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Biomedical subjects

E Dreyer

Publications and source records attributed to E Dreyer.

At least 19 recordsLinked to original sources
PubMed2006

Temperature response of photosynthesis and internal conductance to CO2: results from two independent approaches.

The internal conductance to CO(2) transfer from intercellular spaces to chloroplasts poses a major limitation to photosynthesis, but few studies have investigated its temperature response. The aim of this study was to determine the temperature response of photosynthesis and internal conductance between 10 degrees C and 35 degrees C in seedlings of a deciduous forest tree species, Quercus canariensis. Internal conductance was estimated via simultaneous measurements of gas exchange and chlorophyll fluorescence ("variable J method"). Two of the required parameters, the intercellular photocompensation point (C(i)*) and rate of mitochondrial respiration in the light (R(d)), were estimated by the Laisk method. These were used to calculate the chloroplastic photocompensation point (Gamma*) in a simultaneous equation with g(i). An independent estimate of internal conductance was obtained by a novel curve-fitting method based on the curvature of the initial Rubisco-limited portion of an A/C(i) curve. The temperature responses of the rate of Rubisco carboxylation (V(cmax)) and the RuBP limited rate of electron transport (J(max)) were determined from chloroplastic CO(2) concentrations. The rate of net photosynthesis peaked at 24 degrees C. C(i)* was similar to reports for other species with a C(i)* of 39 micromol mol(-1) at 25 degrees C and an activation energy of 34 kJ mol(-1). Gamma* was very similar to the published temperature response for Spinacia oleracea from 20 degrees C to 35 degrees C, but was slightly greater at 10 degrees C and 15 degrees C. J(max) peaked at 30 degrees C, whereas V(cmax) did not reach a maximum between 10 degrees C and 35 degrees C. Activation energies were 49 kJ mol(-1) for V(cmax) and 100 kJ mol(-1) for J(max). Both methods showed that internal conductance doubled from 10 degrees C to 20 degrees C, and then was nearly temperature-independent from 20 degrees C to 35 degrees C. Hence, the temperature response of internal conductance could not be fitted to an Arrhenius function. The best fit to estimated g(i) was obtained with a three-parameter log normal function (R(2)=0.98), with a maximum g(i) of 0.19 mol m(-2) s(-1) at 29 degrees C.

Carbon Dioxide↗
PubMed2006

Relationships between optically assessed polyphenols and chlorophyll contents, and leaf mass per area ratio in woody plants: a signature of the carbon-nitrogen balance within leaves?

Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two optical leaf-clips, SPAD-502 and Dualex, respectively. The area-based measurements were transformed into mass-based data by taking into account the leaf dry mass per area (LMA). Measurements were performed on forest trees and on saplings grown under controlled conditions. While LMA increased with irradiance along a vertical transect in a beech canopy or in saplings grown under different and increasing irradiance levels, mass-based EPhen (EPhen(m)) increased, whereas mass-based Chl (Chl(m)) decreased. This was a signature of a gradual switch of investment from protein into polyphenol production. A similar signature was obtained in saplings grown on nitrogen-deficient soil with respect to fertilized controls. However, nitrogen effects remained moderate compared to irradiance-induced effects. EPhen(m) and Chl(m) both declined with plant ageing-induced increases in LMA, under all tested growth conditions. This was a signature of an accumulation of dry matter that diluted Chl and EPhen. The described competition between Chl and EPhen in leaves fits well with the predictions of the Protein Competition Model (PCM), that is, that the total leaf mass-based polyphenols content (Phen(t)) is controlled by the competition between protein and polyphenol biosynthetic pathways and its metabolic regulation.

Carbon↗
PubMed2005

Cavitation vulnerability in roots and shoots: does Populus euphratica Oliv., a poplar from arid areas of Central Asia, differ from other poplar species?

