bluuebunny/crossref_metadata_2025_split huggingface dataset:
Peroxisomes in Rice Coleoptiles Grown in Air and in Anoxia
Authors: De Bellis L. , Rascio N. , Pistelli L. , Alpi A. 
Published: February 2014

AbstractRice coleoptiles grow under anoxia. When the ultrastructure of anoxic coleoptile cells was examined, it was seen that most organelles maintain their integrity, with the exception of peroxisomes (unspecialized type). The lack of O2 greatly reduced the number of these organelles and altered the ultrastructure of the remaining ones. To examine the effect of O2 on peroxisome development in more detail, coleoptiles grown in air were transferred to N2 and anoxic coleoptiles were transferred to oxygen. Marker enzyme activity was measured in entire coleoptiles as well as in the isolated organelles. As expected, anoxia greatly depressed enzyme activity when imposed from the beginning of the germination process, while it had a lesser effect when imposed for only two days on aerobic seedlings. When coleoptiles were grown constantly under N2, the density of the organelles was 1.216 g/cm3, while the corresponding aerobic organelles showed a buoyant density of 1.241 g/cm3. When transferred to air the anoxic peroxisomes reached the intermediate density of 1.227 g/cm3. The results confirm the particular sensitivity of rice peroxisomes to O2 availability.
Intraspecific Variation in the Amino Acid Content of Floral Nectar
Authors: Gottsberger G. , Arnold T. , Linskens H. F. 
Published: February 2014

AbstractIn order to evaluate the constancy of amino acid composition and concentration, several randomly collected samples of genuine floral nectar from different flowers of several plant species were analysed. Although there seems to exist a rough pattern of species‐specific nectar amino acid composition, amino acid concentration varied strongly from sample to sample. Apart from the lack of constancy in concentration of floral amino acids, our samples do not show amino acid concentration values as assigned typical for the pertinent pollination mode by other workers.
A New Way to Investigate Living Flagellated/Ciliated Cells in the Light Microscope: Immobilization of Cells in Agarose
Authors: Reize Ingo Botho , Melkonian Michael 
Published: February 2014

AbstractA method for cell immobilization of living flagellated/ciliated cells in agarose has been developed that allows single cells to be viewed for prolonged periods of time using high resolution light microscopy. Embedding in ultralow gelling, soft agarose preserves cellular functions of various flagellated/ciliated protists including delicate species, marine dinoflagellates, cryptomonads, contractile ciliates, etc. for days. Cell division, morphogenesis of cell organelles and intracellular movements can thus be studied for the first time in great detail. The method may also be useful for the isolation of flagellated/ciliated protists from nature and for the establishment of axenic clonal cultures in a single step.
Evidence for the Presence of Chlorophyllide b in the Green Alga Scenedesmus obliquus in vivo
Authors: Kotzabasis Kiriakos , Senger Horst 
Published: February 2014

AbstractChlorophyllide b could be extracted from the wild type of Scenedesmus obliquus and its pigment mutant C‐2A'. Its identity was proved by absorption and fluorescence spectroscopy and by a positive hydroxylamine test. Chlorophyllide b could be transformed into pheophorbide b and methylpheophorbide b. The formation of chlorophyllide b from chlorophyll b by dephytylation with chlorophyllase could be ruled out. The stimulation of chlorophyllide b biosynthesis with o‐phenanthroline, as described in the literature, could not be confirmed under physiological conditions.
The Effect of Light and Exogenously Supplied Ammonium Ions on Glutamate Dehydrogenase Activity and Isoforms in Young Mustard (Sinapis alba L.) Seedlings
Authors: Lettgen W. , Britsch L. , Kasemir Helga 
Published: February 2014

AbstractGlutamate dehydrogenase (GDH, E.C. 1.4.1.3) of mustard cotyledons was investigated during the first 4 days of seedling development. The enzyme was found to be composed of seven catalytically active isoforms (each with a molecular mass of 270 kDa) which exhibited a charge heterogeneity when investigated by isoelectric focusing. Antibodies against the purified isoform 7, raised in rabbits, cross‐reacted with each of the isoforms in Western blotting experiments. In addition, each of the isoforms was composed of four immunopositive reacting polypeptides with 19, 21, 23 and 25 kDa. During development of the seedlings, a shift in the isoform pattern towards the more acidic forms was found which was more pronounced when the seedlings were supplied with 15 mM NH4Cl. The time course of changes in total GDH level can be correlated with the time course of disappearance of storage proteins. Both parameters are negatively regulated by light possibly via the photoreceptor, phytochrome. There are some indications that GDH in young mustard cotyledons mainly acts in the deaminating direction.
Light‐Induced Fern‐Spore Germination under Reduced Water Potential
Authors: Psaras G. K. , Haupt W. 
Published: February 2014

