bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural requirements for the perception of ambient temperature signals in homeothermic heat production of skunk cabbage (Symlocarpus foetidus)
Authors: ITO K. , ONDA Y. , SATO T. , ABE Y. , UEMURA M. 
Published: June 2003

ABSTRACTThe spadix of skunk cabbage, Symplocarpus foetidus, is capable of maintaining an internal temperature of around 20 °C even when the ambient temperature drops to around 0 °C. To determine the crucial structure that is required for detection of ambient temperature signals, detailed measurements of the temperatures of the spadix were made under field conditions. The spadix temperature was well regulated even when the spathe or the leaf of the plant was removed. Furthermore, maintenance of the temperature of the central stalk at either 10 or 20 °C had no effect on the thermoregulation when the ambient temperature increased from 10 to 25 °C or decreased from 20 to 8 °C. Therefore, it seemed that the heat production in the spadix required neither the spathe, the leaf, nor the central stalk for perception of the external temperature signals. Finally, analysis of sugar composition in xylem exudates showed that the concentrations of sucrose, glucose, and fructose, all of which are potential energy sources of thermogenesis, did not change significantly at different ambient temperatures. It is concluded that the spadix is a unique organ in which the perception of ambient temperature signals and heat production occurs in S. foetidus.
Root structure and cellular chloride, sodium and potassium distribution in salinized grapevines
Authors: STOREY R. , SCHACHTMAN D. P. , THOMAS M. R. 
Published: June 2003

ABSTRACTX‐ray microanalysis was used to study the patterns of K+, Na+ and Cl– accumulation in salinized (25 mm NaCl) and non‐salinized grapevine (Vitis) roots. The aim was to determine whether NaCl affects patterns of Cl– accumulation differentially in the roots of a Cl–‐excluding genotype and a non‐excluding genotype. Two regions of fibrous roots were analysed: (1) a region 2–3 mm basipetal to the root tip; and (2) a region of the root 10–12 mm basipetal to the root tip where the outermost layer is the hypodermis. The ion contents of the hypodermis, cortex, endodermis and pericycle vacuoles were analysed. Data were also collected from the cytoplasm of the endodermal and pericycle cells. The analyses showed that the ion profiles of the hypodermis and the endodermis were significantly different from those of the cortex and pericycle. The hypodermis and endodermis had higher K+ and lower Na+ and Cl– than surrounding cells. Some changes due to salinity such as increased K+ concentrations in the hypodermis were also noted. Chloride concentrations did not differ between the genotypes in the hypodermis, across the cortex or in the endodermis, but were higher in the pericycle of the excluder in comparison with the non‐excluding genotype. However, K+/Na+ ratios of the cortex and endodermis were higher in the excluder. The pericycle cells exhibited the greatest ability to sequester Na+ and Cl– in vacuoles. Overall the data show cell‐type‐specific ion accumulation patterns and small but significant differences were found between genotypes. The possibility that these accumulation patterns arise from differences in uptake properties of cell types and/or result from the spatial distribution of the cell types along the competing symplastic and apoplastic ion transport pathways across the root is discussed.
On the progressive enrichment of the oxygen isotopic composition of water along a leaf
Authors: FARQUHAR G. D. , GAN K. S. 
Published: June 2003

ABSTRACTA model has been derived for the enrichment of heavy isotopes of water in leaves, including progressive enrichment along the leaf. In the model, lighter water is preferentially transpired leaving heavier water to diffuse back into the xylem and be carried further along the leaf. For this pattern to be pronounced, the ratio of advection to diffusion (Péclet number) has to be large in the longitudinal direction, and small in the radial direction. The progressive enrichment along the xylem is less than that occurring at the sites of evaporation in the mesophyll, depending on the isolation afforded by the radial Péclet number. There is an upper bound on enrichment, and effects of ground tissue associated with major veins are included. When transpiration rate is spatially nonuniform, averaging of enrichment occurs more naturally with transpiration weighting than with area‐based weighting. This gives zero average enrichment of transpired water, the modified Craig–Gordon equation for average enrichment at the sites of evaporation and the Farquhar and Lloyd (In Stable Isotopes and Plant Carbon‐Water Relations, pp. 47–70. Academic Press, New York, USA, 1993) prediction for mesophyll water. Earlier results on the isotopic composition of evolved oxygen and of retro‐diffused carbon dioxide are preserved if these processes vary in parallel with transpiration rate. Parallel variation should be indicated approximately by uniform carbon isotope discrimination across the leaf.
Alterations in Cd‐induced gene expression under nitrogen deficiency in Hordeum vulgare
Authors: FINKEMEIER I. , KLUGE C. , METWALLY A. , GEORGI M. , GROTJOHANN N. , DIETZ K.‐J. 
Published: June 2003

