bluuebunny/crossref_metadata_2025_split huggingface dataset:
Strategies providing success in a variable habitat: I. Relationships of environmental factors and dominance of Cladophora glomerata
Authors: Ensminger I. , Hagen C. , Braune W. 
Published: March 2003

ABSTRACTDominance of macrophytes and their response to environmental factors were studied in the river Ilm, Thuringia/ Germany with special reference to Cladophora glomerata (L.) Kütz. Macroalgae showed a growth peak in spring with C. glomerata, Ulothrix zonata Kütz., Lemanea fluviatilis (L.) C. Agardh and Audouinella sp. being the dominant species. Shortly after this peak, a rapid decline of macrophyte substrate coverage was observed. Only C. glomerata revealed a second growth peak in late summer/early autumn. Frequent disturbances of the macrophyte assemblage by floods resulted repeatedly in an almost complete wash out of benthic organisms. After summer floods C. glomerata was the species that recolonized the substrate. At high‐light sites, faster recovery of C. glomerata was observed as compared to low‐light sites. This is discussed in relation to the life cycle of C. glomerata. Among the physical and chemical parameters that were analysed, irradiance, current velocity, pH, soluble reactive phosphorus and ammonia‐nitrogen accounted for most of the observed patterns of dominance of C. glomerata.
Photosynthesis and conductance of spring wheat ears: field response to free‐air CO2 enrichment and limitations in water and nitrogen supply
Authors: Wechsung F. , Garcia R. L. , Wall G. W. , Kartschall T. , Kimball B. A. , Michaelis P. , Jr P. J. Pinter , Wechsung G. , Grossman‐Clarke S. , Lamorte R. L. , Adamsen F. J. , Leavitt S. W. , Thompson T. L. , Matthias A. D. , Brooks T. J. 
Published: March 2003

ABSTRACTThe mid‐day responses of wheat ear CO2 and water vapour exchange to full‐season CO2 enrichment were investigated using a Free‐Air CO2 Enrichment (FACE) apparatus. Spring wheat [Triticum aestivum (L). cv. Yecora Rojo] was grown in two experiments under ambient and elevated atmospheric CO2 (Ca) concentrations (approximately 370 μmol mol−1 and 550 μmol mol−1, respectively) combined first with two irrigation (Irr) schemes (Wet: 100% and Dry: 50% replacement of evapotranspiration) and then with two levels of nitrogen (N) fertilization (High: 350, Low: 70 kg ha−1 N). Blowers were used for Ca enrichment. Ambient Ca plots were exposed to blower induced winds as well the Ca× N but not in the Ca× Irr experiment. The net photosynthesis for the ears was increased by 58% and stomatal conductance (gs) was decreased by 26% due to elevated Ca under ample water and N supply when blowers were applied to both Ca treatments. The use of blowers in the Ca‐enriched plots only during the Ca× Irr experiment (blower effect) and Low N supply restricted the enhancement of net photosynthesis of the ear due to higher Ca. In the latter case, the increase of net photosynthesis of the ear amounted to 26%. The decrease in gs caused by higher Ca was not affected by the blower effect and N treatment. The mid‐day enhancement of net photosynthesis due to elevated Ca was higher for ears than for flag leaves and this effect was most pronounced under ample water and N supply. The contribution of ears to grain filling is therefore likely to increase in higher Ca environments in the future. In the comparison between Wet and Dry, the higher Ca did not alter the response of net photosynthesis of the ear and gs to Irr. However, Ca enrichment increased the drought tolerance of net photosynthesis of the glume and delayed the increase of the awn portion of net photosynthesis of the ear during drought. Therefore, the role of awns for maintaining high net photosynthesis of the ear under drought may decrease when Ca increases.
Lactate metabolism in potato tubers deficient in lactate dehydrogenase activity
Authors: Sweetlove L. J. , Dunford R. , Ratcliffe R. G. , Kruger N. J. 
Published: March 2003

