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PubMed2006

Immune modulation using mistletoe (Viscum album L.) extracts Iscador.

One repeatedly finds that mistletoe (Viscum album L.) extracts show immune-modulating effects. This is also true in many cases in the experimental setting. Many of the experimental trials cannot, however, be transferred to the clinical situation - or only in a limited way. The aim of this work was to pursue the question of the extent to which the function of immune-competent cells can be influenced by mistletoe extracts. To do this, 3 clinical studies were carried out. Results from the first two studies will be presented here. In a prospective observational study with defined inclusion and exclusion criteria, the impact of two different doses of Iscador M (Malus) or Iscador Qu (Quercus) on the function and number of T-lymphocytes from tumor patients was studied. The immunological tests took place monthly during the first six months. Thirty-one patients were included in the slow dose group and 36 patients in the group with swift dose escalation. It was postulated that too swift increase in dosage would lead to stronger local reactions and impairment of the stimulation capacity of T-cells taken ex vivo and incubated for 72 h. The evaluation showed that patients with stronger local reactions at the injection site have an impairment of mitogen-induced stimulation capacity of T-cells. However, patients with stronger local reaction showed a significant decrease of HLA-DR+ T cells as compared to patients In a GCP-conform, controlled bicentric phase II study the aim was to investigate the efficacy of a perioperative intravenous mistletoe extract application on the modulation of operation-induced immune suppression. For this purpose 105 patients with breast cancer were recruited. At the treatment centre the patients received an infusion of 1 mg Iscador M Spezial prior to the start of an operation, in addition to normal medication, while this was not practised at the control centre. The primary trial objective was the oxidative burst in granulocytes taken from patients ex vivo prior to surgery, and 1 and 3 days after. In order to take account of possible differences in the two groups, propensity scores were used as the basis for a matched pair analysis. It became clear that inhibition of the granulocyte function in the treatment group was significantly less marked (p < 0.001; Wilcoxon). Mistletoe extract-related adverse reactions were not observed. Thus this special form of application could minimise the immune suppression triggered by anaesthesia and operation stress.

Animals↗
PubMed2003

Response of C3 and C4 plants to middle-Holocene climatic variation near the prairie-forest ecotone of Minnesota.

Paleorecords of the middle Holocene (MH) from the North American mid-continent can offer insights into ecological responses to pervasive drought that may accompany future climatic warming. We analyzed MH sediments from West Olaf Lake (WOL) and Steel Lake (SL) in Minnesota to examine the effects of warm/dry climatic conditions on prairie-woodland ecosystems. Mineral composition and carbonate delta(18)O were used to determine climatic variations, whereas pollen assemblages, charcoal delta(13)C, and charcoal accumulation rates were used to reconstruct vegetation composition, C(3) and C(4) plant abundance, and fire. The ratio of aragonite/calcite at WOL and delta(18)O at SL suggest that pronounced droughts occurred during the MH but that drought severity decreased with time. From charcoal delta(13)C data we estimated that the MH abundance of C(4) plants averaged 50% at WOL and 43% at SL. At WOL C(4) abundance was negatively correlated with aragonite/calcite, suggesting that severe moisture deficits suppressed C(4) plants in favor of weedy C(3) plants (e.g., Ambrosia). As climate ameliorated C(4) abundance increased (from approximately 33 to 66%) at the expense of weedy species, enhancing fuel availability and fire occurrence. In contrast, farther east at SL where climate was cooler and wetter, C(4) abundance showed no correlation with delta(18)O-inferred aridity. Woody C(3) plants (e.g., Quercus) were more abundant, biomass flammability was lower, and fires were less important at SL than at WOL. Our results suggest that C(4) plants are adapted to warm/dry climatic conditions, but not to extreme droughts, and that the fire regime is controlled by biomass-climate interactions.

Climate↗
PubMed1997

Estimating the relative roles of top-down and bottom-up forces on insect herbivore populations: a classic study revisited.

