bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the relationship between leaf anatomy and CO2 diffusion through the mesophyll of hypostomatous leaves
Authors: SYVERTSEN J. P. , LLOYD J. , McCONCHIE C. , KRIEDEMANN P. E. , FARQUHAR G. D. 
Published: April 2006

ABSTRACTInternal conductances to CO2 transfer from the stomatal cavity to sites of carboxylation (gi) in hypostomatous sun‐and shade‐grown leaves of citrus, peach and Macadamia trees (Lloyd et al. 1992) were related to anatomical characteristics of mesophyll tissues. There was a consistent relationship between absorptance of photosynthetically active radiation and chlorophyll concentration (mmol m−2) for all leaves, including sclerophyllous Macadamia, whose transmittance was high despite its relatively thick leaves. In thin peach leaves, which had high gi, the chloro‐plast volume and mesophyll surface area exposed to intercellular air spaces (ias) per unit leaf area were similar to those in the thicker leaves of the evergreen species. Peach leaves, however, had the lowest leaf dry weight per area (D/a), the lowest tissue density (Td) and the highest chloro‐plast surface area (Sc) exposed to ias. There were negative correlations between gi and leaf thickness or D/a, but positive correlations between gi and Sc or Sc/Td.We developed a one‐dimensional diffusion model which partitioned gi into a gaseous diffusion conductance through the ias (gias) plus a liquid‐phase conductance through mesophyll cell walls (gcw). The model accounted for a significant amount of variation (r2=0.80) in measured gi by incorporating both components. The gias component was related to the one‐dimensional path‐length for diffusion across the mesophyll and so was greater in thinner peach leaves than in leaves of evergreen species. The gcw component was related to tissue density and to the degree of chloroplast exposure to the ias. Thus the negative correlations between gi and leaf thickness or D/a related to gias whereas positive correlations between gi and Sc or Sc/Td, related to gcw. The gcw was consistently lower than gias, and thus represented a greater constraint on CO2 diffusion in the mesophylls of these hypostomatous species.
Nodule gas exchange and water potential response to rapid imposition of water deficit
Authors: PURCELL L. C. , SINCLAIR T. R. 
Published: April 2006

ABSTRACTThe permeability (P) of the gaseous diffusion barrier in the nodules of soybean [Glycine max (L.) Merr.] decreases when water deficits are extended over a 7 to 10 d period. The mechanism controlling P changes is unclear, but may result from the release of water to intercellular pathways, and an associated change in the nodule water potential. The purpose of these experiments was to impose water deficit treatments rapidly in order to determine the early sequence of the responses of nodule water potential and nodule gas exchange without the complications that arise from long‐term water deficit treatments. A vertical, split‐root system was used to separate nodule drying effects from plant water deficits by replacing humidified air that was passed over upper root nodules in well‐watered plants with dry air, or by replacing the nutrient solution that surrounded lower roots with ‐1.0 MPa polyethylene glycol (PEG) solution, or by a combination of the dry air and PEG treatments. The PEG treatment caused large decreases in both the components of nodule water potential and nodule relative water content, but there was no indication that these factors had immediate, direct effects on either nitrogenase activity or P. After 7 h of the PEG treatment a significant decrease in nitrogenase activity was found but no decrease in P was detected. These results indicate that changes in nitrogenase activity in response to water deficits precede decreases in P. Exposure of nodules to dry air in well‐watered plants had no significant effect on either nitrogenase activity or P during the 7 h treatment.
Contribution of ornithine aminotransferase to proline accumulation in NaCl‐treated radish cotyledons
Authors: HERVIEU F. , LE DILY F. , HUAULT C. , BILLARD J.‐P. 
Published: April 2006

