bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in growth, porosity, and radial oxygen loss from adventitious roots of selected mono‐ and dicotyledonous wetland species with contrasting types of aerenchyma
Authors: Visser E. J. W. , Colmer T. D. , Blom C. W. P. M. , Voesenek L. A. C. J. 
Published: March 2003

ABSTRACTGrowth in stagnant, oxygen‐deficient nutrient solution increased porosity in adventitious roots of two monocotyledonous (Carex acuta and Juncus effusus) and three dicotyledonous species (Caltha palustris, Ranunculus sceleratus and Rumex palustris) wetland species from 10 to 30% under aerated conditions to 20–45%. The spatial patterns of radial oxygen loss (ROL), determined with root‐sleeving oxygen electrodes, indicated a strong constitutive ‘barrier’ to ROL in the basal root zones of the two monocotyledonous species. In contrast, roots of the dicotyledonous species showed no significant ‘barrier’ to ROL when grown in aerated solution, and only a partial ‘barrier’ when grown in stagnant conditions. This partial ‘barrier’ was strongest in C. palustris, so that ROL from basal zones of roots of R. sceleratus and R. palustris was substantial when compared to the monocotyledonous species. ROL from the basal zones would decrease longitudinal diffusion of oxygen to the root apex, and therefore limit the maximum penetration depth of these roots into anaerobic soil. Further studies of a larger number of dicotyledonous wetland species from a range of substrates are required to elucidate the ecophysiological consequences of developing a partial, rather than a strong, ‘barrier’ to ROL.
Simultaneous measurement of water flow velocity and solute transport in xylem and phloem of adult plants of Ricinus communis over a daily time course by nuclear magnetic resonance spectrometry
Authors: Peuke A. D. , Rokitta M. , Zimmermann U. , Schreiber L. , Haase A. 
Published: March 2003

ABSTRACTA new method for simultaneously quantifying rates of flow in xylem and phloem using the FLASH imaging capabilities of nuclear magnetic resonance (NMR) spectrometry was applied in this study. The method has a time resolution of up to 4 min (for the xylem) and was used to measure the velocity of flows in phloem and xylem for periods of several hours to days. For the first time, diurnal time course measurements of flow velocities and apparent volume flows in phloem and xylem in the hypocotyl of 40‐d‐old Ricinus communis L were obtained. Additional data on gas exchange and the chemical composition of leaves, xylem and phloem sap were used to assess the role of leaves as sinks for xylem sap and sources for phloem. The velocity in the phloem (0·250 ± 0·004 mm s−1) was constant over a full day and not notably affected by the light/dark cycle. Sucrose was loaded into the phloem and transported at night, owing to degradation of starch accumulated during the day. Concentrations of solutes in the phloem were generally less during the night than during the day but varied little within either the day or night. In contrast to the phloem, flow velocities in the xylem were about 1·6‐fold higher in the light (0·401 ± 0·004 mm s−1) than in the dark (0·255 ± 0·003 mm s−1) and volume flow varied commensurately. Larger delays were observed in changes to xylem flow velocity with variation in light than in gas exchange. The relative rates of solute transport during day and night were estimated on the basis of relative flow and solute concentrations in xylem and phloem. In general, changes in relative flow rates were compensated for by changes in solute concentration during the daily light/dark cycle. However, the major solutes (K+, NO3−) varied appreciably in relative concentrations. Hence the regulation of loading into transport systems seems to be more important to the overall process of solute transport than do changes in mass flow. Due to transport behaviour, the chemical composition of leaves varied during the day only with regard to starch and soluble carbohydrates.
UV‐B‐induced DNA damage and expression of defence genes under UV‐B stress: tissue‐specific molecular marker analysis in leaves
Authors: Kalbin G. , Hidema J. , Brosché M. , Kumagai T. , Bornman J. F. , Strid Å. 
Published: March 2003