ABSTRACTThe aim of this work was to investigate the effect of decreased activity of lactate dehydrogenase (EC 1.1.1.27; LDH) on lactate metabolism in potato tubers. By expressing a cDNA‐encoding potato tuber LDH in the antisense orientation, we generated transgenic potato plants with a preferential decrease in two of the five isozymes of LDH. Surprisingly, transgenic tubers grown under normoxic conditions did not contain less lactate, but rather instead contained approximately two‐fold more lactate than control tubers. This result is explicable if the decreased isozymes of LDH are responsible for the oxidation of lactate to pyruvate in vivo. This was confirmed by measurements of the rate of metabolism of lactate supplied to tuber discs: the rate in transgenic tubers was approximately half that of control tubers. The decrease in LDH activity had no measurable effect on the accumulation of lactate in cold‐stored tubers under anoxia, nor during the subsequent utilization of this lactate upon return to normoxia. In both control and transgenic tubers, the accumulation of lactate during anoxia was not accompanied by an induction of LDH activity or a change in isozyme distribution. In contrast, the metabolism of lactate after a period of anoxia was accompanied by a two‐fold increase in LDH activity and the induction of two isozymes that were distinct from those which had been decreased in the transgenic plants.
Elevated CO2 stimulates associative N2 fixation in a C3 plant of the Chesapeake Bay wetland
Authors: Dakora F. D. , Drake B. G. 
Published: March 2003

ABSTRACTIn this study, the response of N2 fixation to elevated CO2 was measured in Scirpus olneyi, a C3 sedge, and Spartina patens, a C4 grass, using acetylene reduction assay and 15N2 gas feeding. Field plants grown in PVC tubes (25 cm long, 10 cm internal diameter) were used. Exposure to elevated CO2 significantly (P< 0·05) caused a 35% increase in nitrogenase activity and 73% increase in 15N incorporated by Scirpus olneyi. In Spartina patens, elevated CO2 (660 ± 1 μmol mol−1) increased nitrogenase activity and 15N incorporation by 13 and 23%, respectively. Estimates showed that the rate of N2 fixation in Scirpus olneyi under elevated CO2 was 611 ± 75 ng 15N fixed plant−1 h−1 compared with 367 ± 46 ng 15N fixed plant−1 h−1 in ambient CO2 plants. In Spartina patens, however, the rate of N2 fixation was 12·5 ± 1·1 versus 9·8 ± 1·3 ng 15N fixed plant−1 h−1 for elevated and ambient CO2, respectively. Heterotrophic non‐symbiotic N2 fixation in plant‐free marsh sediment also increased significantly (P< 0·05) with elevated CO2. The proportional increase in 15N2 fixation correlated with the relative stimulation of photosynthesis, in that N2 fixation was high in the C3 plant in which photosynthesis was also high, and lower in the C4 plant in which photosynthesis was relatively less stimulated by growth in elevated CO2. These results are consistent with the hypothesis that carbon fixation in C3 species, stimulated by rising CO2, is likely to provide additional carbon to endophytic and below‐ground microbial processes.
Hydraulic architecture and water flow in growing grass tillers (Festuca arundinacea Schreb.)
Authors: Martre P. , Cochard H. , Durand J.‐L. 
Published: March 2003

ABSTRACTThe water relations and hydraulic architecture of growing grass tillers (Festuca arundinacea Schreb.) are reported. Evaporative flux density, E (mmol s−1 m−2), of individual leaf blades was measured gravimetrically by covering or excision of entire leaf blades. Values of E were similar for mature and elongating leaf blades, averaging 2·4 mmol s−1 m−2. Measured axial hydraulic conductivity, Kh (mmol s−1 mm MPa−1), of excised leaf segments was three times lower than theoretical hydraulic conductivity (Kt) calculated using the Poiseuille equation and measurements of vessel number and diameter. Kt was corrected (Kt*) to account for the discrepancy between Kh and Kt and for immature xylem in the basal expanding region of elongating leaves. From base to tip of mature leaves the pattern of Kt* was bell‐shaped with a maximum near the sheath–blade joint (≈ 19 mmol s−1 mm MPa−1). In elongating leaves, immature xylem in the basal growing region led to a much lower Kt*. As the first metaxylem matured, Kt* increased by 10‐fold. The hydraulic conductances of the whole root system, (mmol s−1 MPa−1) and leaf blades, (mmol s−1 MPa−1) were measured by a vacuum induced water flow technique. and were linearly related to the leaf area downstream. Approximately 65% of the resistance to water flow within the plant resided in the leaf blade. An electric‐analogue computer model was used to calculate the leaf blade area‐specific radial hydraulic conductivity, (mmol s−1 m−2 MPa−1), using , Kt* and water flux values. values decreased with leaf age, from 21·2 mmol s−1 m−2 MPa−1 in rapidly elongating leaf to 7·2 mmol s−1 m−2 MPa−1 in mature leaf. Comparison of and values showed that ≈ 90% of the resistance to water flow within the blades resided in the liquid extra‐vascular path. The same algorithm was then used to compute the xylem and extravascular water potential drop along the liquid water path in the plant under steady state conditions. Predicted and measured water potentials matched well. The hydraulic design of the mature leaf resulted in low and quite constant xylem water potential gradient (≈ 0·3 MPa m−1) throughout the plant. Much of the water potential drop within mature leaves occurred within a tenth of millimetre in the blade, between the xylem vessels and the site of water evaporation within the mesophyll. In elongating leaves, the low Kt* in the basal growth zone dramatically increased the local xylem water potential gradient (≈ 2·0 MPa m−1) there. In the leaf elongation zone the growth‐induced water potential difference was ≈ 0·2 MPa.
Recent advances in the role and biosynthesis of ascorbic acid in plants
Authors: Conklin P. L. 
Published: March 2003

