bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reciprocal diurnal changes of phosphoenolpyruvate carboxylase expression and cytosolic pyruvate kinase, citrate synthase and NADP‐isocitrate dehydrogenase expression regulate organic acid metabolism during nitrate assimilation in tobacco leaves
Authors: Scheible W.‐R. , Krapp A. , Stitt M. 
Published: March 2003

ABSTRACTDiurnal changes of transcript levels for key enzymes in nitrate and organic acid metabolism and the accompanying changes of enzyme activities and metabolite levels were investigated in nitrogen‐sufficient wild‐type tobacco, in transfomants with decreased expression of nitrate reductase, and in nitrate‐deficient wild‐type tobacco. (i) In nitrogen‐sufficient wild‐type plants, transcript levels for nitrate reductase (NR, EC 1.6.6.1), nitrite reductase (NIR, EC 1.7.7.1) and phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31) were high at the end of the night and decreased markedly during the light period. The levels of these three transcripts were increased and the diurnal changes were damped in genotypes with decreased expression of nitrate reductase. The levels of these transcripts were very low in nitrate‐limited wild‐type plants, except for a small rise after irrigation with 0·2 mM nitrate. (ii) The levels of the transcripts for cytosolic pyruvate kinase (PK, EC 2.7.1.40), mitochondrial citrate synthase (CS, EC 4.1.3.7) and NADP‐isocitrate dehydrogenase (NADP‐ICDH, EC 1.1.1.42) were highest at the end of the light period and beginning of the night. These three transcripts increase and the diurnal changes were damped in genotypes with decreased expression of NR. (iii) The diurnal changes of transcript levels were accompanied by changes in the activities of the encoded enzymes. The activities of NR and PEPC were highest in the early part of the light period, whereas the activities of PK and NADP‐ICDH were highest later in the light period and during the first part of the night and CS activity was highest at the end of the night. Activity of PEPC, PK, CS and NADP‐ICDH increased and the diurnal changes were damped in genotypes with low expression of NR. Activity of all four enzymes decreased in nitrate‐limited wild‐type plants. (iv) In the light, malate accumulated, citrate decreased, and about 30% of the assimilated nitrate accumulated temporarily as glutamine, ammonium, glycine and serine. These changes were reversed during the night. (v) It is proposed that the diurnal changes of expression facilitate preferential synthesis of malate to act as a counter‐anion for pH regulation during the first part of the light period when NR activity is high, and preferential synthesis of 2‐oxoglutarate to act as a nitrogen acceptor later in the day when large amounts of nitrogen have accumulated in ammonium, glutamine and other amino acids including glycine in the photorespiration pathway, and NR activity has been decreased.
Does an antagonistic relationship between ABA and ethylene mediate shoot growth when tomato (Lycopersicon esculentum Mill.) plants encounter compacted soil?
Authors: Hussain A. , Black C. R. , Taylor I. B. , Roberts J. A. 
Published: March 2003

ABSTRACTThis study tested the hypothesis that antagonistic interactions between abscisic acid (ABA) and ethylene mediate the effects of soil compaction on shoot growth. Isogenic wild‐type (Ailsa Craig), ABA‐deficient (notabilis) and a transgenic (ACO1AS) tomato genotype with a reduced capacity to synthesize ethylene were examined. Exogenous ABA was also applied. Leaf area was comparable when Ailsa Craig and ACO1AS were grown in uncompacted (1·1 g cm−3) or compacted (1·5 g cm−3) soil, but was lower in notabilis. However, a 1·1/1·5 g cm−3 split‐pot treatment invoked marked genotypic differences, whereby leaf area was comparable to 1·1 g cm−3 control plants in ACO1AS but was intermediate between the 1·1 and 1·5 g cm−3 treatments in Ailsa Craig and notabilis. ABA may be discounted as the root‐sourced signal responsible for reducing leaf area when the roots encountered compacted soil as Ailsa Craig and ACO1AS showed differing responses despite similar increases in xylem sap ABA concentration; leaf area was invariably lower in notabilis. These genotypic differences were correlated with ethylene evolution; thus the greater leaf area in ACO1AS was associated with its reduced ability to synthesize ethylene, whereas the reductions in leaf expansion observed when Ailsa Craig and notabilis encountered compacted soil were accompanied by increased ethylene production. Application of ABA had little effect on ACO1AS, but promoted a recovery of leaf expansion in notabilis, and more surprisingly in Ailsa Craig. These results suggest that antagonistic interactions between ABA and ethylene may regulate leaf expansion when the root system simultaneously encounters uncompacted and compacted soil.
Stem hydraulic supply is linked to leaf photosynthetic capacity: evidence from New Caledonian and Tasmanian rainforests
Authors: Brodribb T. J. , Feild T. S. 
Published: March 2003