AbstractThe aim of this study was to investigate the regulatory effect of ultraviolet‐B (UV‐B) radiation on a number of key stress response genes found in the epidermis and mesophyll of Pisum sativum L., Argenteum mutant. This mutant was chosen for the ease with which the entire epidermis can be removed from the mesophyll tissue. An additional goal was to explore the potential modifying effect of pre‐acclimation of plants to UV‐B radiation prior to exposure by UV‐B during treatment. Results showed that mRNA accumulation was similar during acute short‐term UV‐B exposure for chalcone synthase (Chs) and short‐chain alcohol dehydrogenase (SadA) in both epidermis and mesophyll. In contrast, the mRNA levels differed considerably between tissues for phenylalanine ammonia lyase, chalcone isomerase and lipid transfer protein. After 24 h incubation in visible light after cessation of UV‐B exposure, the regulation of mRNA levels also differed between Chs and SadA, the former showing no expression in the epidermis and the latter none in the mesophyll. Acclimation to low UV‐B levels before acute exposures resulted in delayed induction of Chs and SadA. Measurements of UV‐B‐induced cyclobutane pyrimidine dimers (CPDs) showed a greater formation in epidermis than in mesophyll. In addition, acclimation at low UV‐B levels resulted in significantly higher basal levels of CPDs than in non‐acclimated plants in both mesophyll and epidermis and also in increased damage in concomitant acute exposures. The lack of correlation between the number of CPDs and levels of transcripts for defence genes, indicates that DNA damage does not control transcription of these genes.
Cadmium induces senescence symptoms in leaf peroxisomes of pea plants
Authors: McCarthy I. , Romero‐Puertas M. C. , Palma J. M. , Sandalio L. M. , Corpas F. J. , Gómez M. , Del Río L. A. 
Published: March 2003

AbstractThe effect of growing pea (Pisum sativum L.) plants with a toxic CdCl2 concentration (50 µm) on the metabolism and proteolytic activity of leaf peroxisomes was studied. In peroxisomes purified from plants treated with cadmium, an increase in the total protein concentration and in the activity and protein level of the photorespiratory enzyme glycolate oxidase was found. The glyoxylate cycle enzymes, malate synthase and isocitrate lyase, whose activity is normally very low in leaf peroxisomes, were enhanced by Cd treatment. The activity of the endogenous proteases of leaf peroxisomes was determined. Two leucine‐aminopeptidase isozymes (AP1‐AP2) were detected, and their activity was slightly higher in Cd‐treated plants. Five endopeptidases (EP1‐EP5) were present in pea leaf peroxisomes, and in plants grown with Cd the activity of isozymes EP1‐EP4 was increased. The ultrastructural analysis of pea leaves showed that Cd produced a disorganization of the chloroplast structure, with an increase in the number of plastoglobuli, and the formation of vesicles in the vacuoles. Taken together, these results indicate that Cd induces senescence symptoms in leaf peroxisomes, and probably a metabolic transition of leaf peroxisomes into glyoxysomes, and suggest that the peroxisomal proteases could participate in the metabolic changes produced by Cd.
Nitrogen dynamics during O3‐induced accelerated senescence in hybrid poplar
Authors: Bielenberg D. G. , Lynch J. P. , Pell E. J. 
Published: March 2003

AbstractExperiments were conducted to determine the fate of nitrogen (N) remobilized as a result of ozone (O3)‐induced accelerated senescence in hybrid poplar subjected to declining N availability concurrent with O3 stress. Cuttings were grown in sand culture where the supply of N to the plant could be controlled on a daily basis and reduced in half of the plants when desired. Plants all initially received 3·57 mm N daily until approximately the 20 leaf stage after which daily supply of N was reduced to 0·71 mm. Plants were grown in open‐top chambers in the field (Rock Springs, PA, USA) and received charcoal‐filtered air, half also received supplemental O3 to a level of 0·08 µL L−1. Allocation of newly acquired N was determined with 15N. The specific allocation (mg labelled N mg−1 total N) of labelled N to upper, expanding leaf N was not affected by O3, but was strongly affected by N treatment. However, O3 increased the relative partitioning of labelled N to the expanding leaves and the roots. The balance between partitioning of newly acquired N to the upper leaves and roots was not affected by O3, but was reduced by N withdrawal. Calculated net N flux was strongly negative in the lower leaves of O3‐exposed, N withdrawal plants. Nitrogen uptake was not reduced by O3. The allometric relationships between the roots and shoots were not affected by O3 or N availability. The relative contribution of newly acquired versus remobilized N to new growth appears to be determined by N supply. Ozone exposure alters the allocation of newly acquired N via alterations in plant size, whereas N availability exerts a strong effect upon both plant size and N allocation.
Atmospheric CO2 concentration may directly affect leaf respiration measurement in tobacco, but not respiration itself*
Authors: Jahnke S. , Krewitt M. 
Published: March 2003