ABSTRACTLight‐grown cotyledons of radish (Raphanus sativus L. cv National) subjected to increasing NaCI concentrations displayed a dose‐dependent accumulation of proline at the beginning of their differentiation. Neither erythromycin nor DCMU significantly affected the salt‐induced proline accumulation, which suggests that plastids may not be involved in proline synthesis. Gabaculine has been shown previously to be a powerful and irreversible inhibitor of ornithine aminotransferase [Hervieu et al. (1993) Phyto‐chemistry 34, 231–234]. This inhibitor applied in vivo at a very low concentration (1 mmol m−3) reduced considerably the salt‐induced proline accumulation of radish cotyledons. These results indicate that the ornithine pathway contributes, via an increase of ornithine aminotransferase activity, to proline synthesis, as well as the glutamate pathway, in salt‐treated cotyledons. The use of transcription and translation inhibitors revealed that the salt‐induced increase in ornithine aminotransferase activity may proceed via an activation of the translation of preformed mRNAs. The pre‐existing ornithine aminotransferase mRNAs in radish seeds may be an important adaptation to NaCI, leading to proline accumulation at the beginning of seedling growth.
An open‐air system for exposure of young forest trees to sulphur dioxide and ozone
Authors: McLEOD A. R. 
Published: April 2006

ABSTRACTThe development, construction and operation of an open‐air fumigation system for exposing young forest trees to controlled concentrations of sulphur dioxide and ozone is described. A computer simulation of gas dispersion was used to design an array of pipework sources which minimized spatial variability in exposure concentrations. Five fumigation plots were constructed using the design and were used to fumigate trees during a 7 year study known as the Liphook Forest Fumigation Project. Rates of gas release were controlled by a small computer to follow predetermined patterns of sulphur dioxide concentration and to maintain an elevation above ambient ozone concentration. Effective control of exposure was demonstrated, and examples of experimentally produced concentration frequency distributions are provided. The advantages and shortcomings of the system are discussed with recommendations for future improvements.
The effects of SO2 and O3 fumigation on acid deposition and foliar leaching in the Liphook forest fumigation experiment
Authors: SKEFFINGTON R. A. , SUTHERLAND P. M. 
Published: April 2006

ABSTRACTThe ambient pollution climate at the Liphook forest fumigation site, where coniferous trees were fumigated with SO2 and O3, for 4 years under field conditions, was characteristic of the fringes of the areas where pollutant effects are a problem. Experimental treatments increased SO2 concentrations to levels more characteristic of Eastern Europe, and summer O3 concentrations by 30%. Deposition of SO2 to the soil between the trees (inferred from shallow lysimeters) was significant, the deposition velocity being 2–1 mms−1. Deposition to Scots pine and Sitka spruce canopies was greater, deposition velocities being 8.5 and 9.4 mm s−1, respectively. These high values may perhaps be explained by co‐deposition with NH3. Calculations assume that dry deposition was the sole source of SO42− gain in throughfall, and that there was no significant retention by the trees. There was a trend for O3 to enhance SO2 deposition to both soil and trees. Fumigation with SO2 led to a significant increase in leaching of cations from foliage. Each species neutralized about 63% of the dry‐deposited SO2, predominantly by ion exchange for Ca and K. Equations are provided which allow calculation of foliar leaching given SO2 concentrations or SO42− deposition. Fumigation increased the rate of nutrient cycling considerably, without affecting foliar concentrations or damaging the trees. Ozone treatments did not enhance foliar leaching, calling into question some suggested mechanisms for the causes of forest decline.
The effect of open‐air fumigation with SO2 and O3 on carbohydrate metabolism in Scots pine (Pinus sylvestris) and Norway spruce (Picea abies)
Authors: PEACE E. A. , LEA P. J. , DARRALL N. M. 
Published: April 2006

ABSTRACTThe carbohydrate metabolism of the needles of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) has been examined in trees that were exposed to SO2, and O3, in an open‐air fumigation experiment located in the Liphook forest in southern England. Two‐year‐old seedlings were planted in 1985 in seven experimental plots. Five plots received fumigation treatments of SO2, O3 or a combination of these gases to give a 2 × 3 factorial design with one additional ambient plot Fumigation with SO2, occurred from May 1987 to December 1990 and O3, fumigation occurred from March to December 1988, May to December 1989 and February to December 1990. Five samples of needles for investigation of carbohydrate metabolism were taken between February and July 1989.The concentrations of soluble carbohydrates (including sucrose and hexoses) were greatly reduced in the needles taken from Scots pine growing in the treated plots, and were also reduced, but to a lesser extent, in the needles taken from Norway spruce. Little variation in the concentration of starch in the needles of either species was detected. The activities of the two final enzymes of sucrose synthesis, sucrose phosphate synthase and sucrose 6‐phos‐phate phosphatase, were greatly reduced in the needles of Scots pine and were also reduced, but to a lesser extent, in the needles of Norway spruce in the fumigated plots. These reductions could be correlated with decreases in rates of photosynthetic CO2 assimilation determined by independent groups of researchers working on the Liphook site.
A critical appraisal of a combined stomatal‐photosynthesis model for C3 plants
Authors: LEUNING R. 
Published: April 2006

