bluuebunny/crossref_metadata_2025_split huggingface dataset:
The measurement of stable isotope natural abundance variations
Authors: PRESTON T. 
Published: April 2006

ABSTRACTPrecise stable isotope natural abundance analysis of the elements of organic matter, yields a wealth of information for the biologist. Robust sample preparation methodology and analytical instrumentation is necessary to achieve precise results. Basic principles of isotope ratio mass spectrometry (IRMS) are detailed, with particular regard to sample size, gas production and transfer into the IRMS ion source. Gas preparation methods developed to give quantitative yields of pure simple gases from organic and inorganic materials include vacuum line combustion, ampoule combustion and automated elemental analysers used off and on‐line. The new technique of GC‐C‐IRMS, where individual volatile organic compounds are separated by GC, combusted and analysed on‐line by IRMS, is also described. The conventional dual batch inlet developed by geochemists for the most precise analysis of stable isotopes, is contrasted with continuous flow‐IRMS analysis. The needs of the biological scientist for rapid throughput of small samples are discussed in this context. It is argued that the development of new instrumental approaches will permit many new applications of stable isotope methodology in the biological sciences.
Physical and chemical basis of carbon isotope fractionation in plants
Authors: O'LEARY M. H. , MADHAVAN S. , PANETH P. 
Published: April 2006

ABSTRACTNaturally‐occurring variations in the abundances of the stable isotopes of carbon and other elements can be used to understand the dynamics of natural processes in chemistry, biochemistry, biology, medicine, ecology and other fields. The use of carbon‐13 isotopic abundances as an indicator of photosynthetic function in plants has become common. The purpose of this article is to describe the physical and chemical processes that contribute to the abundances of carbon‐13 in plant materials, and to provide a framework for understanding how those processes control the isotopic contents of natural materials.
Stable sulphur isotopes in plants: a review
Authors: TRUST B. A. , FRY B. 
Published: April 2006

ABSTRACTThe determination of the natural abundances of stable isotopes has become a useful method by which to study the transformations of elements in biological and ecological studies as well as to investigate the mechanisms of chemical reactions. Unlike carbon and nitrogen isotopes, however, stable sulphur isotopes are used infrequently, and their potential as tracers in biochemical and physiological studies are only beginning to be realized. This review provides an overview of research involving stable sulphur isotopes in studies of plant metabolism and pollution. Topics discussed include the mechanisms and accompanying isotopic fractionations involved during the uptake and assimilation of inorganic sulphur compounds by plants, the utility of plants as bioindicators of environmental sulphur pollution, and the emission of isotopically light H2S by plants in response to high concentations of sulphur. Future advances in the field are proposed.
Differential uptake of summer precipitation among co‐occurring trees and shrubs in a pinyon‐juniper woodland
Authors: FLANAGAN L. B. , EHLERINGER J. R. , MARSHALL J. D. 
Published: April 2006

ABSTRACTMeasurements of the ratio of deuterium to hydrogen (D/H) in stem xylem water were used to determine the relative uptake of summer precipitation by four co‐occurring plant species in southern Utah. The species compared included two trees, Juniperus osteosperma and Pinus edulis, and two shrubs, Artemisia tridentata and Chrysothamnus nauseousus. There were significant differences among species in the relative use of summer precipitation. Chrysothamnus nauseosus had stem water D/H ratios in May through August 1990 that were not significantly different from that of groundwater. In contrast, the other three species had stem water D/H ratios that were intermediate between the groundwater value and summer precipitation values, indicating that a mixture of both precipitation and groundwater was being used by these species. The two tree species generally had higher D/H values than did A. tridentata indicating a higher average uptake of summer precipitation, although the roots of J. osteosperma and P. edulis may not be as responsive to small precipitation events as A. tridentata. There was a strong negative correlation between stem water D/H ratios and predawn water potential, which suggests a relationship between plant rooting pattern and water source use. In addition, water‐use efficiency during photosynthetic gas exchange, calculated from leaf carbon isotope composition, differed among species and was strongly correlated with differences in the relative uptake of summer precipitation.
Vascular anatomy of fabaceous nodules of determinate growth
Authors: WALSH K. B. , ATKINS R. S. , LOW C. S. 
Published: April 2006