ABSTRACTThe past few years have provided many advances in the role and biosynthesis of L‐ascorbic acid (AsA) in plants. There is an increasing body of evidence confirming that AsA plays an important role in the detoxification of reactive oxygen species. The role of AsA in photoprotection has been confirmed in vivo with the use of Arabidopsis mutants. A player in the defence against reactive oxygen species, AsA peroxidase, has been extensively studied at the molecular level, and regulation of this key enzymatic activity appears to occur at several levels. As a cofactor in the hydroxylation of prolyl and lysl‐residues by peptidyl‐prolyl and ‐lysyl hydroxylases, AsA plays a part in cell wall synthesis, defence, and possibly cell division. The maintenance of reduced levels of AsA appears to be highly regulated, involving the interplay of both monodehydroascorbate and dehydroascorbate reductases and possibly auxin. A major breakthrough in plant AsA biosynthesis has been made recently, and strong biochemical and genetic evidence suggest that GDP‐mannose and L‐galactose are key substrates. In addition, evidence for an alternative AsA biosynthetic pathway(s) exists and awaits additional scrutiny. Finally, newly described Arabidopsis mutants deficient in AsA will further increase our understanding of AsA biosynthesis
The distribution of xylem hydraulic resistance in the fruiting truss of tomato
Authors: Malone M. , Andrews J. 
Published: March 2003

ABSTRACTThe distribution of hydraulic resistances in xylem throughout the pathway leading to the tomato fruit was investigated. Previous work had indicated that there were large resistances within the supporting sections of this pathway (the peduncle and pedicel), perhaps associated with interruptions in the xylem. These high resistances are believed to impede calcium flux into the fruit and thus impair fruit development. It is shown here that fruit on intact plants do not shrink detectably during drought, even when the drought is sufficient to cause marked shrinkage of leaves and visible wilting of the shoot. In explants, it is possible to induce back‐flow from the fruit into the stem (probably via the xylem) but this flow is small and very slow. These observations support the view that there is a large hydraulic resistance in the pathway between fruit and stem. When pulses of water were made available within explants, by scorching of one leaflet, there was a rapid swelling of leaves and sepals. Such rapid fluxes indicate the presence of strong hydraulic (xylem) connections throughout the pathway between leaf and calyx. This shows that there are no significant hydraulic constrictions in the xylem proximal to the calyx. This finding is contrary to some previous conclusions but it is supported by experiments with dyes which showed continuous, functional xylem throughout the peduncle and pedicel. Calculations show that over 90% of the hydraulic resistance between stem and fruit must reside within the fruit pericarp. Implications for calcium nutrition are discussed.
Influence of atmospheric oxygen on leaf structure and starch deposition in Arabidopsis thaliana
Authors: Ramonell K. M. , Kuang A. , Porterfield D. M. , Crispi M. L. , Xiao Y. , Mcclure G. , Musgrave M. E. 
Published: March 2003

ABSTRACTPlant culture in oxygen concentrations below ambient is known to stimulate vegetative growth, but apart from reports on increased leaf number and weight, little is known about development at subambient oxygen concentrations. Arabidopsis thaliana (L.) Heynh. (cv. Columbia) plants were grown full term in pre‐mixed atmospheres with oxygen partial pressures of 2·5, 5·1, 10·1, 16·2, and 21·3 kPa O2, 0·035 kPa CO2 and the balance nitrogen under continuous light. Fully expanded leaves were harvested and processed for light and transmission electron microscopy or for starch quantification. Growth in subambient oxygen concentrations caused changes in leaf anatomy (increased thickness, stomatal density and starch content) that have also been described for plants grown under carbon dioxide enrichment. However, at the lowest oxygen treatment (2·5 kPa), developmental changes occurred that could not be explained by changes in carbon budget caused by suppressed photorespiration, resulting in very thick leaves and a dwarf morphology. This study establishes the leaf parameters that change during growth under low O2, and identifies the lower concentration at which O2 limitation on transport and biosynthetic pathways detrimentally affects leaf development.
UV‐B and UV‐C induction of NADP‐malic enzyme in tissues of different cultivars of Phaseolus vulgaris (bean)
Authors: Casati P. , Andreo C. S. 
Published: March 2003

