environmental salinity and cell age. Mucilage progressively increased in thickness from the apex (9 SW cells: 12·6 ± 1·8 μm; 15 1/2 SW cells: 4·8 ± 0·7 μm) to the base of the plants (15 SW cells: 44·8 ± 3·3 μm; nine 1/2 SW cells: 23·8 ± 2·5 μm); with a corresponding increase in the sulphated proportion. The mucilage was significantly thicker in SW plants. Hydraulic conductivity (Lp) at the apex of SW plants, measured by transcellular osmosis, was 8·3 × 10–13 m s–1 Pa–1. This was close to Lp of freshwater Chara (8·5 × 10–13 m s–1 Pa–1) which lacked mucilage. Basal SW cells with thicker mucilage had a smaller apparent Lp of 3·5 × 10–13 m s–1 Pa–1. The electrophysiology of the resting state and hypotonic response was compared in cells from the two environments based on current/voltage (I/V) analysis. The resting potential difference (PD) and conductance differed (11 SW cells: – 102·4 ± 10·1 mV, eight SW cells: 18·6 ± 2·4 S m–2; 19 1/2 SW cells: –125·7 ± 5·9 mV, 8·3 ± 0·8 S m–2). The type of cellular response to a hypotonic shock (decrease of 268 mosmol kg–1) also differed. In 1/2 SW plants, only the apical cells with thin mucilage responded classically with depolarization, conductance increase, Ca2+ influx, cessation of cytoplasmic streaming, and K+ and Cl– effluxes. Older cells making up the bulk of the plants responded with depolarization, but continued cytoplasmic streaming, and had only a small increase in conductance; or depolarized transiently without altering the I/V profile, conductance or streaming speed. Most cells remained depolarized and in the K+ state 1 h post‐shock. Cells treated with the K+ channel blocker tetraethylammonium chloride also depolarized and remained depolarized. The SW cells depolarized but otherwise responded minimally to a 268 mosmol kg–1 drop in osmolarity and required a further 268 mosmol kg–1 down‐step to elicit a change in the conductance. A spectrum of responses was measured in successively older and more mucilaginous cells from the same marine plant. We discuss the ecophysiological significance of the mucilage layer which modulates the cellular response to osmotic shock and which can be secreted to different degrees by plants inhabiting environments of different salinity.
Effects of chilling temperature on photosynthetic rates, photosynthetic enzyme activities and metabolite levels in leaves of three sugarcane species
Authors: DU Y.‐C. , NOSE A. , WASANO K.
Published: March 2003

FBPase, fructose‐1,6‐bisphosphatase NADP‐MDH, NADP‐malate dehydrogenase NADP‐ME, NADP‐malic enzyme OAA, oxaloacetic acid PEP, phosphoenolpyruvate PEPcase, phosphoenolpyruvate carboxylase PPDK, pyruvate orthophosphate dikinase Rubisco, ribulose‐1,5‐bisphosphate carboxylase/oxygenase  The aim of this study was to investigate the mechanism of photosynthetic changes in sugarcane leaves in response to chilling temperature by using three species (Saccharum sinense R. cv. Yomitanzan, Saccharum sp. cv. NiF4 and Saccharum officinarum L. cv. Badira) differing in origin and cold sensitivity. Yomitanzan is native to subtropical areas, Badira is native to tropical areas and NiF4 is a hybrid species containing genes of both tropical and subtropical species. At exposure to chilling temperature (10 °C), the photosynthetic rate in the leaves at either 10 °C or 30 °C showed a greater decrease in Badira than in NiF4 and Yomitanzan. After 28 h exposure of plants to the chilling temperature, the extractable activities of pyruvate, orthophosphate dikinase (PPDK) and NADP‐malate dehydrogenase (NADP‐MDH) increased or were relatively stable in the leaves of NiF4 and Yomitanzan, but decreased substantially in Badira. Correspondingly, there was a substantial accumulation of aspartate, and the level of alanine increased in Badira leaves during the chilling treatment. It is suggested that NADP‐MDH and PPDK are key enzymes which may determine the cold sensitivity in photosynthesis of sugarcane.
Accumulation of aluminium in the cell wall pectin in cultured tobacco (Nicotiana tabacum L.) cells treated with a combination of aluminium and iron
Authors: Chang Y.‐C. , Yamamoto Y. , Matsumoto H.
Published: March 2003