ABSTRACTThe vascular anatomy of nodules of 12 genera of tropical pasture and grain legumes of three tribes of theFabaceaeis described. Tracheary strands branch dichotomously and repeatedly from a root connection and generally terminate within sealed pockets of endodermis. Anastomosis of vascular strands at the nodule tip to form a complete xylem circuit was seen in three genera (Vigna, GlycineandLablab). The functional significance of vascular structure is discussed in terms of pathways of solute movement between the infected cells and the root, and the permeability of the nodule cortex to gases.
Quantitative determination of changes induced by NaCl in vacuoles and cellular size of Lycopersicon esculentum root cells
Authors: SÁNCHEZ‐AGUAYO I. , GONZÁLEZ‐UTOR A. L. 
Published: April 2006

ABSTRACTChanges induced by NaCl in the sizes of both cells and vacuolar compartments of tomato seedling roots were determined using morphometric and stereological analysis. Parameters evaluated showed that cellular volume was smaller in roots grown under saline conditions than in control roots. This reduction was greater when NaCl concentration was increased. Similar behaviour can be observed in the vacuolar compartment where high concentrations of NaCl produce a reduction in vacuolar volume although the number of vacuoles per cell does not change under saline conditions.
The dissipation of excess excitation energy in British plant species
Authors: JOHNSON G. N. , YOUNG A. J. , SCHOLES J. D. , HORTON P. 
Published: April 2006

ABSTRACTThe reversible dissipation of excitation energy in higher plants is believed to protect against light‐induced damage to the photosynthetic apparatus. This dissipation is measured as the non‐photochemical quenching of chlorophyll fluorescence. A method is described whereby the saturated capacity for rapidly reversible non‐photochemical quenching can be compared between plant species. This method was applied to 22 common British plant species whose habitat was quantified using an index that describes shade tolerance. An association was found between occurrence in open habitats and a high capacity for non‐photochemical quenching. It was found that, whilst this capacity was species dependent, it did not depend upon the conditions under which the plant was grown. The possible role of zeaxanthin as a determinant of quenching capacity was examined by measuring the contents of xanthophyll cycle carotenoids for each species. Comparing species, no correlation was seen between the saturated level of non‐photochemical quenching and zeaxanthin content expressed relative to either total carotenoid or to chlorophyll. When zeaxanthin was expressed relative to the amount of xanthophyll cycle intermediates (zeaxanthin, antheraxanthin and violaxanthin), a weak correlation was seen.
Relationships between carotenoid composition and growth habit in British plant species
Authors: JOHNSON G. N. , SCHOLES J. D. , HORTON P. , YOUNG A. J. 
Published: April 2006

ABSTRACTThe pigment composition of leaves from a number of different plant species collected from field sites in the region of Sheffield, UK, have been compared using high‐performance liquid chromatography. Expression of pigment content per unit leaf area was dominated by variation in the total leaf chlorophyll. Neither chlorophyll per unit area nor the chlorophyll a/b ratio were found to be correlated with the habitat from which the plants originated. When the amounts of different carotenoids were expressed relative to the total carotenoid pool, it was found that whilst neither total carotene (α‐ +β‐carotene) nor neoxanthin correlated with ability to grow in shade, the leaf content of both lutein and the total xanthophyll cycle carotenoids (zeaxanthin, anther‐axanthin and violaxanthin) did, with lutein content being high in shade species and xanthophyll cycle intermediates low. There was a strong negative correlation between the relative amounts of each of these groups of carotenoids. The ratio of lutein to xanthophyll cycle carotenoids was strongly correlated to an index of shade tolerance.
Impaired phytochrome‐mediated shade‐avoidance responses in the aurea mutant of tomato
Authors: CASAL J. J. , KENDRICK R. E. 
Published: April 2006