Populus euphratica is a poplar species growing in arid regions of Central Asia, where its distribution remains nevertheless restricted to river-banks or to areas with an access to deep water tables. To test whether the hydraulic architecture of this species differs from that of other poplars with respect to this ecological distribution, the vulnerability to cavitation of P. euphratica was compared with that of P. alba and of P. trichocarpa x koreana. The occurrence of a potential hydraulic segmentation through cavitation was also investigated by assessing the vulnerability of roots, stems, and leaf mid-rib veins. Cryo-scanning electron microscopy (cryo-SEM) was used to assess the level of embolism in fine roots and leaf mid-ribs and a low pressure flowmeter (LPFM) was used for stems and main roots. The cryo-SEM technique was validated against LPFM measurements on paired samples. In P. alba and P. trichocarpa x koreana, leaf mid-ribs were more vulnerable to cavitation than stems and roots. In P. euphratica, leaf mid-ribs and stems were equally vulnerable and, contrary to what has been observed in other species, roots were significantly less vulnerable than shoots. P. euphratica was by far the most vulnerable. The water potential inducing 50% loss of conductivity in stems was close to -0.7 MPa, against approximately -1.45 MPa for the two others species. Such a large vulnerability was confirmed by recording losses of conductivity during a gradual drought. Moreover, significant stem embolism was recorded before stomatal closure, indicating the lack of an efficient safety margin for hydraulic functions in this species. Embolism was not reversed by rewatering. These observations are discussed with respect to the ecology of P. euphratica.

Asia↗
PubMed2001

Temperature response of leaf photosynthetic capacity in seedlings from seven temperate tree species.

Seedlings of seven temperate tree species (Acer pseudoplatanus L., Betula pendula Roth, Fagus sylvatica L., Fraxinus excelsior L., Juglans regia L., Quercus petraea Matt. Liebl. and Quercus robur L.) were grown in a nursery under neutral filters transmitting 45% of incident global irradiance. During the second or third year of growth, leaf photosynthetic capacity (i.e., maximal carboxylation rate, Vcmax, maximal photosynthetic electron transport rate, Jmax, and dark respiration, Rd) was estimated for five leaves from each species at five or six leaf temperatures (10, 18, 25, 32, 36 and 40 degrees C). Values of Vcmax and Jmax were obtained by fitting the equations of the Farquhar model on response curves of net CO2 assimilation (A) to sub-stomatal CO2 mole fraction (ci), at high irradiance. Primary parameters describing the kinetic properties of Rubisco (specificity factor, affinity for CO2 and for O2, and their temperature responses) were taken from published data obtained with spinach and tobacco, and were used for all species. The temperature responses of Vcmax and Jmax, which were fitted to a thermodynamic model, differed. Mean values of Vcmax and Jmax at a reference temperature of 25 degrees C were 77.3 and 139 micromol m(-2) s(-1), respectively. The activation energy was higher for Vcmax than for Jmax (mean values of 73.1 versus 57.9 kJ mol(-1)) resulting in a decrease in Jmax/Vcmax ratio with increasing temperature. The mean optimal temperature was higher for Vcmax than for Jmax (38.9 versus 35.9 degrees C). In addition, differences in these temperature responses were observed among species. Temperature optima ranged between 35.9 and above 45 degrees C for Vcmax and between 31.7 and 43.3 degrees C for Jmax, but because of data scatter and the limited range of temperatures tested (10 to 40 degrees C), there were few statistically significant differences among species. The optimal temperature for Jmax was highest in Q. robur, Q. petraea and J. regia, and lowest in A. pseudoplatanus and F. excelsior. Measurements of chlorophyll a fluorescence revealed that the critical temperature at which basal fluorescence begins to increase was close to 47 degrees C, with no difference among species. These results should improve the parameterization of photosynthesis models, and be of particular interest when adapted to heterogeneous forests comprising mixtures of species with diverse ecological requirements.

Acclimatization↗
PubMed2001

Effects of drought stress and high density stem inoculations with Leptographium wingfieldii on hydraulic properties of young Scots pine trees.

We examined drought-induced changes in susceptibility of potted Scots pine (Pinus sylvestris L.) trees to a bark-beetle associated fungus (Leptographium wingfieldii Morelet, from the bark beetle Tomicus piniperda L.). Five-year-old field-grown trees were transplanted to 50-l pots and grown for 1 year before the treatments were applied. Trees in the drought treatment were subjected to several successive, 3-week-long drought cycles, with predawn water potential dropping below -2 MPa at peak drought intensity. The experimental drought cycles were more severe than the natural drought episodes usually recorded in Scots pine stands. Trees were then mass-inoculated with L. wingfieldii at a density close to the critical threshold density of inoculations (400 m(-2)) above which tree resistance is overcome. Inoculation of well-watered trees resulted in induced reaction zones around the inoculation points and very limited damage (resinosis) in the sapwood. Drought alone had no long-lasting consequences on tree water relations, except for a decrease in hydraulic conductance in the youngest segments of the main stem. However, the combination of mass-inoculation and drought stress after inoculation resulted in a dramatic loss of stem hydraulic conductivity that was paralleled by conspicuous damage to the sapwood (resinosis, drying and blue staining). There was a close correlation between amount of visible sapwood damage and loss of hydraulic conductivity. The intensity of induced reactions in the phloem was unaffected by drought stress. We conclude that tree defence against L. wingfieldii is decreased during severe drought stress, resulting in changes in the spread and action of the fungus in the sapwood but not in the phloem.

