bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACT 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

ABSTRACTIn 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

ABSTRACTThe 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

ABSTRACTNAD 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

ABSTRACTThis 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

ABSTRACT 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

SUMMARYThis 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

ABSTRACTStrain 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

ABSTRACTPhotosynthetic 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

ABSTRACTThe 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

AbstractDiurnal 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

AbstractShoot 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

AbstractHomeodomain‐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.
Two different strategies for light utilization in photosynthesis in relation to growth and cold acclimation
Authors: Savitch L. V. , Leonardos E. D. , Krol M. , Jansson S. , Grodzinski B. , Huner N. P. A. , Öquist G. 
Published: March 2003

AbstractSeedlings of Lodgepole pine (Pinus contorta L.) and winter wheat (Triticum aestivum L. cv. Monopol) were cold acclimated under controlled conditions to induce frost hardiness. Lodgepole pine responded to cold acclimation by partial inhibition of photosynthesis with an associated partial loss of photosystem II reaction centres, and a reduction in needle chlorophyll content. This was accompanied by a low daily carbon gain, and the development of a high and sustained capacity for non‐photochemical quenching of absorbed light. This sustained dissipation of absorbed light as heat correlated with an increased de‐epoxidation of the xanthophyll cycle pigments forming the quenching forms antheraxanthin and zeaxanthin. In addition, the PsbS protein known to bind chlorophyll and the xanthophyll cycle pigments increased strongly during cold acclimation of pine. In contrast, winter wheat maintained high photosynthetic rates, showed no loss of chlorophyll content per leaf area, and exhibited a high daily carbon gain and a minimal non‐photochemical quenching after cold acclimation. In accordance, cold acclimation of wheat neither increased the de‐epoxidation of the xanthophylls nor the content of the PsbS protein. These different responses of photosynthesis to cold acclimation are correlated with pine, reducing its need for assimilates when entering dormancy associated with termination of primary growth, whereas winter wheat maintains a high need for assimilates as it continues to grow and develop throughout the cold‐acclimation period. It appears that without evolving a sustained ability for controlled dissipation of absorbed light as heat throughout the winter, winter green conifers would not have managed to adapt and establish themselves so successfully in the cold climatic zones of the northern hemisphere.