In nutrient medium, aluminium (Al) accumulation in tobacco cells occurs only in the presence of ferrous ion [Fe(II)]. The localization of Al was examined to elucidate a mechanism of Al accumulation. After the digestion of Al‐treated cells with cellulase and pectolyase together, the resulting spheroplasts contained as much Al as the intact cells. However, the cell walls isolated from Al‐treated cells also contained as much Al as the intact cells. Comparison of sugar and Al contents in polysaccharide components extracted chemically from cell walls isolated from intact cells and spheroplasts revealed that the enzymes digested most of the cellulose and hemicellulose, but only half of the pectin, and that Al mainly existed in the pectin remaining in the spheroplasts. Gel‐permeation chromatography of the pectin fraction (NH4‐oxalate extract) from the cell walls of the intact cells indicated that Al was associated with small polysaccharides of approximately 3–7 kDa. These results suggest that a minor part of pectin is a major site of Al accumulation. The content of cell wall pectin increased during Al treatment in nutrient medium. Taken together, we hypothesize that Al may bind to the pectin newly produced during Al treatment.
Affinity, capacity and oxygen sensitivity of two different mechanisms for bicarbonate utilization in Ulva lactuca L. (Chlorophyta)
Authors: Axelsson L. , Larsson C. , Ryberg H.
Published: March 2003

Ulva lactuca, collected on the west coast of Sweden at the end of May, was able to utilize the HCO3− pool of seawater only through extracellular dehydration via carbonic anhydrase, followed by uptake of the CO2 formed. A decrease in the CO2 supply via this mechanism resulted in the gradual development of an additional method of HCO3− utilization, namely a direct uptake of HCO3−. Photosynthesis could then be supported by either a ‘HCO3− dehydration mechanism’ or a ‘HCO3− uptake mechanism’. Through selective inhibition of either of these mechanisms, the physiological properties of the other could be assessed. These properties suggest that the HCO3− uptake mechanism of U. lactuca is important under conditions when low concentrations of inorganic C, high pH and high external O2 concentrations would limit photosynthesis supported by the HCO3− dehydration mechanism. Such conditions may occur during intense irradiation of the alga in rockpools or in shallow bays with low rates of water exchange. The results are discussed in relation to a possible coupling between mechanisms for inorganic C acquisition and cell structure (or even morphology) of green macroalgae. They also illustrate some necessary precautions when using Michaelis–Menten kinetics for estimations of Vmax and K1/2 values.
A mathematical model for pH patterns in the rhizospheres of growth zones
Authors: Kim T. K. , Silk W. K.
Published: March 2003

In the classical model by Nye (1981), the main process for the change in pH across the rhizosphere is assumed to be diffusion. The classical model focuses on the non‐growing part of the root and assumes that the distribution of ion fluxes along the root is spatially uniform. We consider the rhizosphere of the growth zone and take into account the root growth rate and spatially varying flux along the root surface. We present both analytical (dimensional analysis) and experimental (computational) evidence of the importance of taking into account the root growth rate. We describe a conceptual and mathematical model to analyse the pH field around the root tip over time. The model is used with published data to show that, for typical growth rates in sandy soil, the pH field becomes steady (independent of time) after 6 h. Dimensional analysis reveals that a version of the Péclet number, related to the quotient of root elongation rate and proton diffusivity, can be used to predict the extent of the rhizosphere and the time required for it to become steady. For Péclet numbers much greater than 1 (soils), the root influences soil pH for distances on the millimetre scale. In contrast, for Péclet numbers much less than one (agar, aqueous solution), the root influences substrate pH for radial distances on the scale of centimetres. We also present some evidence that agar‐contact techniques to measure the soil pH may not be appropriate for measuring the millimetre‐scale gradients in soil pH.
Environmental effects on the early stages of tassel morphogenesis in maize (Zea mays L.)
Authors: Bechoux N. , Bernier G. , Lejeune P.
Published: March 2003

