bluuebunny/crossref_metadata_2025_split huggingface dataset:
The induction of inorganic carbon transport and external carbonic anhydrase in Chlamydomonas reinhardtii is regulated by external CO2 concentration
Authors: Bozzo G. G. , Colman B. 
Published: March 2003

ABSTRACTInduction of the carbon concentrating mechanism (CCM) has been investigated during the acclimation of 5% CO2‐grown Chlamydomonas reinhardtii 2137 mt + cells to well‐defined dissolved inorganic carbon (Ci) limited conditions. The CCM components investigated were active HCO3− transport, active CO2 transport and extracellular carbonic anhydrase (CAext) activity. The CAext activity increased 10‐fold within 6 h of acclimation to 0·035% CO2 and there was a further slight increase over the next 18 h. The CAext activity also increased substantially after an 8 h lag period during acclimation to air in darkness. Active CO2 and HCO3− uptake by C. reinhardtii cells were induced within 2 h of acclimation to air, but active CO2 transport was induced prior to active HCO3− transport. Similar results were obtained during acclimation to air in darkness. The critical Ci concentrations effecting the induction of active Ci transport and CAext activity were determined by allowing cells to acclimate to various inflow CO2 concentrations in the range 0·035–0·84% at constant pH. The total Ci concentration eliciting the induction and repression of active Ci transport was higher during acclimation at pH 7·5 than at pH 5·5, but the external CO2 concentration was the same at both pHs of acclimation. The concentration of external CO2 required for the full induction and repression of Ci transport and CAext activity were 10 and 100 μM, respectively. The induction of CAext and active Ci transport are not correlated temporally, but are regulated by the same critical CO2 concentration in the medium.
Contribution of hydroxycinnamates and flavonoids to epidermal shielding of UV‐A and UV‐B radiation in developing rye primary leaves as assessed by ultraviolet‐induced chlorophyll fluorescence measurements
Authors: Burchard P. , Bilger W. , Weissenböck G. 
Published: March 2003

ABSTRACTEpidermally located ultraviolet (UV)‐absorbing phenolic compounds, flavonoids and hydroxycinnamic acid esters (HCAs), can shield the underlying tissues in plants against harmful UV‐radiation. The relative importance of the two different classes of phenolic compounds for UV‐screening was a matter of recent debate. Using a non‐invasive method based on chlorophyll fluorescence measurements to estimate epidermal UV transmittance, the relationship between epidermal UV shielding and the content of the two different groups of secondary phenolic compounds in the epidermal layers and the underlying photosynthetic mesophyll of developing rye primary leaves grown under supplementary UV‐B radiation was investigated. From the fourth to the tenth day after sowing, epidermally located flavonoids increased in an age‐ and irradiation‐dependent manner, whereas mesophyll flavonoids and epidermal HCAs, mainly ferulic acid and p‐coumaric acid esters, were constitutively present and did not vary in their contents over the observed time period. There was an excellent correlation between epidermal UV‐A and UV‐B absorbances as assessed by chlorophyll fluorescence measurements and contents of epidermal flavonoids. However, HCAs showed an additional contribution to UV‐B shielding. In contrast, mesophyll flavonoids did not seem to play a respective role. When absorbances of the abaxial and adaxial epidermal layers were compared, it became apparent that in fully expanded primary leaves epidermal tissues from both sides were equally effective in absorption of UV‐radiation. However, the earlier and more UV‐exposed abaxial epidermis of young unrolling leaves showed a significantly higher absorption. It is shown that in early stages of development the epidermal HCAs are the dominant UV‐B protective compounds of the primary leaf. This function is increasingly replaced by the epidermal flavonoids during leaf development and acclimation. The application of chlorophyll fluorescence measurements has been proven to be a useful tool for estimating relative contents of these compounds in epidermal tissue.
Effects of photoinhibition on whole‐plant carbon gain assessed with a photosynthesis model
Authors: Werner C. , Ryel R. J. , Correia O. , Beyschlag W. 
Published: March 2003

