bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Root Cooling on Photosynthesis of Artemisia tridentata Seedlings under Different Light Levels
Authors: BassiriRad H. , Caldwell M. M. , Mott K. A. 
Published: February 2014

AbstractRoot chilling has been shown to inhibit shoot photosynthesis yet the mechanism for such an action is not clearly understood. A study was designed to elucidate the mechanism by which root cooling may affect net photosynthesis. Roots of Artemisia tridentata seedlings were cooled from 20°C to 5°C while their shoot temperature remained at 20°C. This was conducted at two light levels (700 and 1300 μmol m−2 s−1). The time course of shoot net photosynthesis (A), stomatal conductance to water vapor (gs), intercellular CO2 concentration (Ci) and root respiration (Rs) were determined on a whole‐plant basis. Root cooling caused a 25% reduction in A at high PPFD, which was preceded by more than 50% reduction of gs and about 10% reduction in Ci. A versus Ci curves for single branches showed no difference between cold and warm soil temperatures, although stomatal conductance was lower for the lower soil temperature. This suggests that a stomatal limitation may have been involved in the inhibition of A. Furthermore, a concomitant decrease of as much as 23% in leaf relative water content (RWC) indicated that root cooling affected stomatal closure due to decreased water supply to the foliage. At lower PPFD, root cooling did not cause a decrease in A of the whole plant despite a moderate drop in gs, Ci and RWC. Cold soil also led to a substantial and rapid reduction in root respiration rate (Rs) regardless of the light level.
The Effect of Nitrogen Supply to Urtica dioica L. Plants on the Distribution of Assimilate Between Shoot and Roots
Authors: Fetene M. , Möller Ina , Beck E. 
Published: February 2014

AbstractIn this study the influence of nitrogen nutrition on the patterns of carbon distribution was investigated with Urtica dioica. The nettles were grown in sand culture at 3 levels of NO−3, namely 3 (low), 15 (medium) and 22 (high) mM. These levels encompassed a range within which nitrogen did not affect total biomass production. The ratio of root: shoot biomass of the low nitrogen plants was, however, significantly higher than that of the nettles grown at medium and high N supply. Carbon allocation from one leaf of each pair of leaves was examined after a 14CO2‐pulse and a subsequent 14C distribution period of one night. Only the youngest two leaf pairs did not export assimilates. Carbon (14C) export to the shoot apex and to the roots, as measured at the individual nodes responded to the nitrogen status: At medium and high nitrogen supply the 3rd, 4th and 5th leaf pairs exported to the shoot apex, while lower leaves exported to the root. At low nitrogen supply only the 3rd leaf exported towards the shoot apex. The results illustrate the plastic response of carbon distribution patterns to the nitrogen supply, even when net photosynthesis, carbon export from the source leaves and biomass production were not affected by the nitrogen supply to the plant.
Some Critical Remarks on the Suitability of the Concept of the Photosynthetic Unit in Photosynthesis Research and Phytoplankton Ecology
Authors: Wilhelm C. 
Published: February 2014

AbstractBased on the classical definition of the photosynthetic unit after Emerson and Arnold, new definitions are presented and their consistency subjected to critical reflection. Modern molecular approaches to determine the physiological condition or even the efficiency of the photosynthetic machinery via determination of the magnitude of the photosynthetic unit are discussed against the background of new data on the dynamics of the thylakoid membrane.
Wax as a Mechanism for Protection against Photoinhibition — A Study of Cotyledon orbiculata
Authors: Robinson Sharon A. , Lovelock Catherine E. , Osmond C. B. 
Published: February 2014

AbstractThe leaves of the Crassulacean acid metabolism plant Cotyledon orbiculata have a waxy coating which is highly reflective but can be easily removed by brushing. This provided an ideal system in which to investigate the role of epidermal wax as a possible photoprotectant. Removal of the wax, prior to exposure to natural sunlight, resulted in substantial decreases in Fv/Fm and in severe cases evidence of photoinhibitory damage, as indicated by a rise in Fo. Leaves from which wax had been removed also showed higher conversion of violaxanthin to zeaxanthin than waxed leaves. Recovery of brushed leaves over a 12 day period was correlated with an increase in the total pool of xanthophyll cycle components. This study suggests that the presence of highly reflective wax on the epidermis may confer significant photoprotection to plants exposed to high solar radiation environments.
Expression of P‐Enolpyruvate Carboxylase and other Aspects of CAM during the Development of Peperomia camptotricha Leaves
Authors: Ting I. P. , Hann Janet , Sipes Deborah , Patel Asmita , Walling Linda L. 
Published: February 2014