The effects of various environmental conditions on the initiation of tassel branches (NTB) and spikelet‐pairs (NSP) were examined in the stress‐sensitive maize inbred F53. Chilling induced the most important effect, with a dramatic decrease in both NTB and NSP, provided it was applied at the end of the vegetative phase and start of the floral transition phase. The primary cause of chilling‐induced abortion of the tassel branches could be oxidative stress in the leaves, since lowering light irradiance during chilling greatly reduced the effect of cold. The comparison of inbreds F53 and F2 revealed that both genotypes exhibited a similar period of cold sensitivity at the floral transition phase, although F2 was considered from field observations as a stress‐insensitive genotype (at least for tassel development). However, our results also showed a chilling acclimation response in inbred F2 but not in inbred F53. The similarities with the work by Lejeune & Bernier (1996Plant, Cell and Environment 19, 217–224.) concerning the effect of chilling on ear initiation in the sensitive inbred, B22, are emphasized.
Effects of short‐term NaCl stress on calmodulin transcript levels and calmodulin‐dependent NAD kinase activity in two species of tomato
Authors: Delumeau Olivier , Paven Marie‐Christine Morère‐Le , Montrichard Françoise , Laval‐Martin Danielle L.
Published: March 2003

NAD kinase is thought to play an important role in the plant cellular responses to biotic and abiotic stress as one of the isoforms of the enzyme is activated by the Ca2+–calmodulin (CaM) complex. NAD kinase activity was measured after short‐term NaCl stress applied to isolated cells from Lycopersicon esculentum, var. Volgogradskij (NaCl‐sensitive tomato) and L. pimpinellifolium, acc. PE2 (NaCl‐tolerant species). NAD kinase activity remained constant in the sensitive species, whereas a sharp decrease was observed in the tolerant one. After salt treatment, an induction of the calmodulin gene(s) was observed in the two species, together with a 30–50% decrease in ‘active’ CaM content, i.e. CaM able to activate purified NAD kinase, in L. pimpinellifolium. The decrease in NAD kinase activity could not, however, be fully explained by this decrease in active CaM content. A similar decrease in NAD kinase activity was also recorded with other ionic stresses and exposure to high temperatures, but not in the case of drought, exposure to low temperatures, hormonal (indole‐3‐acetic acid and abscisic acid) or H2O2 treatments. External Ca2+ certainly plays a role in the biochemical mechanism(s) leading to NAD kinase inhibition, while no role could be shown for intracellular Ca2+. In addition, after salt stress, a modification of the redox state of NAD kinase seems to be responsible for the inhibition of the enzyme.
Changes in leaf photosynthetic parameters with leaf position and nitrogen content within a rose plant canopy (Rosa hybrida)
Authors: Gonzalez‐Real M. M. , Baille A.
Published: March 2003

This paper deals with changes in leaf photosynthetic capacity with depth in a rose (Rosa hybrida cv. Sonia) plant canopy. Measurements of leaf net CO2 assimilation (Al) and total nitrogen content (Nl) were performed in autumn under greenhouse conditions on mature leaves located at different layers within the plant canopy, including the flower stems and the main shoots. These leaves were subjected (i) to contrasting levels of CO2 partial pressure (pa) at saturating photosynthetic photon flux density (I about 1000 μmol m−2 s−1) and (ii) to saturating CO2 partial pressure (pa about 100 Pa) and varying I, while conditions of temperature were those prevailing in the greenhouse (20–38 °C). A biochemical model of leaf photosynthesis relating Al to intercellular CO2 partial pressure (pi) was parameterized for each layer of leaves, supplying corresponding values of the photosynthetic Rubisco capacity (Vlm) and the maximum rate of electron transport (Jm). The results indicated that rose leaves growing at the top of the canopy had higher values of Jm and Vlm, which resulted from a higher allocation of nitrogen to the uppermost leaves. Mean values of total leaf nitrogen, Nl, decreased about 35% from the uppermost leaves of flower stem to leaves growing at the bottom of the plant. The derived values of non‐photosynthetic nitrogen, Nb, varied from 76 mmolN m−2leaf (layer 1) to 60 mmolN m−2leaf (layer 4), representing a large fraction of Nl (50 and 60% in layer 1 and 4, respectively). Comparison of leaf photosynthetic nitrogen (Np=Nl–Nb) and I profiles supports the hypothesis that rose leaves acclimate to the time‐integrated absorbed I. The relationships between I and Np, obtained during autumn, spring and summer, indicate that rose leaves seem also to acclimate their photosynthetic capacity seasonally, by allocating more photosynthetic nitrogen to leaves in autumn and spring than in summer.
Expression of dehydration‐stress‐related genes in the crowns of wheatgrass species [Lophopyrum elongatum (Host) A. Love and Agropyron desertorum (Fisch. ex Link.) Schult.] having contrasting acclimation to salt, cold and drought
Authors: Tabaei‐Aghdaei S. R. , Harrison P. , Pearce R. S.
Published: March 2003