Animals↗
PubMed2000

Immunohistochemical and ultrastructural evaluation of the effects of phosphoric acid etching on dentin proteoglycans.

It has been reported that phosphoric acid (PA) produces structural and molecular alterations in dentin collagen fibrils; however, no relevant information exists on the influence of etching with PA on dentin non-collagenous macromolecules. The present study investigated, by immunohistochemistry and ultrastructural histochemistry, the behavior of dentin proteoglycans (PG) after etching human dentin samples with 35% PA gel (thickened with colloidal silica) or with a 35% PA liquid for 15, 30 and 120 s. Immunolabeling with a mouse monoclonal anti-chondroitin sulfate antibody demonstrated that glycosaminoglycans (GAG) were preserved within dentinal tubules opened to the surface after etching with PA gel. In addition, the cationic tracer polyethyleneimine, used for the ultramicroscopic localization of PG anionic sites, revealed that treatment of dentin samples with PA gel preserved the polyanionic peritubular PG in the etched area. On the other hand, etching with the PA liquid produced loss of peritubular GAG and PG anionic sites in the etched dentin surface. The results obtained indicated that similar concentrations of PA in gel or liquid formulations differently affect the organization of dentin PG. The clinical significance of these in vitro findings and the structural and molecular interactions of dentin PG with adhesive systems are still unknown.

Acid Etching, Dental↗
PubMed1997

Stomatal conductance, growth and root signaling in young oak seedlings subjected to partial soil drying.

Leaf conductance, water relations, growth, and abscisic acid (ABA) concentrations in xylem sap, root apices and leaves were assessed in oak seedlings (Quercus robur L.) grown with a root system divided between two compartments and subjected to one of four treatments: (a) well watered, WW; (b) half of root system exposed to soil drying and half kept well watered, WD; (c) whole root system exposed to drought, DD; and (d) half of root system severed, RE. Sharp decreases in plant stomatal conductance, leaf water potential, hydraulic conductance and leaf growth were observed during DD treatment. No significant differences in plant leaf water potential and stomatal conductance were detected between the WW and WD treatments. Nevertheless, the WD treatment resulted in inhibition of leaf expansion and stimulation of root elongation only in the well-watered compartment. Abscisic acid concentrations did not change in leaves, root tips, or xylem sap of WD- compared to WW-treated plants. Increased concentrations of ABA were observed in xylem sap from DD-treated plant roots, but the total flux of ABA to shoots was reduced compared to that in WW-treated plants, because of decreases in transpiration flux. Similar plant responses to the WD and RE treatments indicate that the responses observed in the WD-treated plants were probably not triggered by a positive signal originating from drying roots.

Journal Article↗
PubMed1994

Axial and radial water flow in the trunks of oak trees: a quantitative and qualitative analysis.

Axial water flow in the trunks of mature oak trees (Quercus petraea (Matt.) Liebl. and Q. robur L.) was studied by four independent techniques: water absorption from a cut trunk, sap flowmeters, heat pulse velocity (HPV) and thermoimaging. Estimation of the total water flow with sap flowmeters, HPV and water absorption yielded comparable results. We concluded from dye colorations, thermograms and axial profiles of sap flow and heat pulse velocity that, in intact trunks, most of the flow occurred in the current-year ring, where early-wood vessels in the outermost ring were still functional. Nevertheless, there was significant flow in the older rings of the xylem. Total water flow through the trunk was only slightly reduced when air embolisms were artificially induced in early-wood vessels, probably because there was little change in hydraulic conductance in the root-leaf sap pathway. Embolization of the current-year vessels reactivated transport in the older rings.

Journal Article↗
PubMed1993

Photosynthesis of oak leaves under water stress: maintenance of high photochemical efficiency of photosystem II and occurrence of non-uniform CO(2) assimilation.