Although most ecologists agree that both top-down and bottom-up forces (predation and resource limitation, respectively) act in concert to influence populations of herbivores, it has proven difficult to estimate the relative contributions of such forces in terrestrial systems. Using a combination of time-series analysis of population counts recorded over 16 years and experimental data, we present the first estimates of the relative roles of top-down and bottom-up forces on the population dynamics of two terrestrial insect herbivores on the English oak (Quercus robur). Data suggest that temporal variation in winter moth, Operophtera brumata, density is dominated by time-lagged effects of pupal predators. By comparison, spatial variation in O. brumata density is dominated by host-plant quality. Overall, top-down forces explain 34.2% of population variance, bottom-up forces explain 17.2% of population variance, and 48.6% remains unexplained. In contrast, populations of the green oak tortrix, Tortrix viridana, appear dominated by bottom-up forces. Resource limitation, expressed as intraspecific competition among larvae for oak leaves, explains 29.4% of population variance. Host quality effects explain an additional 5.7% of population variance. We detected no major top-down effects on T. viridana populations. An unknown factor causing a linear decline in T. viridana populations over the 16-year study period accounts for most of the remaining unexplained variance. We discuss the observed differences between the insect species and the utility of time-series analysis as a tool in assessing the relative importance of top-down and bottom-up forces on herbivore populations.

Journal Article↗
PubMed1999

Ecosystem rooting depth determined with caves and DNA.

Belowground vertical community composition and maximum rooting depth of the Edwards Plateau of central Texas were determined by using DNA sequence variation to identify roots from caves 5-65 m deep. Roots from caves were identified by comparing their DNA sequences for the internal transcribed spacer (ITS) region of the 18S-26S ribosomal DNA repeat against a reference ITS database developed for woody plants of the region. Sequencing the ITS provides, to our knowledge, the first universal method for identifying plant roots. At least six tree species in the system grew roots deeper than 5 m, but only the evergreen oak, Quercus fusiformis, was found below 10 m. The maximum rooting depth for the ecosystem was approximately 25 m. (18)O isotopic signatures for stem water of Q. fusiformis confirmed water uptake from 18 m underground. The availability of resources at depth, coupled with small surface pools of water and nutrients, may explain the occurrence of deep roots in this and other systems.

Base Sequence↗
PubMed1999

Intra-ring variability of Cr, As, Cd, and Pb in red oak revealed by secondary ion mass spectrometry: implications for environmental biomonitoring.

Reconstructing the history of ambient levels of metals by using tree-ring chemistry is controversial. This controversy can be resolved in part through the use of selective microanalysis of individual wood cells. Using a combination of instrumental neutron activation analysis and secondary ion mass spectrometry, we have observed systematic inhomogeneity in the abundance of toxic metals (Cr, As, Cd, and Pb) within annual growth rings of Quercus rubra (red oak) and have characterized individual xylem members responsible for introducing micrometer-scale gradients in toxic metal abundances. These gradients are useful for placing constraints on both the magnitude and the mechanism of heavy metal translocation within growing wood. It should now be possible to test, on a metal-by-metal basis, the suitability of using tree-ring chemistries for deciphering long-term records of many environmental metals.

Arsenic↗
PubMed2000

Patterns of Annual Seed Production by Northern Hemisphere Trees: A Global Perspective.

We tested whether annual seed production (masting or mast fruiting) in Northern Hemisphere trees is an evolved strategy or a consequence of resource tracking by comparing masting patterns with those of annual rainfall and mean summer temperatures, two environmental variables likely to correlate with available resources. There were generally significant negative autocorrelations between the seed crop in year x and year [Formula: see text] (year [Formula: see text] in species of Quercus requiring 2 yr to mature acorns), as expected if resources are depleted in mast years in part by switching resources from growth to reproduction. Spatial autocorrelation in annual seed production generally declined with distance but was statistically significant over large geographic areas. Variability in annual seed production was relatively high and inversely correlated with latitude and generally not bimodally distributed. Patterns of spatial autocorrelation in annual rainfall and summer temperatures are generally similar to those exhibited by annual seed production, and relative variability in annual rainfall is also inversely correlated with latitude. However, these environmental variables exhibit distinctly different patterns of temporal autocorrelation, are much less variable, and are more normally distributed than annual seed production. Combined with the inverse relationship between growth and reproduction previously documented, these results support the hypothesis that variability in annual seed production is an evolved strategy and that annual seed production is more or less normally distributed rather than an all-or-none phenomenon.

mast fruiting↗
PubMed2000

Haploid Origin of Cork Oak Anther Embryos Detected by Enzyme and RAPD Gene Markers.

