bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffusion of inorganic carbon across an unstirred layer: a simplified quantitative approach
Authors: HELDER R. J. 
Published: April 2006

Abstract The quantitative approach used here is based on a model comprising a well‐stirred medium, an unstirred layer, and a CO2 absorbing leaf. The unstirred layer is divided up by planes into a number of sub‐layers. Within each plane the concentration of each solute is everywhere the same as is the electric potential. These variables constitute the basic data. Thus the planes were characterized by their pH value.An equation is derived which enables the calculation of the basic data of a plane from the known data of another plane. In this way it is possible to calculate the basic data for all planes. From these data the rate of assimilation, the thickness of the unstirred layer and its sub‐layers, the fluxes across the sub‐layers and the conversions among the carbon components can be estimated.The CO2 flux decreases, and the HCO−3 flux increases towards the leaf. There are negative fluxes of OH& and CO2–3. H+ fluxes are of minor importance and can be ignored if the pH of the medium is higher than 8.0, provided no non‐inorganic C buffers with appropriate pKa are present.The significance of the carbon diffusion facilitating effect of an inorganic carbon system is expressed in various ways. The values obtained represent maxima, as the assumption is made that the equilibrium reactions are very fast.It is argued that even better effects are possible if the back‐diffusion of CO2–3 could be prevented by lowering the pH of the unstirred layer.
Characteristics of nitrate uptake into seedlings of pea (Pisum sativum L. cv. Feltham First). Changes in net NO−3 uptake following inoculation with Rhizobium and growth in low nitrate concentrations
Authors: DEANE‐DRUMMOND CELIA E. , CHAFFEY N. J. 
Published: April 2006

Abstract Nitrate uptake into intact pea seedlings (Pisum sativum L. cv. Feltham First) grown in hydroponic culture has been investigated. Following inoculation with Rhizobium leguminosarum a twofold increase in net nitrate uptake was observed. Changes in morphological characteristics following inoculation were found to decrease the effective area available for absorption.There was a two‐fold decrease in net nitrate uptake into intact seedlings grown in the presence of N compared with N free media. In the former case net nitrate uptake appeared to stall at regular intervals. In both cases only the initial rates of nitrate uptake were found to be responsive to the external nitrate concentration. The results are discussed in terms of current models for the regulation of NO−3 uptake by higher plants.
HCO−3 uptake through the roots and its effect on the productivity of willow cuttings
Authors: VAPAAVUORI E. M. , PELKONEN P. 
Published: April 2006

Abstract Young willow plants (Salix‘aquatica gigantea’) were grown in hydroponic culture media, and 14C–labelled sodium bicarbonate was fed to the roots. Uptake of 14C‐label in the leaves and shoots was assayed after two different feeding periods (6 h, 48 h). Even during the shortest feeding period, 14C‐label had been transferred to the leaves and shoots. Compared with the longer feeding period, after the 6 h feeding period more label was in the form of acid‐labile products, whereas after the 48 h feeding period most of the label was in acid‐stable products.A second experiment was designed to test whether carbon uptake by roots affects the growth of young willow plants. Uniform rooted cuttings were grown in hydroponic cultures at five different levels of bicarbonate: 0, 0.015, 0.147 0.737, and 1.473 mol m−3 NaHCO3. After a 4‐week growing period we determined the biomass of leaves, shoots, roots and cuttings.Production of total dry matter (shoots, leaves and roots) increased with increasing bicarbonate concentration. Saturation of dry matter production was reached at 0.737 mol m−3 NaHCO3, but a higher concentration of NaHCO3 (1.470 mol m−3) caused a slight decrease in the dry matter production. At 0.737 mol m−3 NaHCO3 the total dry weight increased by 31.1%, which suggests that uptake of dissolved carbon dioxide through the roots might affect carbon budgeting in young willow plants.
Physiological implications of the Münch‐Horwitz theory of phloem transport: effects of loading rates*
Authors: GOESCHL J. D. , MAGNUSON C. E. 
Published: April 2006