ABSTRACTA strong relationship between hydraulic supply of water to leaves and maximum photosynthetic capacity was found in a group of seven conifers and 16 angiosperm species, including two vessel‐less taxa, from similar rainforest communities in New Caledonia and Tasmania (Australia). Stem hydraulic supply was expressed as the hydraulic conductivity of branches in terms of leaf area supplied (KL) and leaf photosynthetic capacity was measured as the mean quantum yield of PSII (ØPSII) in leaves exposed to full sun, as determined by chlorophyll fluorescence analysis. A single, highly significant linear regression (r2= 0·74) described the relationship between hydraulic conductivity and quantum yield in all species. This suggests that the maximum photosynthetic rate of leaves is constrained by their vascular supply. In both rainforest locations, the KL of conifer wood overlapped broadly with that of associated vessel‐bearing and vessel‐less angiosperms indicating a degree of hydraulic convergence in these forests.
Patterns of pinitol accumulation in soybean plants and relationships to drought tolerance
Authors: Streeter J. G. , Lohnes D. G. , Fioritto R. J. 
Published: March 2003

ABSTRACTPrevious studies indicate that methylated cyclitols are potentially important osmolytes in plants. In a search for genetic diversity for pinitol (D‐3‐O‐methyl‐chiro‐inositol) accumulation in soybean (Glycine max (L.) Merr.), two‐ to three‐fold differences in pinitol accumulation in leaf blades were found among Chinese plant introductions. Furthermore, it was found that genotypes that accumulated high concentrations of pinitol, when grown under well‐watered conditions, had been selected for performance in regions of China having low rainfall. Among the carbohydrates analysed, pinitol accumulation was uniquely associated with adaptation to dry areas of China. A detailed study of pinitol accumulation in the soybean plant showed two‐ to three‐fold gradients in pinitol concentration from the bottom to the top of the plant. The gradient shifted during plant development, with consistently higher concentrations of pinitol in the uppermost leaves. Pinitol accumulation was not correlated with activity of the key biosynthetic enzyme, inositol methyl transferase. This result and other lines of evidence indicated that shifting patterns of pinitol accumulation were due to translocation of the cyclitol from lower to upper nodes. Pinitol, proline, and sugars accumulated in leaf blades on soybean plants subjected to drought, but the molar concentration of pinitol in stressed plants was greater than the concentrations of proline or sugars. Although the mechanism by which pinitol participates in drought tolerance is not fully known, our results provide additional correlative evidence linking pinitol and drought tolerance in soybean.
Abscisic acid introduced into the transpiration stream accumulates in the guard‐cell apoplast and causes stomatal closure
Authors: Zhang S. Q. , Outlaw W. H. 
Published: March 2003

AbstractPetioles of water‐sufficient intact Vicia faba L. plants were infused with 1 µm abscisic acid (ABA) to simulate the import of root‐source ABA. This protocol permitted quantitative ABA delivery, up to 300 pmol ABA over 60 min, to the leaf without ambiguities associated with perturbations in plant–water status. The ABA concentrations in whole‐leaf samples and in apoplastic sap increased with the amount infused; ABA degradation was not detected. The ABA concentration in apoplastic sap was consistent with uptake of imported ABA into the leaf symplast, but this interpretation is qualified. Our focus was quantitative cellular compartmentation of imported ABA in guard cells. Unlike when leaves are stressed, the guard‐cell symplast ABA content did not increase because of ABA infusion (P = 0·48; 3·0 ± 0·5 versus 4·0 ± 1·2 fg guard‐cell‐pair−1). However, the guard‐cell apoplast ABA content increased linearly (R2 = 0·98) from −0·2 ± 0·5 to 3·1 ± 1·3 fg guard‐cell‐pair−1 (≈ 3·1 µm) and was inversely related to leaf conductance (R2 = 0·82). Apparently, xylem ABA accumulates in the guard‐cell wall as a result of evaporation of the apoplast solution. This mechanism provides for integrating transpiration rate and ABA concentration in the xylem solution.
Ultraviolet‐B radiation reduces the rates of cell division and elongation in the primary leaf of wheat (Triticum aestivum L. cv Maris Huntsman)
Authors: Hopkins L. , Bond M. A. , Tobin A. K. 
Published: March 2003