AbstractDuring the development of Peperomia camptotricha leaves, metabolism changes from C3‐photosynthesis to Crassulacean acid metabolism (CAM). The youngest leaves showed no diurnal fluctuation of organic acids or P‐enolpyruvate carboxylase (PEPc) activity. There was little evidence for PEPc protein using PEPc antibodies prepared from the CAM form of PEPc, nor was there evidence for PEPc mRNA when tested using a cDNA probe made from CAM P. scandens. As leaves matured, there was a parallel increase in titratable acidity, PEPc activity, PEPc protein, and PEPc mRNA. In leaf whorls 1 through 6, there was a significant linear correlation between the diurnal fluctuation of organic acids and PEPc activity indicating a functional relationship. The specific activity of PEPc increased as leaves matured and the Km (PEP) decreased indicating that the enzyme was becoming more active. The ratio of PEPc protein to PEPc mRNA decreased as leaves matured. During the expression of CAM, the spongy mesophyll where most of the CAM activity occurs increased in thickness and per cent air space, whereas the palisade mesophyll where most of the C3 activity occurs did not increase in size dramatically. The diurnal fluctuation of organic acids and the expression of PEPc activity, protein, and mRNA increased as the thickness of the spongy mesophyll increased. During the expression of CAM in Peperomia camptotricha, there appears to be coordinated expression of PEPc mRNA, protein, and activity, the commencement of diurnal organic acid fluctuation, and the development of the CAM‐like spongy mesophyll. Thus the evidence suggests that CAM in this species is expressed during normal development and not in response to environmental signals.
Quantitative Evaluation of Erotactin Secretion in Eggs of Hormosira banksii (Fucales, Phaeophyceae)
Authors: Maier I. , Clayton M. N. 
Published: February 2014

AbstractThe release of the C11‐hydrocarbon spermatozoid attractant hormosirene by eggs of the Australian fucoid Hormosira banksii has been determined quantitatively using a closed‐loop extraction technique. The eggs secrete erotactin for more than 2 weeks with an exponentially decreasing rate. The initial secretion rate was estimated to be 75 fmol h−1 egg−1 and the total amount of hormosirene produced per egg to be 2.35 pmol (0.35 ng). The results were used to calculate the threshold range for spermatozoid chemotaxis in the pheromone gradient around eggs.
Studies on the Sporogenous Lineage in the Moss Timmiella barbuloides
Authors: Gambardella R. , Duckett J. G. , Alfano F. , Gargiulo M. , Squillacioti C. 
Published: February 2014

AbstractThis correlated immunofluorescence and electron microscope study reveals that the microtubule arrays during meiosis in Timmiella barbuloides mirror those in other mosses but the organization of the metaphase I spindle is quite different. In other mosses the sagittiform metaphase I spindle initially contains four bands of microtubules derived from the tetrahedral system present at prophase. These bands converge towards the division axis and each half spindle contains two focal points of microtubules straddling a cleavage furrow. In Timmiella the sagittiform spindle also contains four microtubular foci derived from the preprophasic tetrahedron. However, one of these contributes to one half spindle, the other half deriving from the three remaining foci orientated at approximately 120° to each other. In contrast to other mosses the sporocytes in Timmiella are hardly lobed, the cleavage‐furrows ill‐defined, the prophasic plastid positioning in the lobes is also more variable and the organelle band in meiocytes comprises mitochondria alone.
Studies on the Localization and Spectral Characteristics of the Fluorescence Emission of Differently Pigmented Wheat Leaves
Authors: Stober1 F. , Lichtenthaler H. K. 
Published: February 2014