ABSTRACTThe inter‐relation between nitrogen availability and cadmium toxicity was studied in roots of barley seedlings with emphasis on the analysis of expression of 10 selected genes relevant for growth in the presence of toxic Cd concentrations. The response to Cd exposure differed quantitatively or qualitatively for the 10 genes in dependence of the N supply. Transcripts of glutathione synthase, glutathione reductase, glutathione peroxidase and dehydroascorbate reductase were measured as parameters involved in antioxidant defence, metallothionein, phosphoenolpyruvate carboxylase and phytochelatin synthase (PCS) were analysed as genes related to heavy metal binding, and vacuolar ATPase subunits VHA‐E and VHA‐c and a NRAMP‐transporter as genes being implicated in Cd transport. Reprogramming of the Cd response was most obvious for PCS and NRAMP whose transcript levels were unaltered and down‐regulated, respectively, in the presence of Cd at adequate N, but strongly up‐regulated upon Cd exposure under conditions of nitrogen deficiency. Different responses to Cd at varying N supply were also seen for the antioxidant genes. The results on gene expression are discussed in context with the changes in biochemical parameters, and underline the importance of evaluating the general growth conditions of a plant when discussing its specific response to a stressor such as Cd.The sequence of the nramp cDNA was filed at the EMBL/GenBank/DDBJ Databases under the accession number AJ514946.
Increases of chlorophyll a/b ratios during acclimation of tropical woody seedlings to nitrogen limitation and high light
Authors: KITAJIMA K. , HOGAN K. P. 
Published: June 2003

ABSTRACTAccording to the theory of optimal nitrogen partitioning within a leaf, the chlorophyll (Chl) a/b ratio is expected to increase when leaf N content decreases. Here, we report the first empirical support for this prediction. The Chl a/b ratio increased while Chl content decreased in response to N limitation in photosynthetic cotyledons and leaves of seedlings of four tropical woody species in the Bignoniaceae. The responses of all four species were in the same direction, but differed in magnitude. For Tabebuia rosea, the species that exhibited the greatest increase in Chl a/b ratios (up to values of 5.9), detailed photosynthetic characteristics were also examined. Light and N availability were positively correlated with the light‐ and CO2‐saturated photosynthetic O2 evolution rate, as well as with leaf carboxylation capacity (Vcmax) and electron transport rate (Vj). Severe N limitation and high light did not cause chronic photo‐inhibition (i.e. no change in quantum yield or in dark‐acclimated Fv/Fm). The observed change in the ratio of Vcmax to leaf N in response to N availability was consistent with likely functional reasons for change in the Chl a/b ratio. Adjustment of the Chl a/b ratio was apparently an integral feature of acclimation to high light conditions and low N availability.
Responses of selected birch (Betula pendula Roth) clones to ozone change over time
Authors: OKSANEN E. 
Published: June 2003

ABSTRACTA long‐term free air ozone fumigation experiment was conducted to study changes in physiological ozone responses during tree ontogeny and exposure time in ozone sensitive and tolerant clones of European white birch (Betula pendula Roth), originated from south and central Finland. The trees were grown in soil in natural microclimatic conditions under ambient ozone (control) and 1.4–1.7 × ambient (elevated) ozone from May 1996 to October 2001, and were measured for stem and foliage growth, net photosynthesis, stomatal conductance, stomatal density, visible injuries, foliar starch content and bud formation. After 6 years of exposure, the magnitude of ozone‐induced growth reductions in the sensitive clone was 12–48% (significant difference), levels similar or greater than those reported earlier for 2‐ and 3‐year‐old saplings undergoing shorter exposures. In the tolerant clone, growth of these larger trees was reduced by 1–38% (significant difference in stem volume), although the saplings had previously been unaffected. In both clones, ozone stress led to significantly reduced leaf‐level net photosynthesis but significantly increased stomatal conductance rates during the late summer, resulting in a lower carbon gain for bud formation and the onset of visible foliar injuries. Increasing ozone sensitivity with duration of exposure was explained by a change in growth form (relatively reduced foliage mass), a lower photosynthesis to stomatal conductance ratio during the late summer, and deleterious carry‐over effects arising from the reduced number of over‐wintering buds.
An apoplastic mechanism for short‐term effects of rare earth elements at lower concentrations
Authors: SUN Y. , LIU D. L. , YU Z. Q. , ZHANG Q. , BAI J. , SUN D. Y. 
Published: June 2003