In vitro-induced cork oak (Quercus suber L.) embryos from anther cultures proved to be of haploid origin both by enzyme and RAPD gene marker analysis. The problem considered was to ascertain if embryo cultures originated either from a single haploid cell, from a microspore, or from multiple haploid cells. Therefore, a heterozygotic gene was searched for in the parent tree. The gene coding for shikimate dehydrogenase (SKDH1) proved to be heterozygous in the parental tree, and subsequently, these allozymes were screened for the embryos induced in anther cultures from the same tree. Only haploid embryos were found, confirming the microspore origin. Different genotypes were not identified inside each anther by isozyme analysis, probably because of selective pressure for one embryo early in development, but both parental SKDH1 alleles were found in the embryos of different anthers. The banding patterns detected by RAPD markers permitted the identification of multiple microspore origins inside each anther.

Journal Article↗
PubMed2000

Hypereosinophilia induced by high-dose intratumoral and peritumoral mistletoe application to a patient with pancreatic carcinoma.

UNLABELLED: A patient with inoperable adenocarcinoma of the pancreas was treated with intraperitumoral and peritumoral injections of a Viscum album L. extract containing 5,700 ng/mL mistletoe lectin, mainly mistletoe lectin 1 (Abnobaviscum Quercus 2) for 5 weeks (1 injection per week). After the third injection (day 22), a marked eosinophilia was observed (1,800 per microliter) that rose to 3,268 per microliter after the fifth injection (day 42). Furthermore, histology performed on day 28 revealed accumulation of eosinophils in ductal lesions and adjacent stroma in addition to the features of ductal adenocarcinoma. In order to investigate whether eosinophilia correlated with immunological features, we analyzed cytokine production of peripheral blood mononuclear cells (PBMC) from this patient after stimulation with antigens known to "unmask" an individual's predisposition for defined immunoreactions, namely purified protein derivative (PPD) as a stimulator of T-helper (TH1)1-cells and tetanus toxoid (TT) as an activator of TH2-cells. PBMC of the patient showed a strong proliferation and production of interleukin (IL)-5 and IL-10 after incubation with TT indicating a type-2 response. Simultaneously, PBMC were induced to proliferate and produce interferon gamma (IFN-gamma) by incubation with PPD suggesting also a type-1 response. These data would readily explain the eosinophilia because eosinophils are effector cells of type-2 reaction but also require type-1 cytokines. Although the overall clinical course of the patient was rapidly progressive, temporary stabilization of the patient's general condition during mistletoe treatment was observed. It is, however, still an open question whether this transient benefit was due to the induction of eosinophilia by a type-2 response. CONCLUSION: Before high-dose intratumoral and peritumoral treatment with a Viscum album L. extract containing mistletoe, lectin 1 can be associated with hypereosinophilia and strong production of TH1 as TH2 cytokines as well.

Adenocarcinoma↗
PubMed2003

Does canopy position affect wood specific gravity in temperate forest trees?

The radial increases in wood specific gravity known in many tree species have been interpreted as providing mechanical support in response to the stresses associated with wind loading. This interpretation leads to the hypothesis that individuals reaching the canopy should (1) be more likely to have radial increases in specific gravity and (2) exhibit greater increases than individuals in the subcanopy. Wood specific gravity was determined for three species of forest trees (Acer rubrum, Fagus grandifolia and Tsuga canadensis) growing in central Massachusetts, USA. Acer rubrum shows radial increases in specific gravity, but these increases are not more pronounced in canopy trees; the other two species show a pattern of radial decreases. The degree of radial increase or decrease is influenced by tree height and diameter. Of the dominant tree species for which we have data, A. rubrum, Betula papyrifera and Pinus strobus show radial increases in specific gravity, whereas F. grandifolia, T. canadensis and Quercus rubra show decreases. The occurrence of radial increases in B. papyrifera and P. strobus, which are often canopy emergents, suggests that it is overall adaptive strategy that is important rather than position (canopy vs. subcanopy) of any individual tree. It is suggested that radial increases in specific gravity are associated with early-successional status or characteristics and decreases with late-successional status or persistence in mature forest.