AbstractWhen atmospheric CO2 concentration increases, various consequences for plant metabolism have been suggested, such as changes in photosynthesis, photorespiration or respiration which can affect growth and carbon sequestration. In addition to long‐term (indirect) effects on respiration, short‐term (direct) effects of CO2 concentration on the respiration of leaves, shoots and roots are described in the literature. In most cases, respiration is reported to be inhibited by increased CO2 concentration, but the mechanism(s) are not yet understood. It has been shown previously that, when the respective technical problems and properties of a gas exchange system are fully considered, a short‐term increase in CO2 (up to 4200 µmol mol−1) had no effect on respiration of Phaseolus or Populus leaves (Jahnke, Plant, Cell and Environment 24, 1139–1151, 2001). However, in the present study, large (apparent) CO2 effects were found with mature Nicotiana leaves whereas, in young leaves, the effect was absent. The experimental results clearly show that the observed direct CO2 effect on dark CO2 efflux in the mature tobacco leaves was caused by leakage of CO2 inside the leaves (and the magnitude of the effect was dependent on the size of the leakage). Nicotiana leaves are, in contrast to Phaseolus and Populus leaves (which are heterobaric), characterized by a homobaric anatomy in which intercellular air spaces are not compartmented and provide a continuous system of open pores in the lateral (paradermal) direction of the leaves. Mesophyll porosity increases with leaf development, which explains the differences between young and mature tobacco leaves. When internal leakage was experimentally restricted, the CO2 inhibition on CO2 efflux was no longer observed. It is concluded that the measured direct CO2 effect(s) on leaf CO2 efflux in the dark are artefactual, and that a true direct CO2 effect on leaf respiration does not exist.
Enhanced tolerances of transgenic tobacco plants expressing both superoxide dismutase and ascorbate peroxidase in chloroplasts against methyl viologen‐mediated oxidative stress
Authors: Kwon S. Y. , Jeong Y. J. , Lee H. S. , Kim J. S. , Cho K. Y. , Allen R. D. , Kwak S. S. 
Published: March 2003

AbstractIn order to better understand the role of antioxidant enzymes in plant stress protection mechanisms, transgenic tobacco (Nicotiana tabacum cv. Xanthi) plants were developed that overexpress both superoxide dismutase (SOD) and ascorbate peroxidase (APX) in chloroplasts. These plants were evaluated for protection against methyl viologen (MV, paraquat)‐mediated oxidative damage both in leaf discs and whole plants. Transgenic plants that express either chloroplast‐targeted CuZnSOD (C) or MnSOD (M) and APX (A) were developed (referred to as CA plants and AM plants, respectively). These plant lines were crossed to produce plants that express all three transgenes (CMA plants and AMC plants). These plants had higher total APX and SOD activities than non‐transgenic (NT) plants and exhibit novel APX and SOD isoenzymes not detected in NT plants. As expected, transgenic plants that expressed single SODs showed levels of protection from MV that were only slightly improved compared to NT plants. The expression of either SOD isoform along with APX led to increased protection while expression of both SODs and APX provided the highest levels of protection against membrane damage in leaf discs and visual symptoms in whole plants.
Cucumber mosaic virus movement protein affects sugar metabolism and transport in tobacco and melon plants
Authors: Shalitin D. , Wang Y. , Omid A. , Gal‐On A. , Wolf S. 
Published: March 2003