AbstractIntensity, spectral characteristics and localization of the UV‐laser (337 nm) induced blue‐green and red fluorescence emission of green, etiolated and white primary leaves of wheat seedlings were studied in a combined fluorospectral and fluoromicroscopic investigation. The blue‐green fluorescence of the green leaf was characterized by a maximum near 450 nm (blue region) and a shoulder near 530 nm (green region), whereas the red chlorophyll fluorescence exhibited maxima in the near‐red (F690) and far‐red (F735). The etiolated leaf with some carotenoids and traces of chlorophyll a, in turn, showed a higher intensity of the blue‐green fluorescence with a shoulder in the green region and a strong red fluorescence peak near 684 to 690 nm, the far‐red chlorophyll fluorescence maximum (F735) was, however, absent. The norfluorazone‐treated white leaf, free of chlorophylls and carotenoids, only exhibited blue‐green fluorescence of a very high intensity. In green and etiolated leaves the blue‐green fluorescence primarily derived from the cell walls of the epidermis and the red fluorescence from the chlorophyll a of the mesophyll cells. In white leaves the blue‐green fluorescence emanated from all cell walls of epidermis, mesophyll and leaf vein bundles. The shape and intensity of the blue‐green and red fluorescence emission is determined by the reabsorption properties of chlorophylls and carotenoids in the mesophyll, thus giving rise to quite different values of the various fluorescence ratios F450/F690, F450/F530, F450/F735 and F690/F735 in green and etiolated leaves.
The Stimulating Effect of a Cold Dark Pretreatment on the Accumulation of Components of Light‐Harvesting Chlorophyll a/b Complexes and on Photosynthetic Activity in Wheat (Triticum aestivum)
Authors: Zwicker H.‐G. , Schulz R. , Schönbohm E. 
Published: February 2014

AbstractRecently we reported on the stimulating effect of a cold dark pretreatment (cold‐dp) on the chlorophyll accumulation (Schönbohm et al., 1988) and on the CO2‐ and O2‐gas exchange (Schönbohm and Czeska‐Werner, 1990) during de‐etiolation of wheat leaves under white light.The goal of the present paper was to study the effect of a cold‐dp on the accumulation of chloroplast pigments, on the kinetics of fluorescence quenching, on the synthesis of Cab‐proteins and on the amounts of cab‐transcripts during de‐etiolation under white light.The following results were obtained:
Not only the chlorophyll synthesis but also the synthesis of xanthophylls and of β‐carotene is highly increased by a cold‐dp.
The kinetics of the PAM‐fluorescence curves demonstrate that the activity and co‐operation of the two photosystems start earlier and with higher efficiency during de‐etiolation in cold‐dp than in warm‐dp wheat leaves.
The amount of cab‐transcripts can be elevated by a cold‐dp.
The amount of Cab‐proteins during de‐etiolation is much higher in cold‐dp than in warm‐dp wheat leaves.
The presented data are in accordance with our earlier published results. Consequences of these results on seedlings growing under natural conditions with fluctuating temperatures during day and night are pointed out.
Peroxisomal Degradation of 2‐Oxoisocaproate. Evidence for Free Acid Intermediates
Authors: Gerbling Heidrun 
Published: February 2014

AbstractPeroxisomes from mung bean hypocotyl (Vigna radiata L.) degrade 2‐oxoisocaproate, the transamination product of leucine, via isobutyryl‐CoA and propionyl‐CoA to acetyl‐CoA. The methyl group at the C‐3 position forms a barrier to β‐oxidation. This barrier is overcome in the peroxisomes by several enzymatic steps. Senecioate (3‐methylcrotonate), 2‐hydroxyisovalerate, and 2‐oxoisovalerate were detected as free acid intermediates. Senecioate, formed from 3‐methylcrotonyl‐CoA, is transformed by enzymatic hydrolysis to 2‐hydroxyisovalerate. 2‐Hydroxyisovalerate is then oxidized to 2‐oxoisovalerate in an H2O2‐producing reaction, exhibiting 1:1 stoichiometry of the products, by a 2‐hydroxyacid oxidase which is different from the peroxisomal marker enzyme glycollate oxidase. 2‐oxoisovalerate is activated by an NAD‐dependent oxidative decarboxylation to isobutyryl‐CoA. Accumulation of 2‐oxoisovalerate in the presence of arsenite, an inhibitor of oxidative decarboxylations, is a feature of this latter pathway of degradation of isovaleryl‐CoA or senecioate. It is concluded that the barrier caused by the methyl group of 2‐oxoisocaproate is surmounted in higher plant peroxisomes in a manner different to that in mammalian mitochondria.
The Protonema of Chara fragilis Desv.: Regenerative Formation, Photomorphogenesis, and Gravitropism
Authors: Hodick D. 
Published: February 2014