Acer↗
PubMed2006

Stem phototropism of trees: a possible significant factor in determining stem inclination on forest slopes.

BACKGROUND AND AIMS: The main stems of trees on forest slopes incline down the slope to various extents that are characteristic of the species. The inclination has been explained as an active response to a horizontally asymmetrical light environment, but the contributing physiological mechanisms are unknown. The present study tested the hypothesis that stem phototropism, gravitropism, or a combination of the two determines the inclination of tree stems on forest slopes. METHODS: Cryptomeria japonica, Pinus densiflora, Quercus myrsinaefolia and Q. serrata were studied. Measurements were made of stem inclination of mature trees on forest slopes in uniform plantations of each species, and changes in stem inclination of potted seedlings in response to illumination treatments (unilateral or overhead) and inclination treatments (artificially inclined or erect). Indices of phototropic and gravitropic responsiveness were evaluated for each species, calculated from the change in stem inclination in response to artificial inclination with unilateral or overhead illumination. KEY RESULTS: Stem inclination on forest slopes varied significantly among species: Q. serrata inclined most in the down-slope direction, C. japonica inclined the least, and P. densiflora and Q. myrsinaefolia were intermediate. The change in stem inclination of seedlings in each treatment varied significantly among species. One-year-old stems of Q. serrata and 2-year-old stems of Q. myrsinaefolia bent toward the light source. Interspecific variation in the change in stem inclination in response to the unilateral illumination or that in the index of phototropic responsiveness was strongly correlated with the variation in stem inclination on forest slopes. CONCLUSIONS: The orientation of woody stems that have finished elongation can be actively controlled by phototropism. Interspecific variation in phototropic responsiveness of trees is a possible significant determinant of interspecific variation in stem inclination on forest slopes.

Geography↗
PubMed2006

Evaluation of medicinal plant hepatotoxicity in co-cultures of hepatocytes and monocytes.

Non-parenchymal cells might play an important role in the modulation of xenobiotic metabolism in liver and its pharmacological and toxicological consequences. Therefore, the role of cell-to-cell interactions in herbal induced liver toxicity was investigated in monocultures of cells from the human hepatocyte cell line (HepG2) and in co-cultures of cells from the HepG2 cell line and cells from the human monocyte cell line (THP1). Cells were treated with various concentrations (1-500 microg ml(-1)) of extracts of Pistacia palaestina, Juglans regia and Quercus ithaburensis for 24 h. Extracts from Cleome droserifolia, a known toxic plant, were taken as positive control. In the co-culture system, toxic effects were observed after exposure to extracts of Pistacia palestina and C. droserifolia. These two extracts significantly reduced by cell viability as measured the MTT test and the LDH assay. Whereas in hepatocyte cultures, only extracts of C. droserifolia were found to affect the cell viability. The production levels of albumin from hepatocytes were not affected by treatment with plant extracts in both culture systems. It seems that the observed reduction in cell viability after exposure to extracts of P. palestina in co-cultures but not in monocultures is a result of monocyte-derived factors. The use of liver cell co-cultures is therefore a useful approach to investigate the influence of intercellular communication on xenobiotic metabolism in liver.

Journal Article↗
PubMed1997

Multilocus and multitrait measures of differentiation for gene markers and phenotypic traits.