AbstractIn addition to its influence on plasmodesmal function, tobacco mosaic virus movement protein (TMV‐MP) causes an alteration in carbon metabolism in source leaves and in resource partitioning among the various plant organs. The present study was aimed at characterizing the influence of cucumber mosaic virus (CMV)‐MP on carbohydrate metabolism and transport in both tobacco and melon plants. Transgenic tobacco plants expressing the CMV‐MP had reduced levels of soluble sugars and starch in their source leaves and a significantly reduced root‐to‐shoot ratio in comparison with control plants. A novel virus‐vector system was employed to express the CMV‐coat protein (CP), the CMV‐MP or the TMV‐MP in melon plants. This set of experiments indicated that the viral MPs cause a significant elevation in the proportion of sucrose in the phloem sap collected from petioles of source leaves, whereas this sugar was at very low levels or even absent from the sap of control melon plants. The mode by which the CMV‐MP exerts its effect on phloem‐sap sugar composition is discussed in terms of possible alterations in the mechanism of phloem loading.
Profiles of light absorption and chlorophyll within spinach leaves from chlorophyll fluorescence
Authors: Vogelmann T. C. , Evans J. R. 
Published: March 2003

AbstractChlorophyll fluorescence was used to estimate profiles of absorbed light within chlorophyll solutions and leaves. For chlorophyll solutions, the intensity of the emitted fluorescence declined in a log–linear manner with the distance from  the  irradiated  surface  as  predicted  by  Beer's  law. The amount of fluorescence was proportional to chlorophyll  concentration  for  chlorophyll  solutions  given  epi‐illumination on a microscope slide. These relationships appeared to hold for more optically complex spinach leaves. The profile of chlorophyll fluorescence emitted by leaf cross sections given epi‐illumination corresponded to chlorophyll content measured in extracts of leaf paradermal sections. Thus epifluorescence was used to estimate relative chlorophyll content through leaf tissues. Fluorescence profiles across leaves depended on wavelength and orientation, reaching a peak at 50–70 µm depth. By infiltrating leaves with water, the pathlengthening due to scattering at the airspace : cell wall interfaces was calculated. Surprisingly, the palisade and spongy mesophyll had similar values for pathlengthening with the value being greatest for green light (550 > 650 > 450 nm). By combining fluorescence profiles with chlorophyll distribution across the leaf, the profile of the apparent extinction coefficient was calculated. The light profiles within spinach leaves could be well approximated by an apparent extinction coefficient and the Beer–Lambert/Bouguer laws. Light was absorbed at greater depths than predicted from fibre optic measurements, with 50% of blue and green light reaching 125 and 240 µm deep, respectively.
Photosynthetic parameters in seedlings of Eucalyptus grandis as affected by rate of nitrogen supply
Authors: GRASSI G. , MEIR P. , CROMER R. , TOMPKINS D. , JARVIS P. G. 
Published: March 2003

AbstractSeedlings of Eucalyptus grandis were grown at five different rates of nitrogen supply. Once steady‐state growth rates were established, a detailed set of CO2 and water vapour exchange measurements were made to investigate the effects of leaf nitrogen content (N), as determined by nitrogen supply rate, on leaf structural, photosynthetic, respiratory and stomatal properties. Gas exchange data were used to parametrize the Farquhar–von Caemmerer photosynthesis model. Leaf mass per area (LMA) was negatively correlated to N. A positive correlation was observed between both day (Rd) and night respiration (Rn) and N when they were expressed on a leaf mass basis, but no correlation was found on a leaf area basis. An Rd/Rn ratio of 0·59 indicated a significant inhibition of dark respiration by light. The maximum net CO2 assimilation rate at ambient CO2 concentration (Amax), the maximum rate of potential electron transport (Jmax) and the maximum rate of carboxylation (Vcmax) significantly increased with N, particularly when expressed on a mass basis. Although the maximum stomatal conductance to CO2 (gscmax) was positively correlated with Amax, there was no relationship between gscmax and N. Leaf N content influenced the allocation of nitrogen to photosynthetic processes, resulting in a decrease of the Jmax/Vcmax ratio with increasing N. It was concluded that leaf nitrogen concentration is a major determinant of photosynthetic capacity in Eucalyptus grandis seedlings and, to a lesser extent, of leaf respiration and nitrogen partitioning among photosynthetic processes, but not of stomatal conductance.
Limits to xylem refilling under negative pressure in Laurus nobilis and Acer negundo
Authors: HACKE U. G. , SPERRY J. S. 
Published: March 2003