ABSTRACTInternode extension‐growth responses to neighbouring plants and to red to far‐red ratios (R:FR) were investigated in wild‐type (WT) and aurea (au)‐mutant seedlings of tomato grown under natural radiation. The genomic location of the au mutant is not known, but one of its consequences is the reduced phytochrome level. In WT seedlings, internode growth was promoted by the presence of non‐shading neighbours reflecting far‐red light (FR), the shade of a tall canopy, FR provided as a supplement during the photoperiod, and FR pulses either provided at the end of the day or delayed into the dark period. Supplementary FR during the photoperiod also promoted growth in herbicide‐treated partially bleached WT seedlings. The au mutant showed higher background extension‐growth rates, but only responded to the most severe treatments: deep shade light and very low R:FR at the end of the day, i.e. au‐mutant seedlings were less sensitive than WT seedlings to R:FR signals. Wild‐type seedlings were transferred from the glasshouse to a growth room and exposed to white light with two levels of phytochrome‐absorbable radiation but similar phytochrome photoequilibria and radiation for photosynthesis. The plants exposed to the lowest level showed a transient increase of internode extension growth rate and a simultaneous reduction of response to FR pulses, i.e. reproduced some of the features of au‐mutant seedlings. Phytochrome itself could set the degree of response to Pfr during neighbour detection.
The spatial distribution of chloroplast water in Acer platanoides sun and shade leaves
Authors: McCAIN D. C. , CROXDALE J. , MARKLEY J. L. 
Published: April 2006

ABSTRACTWe evaluated a new, two‐dimensional (2‐D) nuclear magnetic resonance (NMR) imaging technique as a method for measuring the distribution of chloroplasts in leaves. NMR images that showed the distribution of chloroplast water and of total water as a function of depth into Acer platanoides sun and shade leaves were compared with the distribution of chlorophyll in the same leaf types (as measured by fluorescence microscopy), with the cellular structure (by scanning electron microscopy), and with published information. Results showed that the volume fraction of chloroplast water was much larger in shade than in sun leaves, and that it averaged about one‐third larger in the palisade than in the spongy parenchyma region of both leaf types. Chlorophyll fluorescence was more intense in shade than in sun leaves. In sun leaves, fluorescence was maximal in the palisade region near the junction with the spongy parenchyma, while in shade leaves, fluorescence was maximal in the upper part of the spongy layer. We concluded that 2‐D NMR imaging reliably indicates the location of chloroplast water.
Determination of foliar uptake of chemicals: influence of leaf surface microflora
Authors: SCHREIBER L. , SCHÖNHERR J. 
Published: April 2006

ABSTRACTAnalysing uptake and desorption kinetics of methylglucose in needles of Picea abies (L.) Karst., the effect of NaN3 on methylglucose uptake, and the correlation between different degrees of colonization of needle surfaces with epiphytes and equilibrium uptake of methylglucose, showed that methylglucose was taken up only by epiphytes but not by the needles themselves. Thus, amounts of methylglucose taken up are a measure of the amounts of epiphytic microorganisms. Uptake of methylglucose into epiphytes was very rapid and equilibrium was obtained within 2h. Amounts taken up could completely be desorbed again from epiphytes within 2‐6 h. It is pointed out that the possible influence of leaf surface microorganisms must be considered in studies of foliar uptake of chemicals, in order to avoid erroneous conclusions.
Gravity sensing in oat coleoptiles: scatter in growth orientation under different g‐conditions
Authors: JOHNSSON A. , CHAPMAN D. K. , BROWN A. , JOHNSON‐GLEBE C. , KARLSSON C. , HEATHCOTE D. G. 
Published: April 2006