Net CO(2) assimilation rates (A), stomatal conductance to water vapor (g(w)), photosynthetic O(2) evolution in 5% CO(2) (A(max)) and photochemical efficiency of photosystem II were monitored in leaves of young oak saplings (Quercus petraea Matt. Liebl.) in response to increasing drought. Both A and g(w) declined rapidly as soon as predawn leaf water potential dropped below -1.0 MPa. The calculated intercellular concentration of CO(2) first declined and then increased again as drought intensity increased, suggesting that both stomatal closure and a decreased ability of mesophyll chloroplasts to fix available CO(2) were involved in the drought-induced reductions in A and g(w). However, this assumption was not supported by the observations that, with increasing drought, the decline in A(max) was limited, and the photochemistry of photosystem II and the quantum yield of light-driven electron transport remained stable. Autoradiograms of (14)CO(2)-fed leaves revealed non-uniform assimilation rates during water stress. The consequences of a potential artifact induced by this patchiness on the calculation of intercellular CO(2) concentration are discussed.

Journal Article↗
PubMed1993

New methods for assessment of enzyme activity: do they help to optimize enzyme treatment?

Several factors related to the patient and the pancreatin formulation influence the efficacy of enzyme supplementation. Up to now, only few tests exist to judge the efficacy of enzyme replacement therapy in pancreatic insufficiency. Tube tests and fecal fat excretion studies are cumbersome, time-consuming and unpleasant. Recently, several breath tests for the detection of pancreatic insufficiency have been developed. The cholesteryl octanoate breath test differentiated between healthy controls and patients with pancreatic insufficiency already after a 30-min collection period. Using this test, it was demonstrated that a pancreatin preparation containing small microspheres (1.0-1.2 mm) induces high duodenal lipolytic activity parallel to gastric emptying of food. In contrast, the gastric emptying of large microspheres (1.8-2.0 mm) is significantly delayed. The cholesteryl octanoate breath test detects pancreatic insufficiency within 30-60 min and offers the possibility of monitoring the in vivo release of pancreatin preparations.

Amylases↗
PubMed1992

Phosphorylation and activation of tyrosine hydroxylase in PC18 cells: a cell line derived from rat pheochromocytoma PC12 cells.

Treatment of rat pheochromocytoma PC18 cells (a variant subclone of PC12 cells) with forskolin produced increased activity and phosphorylation of tyrosine hydroxylase. In contrast, treatment of the PC18 cells with 56 mM K+, A23187, phorbol-12-myristate-13-acetate (PMA) or phorbol-12,13-dibutyrate (PDB) did not affect the activity and only slightly increased the phosphorylation of tyrosine hydroxylase. None of the treatments except forskolin increased cyclic AMP levels in PC18 cells. Furthermore, 45Ca2+ uptake into PC18 cells was not affected by 56 mM K+, PDB or forskolin; however, A23187 increased 45Ca2+ uptake 4-fold over basal uptake. Nevertheless, no activation and little increase in phosphorylation of tyrosine hydroxylase was observed in PC18 cells treated with A23187. When tyrosine hydroxylase levels in PC18 cells were elevated by treatment with dexamethasone, activation of tyrosine hydroxylase by 56 mM K+, PDB or A23187 was still not observed. Both purified Ca2+/calmodulin-dependent protein kinase and cyclic AMP-dependent protein kinase catalyzed the phosphorylation of tyrosine hydroxylase purified from PC18 cells in vitro. Furthermore, crude cell extracts from PC12 cells and PC18 cells possessed Ca2+/calmodulin-dependent protein kinase activity that catalyzed the phosphorylation of purified tyrosine hydroxylase. These results suggest that tyrosine hydroxylase activity in PC18 cells is regulated by a cyclic AMP-dependent mechanism. However, due to a number of abnormalities the Ca(2+)-dependent mechanisms do not result in the activation of tyrosine hydroxylase and only slightly increase the phosphorylation of the enzyme in PC18 cells.

Animals↗
PubMed1992

The mechanism of internalization of platelet-activating factor in activated human neutrophils. Enhanced transbilayer movement across the plasma membrane.