Abstract Predicted effects of phloem loading rates on the five profiles of unloading rate, osmotic water flux, pressure, transport speed and concentration, in hypothetical sieve tubes with different sink properties, were calculated using the steady‐state mathematical expression of the Münch hypothesis of phloem transport. The prediction that increased loading rates always increases the concentration, and generally increase the speed of translocates through the sieve tube, is emphasized since these parameters are accessible for experimental testing. This particular prediction contrasts with a previous prediction (Tyree, Christy, & Ferrier, 1974), that where concentration was held constant at the loading end, concentration along the rest of the sieve tube would decrease, while speed would increase greatly.Where the unloading mechanism was assigned saturable (enzyme‐like) kinetics, increased loading rates (in the range well below the Vmax of the sink) caused both transport speed and concentration to increase. However, as loading rates approached the Vmax of the sinks, speed reached a maximum and then declined, and concentration increased substantially. This was particularly true at very high values of Km, e.g. > 0.1 mol cm−3.
Sealed lysimeters for the direct estimation of dinitrogen fixation by grain legume crops
Authors: SIMS A. P. , BARBER D. J. , FOLKES B. F. , WALLS D. 
Published: April 2006

Abstract A new technique has been devised for the direct estimation of the contribution of N2‐fixation to the total nitrogen of a legume crop. Sealed lysimeters and ancillary equipment are described by which it is possible to enclose in a gas‐tight system the roots of some of the plants within the crop, together with their associated core of soil. The normal soil atmosphere can then be replaced by one containing 15N2, thus allowing, from the 15N content of the resulting plants direct calculation of the N2‐fixation. Regular monitoring is necessary to ensure that soil O2, CO2 and moisture contents are maintained at normal field levels.The results indicate that the technique is capable of achieving its objectives and, provided the seedlings establish well initially, the resultant plants fully match the field average at final harvest. It has been possible to maintain the labelling of the soil atmosphere sufficiently constant to ensure that reliable and highly reproducible estimates of N2‐fixation are obtained. Using Pisum sativum cv. Meteor at densities of 160 plants m−2, fixation accounted for about 90% of the total nitrogen uptake. The limitations and merits of the method are compared with those of the 15N‐fertilizer dilution method.
Metabolic response of Medicago sativa L. and Lotus corniculatus L roots to anoxia
Authors: BARTA A. L. 
Published: April 2006

Abstract Differential rates of fermentation and energy production have been implicated in the response of plant species to extended root anoxia. This study describes the metabolic response to anaerobiosis of waterlogging‐tolerant birdsfoot trefoil (Lotus corniculatus L.) and waterlogging‐sensitive alfalfa (Medicago sativa L.). Studies were carried out on glasshouse‐grown plants subjected to root anaerobiosis in nutrient solution. Rate of fermentation, as estimated by CO2 evolution, declined significantly upon anaerobiosis in both species but was proportionally less, relative to the aerobic control, in trefoil. Another indicator of carbon flux through glycolysis, the concentration of glucose‐6‐phosphate, was also significantly lower in trefoil roots relative to aerobic controls. Both species showed significantly increased root exudation of K+, sugars and andno‐N, especially during the first 2 d of root anaerobiosis, indicating changes in membrane selective permeability.The energy status of roots subjected to anaerobiosis declined sharply in both species but trefoil roots maintained higher ATP/ADP ratios for up to 4 d of anaerobiosis. The results are consistent with the hypothesis that increased fermentation activity maintains a more favourable root energy status. This higher energy status may facilitate survival by maintaining crucial root activities, such as maintenance of membrane stability.
Comparative ecophysiology of CAM and C3 bromeliads. I. The ecology of the Bromeliaceae in Trinidad
Authors: SMITH J. A. C. , GRIFFITHS H. , LÜTTGE U. 
Published: April 2006