ABSTRACTDark‐grown oat seedlings depart from the expected vertical orientation, suggesting that the coleoptile is less responsive to the lateral component of a gravitational stimulus than would be expected. This phenomenon was studied by investigating the gravitropic curvatures of oat (Avena sativa L. cv. Seger) coleoptiles at 10g and over a range of longitudinally applied centripetal accelerations up to 19·4g. In most experiments, the plants were grown and observed at a particular g‐level throughout the experiment. Time‐lapse video recordings permitted studies of the scatter, measured as the variability of the plants' angle from the vertical (or root mean square value, RMS). The coleoptiles' heights at the end of the experiments were not significantly altered under the centrifugation. Scatter increased with plant age and decreased with increasing g. It decreased in an almost linear fashion as a function of the logarithm of the g‐acceleration. In a series of experiments, the g‐level was changed from 10g to a higher test g‐acceleration. The scatter was then reduced within half an hour after the g‐transition. It is pointed out that the experiments confirm that the scatter is g‐related but that it was not predicted quantitatively by present theories of the oat coleoptile's gravitropic response kinematics.
Cold‐induced purpling of Pinus contorta seedlings depends on previous daylength treatment
Authors: CAMM E. L. , McCALLUM J. , LEAF E. , KOUPAI‐ABYAZANI M. R. 
Published: April 2006

ABSTRACTThe characteristic cold‐induced foliar accumulation of anthocyanin (‘purpling’) seen in many species of pine seedlings in the autumn can be contingent upon photoperiod received months previously. In nursery‐grown seedlings of Pinus contorta Dougl. var. latifolia Engelm., a 4‐week exposure during August of 10‐h days followed by return to ambient photoperiod diminished the frequency of purpling following the November onset of cold weather (21% compared to 71% of the untreated controls). Anthocyanin accumulation (primarily cyanidin 3‐glucoside) was controlled differently than general phenolic metabolism, and involved the integration of two temporally separated environmental signals.
Plants as competing populations of redundant organs
Authors: SACHS T. , NOVOPLANSKY A. , COHEN D. 
Published: April 2006

ABSTRACTAt any given time, a vascular or land plant may be a colony of functional sectors, each consisting of a shoot and its associated roots. In most plants, however, the activity of the cambium can change the relative vascular contacts of neighbouring shoots. Vascular tissues can even differentiate along new orientations, forming contacts that change the sectorial structure of the plant. Such reoriented differentiation is induced by the same auxin from developing leaves as are other types of vascular differentiation. The occurrence of vascular reorientation is determined by two criteria: the presence of an auxin flow that exceeds the transport capacity of the tissues that follow the previous, established orientation and the availability of nearby channels that are not fully occupied, not‘protected’ by their own flow of auxin. These controls of vascular orientation suggest that neighbouring shoots (and neighbouring roots) compete with one another, by means of signals indicating their state and their environment, for vascular contacts with the rest of the plant. Such internal competition between genetically equivalent shoots is an adaptation to heterogeneous environments: it is the shoots in the best conditions available to the plant that receive the support of a greater part of the root system. The potential for changes of vascular contacts points to open problems and to neglected aspects of the role of the cambium in plant organization.
The boundary layer and the apparent responses of stomatal conductance to wind speed and to the mole fractions of CO2 and water vapour in the air
Authors: APHALO P. J. , JARVIS P. G. 
Published: April 2006

ABSTRACTThe experiments and simulations reported in this paper show that, for stomata sensitive to both CO2 and water vapour concentrations, responses of stomatal conductance (gws) to boundary layer thickness have two components, one resulting from changes in intercellular CO2 concentration (χci) and another from changes in leaf surface water vapour saturation deficit (Dws). The experiments and simulations also show that the boundary layer conductance (gwb) can significantly alter the apparent response of gws to ambient air CO2 mole fraction (χca) and water vapour mole fraction (χwa). Because of the feedback loop involved the responses of gws for χca and χwa each include responses to both χci and Dws. The boundary layer alters the state of the variables sensed by the guard cells—i.e. χci and Dws—and so it is a source of feedback. Thus, when scaling up from responses of stomata to the response of gws for a whole leaf, the effect of the boundary layer must be considered. The results indicate that, for given responses of gws to χci and Dws, the apparent responses of gws to Dwa and χca depend on the size of the leaf and wind speed, showing that this effect of the boundary layer should be considered when comparing data measured under different conditions, or with different methods.
Interactive effects of high temperature and elevated carbon dioxide concentration on cowpea [Vigna unguiculata(L.) Walp.]
Authors: AHMED F. E. , HALL A. E. , MADORE M. A. 
Published: April 2006