ABSTRACTThe ability of juvenile Laurus nobilis and Acer negundo plants to refill embolized xylem vessels was tested under conditions of soil drought when xylem sap pressure was substantially negative, thus violating the expected condition that pressure must rise to near atmospheric for refilling. Intact potted plants were dried to a stem water potential (ΣW) corresponding with approximately 80% loss of hydraulic conductivity (PLC) in shoots. Then plants were re‐watered and kept at a less negative target ΨW for 1–48 h. The ΨW was measured continuously with stem psychrometers. Rewatered L. nobilis held at the target ΨW for 1 h showed no evidence for refilling unless ΨW was within a few tenths of a MPa of zero. In contrast, re‐watered L. nobilis held for 24 and 48 h at water potentials well below zero showed a significant reduction in PLC. The recovery was highly variable, being complete in some stem segments, and scarcely evident in others. Embolism repair was accompanied by a significant but moderate decrease in the osmotic potential (Ψ) of the bulk xylem sap (Ψ = −67 kPa in recovering plants versus −31 kPa in controls). In contrast, embolized and re‐watered A. negundo plants held for 24 h at target ΨW of −0·9 and −0·3 MPa showed no embolism reversal. The mechanism allowing L. nobilis plants to refill under negative pressure is unknown, but does not appear to operate in A. negundo, and is slower to act for drought‐induced embolism than when embolism was artificially induced by air injection as previously shown for L. nobilis.
Clonality and long‐distance migration of Puccinia striiformis f.sp. tritici in north‐west Europe
Authors: Hovmøller M. S. , Justesen A. F. , Brown J. K. M. 
Published: March 2003

The biotrophic fungus Puccinia striiformis f.sp. tritici, a basidiomycete that causes yellow rust on wheat, is spread by wind‐dispersed spores. Analysis of amplified fragment length polymorphism (AFLP) variation showed that the fungus frequently migrates between the UK, Germany, France and Denmark. There is no biological evidence for sexual or parasexual reproduction under natural conditions, and this was supported by the lack of recombination, as revealed by AFLP, over the time and area represented by the samples in this study. A phylogeographic analysis revealed that there was effectively a single, clonal population in the four countries, up to 1700 km apart, consistent with a ‘continent‐island’ model in which Denmark is the recipient of migrants from other countries. In five cases, specific pathogen clones were dispersed between the UK and Denmark, and on at least two recent occasions clones were also spread from the UK to Germany and France, causing outbreaks of yellow rust on wheat cultivars that were previously resistant to the disease in these countries. The agronomic consequences of migration were enhanced because of the limited genetic diversity for yellow rust resistance in wheat cultivars in the area. These results demonstrate that long‐distance migration of pathogen clones, coupled with low diversity in the host species, may cause previously useful resistance genes to become ineffective for disease control on a continental scale.
Genetic analyses of resistance of the wheat differential cultivars Carstens V and Spaldings Prolific to two races of Puccinia striiformis
Authors: Calonnec A. , Johnson R. , De Vallavieille‐Pope C. 
Published: March 2003

Genetic analysis of resistance of wheat seedlings to two races of Puccinia striiformis was conducted on F1, F2 and F3 generations from crosses Carstens V (CV) × Lee, Spaldings Prolific (SPA) × Lee and CV × SPA. F2 generations from crosses of CV and SPA with Strubes Dickkopf (SD) were also studied. The plants were classified into six resistance classes and analysed by factorial correspondence analysis and nonhierarchical classification. The two P. striiformis isolates tested were a French isolate of race 43E138 and a Lebanese isolate of race 2E16, selected for the differences in their virulence spectra for the common differential cultivars Strubes Dickkopf and Nord Desprez. Resistance of CV and SPA was recessive and dominant to races 43E138 and 2E16, respectively. CV possessed three or four resistance genes, one of them being expressed with both races. Two genes of CV had a cumulative effect for resistance to 43E138 and two or three gave dominant resistance to 2E16. SPA had three resistance genes, all of which gave resistance to 2E16 and two of which also gave resistance to 43E138. SPA had one gene in common with CV for resistance to both races. Furthermore, the gene for resistance to race 2E16 in CV and SPA was allelic with a gene in SD, and was probably Yr25.