ABSTRACTThe short‐term effects of rare earth elements on pollen germination and tube growth were tested. Concentrations of 2.5∼20 µm lanthanum(La3+) or cerium (Ce3+)increased pollen germination and pollen tube growth, whereas concentrations higher than 40 µm La3+ and Ce3+ inhibited this process. The most effective concentration of La3+ needed for promotion shifted from 10 to 40 µm, depending on the Ca2+ concentration in the medium. Calmodulin (CaM) antagonist W7‐agarose and anti‐CaM antibody depressed La3+‐promoted pollen germination and tube growth in a dose‐dependent manner. La3+–CaM complexes (La3+–CaM) increased pollen germination and tube growth more than CaM or La3+ alone. Pertussis toxin (PTX) inhibited La3+‐promoted pollen germination and tube growth. Cholera toxin (CTX) partially recovered the inhibition of the above La3+‐promoted process by the anti‐CaM antibody. Concentrations of 10−7∼10−9 m La3+–CaM increased GTPase activity inside plasma membrane vesicles of the pollen tube, but apo‐CaM or La3+ alone had no positive effects. The results suggest that apoplastic CaM may be involved in the promotion effects of lower concentrations of La3+ on pollen germination and tube growth, and the heterotrimeric G‐protein on the plasma membrane may transduce La3+‐activated CaM signalling. The present studies provide an apoplastic mechanism for short‐term effects of rare earth elements at lower concentrations in the pollen system.
Rapid microalgal metabolism of selenate to volatile dimethylselenide
Authors: NEUMANN P. M. , DE SOUZA M. P. , PICKERING I. J. , TERRY N. 
Published: June 2003

ABSTRACTAn axenically cultured isolate of single‐celled freshwater microalgae (Chlorella sp.) metabolized toxic selenate to volatile dimethylselenide at exceptionally high rates when transferred from mineral‐nutrient solution to water for 24 h. The Se‐volatilization rates were orders of magnitude higher than those similarly measured for wetland macroalgae and higher plants. Ninety percent of 20 µm selenate supplied to the microalgae incubated without nutrients was removed through accumulation and volatilization. Additions of 1 mm sulphate but not nitrate, inhibited Se accumulation and volatilization so that only 1.8% of the supplied selenate was removed. The microalgae cultured in nutrient solution without sulphate showed increased 35S‐sulphate‐transporter activity. Selenium K‐edge X‐ray absorption spectroscopy of selenate‐treated microalgae cultured with or without mineral nutrients, showed that 87% of the selenate accumulated during 24 h was reductively metabolized to intermediate organic compounds such as selenomethionine and selenocystine. This is in complete contrast to higher plants that show very limited reduction of selenate. It appears that high rates of Se accumulation and volatilization by the sulphate‐deprived microalgae resulted from reduced competition with chemically analogous sulphate ions for selenate uptake via up‐regulated sulphate/selenate transporters and rapid reductive metabolism of selenate. Hyper‐volatilization of selenate by microalgal cells may provide a novel detoxification response.
Differential expression of three members of the AMT1 gene family encoding putative high‐affinity NH4+ transporters in roots of Oryza sativa subspecies indica
Authors: KUMAR A. , SILIM S. N. , OKAMOTO M. , SIDDIQI M. Y. , GLASS A. D. M. 
Published: June 2003