Abstract This article deals with the physiological ecology of the Bromeliaceae, a large neotropical family containing both terrestrial and epiphytic forms, as well as many species with crassulacean acid metabolism (CAM).The article is in two parts. In the first, we review what is known of the occurrence of CAM and C3 species in the Bromeliaceae. The photosynthetic pathways are discussed in the context of the major taxonomic divisions within the family and the great diversity of bromeliad life‐forms. Of the three subfamilies, the Pitcairnioideae contain both C3 and CAM species and are essentially all terrestrial. In contrast, the Tillandsioideae are entirely epiphytic or saxicolous, with CAM species being restricted to the genus Tillandsia, And in the Bromelioideae all species show CAM, but terrestrial and epiphytic forms are found in about equal numbers. The evidence suggests that both CAM and the epiphytic habit arose more than once in the family's evolutionary history.In the second part we consider the photosynthetic ecology of the various bromeliad life‐forms in more detail using the specific example of Trinidad (West Indies). CAM bromeliads tend to be centred on the drier regions of the island and C3 forms on the wetter areas. However, at any one site there is a marked vertical stratification of species within the forest profile. Based on the known habitat preferences of the bromeliads, six contrasting sites were selected for field studies in Trinidad. These ranged from arid coastal scrub to montane rain forest, the vegetational and climatic characteristics of which are described here. The constancy of δ13C values (carbon‐isotope ratios) for individual CAM species in these markedly different habitats emphasized the need for ecophysiological studies to characterize environmental effects on CO2 assimilation and transpiration. The following papers in this series present the results of a comparative investigation of gas exchange and leaf water relations of CAM and C3 bromeliads in situ at the various sites.
Comparative ecophysiology of CAM and C3 bromeliads. III. Environmental influences on CO2 assimilation and transpiration
Authors: GRIFFITHS H. , LÜTTGE U. , STIMMEL K.‐H. , CROOK C. E. , GRIFFITHS N. M. , SMITH J. A. C. 
Published: April 2006

Abstract Field measurements of the gas exchange of epiphytic bromeliads were made during the dry season in Trinidad in order to compare carbon assimilation with water use in CAM and C3 photosynthesis.The expression of CAM was found to be directly influenced by habitat and microclimate. The timing of nocturnal CO2 uptake was restricted to the end of the dark period in plants found at drier habitats, and stomatal conductance in two CAM species was found to respond directly to humidity or temperature. Total night‐time CO2 uptake, when compared with malic‐acid formation (measured as the dawn‐dusk difference in acidity, ΔH+), could only account for 10–40% of the total ΔH+ accumulated. The remaining malic acid must have been derived from the refixation of respired CO2 (recycling). Within the genus Aechmea (12 samples from four species), recycling was significantly correlated with night temperature at the six sample sites. Recycling was lowest in A. fendleri (54% of ΔH+ derived from respired CO2), a CAM bromeliad with little water‐storage parenchyma that is restricted to wetter, cooler regions of Trinidad.Gas‐exchange rates of C3 bromeliads were found to be similar to those of the CAM bromeliads, with CO2 uptake from 1 to 3 μmol m−2 s−1 and stomatal conductances generally up to 100 mmol m−2 s−1. The midday depression of photosynthesis occurred in exposed habitats, although photosynthetically active radiation (PAR) limited photosynthesis in shaded habitats. CO2 uptake of the C3 bromeliad Guzmania lingulata was saturated at around 500 μmol m−2 s−1 PAR, suggesting that epiphytic plants found in the shaded forest understorey are shade‐tolerant rather than shade‐demanding.Transpiration ratios (TR) during CO2 fixation in CAM (Phase I and IV) and C3 bromeliads were compared at different sites in order to assess the efficiency of water utilization. For the epiphytes displaying marked uptake of CO2, TR were found to be lower than many previously published values. In addition, the average TR values were very similar for dark CO2 uptake in CAM (42 ± 41, n= 12), Phase IV of CAM (69 ± 36, n= 3) and for C3 photosynthesis (99 ± 73, n= 4) in these plants. It appears that recycling of respired CO2 by CAM bromeliads and efficient use of water in all phases of CO2 uptake are physiological adaptations of bromeliads to arid microclimates in the humid tropics.
Quantitative short‐term uptake of inorganic phosphate by the Chara hispida rhizoid
Authors: BOX R. J. 
Published: April 2006

Abstract The rhizoid of Chara hispida L. made a small contribution to the uptake of inorganic phosphate under laboratory conditions. At 1 mmol m−3 phosphate the rhizoid contributed about 4% to the uptake of the whole plant over 4 h. Under these conditions about half of the phosphate taken up by the rhizoid was translocated into the shoot. The rates of uptake and translocation increased with increasing external phosphate concentrations.When the shoot was in darkness, 32P‐translocation from the rhizoid was less than half of that found when the shoot was illuminated. When the rhizoid medium was anaerobic the translocation rate was lower than the rate in aerobic conditions and illumination of the shoot had no effect on the uptake or translocation of phosphate.Translocated 32P accumulated in the apical growing regions of the plant. This was first noted in the secondary apices nearest to the rhizoids.
Quantum yields of photosynthesis at temperatures between −;2°C and 35°C in a cold‐tolerant C3 plant (Pinus sylvestris) during the course of one year
Authors: LEVERENZ J. W. , ÖQUIST G. 
Published: April 2006