ABSTRACTA canopy photosynthesis model was modified to assess the effect of photoinhibition on whole‐plant carbon gain. Photoinhibitory changes in maximum quantum yield of photosystem II (Fv/Fm) could be explained solely from a parameter (Lflux) calculated from the light micro‐environment of the leaves. This relationship between Fv/Fm and the intercepted cumulative light dose, integrated and equally weighted over several hours was incorporated into the model. The effect of photoinhibition on net photosynthesis was described through relationships between photoinhibition and the shaping parameters of the photosynthetic light‐response curve (quantum use efficiency, convexity, and maximum capacity). This new aspect of the model was then validated by comparing measured field data (diurnal courses of Fv/Fm) with simulation results. Sensitivity analyses revealed that the extent of photoinhibitory reduction of whole‐plant photosynthesis was strongly dependent on the structural parameters (LAI and leaf angle). Simulations for a Mediterranean evergreen oak, Quercus coccifera, under climatic conditions which cause mild photoinhibition revealed a daily loss of 7·5–8·5% of potential carbon gain in the upper sunlit canopy layers, a 3% loss in the bottom canopy, and an overall loss of 6·1%. Thus, this canopy photoinhibition model (CANO‐PI) allows the quantitative evaluation of photoinhibition effects on primary production.
Regulation of the induction of bicarbonate uptake by dissolved CO2 in the marine diatom, Phaeodactylum tricornutum
Authors: Matsuda Y. , Hara T. , Colman B. 
Published: March 2003

ABSTRACTPhysiological properties of photosynthesis were determined in the marine diatom, Phaeodactylum tricornutum UTEX640, during acclimation from 5% CO2 to air and related to H2CO3 dissociation kinetics and equilibria in artificial seawater. The concentration of dissolved inorganic carbon at half maximum rate of photosynthesis (K0·5[DIC]) value in high CO2‐grown cells was 1009 mmol m−3 but was reduced three‐fold by the addition of bovine carbonic anhydrase (CA), whereas in air‐grown cells K0·5[DIC] was 71 mmol m−3, irrespective of the presence of CA. The maximum rate of photosynthesis (Pmax) values varied between 300 and 500 μmol O2 mg Chl−1 h−1 regardless of growth pCO2. Bicarbonate dehydration kinetics in artificial seawater were re‐examined to evaluate the direct HCO3− uptake as a substrate for photosynthesis. The uncatalysed CO2 formation rate in artificial seawater of 31·65°/oo of salinity at pH 8·2 and 25 °C was found to be 0·6 mmol m−3 min−1 at 100 mmol m−3 DIC, which is 53·5 and 7·3 times slower than the rates of photosynthesis exhibited in air‐ and high CO2‐grown cells, respectively. These data indicate that even high CO2‐grown cells of P. tricornutum can take up both CO2 and HCO3− as substrates for photosynthesis and HCO3− use improves dramatically when the cells are grown in air. Detailed time courses were obtained of changes in affinity for DIC during the acclimation of high CO2‐grown cells to air. The development of high‐affinity photosynthesis started after a 2–5 h lag period, followed by a steady increase over the next 15 h. This acclimation time course is the slowest to be described so far. High CO2‐grown cells were transferred to controlled DIC conditions, at which the concentrations of each DIC species could be defined, and were allowed to acclimate for more than 36 h. The K0·5[DIC] values in acclimated cells appeared to be correlated only with [CO2(aq)] in the medium but not to HCO3−, CO32−, total [DIC] or the pH of the medium and indicate that the critical signal regulating the affinity of cells for DIC in the marine diatom, P. tricornutum, is [CO2(aq)] in the medium.
Specific and constitutive expression of oxalate oxidase during the ageing of leaf sheaths of ryegrass stubble
Authors: Davoine C. , Le Deunff E. , Ledger N. , Avice J.‐C. , Billard J.‐P. , Dumas B. , Huault C. 
Published: March 2003

AbstractChanges in the activity of oxalate oxidase (OxO) and of the concentrations of oxalate and H2O2 were investigated during the ageing of leaf sheaths of ryegrass (Lolium perenne L.) stubble. The accumulation of H2O2 during ageing coincides with the increases of both oxalate level and OxO activity. Western and Northern blot analyses using protein and RNA extracts of the different categories of leaf sheaths suggested that OxO gene expression, as well as Ca‐oxalate synthesis, are crucial events of ageing for leaf sheaths. Immunocytochemistry experiments have revealed that OxO, which is an extracellular enzyme, is nearly always present in the parenchymatous cells surrounding the vascular bundles and in the cells of the lower epidermis. Overall, results suggest that in ryegrass that synthesizes both Ca‐oxalate and OxO, the production of H2O2 and Ca2+ during ageing of stubble might be involved in the constitutive defences against pathogens, thus allowing the phloem mobilization of nutrient reserves from the leaf sheaths towards elongating leaf bases of ryegrass.
Changes in synthesis and degradation of Rubisco and LHCII with leaf age in rice (Oryza sativa L.) growing under supplementary UV‐B radiation
Authors: Takeuchi A. , Yamaguchi T. , Hidema J. , Strid A. , Kumagai T. 
Published: March 2003