Multilocus measures of differentiation taking into account gametic disequilibrium are developed. Even if coupling and repulsion heterozygotes cannot be separated at the multilocus level, a method is given to calculate a composite measure of differentiation (CFst) at the zygotic level, which accounts for allelic associations combining both gametic and nongametic effects. Mean and maximum differentiations may be relevant when multilocus measures are computed. Maximum differentiation is the highest eigenvalue of the Fst matrix, whereas mean differentiation corresponds to the mean value of all eigenvalues of the Fst matrix. Gametic disequilibrium has a stronger effect on maximum differentiation than on mean differentiation and takes into account the anisotropy that may exist between within- and between-population components of disequilibria. Multilocus mean and maximum differentiation are calculated for a set of 81 Quercus petraea (sessile oak) populations assessed with eight allozyme loci and two phenotypic traits (bud burst and height growth). The results indicate that maximum differentiation increases as more loci (traits) are considered whereas mean differentiation remains constant or decreases. Phenotypic traits exhibit higher population differentiation than allozymes. The applications and uses of mean and maximum differentiations are further discussed.

Analysis of Variance↗
PubMed1998

Laboratory and field evaluations of oviposition responses of Aedes albopictus and Aedes triseriatus (Diptera: Culicidae) to oak leaf infusions.

Organic infusions created by fermenting white oak (Quercus alba L.) leaves in water were evaluated as sources of attractant odorants and contact oviposition stimulants for gravid Aedes albopictus (Skuse) and Aedes triseriatus (Say). Infusions were bioassayed in the laboratory by giving single females a choice of ovipositing in 1 container with infusion and 7 containers with water. Ae. albopictus laid significantly more eggs in containers with infusion, regardless of concentration (dilutions ranging from 10 to 100%) or age (fermentation periods of 7, 28, 60 d), than in containers holding water. The largest proportion of eggs (76.8%) was deposited in response to a 60% concentration of 7-d-old infusion. In contrast, Ae. triseriatus exhibited variable oviposition responses but generally deposited the largest number of eggs in only a few concentrations of older age infusions. In binary "sticky screen" bioassays, there was no difference between the numbers of females attracted to infusion or water, indicating that oviposition responses to infusion were mediated by contact chemostimulants rather than by attraction to odorants. Oviposition responses to infusions by field populations of Ae. albopictus and Ae. triseriatus in Raleigh, NC, were evaluated with pairs of oviposition traps, one containing infusion and the other containing water. Generally, Ae. albopictus laid significantly more eggs in ovitraps containing infusion regardless of its age (7, 28, and 60 d old) or the mass of leaves fermented (126 g = 1x or 504 g = 4x) than in water. In contrast, Ae. triseriatus deposited an equivalent number of eggs in traps containing water or 1x, 80% infusion regardless of its age; however, the oviposition response to ovitraps containing 4x, 7-d-old, 50% infusion was significant. Placement of an automobile tire behind an ovitrap did not increase the number of Ae. albopictus eggs laid in ovitraps containing 4x, 7-d-old, 50% infusion or water relative to ovitraps without a tire. Our research indicates that baiting ovitraps with oak leaf infusion would increase the sensitivity of surveillance efforts for Ae. albopictus and Ae. triseriatus.

Aedes↗
PubMed1976

Carcinogenicity of Camellia sinensis (tea) and some tannin-containing folk medicinal herbs administered subcutaneously in rats.

In an attempt to correlate the high incidence of esophageal carcinoma in natives of certain places with their habit of using herbaceous folk medicines, we performed bioassays of several plant extracts and the fractions prepared from them. Fourteen extracts and fractions from 6 plants were injected sc into NIH Black rats. The tannin fractions from Quercus falcata pagodaefolia, Diospyros virginiana, and Camellia sinensis were very active and produced tumors at the injection site in 66% or more of the treated animals. Tannin fractions from 3 other plants and total aqueous extracts from 5 to 6 tested plants were also tumorigenic rats. The induced tumors were malignant fibrous histiocytomas similar, if not identical, to those encountered in humans. The experiment indicated a possibility of induction of tumor in man by the tested plant materials.

Animals↗
PubMed2003

12CO2 emission from different metabolic pathways measured in illuminated and darkened C3 and C4 leaves at low, atmospheric and elevated CO2 concentration.