Agropyron desertorum and Lophopyrum elongatum were grown in a control environment or acclimated in high‐salt (daily exposure to 75 or 150 mM NaCl for 6 d), cold (6/2 °C for 14 d) or drought environments (watering withheld for 6 d). Lophopyrum elongatum was constitutively tolerant to salt and also acclimated more to salt than did A. desertorum whereas A. desertorum acclimated more to cold and drought. Dehydrin and non‐specific lipid transfer protein (nsLTP) mRNA sequences and polypeptides increased more, during acclimation to cold and drought, in A. desertorum than in L. elongatum crowns. Expression of immunologically identified dehydrin polypeptides was much higher in drought‐acclimated A. desertorum than in any other species/treatment combination. The most strongly expressed were 42 and 20 kDa. No change in dehydrin or nsLTP polypeptides were detected in the crowns during acclimation to salt. Overall, there was stronger acclimation to dehydrative stresses, at the molecular level, in A. desertorum than in L. elongatum crowns. Differences in dehydrin and nsLTP mRNA and polypeptide expression during acclimation to different stresses indicated that plants sense the differences between different primary potential causes of cellular dehydration.
Genotoxic effect of cadmium is associated with apoptotic changes in tobacco cells
Authors: Fojtová Miloslava , Kovařík Aleš
Published: March 2003

This work explores the influence of cadmium on a suspension cell culture of Nicotiana tabacum (TBY‐2) by examining cell morphology, viability and DNA integrity. Changes in these parameters were strikingly dependent on concentration of cadmium in the culture medium: a concentration of 50–100 mmol m−3 CdSO4 induced apoptotic changes including DNA fragmentation into oligonucleosomal units, while 1 mol m−3 Cd2+ showed strong cytotoxicity, but no fragmentation of DNA. Low cadmium concentrations (below 10 mmol m−3) affected neither cell viability nor DNA integrity. A detailed kinetic study showed a significant delay in the onset of apoptosis after the application of high concentrations of cadmium. From days 0–3 after the application of 50 mmol m−3 CdSO4, the morphology of the cells, their viability and growth were indistinguishable between control and treated cells, and ‘domain’ DNA fragmentation into 50–200 kb fragments was observed at the DNA level. After this (days 4–7), there was a characteristic and rapid decrease in cell viability, distinct changes in cell morphology and oligonucleosomal fragmentation. The results suggest that chronic exposure of plant cells to cadmium can trigger programmed cell death.
Molybdenum cofactor amounts in Chlamydomonas reinhardtii depend on the Nit5 gene function related to molybdate transport
Authors: Llamas A. , Kalakoutskii K. L.
Published: March 2003

Strain 21gr from Chlamydomonas reinhardtii is a cryptic mutant defective in the Nit5 gene related to the biosynthesis of molybdenum cofactor (MoCo). In spite of this mutation, this strain has active MoCo and can grow on nitrate media. In genetic crosses, the Nit5 mutation cosegregated with a phenotype of resistance to high concentrations of molybdate and tungstate. Molybdate/tungstate toxicity was much higher in nitrate than in ammonium media. Strain 21gr showed lower amounts of MoCo activity than the wild type both when grown in nitrate and after growth in ammonium and nitrate induction. However, nitrate reductase (NR) specific activity was similar in wild type and 21gr cells. Tungstate, either at nanomolar concentrations in nitrate media or at micromolar concentrations during growth in ammonium and nitrate induction, strongly decreased MoCo and NR amounts in wild‐type cells but had a slight effect in 21gr cells. Molybdate uptake activity of ammonium‐grown cells from both the wild‐type and 21gr strains was small and blocked by sulphate 0·3 mM. However, cells from nitrate medium showed a molybdate uptake activity insensitive to sulphate. This uptake activity was much higher and more sensitive to inhibition by tungstate in the wild type than in strain 21gr. These results suggest that strain 21gr has a high affinity and low capacity molybdate transport system able to discriminate efficiently tungstate, and lacks a high capacity molybdate/tungstate transport system, which operates in wild‐type cells upon nitrate induction. This high capacity molybdate transport system would account for both the stimulating effect of molybdate on MoCo amounts and the toxic effects of tungstate and molybdate when present at high concentrations.
No photosynthetic down‐regulation in sweetgum trees (Liquidambar styraciflua L.) after three years of CO2 enrichment at the Duke Forest FACE experiment
Authors: Herrick J. D. , Thomas R. B.
Published: March 2003