AbstractThe effects of supplementary ultraviolet‐B (UV‐B) radiation on the changes in synthesis and degradation of ribulose ‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) and light‐harvesting chlorophyll a/b binding protein of PSII (LHCII) were examined, as well as mRNA levels for small and large subunits of Rubisco (rbcS and rbcL, respectively) and LHCII (cab) with leaf age in UV‐sensitive rice (Norin 1) and UV‐resistant rice (Sasanishiki). Both Rubisco and LHCII were actively synthesized until the leaf had fully expanded, and then decreased with increasing leaf age. Synthesis of Rubisco, but not LHCII, was significantly suppressed by UV‐B in Norin 1. The degradation of Rubisco was enhanced by UV‐B around the time of leaf maturation in the two cultivars. The levels of rbcS and rbcL were reduced by UV‐B at the early stages after leaf emergence in both cultivars. Cab transcripts were first present at high levels in the two cultivars, but drastically decreased due to UV‐B treatment immediately after leaf emergence in Norin 1. It was shown that synthesis and degradation of Rubisco and LHCII greatly changed with leaf age: Rubisco synthesis was significantly suppressed by supplementary UV‐B radiation at the transcription step during the early leaf stages. It was also suggested that the difference in UV‐B sensitivity in Rubisco synthesis between the two rice cultivars might be due to specific suppression both transcriptionally and post‐transcriptionally.
A hydrothermal time model explains the cardinal temperatures for seed germination
Authors: Alvarado V. , Bradford K. J. 
Published: March 2003

AbstractTemperature (T) and water potential (y) are two primary environmental regulators of seed germination. Seeds exhibit a base or minimum T for germination (Tb), an optimum T at which germination is most rapid (To), and a maximum or ceiling T at which germination is prevented (Tc). Germination at suboptimal T can be characterized on the basis of thermal time, or the T in excess of Tb multiplied by the time to a given germination percentage (tg). Similarly, germination at reduced y can be characterized on a hydrotime basis, or tg multiplied by the y in excess of a base or threshold y that just prevents germination (yb). Within a seed population, the variation in thermal times to germination among different seed fractions (g) is based on a normal distribution of yb values among seeds (yb(g)). Germination responses across a range of suboptimal T and y can be described by a general hydrothermal time model that combines the T and y components, but this model does not account for the decrease in germination rates and percentages when T exceeds To. We report here that supra‐optimal temperatures shift the ψb(g) distribution of a potato (Solanum tuberosum L.) seed population to more positive values, explaining why both germination rates and percentages are reduced as T increases above To. A modified hydrothermal time model incorporating changes in ψb(g) at T > To describes germination timing and percentage across all T and ψ at which germination can occur and provides physiologically relevant indices of seed behaviour.
Genetic control of resistance to fenpropimorph in Ustilago maydis
Authors: Markoglou  , Ziogas  
Published: March 2003

Fenpropimorph‐resistant mutants of Ustilago maydis were obtained at high frequency (30 × 10−6) after UV‐irradiation followed by selection on media containing fenpropimorph (50 μg mL−1). Genetic analysis of 30 such mutants resulted in the identification of two unlinked chromosomal loci, the U/fpm‐1 locus with two allelic genes (U/fpm‐1A and U/fpm‐1B) and the U/fpm‐2 locus. The mutant genes U/fpm‐1A and U/fpm‐2 are responsible for high resistance levels (Rf: 75–100 or 257–286 based on MICs or ED50s, respectively), while the U/fpm‐1B mutation gives only a small reduction (approximately 7–10‐fold) in fenpropimorph sensitivity. Cross‐resistance studies with other SBIs showed that the major gene (U/fpm‐1A and U/fpm‐2) mutants were cross‐resistant to the related compound fenpropidin (Rf: 15–20 or 53–66 based on MICs or ED50s values, respectively) and to tridemorph (Rf: 5 or 7.1–9.5 based on MICs or ED50s values, respectively), but not to the inhibitors of steps of ergosterol biosynthesis preceding the Δ14‐reductase. The minor gene (U/fpm‐1B) mutants also had low‐level resistance (approximately 5‐fold) to tridemorph and to fenpropidin, but in contrast with the major gene mutants they were 2–10 times more sensitive to the triazoles studied (triadimefon, triadimenol, propiconazole and flusilazole) and to the pyridine, pyrifenox.Studies of the fitness of U. maydis mutants showed that in major gene mutants, resistance was not associated with changes in growth rate in liquid culture or pathogenicity on young maize plants. The minor gene mutation reduced significantly the growth rate in liquid culture and the pathogenicity, either in homozygous or heterozygous condition in dikaryotic mycelium.
Sporulation ofPyrenopeziza brassicae(light leaf spot) on oilseed rape (Brassica napus) leaves inoculated with ascospores or conidia at different temperatures and wetness durations
Authors: Karolewski Z. , Evans N. , Fitt B. D. L. , Todd A. D. , Baierl A. 
Published: March 2003