The detection of 12CO2 emission from leaves in air containing 13CO2 allows simple and fast determination of the CO2 emitted by different sources, which are separated on the basis of their labelling velocity. This technique was exploited to investigate the controversial effect of CO2 concentration on mitochondrial respiration. The 12CO2 emission was measured in illuminated and darkened leaves of one C4 plant and three C3 plants maintained at low (30-50 ppm), atmospheric (350-400 ppm) and elevated (700-800 ppm) CO2 concentration. In C3 leaves, the 12CO2 emission in the light (Rd) was low at ambient CO2 and was further quenched in elevated CO2, when it was often only 20-30% of the 12CO2 emission in the dark, interpreted as the mitochondrial respiration in the dark (Rn). Rn was also reduced in elevated CO2. At low CO2, Rd was often 70-80% of Rn, and a burst of 12CO2 was observed on darkening leaves of Mentha sativa and Phragmites australis after exposure for 4 min to 13CO2 in the light. The burst was partially removed at low oxygen and was never observed in C4 leaves, suggesting that it may be caused by incomplete labelling of the photorespiratory pool at low CO2. This pool may be low in sclerophyllous leaves, as in Quercus ilex where no burst was observed. Rd was inversely associated with photosynthesis, suggesting that the Rd/Rn ratio reflects the refixation of respiratory CO2 by photosynthesizing leaves rather than the inhibition of mitochondrial respiration in the light, and that CO2 produced by mitochondrial respiration in the light is mostly emitted at low CO2, and mostly refixed at elevated CO2. In the leaves of the C4 species Zea mays, the 12CO2 emission in the light also remained low at low CO2, suggesting efficient CO2 refixation associated with sustained photosynthesis in non-photorespiratory conditions. However, Rn was inhibited in CO2-free air, and the velocity of 12CO2 emission after darkening was inversely associated with the CO2 concentration. The emission may be modulated by the presence of post-illumination CO2 uptake deriving from temporary imbalance between C3 and C4 metabolism. These experiments suggest that this uptake lasts longer at low CO2 and that the imbalance is persistent once it has been generated by exposure to low CO2.

Carbon Dioxide↗
PubMed2004

A/C(i) curve analysis across a range of woody plant species: influence of regression analysis parameters and mesophyll conductance.

The analysis and interpretation of A/C(i) curves (net CO(2) assimilation rate, A, versus calculated substomatal CO(2) concentration, C(i)) is dependent upon a number of underlying assumptions. The influence of the C(i) value at which the A/C(i) curve switches between the Rubisco- and electron transport-limited portions of the curve was examined on A/C(i) curve parameter estimates, as well as the effect of mesophyll CO(2) conductance (g(m)) values on estimates of the maximum rate of Rubisco-mediated carboxylation (V(cmax)). Based on an analysis using 19 woody species from the Pacific Northwest, significant variation occurred in the C(i) value where the Rubisco- and electron transport-limited portions of the curve intersect (C(i_t)), ranging from 20 Pa to 152 Pa and averaging c. 71 Pa and 37 Pa for conifer and broadleaf species, respectively. Significant effects on estimated A/C(i) parameters (e.g. V(cmax)) may arise when preliminary estimates of C(i_t), necessary for the multiple regression analyses, are set either too high or too low. However, when the appropriate threshold is used, a significant relationship between A/C(i) and chlorophyll fluorescence estimates of carboxylation is achieved. The use of the V(cmax) parameter to describe accurately the Rubisco activity from the A/C(i) curve analysis is also dependent upon the assumption that C(i) is approximately equal to chloroplast CO(2) concentrations (C(c)). If leaf mesophyll conductance is low, C(c) will be much lower than C(i) and will result in an underestimation of V(cmax) from A/C(i) curves. A large range of mesophyll conductance (g(m)) values was observed across the 19 species (0.005+/-0.002 to 0.189+/-0.011 mol m(-2) s(-1) for Tsuga heterophylla and Quercus garryana, respectively) and, on average, g(m) was 1.9 times lower for the conifer species (0.058+/-0.017 mol m(-2) s(-1) for conifers versus 0.112+/-0.020 mol m(-2) s(-1) for broadleaves). When this mesophyll limitation was accounted for in V(cmax) estimates, considerable variation still existed between species, but the difference in V(cmax) between conifer and broadleaf species was reduced from c. 11 micromol m(-2) s(-1) to 4 micromol m(-2) s(-1). For example, A/C(i) curve estimates of V(cmax) were 31.2+/-6.2 and 42.2+/-4.4 micromol m(-2) s(-1), and A/C(c) curve estimates were 41.2+/-7.1 micromol m(-2) s(-1) and 45.0+/-4.8 micromol m(-2) s(-1), for the conifer and broadleaf species, respectively.