AbstractThe phytochrome‐mediated spore germination of the fern Dryopteris filix‐mas was studied under reduced water content. Spores were sown on solutions containing polyethylene glycol (PEG), sorbitol, or mannitol as osmotically active substances, yielding water potential values (ψ) between − 500 and − 3500 kPa for most of the experiments.Our main results can be summarized as follows:
The germination of the spores is completely blocked by ψ ≤ −1200 kPa (≥ 300 g/l PEG).
Reduced water content of the spores, at least up to 300 g/l PEG, does not impair the phototransformation of phytochrome from its inactive form Pr to its active form Pfr.
The inhibiting effect of the osmoticum is phase‐specific: the reduced water content of the spores impairs the coupling of the phytochrome system to the transduction chain. Under these conditions, Pfr is found to be stable for several days.
In addition, the reduced water potential acts on the terminal response, although differently on different parameters of germination: Whereas formation of the rhizoid is completely blocked by 180 g/1 PEG, chlorophyll formation requires 300 g/1 PEG to become slightly retarded.
Effects of Solar Radiation on Photoorientation, Motility and Pigmentation in a Freshwater Cryptomonas
Authors: Häder D.‐P. , Häder Maria 
Published: February 2014

AbstractThe effects of solar radiation on motility, photoorientation and pigmentation have been studied in a freshwater Cryptomonas species. The diaphototactic orientation performed by the cells is impaired within about 90 min of solar radiation. Likewise, the percentage of motile cells within the population and the average velocity of the swimming cells decreases within about the same exposure time. This effect is not due to a thermal stress but rather seems to be caused by the solar UV‐B component, since decreasing short wavelength UV radiation by means of an artificial ozone filter or UV cut‐off filters increased the tolerated exposure time. Solar radiation also bleached the photosynthetic pigments of the cells as shown by absorption difference spectra.
Co‐Localization of Particle Transport with Microtubules in Cytoplasmic Exudates of the Siphonous Green Alga Bryopsis
Authors: Menzel D. , Elsner‐Menzel Christine 
Published: February 2014

AbstractOrganelles in the cortical cytoplasm of the siphonous green alga Bryopsis display various types of motile activities. One of them, saltatory movement along axially oriented linear tracks is typical for mitochondria and other small particles. A method is described which allows in vitro observation of such movements in thin layers of cytoplasm extruded from the alga and attached to a poly‐l‐lysine coated glass surface. By comparing video recordings of motile activities with the position of cytoskeletal elements visualized by immunofluorescence in the same area of a cytoplasmic exudate, it can be shown that tracks along which particles have moved in vitro are identical with microtubules (MTs). Depolymerization of MTs in the cytoplasmic exudates by MT‐specific inhibitors stops particle movement, whereas depolymerization of actin filaments with cytochalasin D disrupts actin bundles but has little effect on particle motility. These data are consistent with the model of MT guided particle transport.
Life Cycle and Morphology ofBryopsidella ostreobiformisspec. nov. (Bryopsidaceae, Chlorophyta) from the Mediterranean, under Culture Conditions, with Comments on the Phylogeny of theBryopsis/DerbesiaComplex
Authors: Calderón‐Sáenz E. , Schnetter R. 
Published: February 2014

AbstractBryopsidella ostreobiformissp. nov. is presented as the second species of the genus. The latter is amended to accomodate this new species. The derbesioid sporophyte is capable of producing three‐ to eight‐rayed stellate propagules. The dioecious gametophyte is a heterotrichous thallus with branched, prostrate filaments and unbranched, erect ones, and does not resembleBryopsis. The life cycle is distinctly diplohaplontic, with a diploid sporophyte and a haploid gametophyte.B. ostreobiformisis postulated as the starting point of a hypothetical evolutionary sequence of life histories in theDerbesia/Bryopsiscomplex.
Phosphate Uptake by Eukaryotic Algae in Cultures and by a Mixed Phytoplankton Population in a Lake: Analysis by a Force‐Flow Relationship*
Authors: Falkner Renate , Falkner Univ.‐Doz. Dr Gemot 
Published: February 2014