ABSTRACTLimitations in carbohydrate supplies have been implicated as a factor responsible for reproductive failure under heat stress. Heat stress affects two stages of reproductive development in cowpea [Vigna unguiculata(L.) Walp.], and genotypes are available with tolerance and sensitivity to heat during these different stages. The objectives of this study were to determine the responses of these cowpea lines to ambient and elevated [CO2], under heat stress and optimal temperature, and test whether differences in carbohydrate supplies due to genotypes, CO2enrichment and heat stress are associated with differences in sensitivity to heat during reproductive development. Plants were grown in reach‐in growth chambers and subjected to day/night temperatures of either 33/20 or 33/30°C, and [CO2] levels of either 350 or 700 μmol mol‐1. Under intermediate night temperature (33/20°C), all lines set substantial numbers of pods. Under high night temperature (33/30°C) with either ambient or elevated [CO2], one heat‐sensitive line produced no flowers and the other set no pods, whereas the heat‐tolerant line abundantly set pods. High night temperature reduced the overall carbohydrate content of the plants, especially peduncle sugars, and caused decreases in photosynthetic rates. The high pod set of the heat‐tolerant line, under high night temperature, was associated with higher levels of sugars in peduncles compared with the heat‐sensitive lines. The heat‐tolerant line accumulated substantial shoot biomass, exhibited less accumulation of starch in leaves, and possibly had less down‐regulation of photosynthesis in response to CO2enrichment and heat stress than the heat‐sensitive lines. Elevated [CO2] resulted in higher overall carbohydrate levels in heat‐sensitive lines (starch in leaves, stems and peduncles), but it did not increase their heat tolerance with respect to flower production or pod set. Heat‐induced damage to floral buds and anthers in the sensitive lines was associated with low sugars levels in peduncles, indicating that heat had greater effects on assimilate demand than on leaf assimilate supply. The heat‐tolerant line was the most responsive genotype to elevated [CO2] with respect to pod production under either high or intermediate temperatures.
Nitrogen and phosphorus dynamics of a tallgrass prairie ecosystem exposed to elevated carbon dioxide
Authors: OWENSBY C. E. , COYNE P. I. , AUEN L. M. 
Published: April 2006

ABSTRACTA tallgrass prairie ecosystem was exposed to ambient and twice‐ambient CO2 concentrations in open‐top chambers and compared to unchambered ambient CO2 during the entire growing season from 1989 through 1991. Dominant species were Andropogon gerardii (C4), A. scoparius (C4), Sorghastrum nutans (C4) and Poa pratensis (C3). Nitrogen and phosphorus concentrations in A. gerardii, P. pratensis and dicotyledonous herbs above ground biomass were estimated by periodic sampling throughout the growing season in 1989 and 1990. In 1991, N and P concentrations in peak biomass were estimated by an early August harvest. N and P concentrations in root production as a function of treatment were estimated using root ingrowth bags that remained in place throughout the growing season. Total N and P in above‐ and belowground biomass were calculated as products of concentration and peak biomass by species groups. N concentration in A. gerardii and dicotyledonous herb aboveground biomass was lower and total N higher in elevated CO2 plots than in ambient CO2 plots. N concentration in P. pratensis aboveground biomass was lower in elevated CO2 plots than in ambient, but total N did not differ among treatments in 2 out of 3 years. In 1990, N concentration in root ingrowth bag biomass was lower and total N greater in elevated CO2 than in ambient CO2 plots. Root ingrowth bag biomass N concentration did not differ among treatments in 1991, but total N was greater in elevated CO2 plots than in ambient CO2 plots. P concentration was lower under elevated CO2 compared to ambient in 1989, but did not differ substantially among treatments in 1990 or 1991. In all years, total P in aboveground A. gerardii and root ingrowth bag biomass was greater under elevated CO2 than ambient. P concentration and total P in P. pratensis was similar among treatments.