Abstract Quantum yields of photosynthetic CO2 uptake by Pinus sylvestris (L.) shoots were measured at temperatures between −; 2°C and 35°C from September 1984 to September 1985. The ratio of variable to peak fluorescence of photosystem II (Fv/Fp) was also measured. Quantum yield measured at 25°C varied with time from a low winter value of 0.017 to a high summer value of 0.057. This variation was strongly correlated to variation in FvFp(r2= 0.91).The response of quantum yield to temperature changed with season. During winter, quantum yield was essentially constant between 0°C and 35°C. The constancy above 5°C was associated with a strong increase in intercellular space CO2 (Ci) with temperature. In June, the quantum yield peaked at 5°C, decreased sharply below 5°C, and was rather constant between 25°C and 35°C. This insensitivity to increased temperature above 25°C was attributed to a large increase in Ci In contrast, by September, the quantum yield was less sensitive to temperature below 5°C and more sensitive above 25°C, despite an unchanged Ci response with increasing temperatures as compared with June. In August, quantum yields were lowered at 0, 5 and 15°C, apparently as a result of high carbohydrate levels in the leaves. Overall, the results suggest that there are sites other than in photosystem II or at ribulose bisphosphate carboxylase/oxygenase at which the quantum yield of photosynthetic CO2 uptake is affected. Possible causes for the changes in efficiency are discussed.
Salt tolerance in Aster tripolium L. II. Ionic regulation
Authors: SHENNAN C. , HUNT R. , MACROBBIE E. A. C. 
Published: April 2006

Abstract Measurements of tissue ion contents (Na, K and Cl) were carried out at frequent intervals on plants of Aster tripolium L. grown at a range of salinities for 36 d. Aster tripolium behaved as a typical halophyte showing high levels of inorganic ion accumulation even at low salinities. As salinity increased Na replaced K to a large extent in the shoot but root K was unaffected up to 500 mol m−3 external NaCl. Shoot (Na + K) concentration on a tissue water basis was maintained constant in all treatments throughout the experiment, whereas shoot (Na + K) on a dry weight basis showed marked fluctuations in some treatments. An increase in (Na + K) per gram dry weight was, however, accompanied by a parallel increase in fresh weight: dry weight (FW : DW) ratio. Transport of (Na + K) to the shoot per unit root weight changed during the experiment in the manner expected, given the observed changes in shoot relative growth rate and FW : DW to result in a constant shoot (Na + K) concentration on a water basis.Chloride was the major balancing anion in the shoot at high salinity, but never accounted for more than 38% of the (Na + K) found in the root tissue. At all salinities (Na + K) salts accounted for the majority of the measured shoot sap osmotic potential. The interactions between salinity, growth, ion transport and osmotic adjustment are discussed.
Effects of frost hardening, dehardening and freezing stress onin vivochlorophyll fluorescence of seedlings of Scots pine (Pinus sylvestrisL.)
Authors: STRAND M. , ÖQUIST G. 
Published: April 2006

Abstract.The kinetics ofin vivochlorophyll fluorescence of photosystem II (PS II) was measured at room temperature and 77 K during frost hardening of seedlings of Scots pine (Pinus sylvestrisL.), and after exposure of frost‐hardened shoots to sub‐freezing temperatures.A more pronounced decrease in variable fluorescence yield for the upper exposed than for the lower shaded surface of the needles suggested that some photoinhibition occurred during prolonged frost hardening at 50 μmol photons m−2s−1and 4°C.Reversible inhibition of photosynthesis after exposure to sub‐freezing temperatures was initially manifested as an increase of steady‐state energy‐dependent fluorescence quenching (qE) and a reduction in the rate of O2evolution. Further inhibition after treatment at still lower temperatures caused a progressive decline of steady‐state photochemical quenching (qQ) and the rate of O2evolution, whereas qEremained high. This implies an inactivation of enzymes in the photosynthetic carbon reduction cycle decreasing the consumption of ATP and NADPH, which is likely to cause an increase of membrane energization and a reduction of the primary electron acceptor (QA) of PS II. Alternatively, the changes in qQand qEmight be attributed to an inhibition of photophosphorylation. Severe, irreversible damage to photosynthesis resulted in a suppression of qEand of variable fluorescence yield, probably because the photochemical efficiency of PS II was impaired.Changes in the fast fluorescence kinetics at room temperature after severe freezing damage were interpreted as an inhibition of the electron flow from QAto the plastoquinone pool. It is suggested that irreversible freezing injury to needles of frost‐hardenedP. sylvestriscauses damage to the QB,‐protein.
Persistent xylem cross‐walls reduce the axial hydraulic conductivity in the apical 20 cm of barley seminal root axes: implications for the driving force for water movement
Authors: SANDERSON J. , WHITBREAD FIONA C. , CLARKSON D. T. 
Published: April 2006