AbstractThe phosphate uptake behaviour of monospecific cultures of green algae in the laboratory and of mixed phytoplankton populations in a mesotrophic lake has been analyzed with the aid of a force‐flow relationship. This analysis yields two parameters:
A conductivity coefficient, that characterizes the activity of the phosphate uptake system.
An external threshold phosphate concentration, below which uptake of phosphate is excluded on energetic grounds.
When the phosphate concentration lies below the threshold value, the algae show an activation of the uptake system, reflected in an increase in the conductivity coefficient. Correspondingly, excess phosphate above the threshold value leads to a diminuation of the conductivity.Using this simple analysis, phosphate discharge into lake water may be readily monitored.
Potassium Channels in Eremosphaera viridis: Modulation of Channel Opening, Conductance and Inhibition*
Authors: Köhler K. , Förster B. , Kolbowski J. 
Published: February 2014

AbstractI/V relationships were performed by the voltage clamp technique in the sphaerical green alga Eremosphaera viridis de Bary. We focused on the course of the transient potential (TP) found in light‐off experiments when specific potassium channels open. I/V measurements done during this period show a N‐shaped curve. The shape depended on external potassium. TPs could be released by light‐off and by addition of barium, strontium, or α‐naphthyl phosphate. We calculated the number of specific potassium channels to be between 1750 and 34 825 channels per cell.Barium (1 mol × m−3) and tetraethylammonium (10 mol × m−3) inhibited TPs. I/V relationships demonstrated, when N‐shaped, that potassium channels start to close at voltages more negative than −195 mV (0.1 mol × m−3 K+), −160 mV (1 mol × m−3 K+) and −148 mV (10 mol × m−3 K+). In the region of −300 mV conditions similar to those at rest are reached. External sodium suppressed the development of N‐shaped I/V relationships and reduced the membrane conductance during a TP between 8 % and 29 %. This indicates an influence of external sodium on potassium channels.
Chlorophyll Fluorescence of Lichens Containing Green and Blue‐Green Algae During Hydration by Water Vapor Uptake and by Addition of Liquid Water*
Authors: Lange O. L. , Bilger W. , Rimke S. , Schreiber U. 
Published: February 2014

AbstractThe fluorescence yield at room temperature of the lichens Ramalina maciformis and Peltigera rufescens, containing either green or blue‐green algae (Cyanobacteria) as phycobionts, has been investigated during rehydration of the dry lichens by water vapor uptake or by wetting with liquid water. In the dry state the fluorescence yield with all reaction centers open, Fo, was low and no variable fluorescence could be induced with both species. Whereas R. maciformis, containing green algae, regained normal fluorescence behavior during water vapor uptake, the photosynthetic apparatus of the blue‐green algae‐containing P. rufescens stayed inhibited and could be reactivated only by addition of liquid water. During stepwise rehydration at increasing air humidities, a pattern was established for the recovery of the different fluorescence parameters in R. maciformis. At a dry‐weight related water content between 30 and 40%, Fo rose sharply. Maximal variable fluorescence yield expressed as (Fv)m/Fo, strongly increased in the same range of water content and remained constant above a water content of 50%. Non‐photochemical fluorescence quenching, qNP, determined at the end of a period of actinic illumination, decreased with increasing water vapor uptake. While spraying the lichen with liquid water did not induce a further decrease of qNP, slow dehydration at lowered air humidity led to a minimal value of qNP at a water content of 65 % indicating optimal photosynthetic rate under these conditions. These results extend the conclusions drawn from earlier gas exchange experiments that blue‐green algae‐containing lichens are unable to reactivate photosynthesis by water vapor uptake. During a re‐ and de‐hydration cycle, no hysteresis in the hydration dependence of the fluorescence parameters was found. From this and the presence of a stable and low Fo value at prolonged incubation in nearly water vapor saturated air, we conclude that the reactivation of photosynthesis in blue‐green algae‐containing lichens is not prevented through high diffusion resistances for water.
Turnover of O‐Glucosides of Dihydrozeatin and Dihydrozeatin‐9‐riboside During the Cell Growth Cycle of Photoautotrophic Cell Suspension Cultures of Chenopodium rubrum
Authors: Fußeder A. , Ziegler P. , Peters W. , Beck E. 
Published: February 2014