Recent studies suggest that cellular internalization of platelet-activating factor (PAF), a potent ether phospholipid mediator of inflammation, is modulated by, as yet undefined cellular mechanisms. Using an albumin extraction method, the internalization of PAF and several PAF analogues was studied in the resting and stimulated human neutrophil. Our data demonstrate that internalization of these analogues is largely dependent on the state of cellular activation and that the process is not specific for certain unique structural features of the PAF molecule including the 1-position ether linkage, 2-position acetyl substitution, or choline polar head group. Furthermore, the internalization process was shown not to be dependent on the PAF receptor, metabolism of the molecule, or the process of endocytosis. Data are presented to suggest that the route of internalization of PAF is enhanced transbilayer movement (flipping) across the plasma membrane occurring as a result of changes in membrane physical properties accompanying cellular activation. It is proposed that in addition to enhanced internalization of PAF, modulation of PAF biosynthesis and net release from the stimulated neutrophil may be consequences of enhanced transbilayer movement of PAF across the activated plasma membrane.

Biological Transport↗
PubMed1992

Effects of severe dehydration on leaf photosynthesis in Quercus petraea (Matt.) Liebl.: photosystem II efficiency, photochemical and nonphotochemical fluorescence quenching and electrolyte leakage.

Leaf disks of oak (Quercus petraea (Matt.) Liebl.) trees were subjected to rapid dehydration in air in the dark. Optimal photochemical efficiency of PS II (F(v)/F(M)), photochemical (q(P)) and nonphotochemical (q(NP)) quenchings of chlorophyll a fluorescence, and relative conductivity (C(r)) of leaf disk diffusate were measured in leaf disks with different water deficits (D). No effect of dehydration was detected before D reached values above 0.30. When D increased from 0.30 to 0.50, q(NP) increased without any change in q(P), which may indicate that thermal deexcitation of PS II increased, allowing reduced photochemical activity and maintenance of a large pool of oxidized primary acceptors (QA), although carbon reduction was impaired. Large changes in electron transport chain activity, leading to decreases in both q(P) and q(NP), appeared only in leaf disks subjected to severe water deficits (D > 0.60) and were correlated with a modification of membrane structure. However, stability of F(v)/F(M) indicated that the functional integrity of PS II was not altered until D reached values above 0.75. We conclude that the photosynthetic apparatus of Q. petraea is rather insensitive to leaf dehydration per se during drought under natural conditions.

Journal Article↗
PubMed1990

Chromatic induction and brightness contrast: a relativistic color model.

It has been suggested that object colors in a colored environment are the result of combining in perception the (relative) brightness of each spectral component rather than of just mixing the spectral luminances. We tested this hypothesis with the following experiment: A pair of center-surround targets made of colored papers was illuminated with trichromatic white light. Two identical central color plates (test and match field, respectively) were surrounded by frames of different colors and thus looked different because of simultaneous color contrast. Observers were asked to match the colors by changing the illumination of the match field by means of a color-mixture projector (color match, CM). This color-matched reflectance was measured with a photometer, and its CIE coordinates were determined. We then illuminated the display with one of the three primaries that made up our trichromatic white light. The different reflectances of the different surrounds at each primary induced simultaneous brightness contrast. The brightnesses of the two central plates were therefore different. Observers were asked to change the intensity of the illumination of the match field at the respective primary so that it looked equally bright as the test field. This procedure was repeated for each primary (primary brightness match, PBM). Then the whole display except for the match field was illuminated with the trichromatic white as before, while the latter was illuminated with a trichromatic mixture consisting of the primaries at the intensities as set in the PBM experiment, and the CIE values were determined with the photometer. The CIE values of the match field after the CM and PBM procedures were nearly identical. This indicates that composite colors are composed in perception by combining the scaled (or relative) brightness of each spectral component and that this brightness scaling is largely restricted to interactions in the same spectral region. The results are compared with those of other models concerned with contrast colors as well as with neurophysiological data. Some limitations are mentioned.

Adult↗
PubMed1987

A semi-automated data processing system for root growth analysis: application to a growing oak seedling.

A data acquisition and processing system for analyzing root structure and growth is presented. Two-dimensional drawings are made of root systems growing against the inclined, transparent wall of a rhizotron. For analysis, a root is treated as a number of straight segments between points determined by the position of root apices at successive times of observation and the insertion points of lateral roots. The coordinates of the points are digitized by means of a graphics tablet and the description of the root system completed with information about root branching pattern and root order. From the recorded data, various root characteristics and growth parameters can be computed with a program available from the authors. Use of the data processing system in studies of root architecture is discussed and its application in the analysis of root growth of a pedunculate oak seedling (Quercus robur L.) reported.

Journal Article↗