ABSTRACTGas‐exchange measurements on Eucalyptus grandis leaves and data extracted from the literature were used to test a semi‐empirical model of stomatal conductance for CO2gSc=go+a1A/(cs‐I) (1+Ds/Do)]where A is the assimilation rate; Ds and cs are the humidity deficit and the CO2 concentration at the leaf surface, respectively; g0 is the conductance as A → 0 when leaf irradiance → 0; and D0 and a1 are empirical coefficients. This model is a modified version of gsc=a1A hs/cs first proposed by Ball, Woodrow & Berry (1987, in Progress in Photosynthesis Research, Martinus Mijhoff, Publ., pp. 221–224), in which hs is relative humidity. Inclusion of the CO2 compensation point, τ, improved the behaviour of the model at low values of cs, while a hyperbolic function of Ds for humidity response correctly accounted for the observed hyperbolic and linear variation of gsc and ci/cs as a function of Ds, where Ci is the intercellular CO2 concentration. In contrast, use of relative humidity as the humidity variable led to predictions of a linear decrease in gsc and a hyperbolic variation in ci/cs as a function of Ds, contrary to data from E. grandis leaves. The revised model also successfully described the response of stomata to variations in A, Ds and cs for published responses of the leaves of several other species. Coupling of the revised stomatal model with a biochemical model for photosynthesis of C3 plants synthesizes many of the observed responses of leaves to light, humidity deficit, leaf temperature and CO2 concentration. Best results are obtained for well‐watered plants.
The cellular pathway of photosynthate transfer in the developing wheat grain. III. A structural analysis and physiological studies of the pathway from the endosperm cavity to the starchy endosperm
Authors: WANG H. L. , PATRICK J. W. , OFFLER C. E. , WANG X. ‐D. 
Published: April 2006

ABSTRACTThe cellular pathway of sucrose transfer from the endosperm cavity to the starchy endosperm of developing grains of wheat (Triticum turgidum) has been elucidated. The modified aleurone and sub‐aleurone cells exhibit a dense cytoplasm enriched in mitochondria and endoplasmic relicilium. Significantly, the sub‐aleurone cells are characterized by secondary wall ingrowths. Numerous plasmodesmata interconnect all cells between the modified aleurone and starchy endosperm. The pro‐tonophore carbonylcyanide‐m‐chlorophenyl hydrazone (CCCP) slowed [14C]sucrose uptake by grain tissue slices enriched in modified aleurone and sub‐aleurone cells but had no effect on uptake by the starchy endosperm. The fluorescent weak acid sulphorhodamine G (SRG) was preferentially accumulated by the modified aleurone and sub‐aleurone cells, and this uptake was sensitive to CCCP. The combined plasma membrane surface areas of the modified aleurone and sub‐aleurone cells appeared to be sufficient to support the in vivo rates of sucrose transfer to the starchy endosperm. Plasmolysis of intact excised grain inhibited [14C]sucrose transfer from the endosperm cavity to the starchy endosperm. The sulphydryl group modifier p‐chloromercuribenzenesulphonie acid (PCMBS) decreased [14C]sucrose uptake by the modified aleurone and sub‐aleurone cells but had little effect on uptake by the starchy endosperm. In contrast, when PCMBS and [14C]sucrose were supplied to the endosperm cavity of intact excised grain, PCMBS slowed accumulation by all tissues equally. Estimates of potential sucrose fluxes through the interconnecting plasmodesmata were found to be within the published range. It is concluded that the bulk of sucrose is accumulated from the endosperm cavity by the modified aleurone and sub‐aleurone cells and subsequently transferred through the symplast to the starchy endosperm.
The concentration of xylem sap constituents in root exudate, and in sap from intact, transpiring castor bean plants (Ricinus communis L.)
Authors: SCHURR U. , SCHULZE E. ‐D. 
Published: April 2006