SummaryThe cellular levels of O‐glucosides of 3H‐(diH)Z and 3H‐(diH)[9R]Z, the major short‐term metabolites of 3H‐(diH)Z having been exogenously supplied to photoautotrophically growing suspension cell cultures of Chenopodium rubrum, decreased significantly during further culture, irrespective of whether the cells were maintained in the stationary phase or were transferred to conditions restoring cell divison. Metabolism of both compounds was more pronounced during the active growth phase than during the stationary phase. The O‐glucosides were converted preferentially to polar compounds of as yet unknown nature, which were partly excreted into the medium. The cellular pools of both glycosides remained compartmented within the vacuole. In contrast to the O‐glycosides, the small cellular pools of the aglycones 3H‐(diH)Z and 3H‐(diH)[9R]Z maintained their level during the experimental period of 30 days. Small amounts of the glucosides, as well as of the aglycones, were recovered from the medium and could have resulted from the lysis of a few cells. The results demonstrate, for the first time, that O‐glucosides of cytokinins are not irreversibly deposited within the vacuole of plant cells but may serve to maintain a small, but more or less constant pool of extra‐vacuolar, presumably cytosolic, aglycones. (DiH)Z and its derivatives could be demonstrated to be endogenous cytokinins of Chenopodium rubrum suspension cultured cells occurring along with those of the isopentenyladenine and zeatin types.
Membrane Particles, Proteins and ATPase Activity of Tonoplast Vesicles of Mesembryanthemum crystallinum in the C‐3 and CAM State*
Authors: Klink R. , Haschke H.‐P. , Kramer D. , Lüttge U. 
Published: February 2014

AbstractDimensions and area densities of membrane particles were studied by electron microscopy of replicas of freeze‐fractured suspensions of tonoplast vesicles of Mesembryanthemum crystallinum L. in the C‐3 state and after induction of crassulacean acid metabolism (CAM) by salinity. The results are compared with the relative contribution of tonoplast‐ATPase protein to total membrane protein obtained from integration of elution profiles in size‐exclusion chromatography. Coverage of tonoplast area by globular membrane particles was 20% and 36 % and ATPase in relation to total membrane protein was 33 % and 35 % in C‐3 and CAM M. crystallinum, respectively. Thus, by order of magnitude, it is most likely that the particles represent the ATPase. In Kalanchoë daigremontiana Hamet et Perrier de la Bâthie the ATPase also constituted 36% of total tonoplast protein. Induction of CAM in M. crystallinum was associated with an increase in specific ATPase activity of the tonoplast and an increase of the size and area coverage of tonoplast particles, whereas the relative contribution of ATPase protein to total tonoplast protein and the molecular mass of the ATPase holoenzyme, as seen in size‐exclusion chromatography, remained almost unchanged.
The Effect of Phosphinothricin (Glufosinate) on Glutathione Synthesis in Plants
Authors: Herold A. , Wendler C. , Wild A. 
Published: February 2014

AbstractThe inhibitory effect of DL‐phosphinothricin (glufosinate) on glutathione synthesis was studied in vivo and in vitro. The influence of phosphinothricin on γ‐glutamylcysteine synthetase was compared with the already known effects of l‐buthionine sulfoximine and l‐methionine sulfoximine. The results showed that phosphinothricin and buthionine sulfoximine are inhibitors of γ‐glutamylcysteine synthetase of plants. With both substances the enzyme was inhibited by 50 % at a concentration of 7 . 10−4M (pI50 = 3.15). Methionine sulfoximine reduced the enzyme activity by 50% at 5 . 10−2 M (pI50 = 1.30). It is discussed that the target enzyme of phosphinothricin is the glutamine synthetase whereas the γ‐glutamylcysteine synthetase is only an accessory target.
A Virus Infection in the Marine Brown Alga Ectocarpus siliculosus (Phaeophyceae)
Authors: Müller D. G. , Kawai H. , Stache B. , Lanka S. 
Published: February 2014

AbstractLaboratory cultures of Ectocarpus siliculosus originating from New Zealand showed a defect in gametangium formation. Nuclear divisions in gametangium initials are not followed by cell wall formation. In the resulting multinucleate cells nuclear DNA increases dramatically, and nuclear membranes disintegrate. Eventually, the entire structure is filled with hexagonal particles of approximately 130 nm diameter. These were isolated and shown by EM to consist of a dense core surrounded by a 3‐layered shell. They are released into the culture medium when the host cells burst. Ectocarpus gametes from healthy cultures could be infected by these particles. The resulting partheno‐sporophytes developed pathological symptoms, suggesting that the particles are viruses.The expression of the defect is temperature dependent. At 10°C all gametangia are abnormal, while between 15 and 20 °C defective and normal gametangia and gametes are formed on the same plant. Partheno‐sporophytes developing from such gametes carry the viral particles expressed in deformed unilocular and plurilocular sporangia.
Is Cell Elongation Regulated by Extracellular Auxin?
Authors: Knauth Beate , Klämbt D. 
Published: February 2014