Photosynthetic capacity and leaf properties of sun and shade leaves of overstorey sweetgum trees (Liquidambar styraciflua L.) were compared over the first 3 years of growth in ambient or ambient + 200 μL L−1 CO2 at the Duke Forest Free Air CO2 Enrichment (FACE) experiment. We were interested in whether photosynthetic down‐regulation to CO2 occurred in sweetgum trees growing in a forest ecosystem, whether shade leaves down‐regulated to a greater extent than sun leaves, and if there was a seasonal component to photosynthetic down‐regulation. During June and September of each year, we measured net photosynthesis (A) versus the calculated intercellular CO2 concentration (Ci) in situ and analysed these response curves using a biochemical model that described the limitations imposed by the amount and activity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Vcmax) and by the rate of ribulose‐1,5‐bisphosphate (RuBP) regeneration mediated by electron transport (Jmax). There was no evidence of photosynthetic down‐regulation to CO2 in either sun or shade leaves of sweetgum trees over the 3 years of measurements. Elevated CO2 did not significantly affect Vcmax or Jmax. The ratio of Vcmax to Jmax was relatively constant, averaging 2·12, and was not affected by CO2 treatment, position in the canopy, or measurement period. Furthermore, CO2 enrichment did not affect leaf nitrogen per unit leaf area (Na), chlorophyll or total non‐structural carbohydrates of sun or shade leaves. We did, however, find a strong relationship between Na and the modelled components of photosynthetic capacity, Vcmax and Jmax. Our data over the first 3 years of this experiment corroborate observations that trees rooted in the ground may not exhibit symptoms of photosynthetic down‐regulation as quickly as tree seedlings growing in pots. There was a strong sustained enhancement of photosynthesis by CO2 enrichment whereby light‐saturated net photosynthesis of sun leaves was stimulated by 63% and light‐saturated net photosynthesis of shade leaves was stimulated by 48% when averaged over the 3 years. This study suggests that this CO2 enhancement of photosynthesis will be sustained in the Duke Forest FACE experiment as long as soil N availability keeps pace with photosynthetic and growth processes.
Leaf area is stimulated in Populus by free air CO2 enrichment (POPFACE), through increased cell expansion and production
Authors: Ferris R. , Sabatti M. , Miglietta F. , Mills R. F. , Taylor G.
Published: March 2003

The effects of free‐air CO2 enrichment (FACE) on leaf growth in Populus, was studied. For the first time in field conditions, both the production and expansion of leaf cells were shown to be sensitive to atmospheric carbon dioxide. Leaf area expansion rate and final leaf size were stimulated under FACE for three species (Populus x euramericana (I‐214), P. nigra (Jean Pourtet) and P. alba (2AS‐11), with the largest effect observed for P. x euramericana (61%). In this species and in P. nigra, both epidermal cell size and cell number were increased, whereas for P. alba, only cell production was increased in FACE. Two findings suggest that changes in the cell wall may be important in explaining larger leaf cells in FACE: (i) Leaf cell wall extensibility of rapidly growing leaves increased in all species in FACE; and (ii) an increase in xyloglucan endotransglycosylase activity, a cell wall‐loosening enzyme, was increased in FACE and associated with leaf growth rate. The results suggest that the mechanisms by which FACE promotes leaf growth differ, depending on species. Despite this, increases in final leaf size provide an important component driving increased biomass accumulation in POPFACE, during this first year of rapid growth, prior to canopy closure. The question as to whether these effects are the result of a direct response to CO2, or are driven indirectly through substrate availability remains unresolved, although evidence from the literature suggests that the latter mechanism is most likely.
Strategies providing success in a variable habitat: III. Dynamic control of photosynthesis in Cladophora glomerata
Authors: Ensminger I. , Xyländer M. , Hagen C. , Braune W.
Published: March 2003