AbstractThe primary leaf of wheat (Triticum aestivum L. cv Maris Huntsman) was used as a model system to examine how elevated ultraviolet‐B (UV‐B; λ= 280–320 nm) radiation affected growth. A reduction in the rate and duration of growth of the primary leaf, in response to UV‐B, was the result of changes in both the rate and extent of cell division and elongation. UV‐B reduced the proportion of mitotically active cells (mitotic index) and increased the time taken for cell division (cell doubling time). Thus the supply of cells into the elongation zone was reduced, and this, coupled to a reduction in the rate of elongation, resulted in reduced leaf growth. This analysis of the spatial distribution of growth provided a means of calculating the age of cells within the leaves. Cells of UV‐B‐treated leaves were found to age more quickly than those of the controls. This analysis will enable future studies to take account of age‐related changes when interpreting the response of plants to any number of environmental stresses that affect leaf development.
Examination of the dehiscence zone in soybean pods and isolation of a dehiscence‐related endopolygalacturonase gene
Authors: Christiansen L. C. , Dal Degan F. , Ulvskov P. , Borkhardt B. 
Published: March 2003

AbstractMicroscopic examination of cross sections of dorsal and ventral sutures of soybean pods (Glycine max cv. TGx1835‐2E) at two different stages of maturity revealed that the dehiscence zone of soybean pods is functionally equivalent to the dehiscence zone known from crucifers. Enzymatic assays demonstrated the presence of endo‐1,4‐β‐glucanases and endopolygalacturonases, the activity of which accumulated in the dehiscence zone and peaked during maturation. A single partial cDNA encoding an endopolygalacturonase was isolated by polymerase chain reaction and this clone was used to isolate the complete gene encoding the endopolygalacturonase in question. Approximately 1·2 kb of 5′ upstream sequence was cloned in the plant transformation vector pCAMBIA1301 in front of the uidA (GUS) gene and transformed into Arabidopsis thaliana. Expression analysis of the soybean endopolygalacturonase transcript revealed that the endopolygalacturonase is primarily found in dehiscence‐related tissue and is presumably involved in the breakdown of the middle lamella prior to dehiscence. This result was corroborated by GUS stainings of the transgenic Arabidopsis lines
Changes in the acquisition and partitioning of carbon and nitrogen in the gibberellin‐deficient mutants A70 and W335 of tomato (Solanum lycopersicum L.)
Authors: Nagel O. W. , Lambers H. 
Published: March 2003

AbstractEven though the growth‐promoting effects of gibberellins (GAs) in plants are well established, little is known about GA action on carbon metabolism and the available reports seem contradictory. We studied the effects of GA deficiency in mutants of tomato (Solanum lycopersicum L.) on rates of carbon acquisition and the allocation of acquired carbon to growth and respiration of leaves, stems and roots. Carbon budgets were calculated from 24 h measurements of photosynthesis and respiration. The partitioning of nitrogen compounds to leaves, stems and roots, which strongly influences carbon budgets, was also studied. The GA‐deficient mutants acquired less carbon per unit plant mass per day than did the wild type and used a larger fraction of it for root growth and root respiration. To find out to what extent these changes were just consequences of restriction of growth, the experiment was repeated at a low exponential nitrate addition rate, which forced all genotypes to grow at the same rate. Under these conditions, the low‐GA mutants still photosynthesized and respired faster and partitioned more carbon to root growth than the wild type did. The reasons for the observed differences in carbon economies between the wild type and the low‐GA mutants are discussed.
ATP citrate lyase: cloning, heterologous expression and possible implication in root organic acid metabolism and excretion
Authors: Langlade N. B. , Messerli G. , Weisskopf L. , Plaza S. , Tomasi N. , Smutny J. , Neumann G. , Martinoia E. , Massonneau A. 
Published: March 2003