ABSTRACTIn order to investigate the molecular basis of high‐affinity ammonium absorption by roots of rice plants (Oryza sativa subspecies indica) the expression patterns of three members of the AMT1 family of genes in rice seedling roots in response to altered nitrogen provision and diurnal changes in irradiance were examined. The 13NH4+ influx and transcript levels of OsAMT1.1 in roots decreased several fold within 48 h when plants acclimated to 10 µm external NH4+ for 3 weeks were transferred to 10 mm NH4+. Likewise when plants acclimated in 10 mm NH4+ were transferred to 10 µm NH4+, there was an equally rapid up‐regulation of OsAMT1.1 and 13NH4+ influx in the roots. Changes in transcript abundance of OsAMT1.2 following these treatments were approximately 50% less than in OsAMT1.1, and changes of OsAMT1.3 expression were even less. By contrast, in response to the diurnal changes of irradiance, root transcript abundance of OsAMT1.3 and 15NH4+ influx increased approximately three‐fold late in the photoperiod, whereas OsAMT1.1 and OsAMT1.2 exhibited only modest changes. The present results suggest that high‐affinity NH4+ influx is differentially regulated at the transcriptional level through the expression of three members of the OsAMT1 family of genes in roots of rice seedlings in response to changes of N status and daily irradiance. In general, these findings are in agreement with earlier observations in Arabidopsis and tomato.
Leaf‐level phenotypic variability and plasticity of invasive Rhododendron ponticum and non‐invasive Ilex aquifolium co‐occurring at two contrasting European sites
Authors: NIINEMETS Ü. , VALLADARES F. , CEULEMANS R. 
Published: June 2003

ABSTRACTTo understand the role of leaf‐level plasticity and variability in species invasiveness, foliar characteristics were studied in relation to seasonal average integrated quantum flux density (Qint) in the understorey evergreen species Rhododendron ponticum and Ilex aquifolium at two sites. A native relict population of R. ponticum was sampled in southern Spain (Mediterranean climate), while an invasive alien population was investigated in Belgium (temperate maritime climate). Ilex aquifolium was native at both sites. Both species exhibited a significant plastic response to Qint in leaf dry mass per unit area, thickness, photosynthetic potentials, and chlorophyll contents at the two sites. However, R. ponticum exhibited a higher photosynthetic nitrogen use efficiency and larger investment of nitrogen in chlorophyll than I. aquifolium. Since leaf nitrogen (N) contents per unit dry mass were lower in R. ponticum, this species formed a larger foliar area with equal photosynthetic potential and light‐harvesting efficiency compared with I. aquifolium. The foliage of R. ponticum was mechanically more resistant with larger density in the Belgian site than in the Spanish site. Mean leaf‐level phenotypic plasticity was larger in the Belgian population of R. ponticum than in the Spanish population of this species and the two populations of I. aquifolium. We suggest that large fractional investments of foliar N in photosynthetic function coupled with a relatively large mean, leaf‐level phenotypic plasticity may provide the primary explanation for the invasive nature and superior performance of R. ponticum at the Belgian site. With alleviation of water limitations from Mediterranean to temperate maritime climates, the invasiveness of R. ponticum may also be enhanced by the increased foliage mechanical resistance observed in the alien populations.
Contrasting strategies for UV‐B screening in sub‐Arctic dwarf shrubs
Authors: SEMERDJIEVA S. I. , SHEFFIELD E. , PHOENIX G. K. , GWYNN‐JONES D. , CALLAGHAN T. V. , JOHNSON G. N. 
Published: June 2003