In controlled environment experiments, sporulation ofPyrenopeziza brassicaewas observed on leaves of oilseed rape inoculated with ascospores or conidia at temperatures from 8 to 20°C at all leaf wetness durations from 6 to 72 h, except after 6 h leaf wetness duration at 8°C. The shortest times from inoculation to first observed sporulation (l0), for both ascospore and conidial inoculum, were 11–12 days at 16°C after 48 h wetness duration. For both ascospore and conidial inoculum (48 h wetness duration), the number of conidia produced per cm2leaf area with sporulation was seven to eight times less at 20°C than at 8, 12 or 16°C. Values of Gompertz parametersc(maximum percentage leaf area with sporulation),r(maximum rate of increase in percentage leaf area with sporulation) andl37(days from inoculation to 37% of maximum sporulation), estimated by fitting the equation to the observed data, were linearly related to values predicted by inserting temperature and wetness duration treatment values into existing equations. The observed data were fitted better by logistic equations than by Gompertz equations (which overestimated at low temperatures). For both ascospore and conidial inoculum, the latent period derived from the logistic equation (days from inoculation to 50% of maximum sporulation,l50) ofP. brassicaewas generally shortest at 16°C, and increased as temperature increased to 20°C or decreased to 8°C. Minimum numbers of spores needed to produce sporulation on leaves were ≈25 ascospores per leaf and ≈700 conidia per leaf, at 16°C after 48 h leaf wetness duration.
Spatial and temporal distribution of diagenetic alterations in siliciclastic rocks: implications for mass transfer in sedimentary basins
Authors: Morad S. , Ketzer J. M. , De Ros L. F. 
Published: March 2003

SummaryThe spatial and temporal distribution of diagenetic alterations in siliciclastic sequences is controlled by a complex array of interrelated parameters that prevail during eodiagenesis, mesodiagenesis and telodiagenesis. The spatial distribution of near‐surface eogenetic alteration is controlled by depositional facies, climate, detrital composition and relative changes in sea‐level. The most important eogenetic alterations in continental sediments include silicate dissolution and the formation of kaolinite, smectite, calcrete and dolocrete. In marine and transitional sediments, eogenetic alterations include the precipitation of carbonate, opal, microquartz, Fe‐silicates (glaucony, berthierine and nontronite), sulphides and zeolite. The eogenetic evolution of marine and transitional sediments can probably be developed within a predictable sequence stratigraphic context. Mesodiagenesis is strongly influenced by the induced eogenetic alterations, as well as by temperature, pressure and the composition of basinal brines. The residence time of sedimentary sequences under certain burial conditions is of key importance in determining the timing, extent and patterns of diagenetic modifications induced. The most important mesogenetic alterations include feldspar albitization, illitization and chloritization of smectite and kaolinite, dickitization of kaolinite, chemical compaction as well as quartz and carbonate cementation. Various aspects of deep‐burial mesodiagenesis are still poorly understood, such as: (i) whether reactions are accomplished by active fluid flow or by diffusion; (ii) the pattern and extent of mass transfer between mudrocks and sandstones; (iii) the role of hydrocarbon emplacement on sandstone diagenesis; and (iv) the importance and origin of fluids involved in the formation of secondary inter‐ and intragranular porosity during mesodiagenesis. Uplift and incursion of meteoric waters induce telogenetic alterations that include kaolinitization and carbonate‐cement dissolution down to depths of tens to a few hundred metres below the surface.
The structure and fluid mechanics of turbidity currents: a review of some recent studies and their geological implications
Authors: Kneller Ben , Buckee Clare 
Published: March 2003