AbstractThe effects of the treatment of different tissues of three bean cultivars (Pinto, Vilmorin and Arroz) with ultra‐violet (UV) UV‐B and UV‐C radiation and red light on the activity, quantity and RNA levels of NADP‐malic enzyme (NADP‐ME) were determined. Exposure to UV‐B radiation for 8 h caused a marked increase of NADP‐ME from leaves, stems and roots in the three cultivars studied. A similar induction was observed in the leaves and stems after 8 h of exposure under UV‐C, but not in the roots, suggesting that a different signal might be acting to induce the expression of NADP‐ME after UV‐B and UV‐C exposure. In contrast, red light was ineffective in inducing NADP‐ME in either tissue, so the regulation of the expression of this enzyme is phytocrome‐independent. The activity of superoxide dismutase, ascorbate peroxidase, catalase and peroxidase was also different in plants treated with UV‐B, UV‐C and photosynthetically active radiation, suggesting that various pathways may be acting in the regulation of these enzymes by UV‐B and UV‐C. Reactive oxygen species (ROS) were also required for UV‐B induction of NADP‐ME, as the addition of ascorbic acid before UV‐B treatment prevented NADP‐ME induction, whereas salicylic acid was not effective in inducing the enzyme, showing that NADP‐ME induction by UV‐B is ROS dependent but salicylic acid independent.
Antioxidant activities of red versus green leaves in Elatostema rugosum
Authors: Neill S. O. , Gould K. S. , Kilmartin P. A. , Mitchell K. A. , Markham K. R. 
Published: March 2003

AbstractAnthocyanin biosynthesis in leaves increases under stresses which also generate reactive oxygen species (ROS). In the present study the hypothesis that red leaves are better equipped to scavenge ROS than green leaves was tested. Antioxidants in leaf extracts from red and green morphs of Elatostema rugosum were identified, and activities quantified using enzymatic and α,α‐diphenyl‐β‐picrylhydrazyl (DPPH) assays and cyclic voltammetry. Red leaves from E. rugosum held greater amounts of superoxide dismutase, catalase, anthocyanins, and hydroxycinnamic acids, were significantly more effective at scavenging DPPH radicals, and produced higher voltammetric currents than green leaves. Anthocyanins contributed to the antioxidant pool more than all other constituent phenolics. Anthocyanin concentrations, and antioxidant activities declined with leaf age. Purified anthocyanin fractions displayed oxidative activities at both pH 7·0 and pH 5·5. Implications of the antioxidant potential of anthocyanin in its cytoplasmic and vacuolar locations are discussed.
Activation of an oxidative burst is a general feature of sensitive plants exposed to the air pollutant ozone
Authors: Wohlgemuth H. , Mittelstrass K. , Kschieschan S. , Bender J. , Weigel H.‐J. , Overmyer K. , Kangasjärvi J. , Sandermann H. , Langebartels C. 
Published: March 2003

AbstractOzone exposure stimulates an oxidative burst in leaves of sensitive plants, resulting in the generation and accumulation of hydrogen peroxide (H2O2) in tobacco and tomato, and superoxide (O2–•) together with H2O2 in Arabidopsis accessions. Accumulation of these reactive oxygen species (ROS) preceded the induction of cell death, and both responses co‐occurred spatially in the periveinal regions of the leaves. Re‐current ozone exposure of the sensitive tobacco cv. Bel W3 in closed chambers or in the field led to an enlargement of existing lesions by priming the border cells for H2O2 accumulation. Open top chamber experiments with native herbaceous plants in the field showed that Malva sylvestris L. accumulates O2–• at those sites that later exhibit plant cell death. Blocking of ROS accumulation markedly reduced ozone‐induced cell death in tomato, Arabidopsis and M. sylvestris. It is concluded that ozone triggers an in planta generation and accumulation of H2O2 and/or O2–• depending on the species, accession and cultivar, and that both these reactive oxygen species are involved in the induction of cell death in sensitive crop and native plants.
Induction of the Na+/Pi cotransport system in the plasma membrane of Chara corallina requires external Na+ and low levels of Pi
Authors: Mimura T. , Reid R. J. , Ohsumi Y. , Smith F. A. 
Published: March 2003