ABSTRACTThe content and distribution of UV‐absorbing phenolic compounds was investigated in leaves of three species of Vaccinium co‐existing at a site in north Sweden. Vaccinium myrtillus L., Vaccinium vitis‐idaea L., and Vaccinium uliginosum L. exhibit markedly different strategies, in terms of localization and content of leaf phenolics and in their responses to UV‐B enhancement. Plants were exposed to either ambient radiation or to enhancement of UV‐B corresponding to 15% (clear sky) depletion of stratospheric ozone for approximately 10 years prior to commencement of this study. Vaccinium myrtillus contained the highest concentration of methanol‐extractable UV‐B‐absorbing compounds, which was elevated in plants exposed to enhanced UV‐B. Fluorescence and confocal laser scanning microscopy showed that these compounds were distributed throughout the leaf, and were particularly concentrated in chlorophyll‐containing cells. In V. vitis‐idaea, most phenolic compounds were cell wall‐bound and concentrated in the walls of the epidermis; this pool increased in response to UV‐B enhancement. It is suggested that these two plants represent extreme forms of two divergent strategies for UV‐B screening, the different responses possibly being related to leaf longevity in the two species. The response of V. uliginosum was intermediate between the other two, with high concentrations of cell wall‐bound phenolics in the epidermis but with this pool decreasing, and the methanol‐soluble pool tending to increase, after exposure to enhanced UV‐B. One explanation for this response is that this plant is deciduous, like V. myrtillus, but has leaves that are structurally similar to those of V. vitis‐idaea.
Association of Vertical Root‐Pulling Resistance with Root Lodging and Grain Yield in Selected S1 Maize Lines Derived from a Tropical Low‐Nitrogen Population
Authors: Kamara A. Y. , Kling J. G. , Menkir A. , Ibikunle O. 
Published: June 2003

AbstractRoot lodging and poor soil fertility are major constraints to maize production in the Guinea savannah of West Africa. Vertical root‐pulling resistance is an indicator of the rooting characteristics of maize cultivars and could be used to select cultivars which have higher resistance to root lodging, take up nitrogen efficiently and have high yield. Twenty maize breeding lines were evaluated in the southern Guinea savannah of Nigeria for vertical root‐pulling resistance, yield and root lodging in the 2000 and 2001 cropping seasons. There were significant differences amongst the breeding lines for all the characteristics measured. Vertical root‐pulling resistance correlated positively with grain yield (r = 0.71, P < 0.01). There was a moderate negative correlation between vertical root‐pulling resistance and root lodging (r = −0.46, P < 0.05). This suggested that selecting for high root‐pulling resistance will improve grain yield and reduce root lodging. There was no significant association between root lodging and grain yield (r = −0.14, P < 0.22). This was attributed to two factors; weak root systems and high cob weight, both of which caused significant lodging.
Lack of Interaction between Extreme High‐Temperature Events at Vegetative and Reproductive Growth Stages in Wheat
Authors: Wollenweber B. , Porter J. R. , Schellberg J. 
Published: June 2003

AbstractIncreased climatic variability and more frequent episodes of extreme conditions may result in crops being exposed to more than one extreme temperature event in a single growing season and could decrease crop yields to the same extent as changes in mean temperature. The developmental stage of the crop exposed to increased temperatures will determine the severity of possible damage experienced by the plant. It is not known whether or not the damaging effects of heat episodes occurring at different phenological stages are additive. In the present study, the interaction of high‐temperature events applied at the stages of double ridges and anthesis in Triticum aestivum (L.) cv. Chablis was investigated. Biomass accumulation of control plants and that of plants experiencing high temperatures during the double‐ridge stage were similar and were reduced by 40 % when plants were subjected to a heat event at anthesis. Grain number on the main and side tillers declined by 41 %, and individual grain weight declined by 45 % with heat stress applied at the double‐ridge stage and anthesis or at anthesis alone. The harvest index was reduced from 0.53 to 0.33. Nitrogen contents in leaves were reduced by 10 % at the double‐ridge stage and by 25 % at anthesis. The maximum rates of CO2 assimilation increased with heat stress at the double‐ridge stage and higher rates were maintained throughout the growing season. The results clearly indicate that an extreme heat event at the double‐ridge stage does not affect subsequent growth or the response of wheat to heat stress at anthesis.
Faults in Determining Nitrogenase Activity
Authors: Singh G. , Wright D. 
Published: June 2003

AbstractThe effects of three treatments performed before the acetylene reduction assay, i.e. shoot removal, shoot removal plus root shaking, and no disturbance (intact plants), and of the length of the incubation period (10, 30 or 60 min) on nitrogenase activity were investigated in pea (Pisum sativumL.). The shoot removal plus root shaking treatment decreased nitrogenase activity to a greater extent than shoot removal. Nitrogenase activity was significantly higher when measured after a 10‐min incubation period than after a 30‐ or 60‐min incubation period. In another experiment, plants disturbed 15 min before the assay had a higher activity than plants disturbed 75 or 135 min before the assay. Similar results were obtained when activity was expressed as total nitrogenase activity and as specific nitrogenase activity.