SummaryThe literature on the structure and behaviour of gravity currents is reviewed, with emphasis on some recent studies, and with particular attention to turbidity currents, though reference is also made to comparable behaviour in pyroclastic flows. Questions of definition are discussed, in particular the distinction between dense currents, which may deposit en masse, and more dilute currents. High‐density dispersions may exist as a discrete, independently moving layer beneath a more dilute flow, as the basal part of a continuous density distribution or possibly as a transient depositional layer. Existing theory appears inadequate to explain the behaviour of some high‐density dispersions. Surge‐type currents are contrasted with quasi‐steady currents, which may be generated by a variety of mechanisms including direct feed by rivers in flood. Such fluvially generated currents provide one means of generating currents with reversing buoyancy. Geologically significant turbidity currents are impractical for direct study owing to their large scale and (often) destructive nature. Small‐scale laboratory currents offer a wealth of insights into turbidity current behaviour. This paper summarizes recent experimental studies that focus on the physical structure of gravity currents, with emphasis on the velocity and turbulence structure, the vertical density distribution and the stability of stratification. Preliminary quantification of the turbulence structure (including controls on turbulent entrainment, turbulent kinetic energy, Reynolds stresses and turbulence production) has been facilitated by recent technological developments that have allowed the measurement of instantaneous fluctuations in both velocity and concentration. Laboratory models, however, generally involve substantial simplification, and require compromises in some parameters to achieve adequate scaling of the parameters of most interest. Mathematical modelling also provides important insights into turbidity current behaviour. We discuss various approaches to modelling, ranging from simple hydraulic equations to systems of partial differential equations that explicitly treat conservation of momentum, fluid and sediment mass, and turbulent kinetic energy. The application for which the model is designed (i.e. to calculate mean head velocity or to create an instantaneous two‐dimensional contour plot of downstream velocity in a current) determines the complexity of the mathematical model required. The behaviour of suspension currents around topography is complex and depends upon the relative height of the topography, and upon the density and velocity structure of the current. Many interactions with topography are well described by the internal Froude number, Fri. Both reflection and deflection of currents may occur on the upstream side of topography, depending upon Fri. On the downstream side of topography, flow separation, lee waves or hydraulic jumps may occur.
Late Pleistocene–early Holocene fluvial facies and depositional processes in the Fehmarn Belt, between Germany and Denmark, revealed by high‐resolution seismic and lithofacies analysis
Authors: Novak Bernhard , Björck Svante 
Published: March 2003

AbstractIn the narrow offshore border zone between Germany and Denmark, 550 km of high‐density 3·5‐kHz subbottom seismic reflection profiles were recorded within a 70‐km2 area in order to reconstruct the seismic stratigraphy of late Pleistocene to early Holocene lacustrine and fluvial environments. Using detailed line drawings, seismic facies analyses and a hierarchy of bounding surfaces, a depositional unit was recognized and subdivided into subunits 4a (oblique‐parallel), 4b (mound, oblique‐tangential), 4c (sigmoid, oblique), 4d and 4e (shingled and parallel). The base of this seismic facies association defines a wide U‐shaped valley with well‐defined scours and, in the valley sides, ‘steps’ are located above deep steep‐dipping reflections. Stratigraphic control was available from 32 coring sites (5‐ to 12‐m‐deep vibrocores). Subunit 4b represents coarsening‐up silt and sand, and samples from subunit 4d show fining‐up fine sand, silt and clay. The seismic facies association is proposed to have formed by a fluvial event of short duration some time in the period between 10·3 14C ka BP and 9·0 14C ka BP. Subunits 4a to 4e represent gradually decreasing flow power. A peak flow initiated the fluvial event, after which water discharge and level fell rapidly. Subsequently, the normal background discharge from the Baltic Sea area dominated the flow style. Reflections beneath the ‘step’‐like valley side with high dip angles are interpreted as faults. This tectonic activity resulted in subsidence in the analysed area and could possibly have influenced the fluvio‐dynamic development. The seismic stratigraphic succession reveals a high‐resolution record of sediments in this area. In particular, the stepwise uncovering of the morphology of the subunits, preserved in high‐resolution seismic facies associations, is proposed as a useful tool in modelling the dynamic development of the near sea‐floor environment.