ABSTRACTRoot exudates were sampled from detopped root systems of castor bean (Ricinus communis). Different volume flux rates were imposed by changing the pneumatic pressure around the root system using a Passioura‐type pressure chamber. The concentrations of cations, anions, amino acids, organic acids and abscisic acid decreased hyperbolically when flux rates increased from pure root exudation up to values typical for transpiring plants. Concentrations at low and high fluxes differed by up to 40 times (phosphate) and the ratio of substances changed by factors of up to 10. During the subsequent reduction of flux produced by lowering the pneumatic pressure in the root pressure chamber, the concentrations and ratios of substances deviated (at a given flux rate) from those found when flux was increased. The flux dependence of exudate composition cannot therefore be explained by a simple dilution mechanism. Xylem sap samples from intact, transpiring plants were collected using a Passioura‐type root pressure chamber. The concentrations of the xylem sap changed diurnally. Substances could be separated into three groups: (1) calcium, magnesium and amino acid concentrations correlated well with the values expected from their concentration‐flux relationships, whereas (2) the concentrations of sulphate and phosphate deviated from the expected relationships during the light phase, and (3) nitrate and potassium concentrations in intact plants varied in completely the opposite manner from those in isolated root systems. Abscisic acid concentrations in the root exudate were dependent on the extent of water use and showed strong diurnal variations in the xylem sap of intact plants even in droughtstressed plants. Calculations using root exudates overestimated export from the root system in intact plants, with the largest deviation found for proton flux (a factor of 10). We conclude that root exudate studies cannot be used as the sole basis for estimating fluxes of substances in the xylem of intact plants. Consequences for studying and modelling xylem transport in whole plants are discussed.
Mitochondria contribute to increased photosynthetic capacity of leaves of winter rye (Secale cereale L.) following cold‐hardening
Authors: HURRY V. , TOBIÆSON M. , KRÖMER S. , GARDESTRÖM P. , ÖQUIST G. 
Published: April 2006

ABSTRACTCold‐hardening of winter rye (Secale cereale L. cv. Musketeer) increased dark respiration from −2.2 to −3.9 μmol O2 m−2s−1 and doubled light‐and CO2‐saturated photosynthesis at 20°C from 18.1 to 37.0μmol O2 m−2 s−1 We added oligomycin at a concentration that specifically inhibits oxidative phosphorylation to see whether the observed increase in dark respiration reflected an increase in respiration in the light, and whether this contributed to the enhanced photosynthesis of cold‐hardened leaves. Oligomycin inhibited light‐ and CO2‐saturated rates of photosynthesis in non‐hardened and cold‐hardened leaves by 14 and 25%, respectively, and decreased photochemical quenching of chlorophyll a fluorescence to a greater degree in cold‐hardened than in non‐hardened leaves. These data indicate an increase both in the rate of respiration in the light, and in the importance of respiration to photosynthesis following cold‐hardening. Analysis of metabolite pools indicated that oligomycin inhibited photosynthesis by limiting regeneration of ribulose‐1,5‐bisphosphate. This limitation was particularly severe in cold‐hardened leaves, and the resulting low 3‐phospho‐glycerate pools led to a feed‐forward inhibition of sucrose‐phosphate synthase activity. Thus, it does not appear that oxidative phosphorylation supports the increase in photo‐synthetic O2 evolution following cold‐hardening by increasing the availability of cytosolic ATP. The data instead support the hypothesis that the mitochondria function in the light by using the reducing equivalents generated by non‐cyclic photosynthetic electron transport.
Photomorphogenesis and canopy dynamics. Phytochrome‐mediated proximity perception accounts for the growth dynamics of canopies of Populus trichocarpa × deltoides‘Beaupré’
Authors: GILBERT I. R. , SHAVERS G. P. , JARVIS P. G. , SMITH H. 
Published: April 2006