Biological Transport↗
PubMed2005

How are leaves plumbed inside a branch? Differences in leaf-to-leaf hydraulic sectoriality among six temperate tree species.

The transport of water, sugar, and nutrients in trees is restricted to specific vascular pathways, and thus organs may be relatively isolated from one another (i.e. sectored). Strongly sectored leaf-to-leaf pathways have been shown for the transport of sugar and signal molecules within a shoot, but not previously for water transport. The hydraulic sectoriality of leaf-to-leaf pathways was determined for current year shoots of six temperate deciduous tree species (three ring-porous: Castanea dentata, Fraxinus americana, and Quercus rubra, and three diffuse-porous: Acer saccharum, Betula papyrifera, and Liriodendron tulipifera). Hydraulic sectoriality was determined using dye staining and a hydraulic method. In the dye method, leaf blades were removed and dye was forced into the most proximal petiole. For each petiole the vascular traces that were shared with the proximal petiole were counted. For other shoots, measurements were made of the leaf-area-specific hydraulic conductivity for the leaf-to-leaf pathways (k(LL)). In five out of the six species, patterns of sectoriality reflected phyllotaxy; both the sharing of vascular bundles between leaves and k(LL) were higher for orthostichous than non-orthostichous leaf pairs. For each species, leaf-to-leaf sectoriality was determined as the proportional differences between non-orthostichous versus orthostichous leaf pairs in their staining of shared vascular bundles and in their k(LL); for the six species these two indices of sectoriality were strongly correlated (R2=0.94; P <0.002). Species varied 8-fold in their k(LL)-based sectoriality, and ring-porous species were more sectored than diffuse-porous species. Differential leaf-to-leaf sectoriality has implications for species-specific co-ordination of leaf gas exchange and water relations within a branch, especially during fluctuations in irradiance and water and nutrient availability.

Biological Transport↗
PubMed2006

Hydrogen peroxide concentrations in leaves under natural conditions.

While H2O2 has been implicated in numerous plant environmental responses, normal levels and variabilities are poorly established, and estimates of leaf tissue concentrations span more than three orders of magnitude, even in a single species under similar conditions. Here, leaf tissue H2O2 contents under natural conditions are reported after determining (i) that H2O2 in extracts was stable with time, (ii) that H2O2 added to the extract was recovered quantitatively, and (iii) that the H2O2 calibration curve was unaffected (or quantifiably affected) by the extract. The broad applicability of the protocol and variability in leaf concentrations were demonstrated using tissue collected from several habitats in association with three, more extensive, experiments. The first involved nychthemeral studies of the mangrove, Rhizophora mangle L. Lowest H2O2 levels occurred in the early morning and near sunset, with higher levels both at midday and at night. Second, using five temperate species in Spring, concentrations were compared on a warm, sunny day and a cool, cloudy day. Higher concentrations were found on the warm day for Aesculus glabra Willd., Glechoma hederacea L., Plantago major L., and Viola soraria Willd., while there were no differences in Quercus macrocarpa Michx. Finally, the effects of elevated CO2 and ozone were examined in soybean, Glycine max L. Pioneer 93B15 under Free Air gas Concentration Enrichment (FACE) conditions. Both supplements led to elevated H2O2. Overall, mean leaf, midday, and mid-summer H2O2 concentrations ranged from 0.67 micromol (gFW)(-1) in mangrove to 3.6 micromol (gFW)(-1) in A. glabra Willd. Greatest within-species differences were only 2.5-fold in any of the studies.

Environment↗