AbstractExperiments with isolated epidermal strips of maize coleoptiles, pretreated with auxin and further incubated on sucrose agar containing different concentrations of auxin (indole‐3‐acetic acid, IAA or naphthalene‐1‐acetic acid, NAA) and/or naphthylphthalamic acid (NPA), are described. Preincubation for 2h with 2 . 10−4M IAA or 10−5M NAA in buffer, followed by 30 min wash in buffer results in measurable cell elongation during a subsequent incubation for 6 h on sucrose agar. Addition of 10−4M NPA inhibited the response to auxin and this inhibition could be reversed by providing IAA in addition to NPA. Inner tissue fragments (without outer epidermis) did not respond to external IAA. These results lead to the conclusion that auxin secretion at the outer epidermis may be an essential step in auxin‐regulated coleoptile growth.
Contributions to the Biomechanics of Plants. I. Stabilities of Plant Stems with Strengthening Elements of Different Cross‐Sections Against Weight and Wind Forces*
Authors: Speck Th. , Spatz H. — Chr , Vogellehner D. 
Published: February 2014

AbstractBiophysical considerations allow estimates of the mechanical stresses on self‐bearing vertical stems of plants. Even at moderate wind velocities the stresses induced by aerodynamic forces dominate over those induced by the own weight. Using polar coordinates, analytical expressions of cross‐sectional area and axial second moment of area for centrisymmetric structures with symmetries threefold or higher are derived. Calculating the relative section modulus for various (centrisymmetric) arrangements of stabilizing structures leads to an estimate of the “mechanical effectivity” of these structures. If for plant stems, seen as composite materials, the second moments of area and the elastic moduli are known, the contribution of the different tissues to mechanical stability can be determined quantitatively. The mechanical design of early “vascular” land plants and of stems of (fossil) trees and lianas in different ontogenetic stages can be assessed.
Contributions to the Biomechanics of Plants.; II. Stability Against Local Buckling in Hollow Plant Stems*
Authors: Spatz H. — Chr , Speck Th. , Vogellehner D. 
Published: February 2014

AbstractHollow plant stems are, compared to solid ones, endangered by a particular kind of mechanical damage: local buckling. In upright stems centric forces due to the weight of the plant itself are not critical. Bending, however, as caused by wind forces causes transverse stresses that lead to local buckling, long before the critical tension or compression stresses are reached.A new numerical method is proposed to treat local buckling of hollow plant stems caused by bending forces. The results emphasize the importance of transverse reinforcements in the nodes and/or the nodal thickenings for the stability of hollow structures.
Activities of Photosystems I and II in Chlamydomonas segnis Adapted and Adapting to Air and Air‐enriched with Carbon Dioxide*
Authors: Badour S. S. , Irvine B. R. 
Published: February 2014

AbstractActivities of photosystems I and II were compared at a saturating irradiance in air‐ and 5% CO2‐adapted and adapting Chlamydomonas segnis at the active phase of photosynthesis during the cell cycle. PSII activity was 200% greater in air‐ than in 5% CO2‐adapted cells, while PSI activity was similar in both types of cells and matched the level of PSII activity in air‐adapted cells. As a result, air‐ and 5% CO2‐adapted cells were characterized by low and high PSI/PSII ratios, respectively. In air‐adapted cells, the greater PSII activity (rate of O2 evolved) exceeded that of photosynthetic (Ps) O2 evolution, resulting in a Ps/PSII ratio below unity. This was associated with higher levels of catalase activity, lower l‐ascorbate content, and higher dehydro‐l‐ascorbate content than in 5% CO2‐adapted cells. During adaptation to air or 5% CO2 for 6 h in light, PSI rather than PSII was sensitive to changes in the concentration of CO2, and the adapting cells acquired the characteristics of air‐ and 5% CO2‐adapted cells as indicated by PSI/PSII, Ps/PSII, catalase activity, l‐ascorbate and dehydro‐l‐ascorbate contents. The results are discussed in the light of changes in the molecular organization of the thylakoid membranes and enhanced non‐cyclic electron transport coupled with O2‐uptake (Mehler reaction) for the generation of the ATP required for CO2/HCO−3‐transport in air‐adapted and adapting cells.