AbstractIt was shown in previous studies that the giant freshwater alga Chara corallina does not control its Na+‐dependent Pi uptake by monitoring the internal Pi concentration and it was hypothesized that Chara may instead detect changes in Pi supply from the environment. The present work investigated the conditions that control the induction and inactivation of high affinity Na+/Pi influx in Chara. Withdrawal of Pi from the external medium resulted in a gradual increase in the rate of uptake measured immediately after Pi was resupplied. The increase continued for at least 7 d of starvation. In the initial stages, 0·5 or 1 µm Pi were more effective at inducing transport activity than no Pi, suggesting that low levels of Pi are actually required for induction. The high Na+‐dependent Pi uptake observed in Pi‐starved cells was inactivated by treatment with as little as 1 µm Pi over 6 d. External Na+ plays a major role in controlling the capacity for Na+/Pi cotransport activity, and in the absence of Na+, both induction and inactivation were either delayed or abolished. Na+ starvation stimulated Na+ uptake even though there were no measurable changes in the concentrations of Na+, or of K+ or Pi in either the vacuole or cytoplasm. It was concluded that both substrate (Pi) and driver ion (Na+) are required at adequate concentrations for the induction of the cotransporter. In the case of Pi, it was suggested that passive leakage of Pi from the cell into the apoplast is sufficient for this purpose but that supplementation by up to 1 µm Pi is more effective at the earlier stage. A mechanism for sensing the external supply of Pi is proposed.
Environmental and metaboliccontrol of LHCII protein phosphorylation: revealing the mechanismsfor dual regulation of the LHCII kinase
Authors: Hou C.‐X. , Pursiheimo S. , Rintamäki E. , Aro E.‐M. 
Published: March 2003

AbstractLight‐harvesting complex II (LHCII) protein phosphorylation inplant chloroplasts is under complex regulation. Combination of the invivo monitoring of LHCII protein phosphorylation (by immunoblotting)with the in vitro[γ‐32P]ATPphosphorylation assays revealed that the basic activation/deactivationmodel of the LHCII kinase, regulated by reversible occupation/releaseof plastoquinol at the plastoquinol oxidation (Qo) siteof the cytochrome b6f (cyt b6f) complex, isconsistent with, but not sufficient to explain the data obtainedwith isolated chloroplasts, leaf discs or intact leaves. Not onlythe light conditions but also the metabolic state of the entireplant, particularly the sugar metabolism, exerted a control overLHCII protein phosphorylation. Feeding of leaves with glucose (alsowith glutathione) activated the LHCII kinase in darkness. On the otherhand, independently of the basic activation/deactivationmechanism of the kinase, a strong inhibition of LHCII protein phosphorylationoccurred in vivo at increasing irradiances and even at lowlight conditions, depending on the metabolic state of the plant.Both the experiments with intact chloroplasts and the reconstitutionexperiments with isolated thylakoids to mimic LHCII kinase inhibition,disclosed that the kinase in its activated state (plastoquinol at theQo site of cyt b6f complex) is protected againstinhibition by thiol reductants. However, directly upon deactivationof the kinase (release of plastoquinol from the Qo site) itbecomes a target for inhibition by thiol reductants. Thus the twointerdependent regulatory systems of the LHCII kinase, the constantlyoccurring activation and deactivation on the one hand and the inhibitionby thiol reductants on the other, are strongly dependent on theconcentration of reducing equivalents in the chloroplast stroma.A scheme demonstrating the interconversion of activated, deactivated andinhibited states of the LHCII kinase in the chloroplast environmentof intact leaves is presented.
Sugarcane yellow leaf virus and sugarcane yellows phytoplasma: elimination by tissue culture
Authors: Parmessur Y. , Aljanabi S. , Saumtally S. , Dookun‐Saumtally A. 
Published: March 2003

Yellow leaf syndrome (YLS) is a recently reported disease of sugarcane, characterized by yellowing of the leaves. Two pathogens: a virus, Sugarcane yellow leaf virus (SCYLV); and a phytoplasma, sugarcane yellows phytoplasma (SCYP), are associated with the disease. The use of tissue culture was investigated as a means to eliminate both SCYLV and SCYP from exotic varieties undergoing quarantine in Mauritius. Of 43 varieties in quarantine, 28 were infected with SCYLV and 19 with SCYP when checked by RT–PCR and nested PCR, respectively. Seventeen varieties were coinfected with both pathogens. Thirty infected varieties were induced to form callus in vitro using leaf rolls as explants. After two subcultures, 19 varieties were successfully regenerated and tested for SCYLV and SCYP. No pathogen could be detected in any regenerated plantlets. All the regenerated plants remained free from both SCYLV and SCYP over a period of 1 year in the glasshouse, confirming that the pathogens had been eliminated by tissue culture.