ABSTRACTThe phytochrome family of signal‐transducing photoreceptors provides plants with the capacity to perceive variations in the relative fluxes of red (R) and far‐red (FR) radiation. This capacity has been proposed to be of ecological value in the perception of the proximity of neighbouring plants and the consequent induction of shade avoidance responses. The work reported here has evaluated this potential by determining quantitatively the effect of neighbour proximity on the growth of canopies of Populus trichocarpa×deltoides‘Beaupré’ trees, and relating the measured variables to the long‐term vectoral radiation quality inside each canopy. The spectral distribution of radiation inside four canopies of Populus trichocarpa×deltoides‘Beaupre’ of different densities was monitored throughout the growing season. Spectral distributions inside the canopies were measured in 10° wedges at different heights and angles. The results are presented as PFD over 400–700 nm (PFD400–700) and PFD over 400–800 nm (PFD400–700). Results are also presented for the calculated phytochrome photoequilibrium (Pfr/P) and red:far‐red ratio (R:FR). Data are presented as in‐canopy angular and height profiles, and as diurnal and seasonal variations. PFD400–700 and Pfr/P were found to be reduced inside each canopy, the reduction being greatest in the most dense canopy, and least in the most open canopy. At any height within each canopy, calculated Pfr/P decreased linearly with time throughout the growing season, until leaf senescence began. The reduction was greater in the denser canopies and was found to be similar for three consecutive field seasons. Linear relationships were found between plant stem growth rate, plant spacing and Pfr/P calculated from radiation propagated approximately horizontally within the canopies. The findings support the role of phytochrome in proximity perception in the natural environment and provide a quantitative basis for investigating the competitive interactions between plants growing in dense stands. The hypothesis is proposed that the dynamics of developing or regenerating canopies can be accounted for on the basis of phytochrome‐mediated perception of the proximity of neighbouring plants.
Comparative microscopic and enzymatic characterization of the leaf necrosis induced in Arabidopsis thaliana by lead nitrate and by Xanthomonas campestris pv. campestris after foliar spray
Authors: LUMMERZHEIM M. , SANDRONI M. , CASTRESANA C. , DE OLIVEIRA D. , VAN MONTAGU M. , ROBY D. , TIMMERMAN B. 
Published: April 2006

ABSTRACTThe heavy metal lead was administered to Arabidopsis thaliana plants by foliar spray. At a concentration of l4mol m−3, the lead nitrate suspension induced densely distributed necrotic lesions on A. thaliana leaves. A number of Arabidopsis ecotypes were tested and a differential response to heavy‐metal toxicity was noted. The necrosis provoked as a result of the phytotoxic effect of lead had a similar appearance to the necrotic lesions observed in a hypersensitive response of A. thaliana to inoculation with Xanthomonas campestris pv. campestris (Lummerzheim et al. 1993, Molecular Plant‐Microbe Interactions 6, 532–544). In addition to this phenotypic resemblance, accumulation of polyphenols and callose depositions observed by microscopic analysis, as well as increases in the activities of the stress‐related proteins β1,3‐glucanases, chitinases and peroxidases, revealed significant similarities in the plant response to the two treatments examined, lead toxicity and bacterial infection. The results allow the establishment of markers for both types of stress.
Multiple xenobiotic‐inducible P450s are involved in alkoxycoumarin and alkoxyresorufin metabolism in higher plants
Authors: BATARD Y. , ZIMMERLIN A. , LE RET M. , DURST F. , WERCK‐REICHHART D. 
Published: April 2006

ABSTRACTO‐Dealkylation of two series of fluorescent 7‐alkoxy‐coumarins and 7‐alkoxyphenoxazones by plant cytochrome P450s was investigated in Helianthus tuberosus tuber tissues treated with prototype P450 inducers, environmental pollutants or agrochemicals. Methoxy‐, ethoxy‐, propoxy‐and butoxycoumarins and methoxy‐ and ethoxyresorufins were metabolized by fplant microsomes. Dealkylation of pentoxy‐ and benzyloxyresorufins was not detected. All dealkylating activities were enhanced by aging plant tissues in the presence of xenobiotics, in some cases up to 20‐fold relative to the activities detected in control tissues. Increases in total P450 in the same tissues never exceeded 3‐fold. The isozymes induced by prototype P450 inducers clearly differed from those in mammalian liver. That multiple P450s with overlapping substrate specificities were involved in the metabolism of both alkoxycoumarins and alkoxyresorufins was demonstrated by (1) the differential induction of the activities in response to exposure to xenobiotics, (2) the differential inhibition of the activities by clotrimazole, paclobutrazole and tetcyclacis in aminopyrine and benzo(a)pyrene‐treated tissues, and(3) the selective inhibition observed with antibodies raised against purified ethoxycoumarin deethylase fractions. Our results suggest that the measurement of the dealkylation of such fluorescent substrates in plants might be useful to monitor environmental pollution.