AbstractWhen exposed to constant white light for four weeks, isolated nodes of Chara fragilis Desv. regenerated side branches, rhizoids, and multicellular protonemata, the latter being similar to those germinated from oospores. When kept in darkness the nodes developed protonemata exclusively. These were single‐celled, colourless, and tip‐growing and, with the light microscope, they looked like rhizoids. Upon exposure to blue light, but not to red or far‐red, the growth rates of the protonemata rapidly declined, the cell apices swelled, and the nucleus migrated acropetally. Within 24 h the cells went through the first of a series of divisions resulting in the formation of multicellular protonemata. When returned to darkness after a blue light pulse of 5 h the cell divisions proceeded normally, but the protonemata showed etiolated growth. While growth of the internode was drastically promoted, the development of the multicellular apex and the lateral initial were suppressed. Both uni‐ and multicellular etiolating protonemata showed negative gravitropism but were phototropically insensitive. It is argued that the single‐celled protonema is an organ specialized for the penetration of mud covering the nodes or oospores of Chara and thus serves to search for light, comparable to etiolated hypocotyls and stems in seedlings of higher plants.
Cellular Dimorphism in the Maize Root Cortex: Involvement of Microtubules, Ethylene and Gibberellin in the Differentiation of Cellular Behaviour in Postmitotic Growth Zones
Authors: Baluška F. , Brailsford R. W. , Hauskrecht M. , Jackson M. B. , Barlow P. W. 
Published: February 2014

AbstractDetailed morphometric analysis of cell shapes and an immunofluorescent study of microtubules were carried out on primary roots of Zea mays L. Two types of cells were found to be formed within the postmitotic isodiametric growth (PIG) region of the root cortex that were differentially responsive to low level of exogenous ethylene. The innermost and central cell rows of the cortex were sensitive to ethylene treatment and showed a disturbed distribution of cortical microtubules (CMTs) as well as changed polarity of cell growth, whereas the 2–3 outermost cell rows were less sensitive in this respect. This suggests that post‐mitotic cells of the inner cortex are specific targets for ethylene action. These properties of the inner cortex are compatible with its cells being involved in the formation of aerenchyma; they may also favour root growth in compacted soil. By contrast, the specific properties of the outer cortex indicate that this tissue domain is necessary for the gaseous impermeability and the mechanical strengthening of subjacent aerenchymatous cortex, especially in the mature region of the root.Ethylene affected neither the pattern of cortical cell expansion in the meristem nor the position of the PIG region with respect to the root tip. This contrasts with gibberellin‐deficiency which affected these parameters in both parts of the cortex. These observations indicate a fundamental difference between the role of these two phytohormones in the morphogenesis and development of maize roots.
The Determination of Phaseic Acid by Monoclonal Antibody‐Based Enzyme immunoassay
Authors: Gergs U. , Hagemann K. , Zeevaart J. A. D. , Weiler E. W. 
Published: February 2014

AbstractA monoclonal antibody PA3‐2‐B3, IgG1 (Λ) is described which specifically recognizes phaseic acid and shows very little cross‐reactivity (0.14%) with abscisic acid or dihydrophaseic acid (0.88%). Based on this antibody, an enzyme immunoassay was developed which displays a linearity range from 15 pg to 3 ng of phaseic acid. Results obtained with this assay agree with those obtained by gas chromatography‐electron capture detection. Using the novel enzyme immunoassay, as well as an established immunoassay for abscisic acid, levels of these two compounds in leaves of Phaseolus vulgaris were determined as a function of plant age, water stress, recovery from stress, and feeding of abscisic acid through the transpiration stream. The production of phaseic acid in a microsomal system from bean leaves was demonstrated. The results show a regulation of the plant's capacity to metabolize abscisic acid to phaseic acid as a function of water stress.
The Effect of Lateral Root Outgrowth on the Structure and Permeability of the Onion Root Exodermis
Authors: Peterson Carol A. , Moon Greg J. 
Published: February 2014