Diurnal patterns of photosynthesis were studied in July and April populations of Cladophora glomerata (L.) Kütz. from open and from shaded sites. Summer samples exposed to full sunlight showed decreased efficiency of open photosystem II at noon, and only slight differences were found between samples that had grown at open or at shaded sites. Electron transport rate was limited at highest fluence rates in shade plants, and non‐photochemical quenching (NPQ) revealed faster regulation in samples from open sites. Daily course of de‐epoxidation was not linearly correlated with the course of NPQ. The comparison of samples from open and from shaded sites revealed a higher capacity of thermal energy dissipation and an increase in the total amount of xanthophyll‐cycle pigments (21%) in samples from open sites. In April, down‐regulation of the efficiency of open photosystem II was related to lower water temperature, and hence, increased excitation pressure. In April the pool size of xanthophyll‐cycle pigments was increased by 21% in comparison with summer and suggested higher levels of thermal energy dissipation via de‐epoxidized xanthophylls. In both, summer and spring the amount of xanthophyll‐cycle pigments was 20% higher in samples from open sites. Acclimation of C. glomerata to growth light conditions was further shown by experimental induction of NPQ, indicating NPQ increases of 23%, and increases of 77% in the reversible component of NPQ in open site samples. The effect of temperature on photosynthetic rate was non‐linear, and different optimum temperatures of electron transport rate and oxygen evolution were exhibited.
Interaction with ethylene: changing views on the role of abscisic acid in root and shoot growth responses to water stress
Authors: Sharp R. E.
Published: March 2003

Shoot and root growth are differentially sensitive to water stress. Interest in the involvement of hormones in regulating these responses has focused on abscisic acid (ABA) because it accumulates in shoot and root tissues under water‐limited conditions, and because it usually inhibits growth when applied to well‐watered plants. However, the effects of ABA can differ in stressed and non‐stressed plants, and it is therefore advantageous to manipulate endogenous ABA levels under water‐stressed conditions. Studies utilizing ABA‐deficient mutants and inhibitors of ABA synthesis to decrease endogenous ABA levels, and experimental strategies to circumvent variation in plant water status with ABA deficiency, are changing the view of the role of ABA from the traditional idea that the hormone is generally involved in growth inhibition. In particular, studies of several species indicate that an important role of endogenous ABA is to limit ethylene production, and that as a result of this interaction ABA may often function to maintain rather than inhibit shoot and root growth. Despite early speculation that interaction between these hormones may influence many of the effects of water deficit, this topic has received little attention until recently.
Hahb‐4, a homeobox‐leucine zipper gene potentially involved in abscisic acid‐dependent responses to water stress in sunflower*
Authors: Gago G. M. , Almoguera C. , Jordano J. , Gonzalez D. H. , Chan R. L.
Published: March 2003

Homeodomain‐leucine zipper proteins constitute a family of transcription factors found only in plants. We have characterized a full‐length cDNA encoding the sunflower homeobox‐leucine zipper protein Hahb‐4 (Helianthus annuus homeobox‐4). The complete cDNA is 674 base pairs long and contains an open reading frame of 177 amino acids that belongs to the Hd‐Zip I subfamily. Northern blot and RNAse A protection analysis show that the expression of Hahb‐4 is rapidly, strongly and reversibly induced by water deficit in whole seedlings, roots, stems and leaves. A similar fast induction of Hahb‐4 expression is observed when seedlings are subjected to a treatment with the hormone abscisic acid (ABA). Nuclei prepared from seedlings treated with ABA or subjected to water stress show a significant increase of protein(s) that specifically bind the sequence 5′‐CAAT(A/T)ATTG‐3′, recognized in vitro by Hahb‐4, suggesting that an active protein is synthesized in response to these treatments. The promoter region of the Hahb‐4 gene contains sequences that fit the consensus for a G‐box present in some ABA responsive elements (ABREs). We propose that Hahb‐4 may function in signalling cascade(s) that control(s) a subset of the ABA‐mediated responses of sunflower to water stress.