Abstract. Xylem vessels in the apical 25 cm of barley seminal axes were examined by scanning electron microscopy of fractured freeze dried or critical point dried specimens. In the apical 11 cm, there were three cross walls cm−1 root in the central xylem vessel. The frequency then declined with distance but did not become less than 1.0 cm−1 root until the 22–25‐cm zone.Suction was applied to the proximal end of segments of seminal axes whose surfaces had been sealed with wax to prevent radial entry of water. Perfusion of the xylem with solutions of Tinopal CBS‐X revealed the conductive xylem vessels by fluorescent staining of their walls. In the apical 20 cm of the axis, only a variable number of smaller xylem vessels conduct water. Beyond this zone, the much larger central vessel becomes functional.The flow of water (Jv) in the apical zone was very much less for a given presure (△P) than in the proximal zone > 25 cm from the tip, and could be predicted by the Poiseuille equation provided the correct number of functional vessels are known. This information, together with earlier results on water uptake along the root length are used to predict the attenuation of the hydrostatic driving force for water uptake along the root length.Estimates of K+ concentrations in stelar parenchyma and xylem vessels were made by electron microproble X‐ray analysis. These results show that [K+] in the xylem vessels may be two to three times greater in the zone 1–2 cm from the root tip than in the basal zone. Such a gradient of solute potential may, to some extent, offset the decreasing influence of the leaf water potential in apical zones where xylem is not fully conductive.
The carbon canopy economy of the association between cowpea and the parasitic angiosperm Striga gesnerioides
Authors: GRAVES J. D. , PRESS M. C. , SMITH S. , STEWART G. R. 
Published: April 2006

ABSTRACTThe association between the parasite Striga gesnerioides and cowpea (Vigna unguiculata) was investigated using measurements of growth and gas exchange together with calculations of the carbon budget of the association. Striga gesnerioides has a very low photosynthetic capacity coupled with high rates of respiration. Even at photosynthetic light saturation shoots exhibit no net carbon gain. Thus S. gesnerioides is highly dependent on its host for carbon as well as for water and inorganic solutes. It is estimated that 70% of the carbon transferred from host to parasite is used in parasite respiration. Infected cowpea had a lower photosynthetic capacity, at times less than half that of uninfected plants. Infection with S. gesnerioides reduced the growth of cowpea by 75%. Calculations indicate that the loss of carbon from the host by export to the parasite is more important than reduced photosynthetic capacity of the host in accounting for the observed growth reductions.
β‐oxidation enzymes and the carnitine‐dependent oxidation of palmitate and palmitoyl CoA in mitochondria from avocado
Authors: MASTERSON C. , WOOD C. , THOMAS D. R. 
Published: April 2006

ABSTRACTTwo sites for the β‐oxidation of fatty acids in avocado (Persea americana L.) mesocarp exist. One site is the microbody, the other the mitochondrion. It is apparent that the mitochondrial membrane barrier, which remains intact after sucrose density gradient centrifugation, prevents rapid access of acyl CoA substrates to matrix β‐oxidation sites. Thus, intact mitochondria showed little β‐oxidation enzyme activity. Rupturing of the mitochondrial membrane allowed rapid access of the acyl CoA substrates to matrix sites. Consequently, in ruptured mitochondria, high O2‐oxidation enzyme activities were measured. O2 uptake studies further distinguished the two organellar sites of β‐oxidation. During palmitoyl CoA oxidation, O2 uptake was reduced by catalase and increased by KCN in the microbodies, whilst mitochondrial O2 uptake was unaffected by catalase and reduced by KCN. This reflected the differing fates of FADH2, produced during the first β‐oxidation step, in the two organelles. In addition, only the mitochondrial β‐oxidation of fatty acids was carnitine‐dependent.