AbstractLateral root development in onion is accompanied by a variety of anatomical and permeability changes in some cells of the adventitious root. The endodermal Casparian band of the parent root is disrupted early in the development of the lateral but later extends so as to be continuous with the developing Casparian band of the new root. The lateral root emerges through a longitudinal split in the adventitious root exodermis and epidermis. Following this, the cell walls and intercellular air spaces adjacent to the lateral become incrusted with suberin and a small amount of lignin, forming a collar of modified tissue around the lateral. Subsequent radial expansion of the lateral distorts the adjacent cells of the adventitious root and forces a tight association between it and the lateral. The apoplastic permeability of lateral/parent root junctions was tested using Cellufluor, an apoplastic fluorescent dye which binds to cellulose. Prior to lateral root emergence, no dye enters the parent root cortex due to the Casparian band of the exodermis. Immediately after emergence, dye often penetrates through the break in the exodermal Casparian band and diffuses into the first cortical cell layer. However, when the collar of suberized cells develops (two days after lateral root emergence), movement of the dye into an undisturbed adventitious root is usually prevented (i.e., in 77% of the cases examined). In contrast, only 17% of the root systems which were transplanted just prior to treatment excluded the dye. This indicates that the apoplastic seals around the laterals are sensitive to movement and we recommend that only undisturbed root systems be used for permeability studies.
Uptake, Transport and Storage of Cardenolides in Foxglove. Cardenolide Sinks and Occurrence of Cardenolides in the Sieve Tubes of Digitalis lanata1
Authors: Christmann J. , Kreis W. , Reinhard E. 
Published: February 2014

AbstractCardiac glycoside transport was investigated on the organ and whole plant level. Uptake experiments were carried out with shoot and root cultures of Digitalis lanata. In both systems primary cardenolides, i.e., those with a terminal glucose in their oligosaccharide side chain, were taken up against their concentration gradient, whereas the glucose‐free secondary cardenolides were not. Active uptake of primary cardenolides was further evidenced by KCN inhibition of uptake. Using plantlets grown in vitro the long‐distance transport of primary cardenolides from the leaves to the roots was demonstrated. Cardenolides were also detected in etiolated leaves, induced on plants with green leaves, which are supposed to be unable to synthezise cardenolides de novo, providing further evidence for long‐distance transport. Several primary cardenolides were detected in the honeydew excreted by aphids fed on Digitalis lanata leaves, indicating that the phloem is a transporting tissue for cardenolides. On the other hand, the xylem sap obtained by applying the pressure‐chamber technique was cardenolide‐free. It was concluded that in Digitalis primary cardenolides serve as both the transport and the storage form of cardenolides. After their synthesis they are either stored in the vacuoles of the source tissue or loaded into the sieve tubes, from which they are unloaded at other sites where they are trapped in the vacuoles of the respective sink tissue.
Glutamine and Glutamate Transport in Cyanophora paradoxa
Authors: Kloos K. , Schlichting R. , Zimmer W. , Bothe H. 
Published: February 2014

AbstractThe present investigation showed that isolated cyanelles from Cyanophora paradoxa selectively enriched glutamine from the external medium, whereas glutamate poorly penetrated into these organelles. Glutamine uptake proceeded in two phases, presumably involving a low and a high affinity system. The uptake of glutamine was significantly enhanced by 2‐oxoglutarate and light. Inhibitor experiments indicated that glutamine and 2‐oxoglutarate were converted to glutamate by a ferredoxin‐dependent glutamate synthase (GOGAT) reaction inside the cyanelles, and the glutamate formed at best slowly left these organelles. Such results were obtained independently of each other by measuring either the 14C‐glutamine uptake or the 2‐oxoglutarate and glutamine‐dependent O2 evolution. Glutamine is suggested to be the N‐compound which is supplied to the eukaryotic host. Glutamine could be exported jointly with 2‐oxoglutarate, possibly employing a common carrier. Cyanelles have apparently evolved glutamine (and oxoglutarate) carrier(s) with properties not yet described for any other organism.
The Life Cycle of Cryptochlora perforans (Chlorarachniophyta)
Authors: Beutlich A. , Schnetter R. 
Published: February 2014

AbstractObservations on the behaviour of different life cycle stages, gamete fusions, and measurements of nuclear DNA contents in Cryptochlora perforans resulted in a first concept concerning life histories in Chlorarachniophyta: the life cycle of Cr. perforans is diplohaplontic (gamete fusion with karyogamy ‐ mitosis ‐ meiosis ‐ mitosis). In the haploid as well as in the diploid life cycle phases amoeboid and coccoid stages occur. The isomorphic gametes are modified amoebae frequently without filopodia. Only haploid flagellate stages are known representing mito‐ or meiozoospores. Diploid coccoid stages have a granular cytoplasmic structure and may be somewhat larger than haploid ones. Nevertheless, positive identification of haploid (gametophytic) and diploid (sporophytic) stages is only possible on the basis of nuclear DNA contents.