AbstractIn order to cope with phosphate deficiency, white lupin produces bottle‐brushed like roots, so‐called cluster or proteoid roots which are specialized in malate and citrate excretion. Young, developing cluster roots mainly excrete malate whereas mature cluster roots mainly release citrate. Mature proteoid roots excrete four to six times more carboxylates compared with juvenile proteoid roots. Using a cDNA‐amplified restriction fragment length polymorphism (AFLP) approach we identified a gene coding for a putative ATP‐citrate lyase (ACL) up‐regulated in young cluster roots. Cloning of the lupin ACL revealed that plant ACL is constituted by two polypeptides (ACLA and ACLB) encoded by two different genes. This contrasts with the animal ACL, constituted of one polypeptide which covers ACLA and ACLB. The ACL function of the two lupin gene products has been demonstrated by heterologous expression in yeast. Both subunits are required for ACL activity. In lupin cluster roots, our results suggest that ACL activity could be responsible for the switch between malate and citrate excretion in the different developmental stages of cluster roots. In primary roots of lupin and maize, ACL activity was positively correlated with malate exudation. These results show that ACL is implicated in root exudation of  organic  acids  and  hence  plays  a  novel  role  in  addition to lipid synthesis. Our results suggest that in addition to lipid biosynthesis, in plants, ACL is implicated in malate excretion.
The relative impacts of daytime and night‐time warming on photosynthetic capacity inPopulus deltoides
Authors: TURNBULL M. H. , MURTHY R. , GRIFFIN K. L. 
Published: March 2003

AbstractIn order to investigate the relative impacts of increases in day and night temperature on tree carbon relations, we measured night‐time respiration and daytime photosynthesis of leaves in canopies of 4‐m‐tall cottonwood (Populus deltoidesBartr. ex Marsh) trees experiencing three daytime temperatures (25, 28 or 31 °C) and either (i) a constant nocturnal temperature of 20 °C or (ii) increasing nocturnal temperatures (15, 20 or 25 °C). In the first (day warming only) experiment, rates of night‐time leaf dark respiration (Rdark) remained constant and leaves displayed a modest increase (11%) in light‐saturated photosynthetic capacity (Amax) during the day (1000–1300 h) over the 6 °C range. In the second (dual night and day warming) experiment,Rdarkincreased by 77% when nocturnal temperatures were increased from 15 °C (0·36 µmol m−2 s−1) to 25 °C (0·64 µmol m−2 s−1).Amaxresponded positively to the additional nocturnal warming, and increased by 38 and 64% in the 20/28 and 25/31 °C treatments, respectively, compared with the 15/25 °C treatment. These increases in photosynthetic capacity were associated with strong increases in the maximum carboxylation rate of rubisco (Vcmax) and ribulose‐1,5‐bisphosphate (RuBP) regeneration capacity mediated by maximum electron transport rate (Jmax). Leaf soluble sugar and starch concentration, measured at sunrise, declined significantly as nocturnal temperature increased. The nocturnal temperature manipulation resulted in a significant inverse relationship betweenAmaxand pre‐dawn leaf carbohydrate status. Independent measurements of the temperature response of photosynthesis indicated that the optimum temperature (Topt) acclimated fully to the 6 °C range of temperature imposed in the daytime warming. Our findings are consistent with the hypothesis that elevated night‐time temperature increases photosynthetic capacity during the following light period through a respiratory‐driven reduction in leaf carbohydrate concentration. These responses indicate that predicted increases in night‐time minimum temperatures may have a significant influence on net plant carbon uptake.
Crosses between isolates of Phytophthora infestans from potato and tomato and characterization of F1 and F2 progeny for phenotypic and molecular markers
Authors: Knapova G. , Schlenzig A. , Gisi U. 
Published: March 2003

Nineteen crosses were carried out in vitro between seven and nine isolates of Phytophthora infestans originating from potato and tomato, respectively. Oospores were produced abundantly in all but two crosses, but oospore germination was generally low (a few per cent) and depended on the combination of parental isolates. The highest fertility in F1 progeny was observed when at least one parental isolate originated from tomato, and the lowest in crosses of isolates from potato; half the crosses were not fertile. Forty‐three F1 and 51 F2 single‐oospore progeny of a selected cross, along with the 16 field isolates, were analysed phenotypically and with molecular markers. Phenotypic characterization included mating type; sensitivity to the phenylamide fungicide metalaxyl‐M; specific virulence on potato R‐gene differentials; and aggressiveness (infected leaf area) on potato and tomato leaf discs (host preference). Isolates and progeny were also assessed for mitochondrial DNA haplotype with RFLP–PCR (restriction fragment length polymorphism–polymerase chain reaction), and characterized with AFLP (amplified fragment length polymorphism) and SSR (simple sequence repeats, microsatellites). Parental isolates were sensitive and resistant to metalaxyl‐M, whereas all F1 were intermediate phenotypes. In the F2 progeny, the majority of isolates (43 of 51) were intermediate in sensitivity and four each were sensitive and resistant to metalaxyl‐M, respectively. In both F1 and F2 progeny, four isolates emerged through selfing. The A1 : A2 ratio was 25 : 18 in F1 and 24 : 21 (plus six self‐fertiles) among the F2 progeny. Many F1 progeny isolates were highly aggressive on both hosts, but 15 and 23% of isolates preferred tomato and potato, respectively. Among F2 progeny, few highly aggressive isolates were recorded and a quarter of isolates lost pathogenicity almost completely. Isolates preferring tomato increased, and those preferring potato significantly decreased in the F2 progeny. Inheritance of mitochondrial haplotype in F1 progeny was uniparental and mostly (25 of 27) from one parent only. Six and four different SSR genotypes were identified in F1 and F2 progeny, respectively, of which two were identical to the parents. The two microsatellite loci, 4B and 4G, segregated in the ratios 15 : 22 : 2 and 22 : 17 in F1 and 24 : 17 and 26 : 15 in F2 progeny, respectively, while the majority of AFLP markers segregated in either a 1 : 0, 1 : 1, 3 : 1 or 1 : 2: 1 ratio. There was no obvious association between AFLP and SSR genotypes, nor between genotypic and phenotypic traits.
Independent Genetic Control of B‐ and T‐Cell Tolerance in Strains of Mouse Selected for Extreme Phenotypes of Oral Tolerance
Authors: Da Silva M. F. S. , Da Costa S. C. G. , Ribeiro R. C. , Sant'anna O. A. , Da Silva A. C. 
Published: March 2003

Two strains of mice were genetically selected for susceptibility (TS‐Ab/HetS strain) or resistance (TR‐Ab/HetS strain) to oral tolerance of the humoral response by using ovalbumin (OVA). The progressive interstrain divergence produced by bi‐directional selective breeding during 15 generations demonstrated the polygenic nature of oral tolerance. This paper shows the humoral and delayed‐type hypersensitivity (DTH) responses, after intragastric administration of OVA and subsequent immunization with that immunogen in complete Freund adjuvant (CFA). Only the TS‐Ab/HetS mice were tolerant for immunoglobulin (Ig)G production with its tolerance degree being the same as that obtained when Al (OH)3 was employed. The DTH reactivity was not correlated to the antibody responsiveness, because both the TS‐Ab/HetS and TR‐Ab/HetS strains had their DTH reactions suppressed. The cyclophosphamide (Cy) pretreatment prevented DTH suppression on TR‐Ab/HetS but do not in TS‐Ab/HetS mice. Interstrain difference was also observed for the splenic index in the Cy‐treated groups, although the number of splenocytes was the same. Flux cytometry cell analysis showed the recovery of CD3+ cell numbers in both strains, but only the TR‐Ab/HetS mice had their CD4/CD8 pattern restored. These results suggest: firstly, the independent control of DTH and humoral tolerance responsiveness; secondly no support for the clonal anergy concept; and thirdly the matrix proteins neo‐synthesis after Cy treatment may facilitate the tolerance abrogation.
Haptoglobin Interacts with the Human Mast Cell Line HMC‐1 and Inhibits its Spontaneous Proliferation
Authors: El‐Ghmati S. M. , Arredouani M. , Van Hoeyveld E. M. , Ceuppens J. L. , Stevens E. A. M. 
Published: March 2003

Haptoglobin (Hp) is an acute phase reactant produced by hepatocytes. There is evidence for an immunomodulatory potential of Hp, though there is no clear evidence yet about the mechanisms of this action. We have previously shown that Hp interacts with the β2‐integrin CD11b/CD18. In addition, other investigators reported the binding of Hp to B lymphocytes through the CD22 receptor, and to neutrophils through two different receptors.In the present study, we investigated the interaction of haptoglobin with the human mast cell line HMC‐1. We report that fluorescein isothiocyanate (FITC)‐labelled haptoglobin binds to this cell line and that binding is increased by calcium in a dose‐ and time‐dependent manner. Hp binding sites on HMC‐1 were upregulated upon stimulation with phorbol myristate acetate (PMA)/A23187 and after treatment with anti‐CD43 and anti‐CD44 monoclonal antibodies (MoAbs). HMC‐1 cells do not express either CD11b/CD18 or CD22 receptors, indicating that the haptoglobin‐binding receptor on this cell line is different from the known receptors. Assessment of cell function showed that Hp inhibits the spontaneous growth of HMC‐1 up till 40% at higher Hp concentrations, but it did not exhibit any effect on the expression of CD54 on the release of either tryptase or IL‐1ra.In conclusion, haptoglobin binds specifically to human mast cells via a receptor different from CD11b/CD18 and CD22, and may play a role in the modulation of mast cell functions. Exploration of Hp effects in mast cell‐dependent diseases such as allergic rhinitis and urticaria seems warranted.