bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selenium in Plants: Uptake, Functions, and Environmental Toxicity
Authors: Läuchli A. 
Published: February 2014

AbstractSelenium (Se) has chemical properties similar to sulfur, but slight differences can lead to altered tertiary structure and dysfunction of proteins and enzymes, if selenocysteine is incorporated into proteins in place of cysteine.In some areas of California with irrigation agriculture elevated Se concentration in drainage and shallow groundwaters caused bioaccumulation of Se in wetlands and Se toxicity to wildlife. Among higher plants Se accumulators are tolerant to high Se concentrations whereas non‐accumulators are Se‐sensitive. Algae show a requirement of Se for growth and development, but no Se essentiality has been demonstrated for higher plants, possibly with the exception of Se accumulators. Higher plants take up Se preferentially as selenate via the high affinity sulfate permease. Contents of Se in agricultural crops are usually below 1 mg kg−1 DW, and hence such crops are considered safe for human and animal consumption even when grown on moderately high Se soils. Sulfate salinity inhibits uptake of selenate by many plant species.Assimilation of selenate by non‐accumulators leads to synthesis of selenocysteine and selenomethionine; Se‐cysteine is readily incorporated into proteins. High Se can interfere with S and N metabolism in non‐accumulators. In contrast, Se accumulators sequester Se mainly in non‐protein selenoamino acids. Among several selenoenzymes identified in bacteria and mammals, Se‐dependent glutathione peroxidase which catalyses the reduction of organic peroxides and H2O2 has been demonstrated convincingly in algae; in higher plants, however, the experimental evidence regarding its occurrence is controversial. All organisms including higher plants contain Se‐cysteyl‐tRNAs that decode UGA. Selenocysteine is proposed to function as 21st proteinaceous amino acid and thus is suggested to have a biological role in higher plants.Biogeochemical cycling of Se involves significant volatilization of methylated selenides such as dimethyl selenide to the atmosphere from higher plants as well as freshwater algae, but Se exchange between oceans and the atmosphere appears to proceed as net flux to the oceans.
Cytological Characterization of a Giant Strain of Euglena gracilis Obtained from Dark‐starved Cultures
Authors: Mares D. , Romagnoli C. , Rubini M. , Fasulo M. P. 
Published: February 2014

AbstractEuglena gracilis green cells were dark‐starved for four months. After this period almost the entire population died, while a few giant, viable cells appeared in the culture. The giantism was maintained after repeated subcultures in growth medium in light or dark conditions. However, the phenomenon was not permanent, and the morphological characteristics of the wild‐type Euglena were gradually restored.In giant cells nuclei enlarged greatly, DNA content increased and the Golgi apparatus greatly proliferated. Chloroplasts and mitochondria increased in number and size and often presented structural modifications when compared with normal Euglena. Importantly, in the giant cells that were maintained in darkness in resting or growth conditions chloroplasts persisted as structured organelles which appeared red‐fluorescent under UV illumination.Whether giantism is a phenotypic or a genotypic change is still debated. In our case, the evolution of this phenomenon, chiefly the enhanced DNA content, suggests that teratism is a multiploid mutation with the possibility of a return to the normoploid condition. Constitutive chloroplasts are present in most algae, except for a few species, among which is Euglena gracilis. The persistence of differentiated plastids in darkness in giant Euglena is considered to be a return to an ancestral condition and may, therefore, be phylogenetically important.
Sieve‐Element Plastids, Nuclear Crystals and Phloem Proteins in the Zingiberales
Authors: Behnke H.‐D. 
Published: February 2014

AbstractThe sieve‐element characters of 40 species from all families making up the monocotyledon order Zingiberales have been studied by transmission electron microscopy. While phloem‐proteins are a typical component of all eight families, the Zingiberaceae are characterized by nondispersive protein bodies derived from nuclear crystals. The sieve‐element plastids are of the form‐P2cs, i.e. contain cuneate protein crystals (as typical of all monocotyledons) and starch grains, those of the family Musaceae have protein filaments in addition (form‐P2cfs). The exclusiveness of the form‐P2c(f)s plastids contributed to the homogeneity of the order and its distinctness among other monocotyledon taxa. When diameters of the sieve‐element plastids from leaf phloem are compared, in the “banana group” the family averages of the Strelitziaceae and the Lowiaceae have, respectively, maximum and minimum values and are clearly different from those in the Musaceae, the family in which they have been included previously. In the “ginger group”, the family averages of the Zingiberaceae, Costaceae, and Marantaceae are close to the order average, with only Cannaceae having minimum values. A comparison of species averages, however, reduces the size differences between families: the value for Ravenala (Strelitziaceae) is close to those of the five Musaceae tested, and that of Globba (Zingiberaceae) even slightly lower than the species average of Canna.
Chloroplast Development in Rye Coleoptiles
Authors: Fröhlich M. , Kutschera U. 
Published: February 2014

AbstractIn the parenchyma cells of 1‐d‐old dark‐grown rye coleoptiles (Secale cereale) proplastids occurred which sometimes contained starch grains. During coleoptile growth in darkness starch‐filled amyloplasts are formed from the preexisting proplastids. No prolamellar bodies were observed in the stroma of the plastids of the etiolated coleoptile. After irradiation of 3‐d‐old etiolated coleoptiles with continuous white light three different types of plastids occurred. In the epidermal cells proplastids were observed. The parenchyma cells below the stomata of the outer epidermis (above the two vascular bundles) contained mature, spindle‐shaped chloroplasts with a well‐developed thylakoid system. In the parenchyma cells that surround the vascular bundles amyloplasts with some thylakoid membranes (chloroamyloplasts) occurred. The mesophyll cells of the primary leaves of dark‐grown seedlings contained etioplasts with large prolamellar bodies. In the primary leaves of irradiated plants chloroplasts similar to those of the parenchyma cells of the coleoptile were observed. Our results show that the rye coleoptile, which grows underground as a heterotrophic organ, is capable of developing mature chloroplasts upon reaching the light above the soil surface. The significance of this expression of photosynthetic capacity for the carbon economy of the developing seedling is discussed.
Paxillus involutus/Pinus sylvestris Mycorrhizae from Heavily Polluted Forest II. Ultrastructural and Cytochemical Observations
Authors: Turnau K. , Kottke I. , Dexheimer J. 
Published: February 2014

AbstractPaxillus involutus/Pinus sylvestris mycorrhizae, collected from experimental plots (situated in a Pino‐Quercetum forest) treated with cadmium dust, were previously reported to accumulate metals like Cd, P, S, N, Al and Si in vacuolar bodies. The Gomori‐Swift test was applied to the same material to reveal if cysteine‐rich proteins might be involved in element detoxification. Vacuolar deposits of high and low phosphate level were both stained. Higher intensity of the Swift reaction was found in the fungal mycelium from mycorrhizae sampled from polluted plots than in mycorrhizae from unpolluted sites. In both cases a higher intensity of the test was revealed in the host cytoplasm close to the Hartig net than in internal parts of roots. Different intensities of the Gomori‐Swift reaction were also observed when the Hartig net was compared to the fungal mantle. A PATAg test was additionally processed and revealed an accumulation of glycogen in rosettes and net‐like structures when samples from cadmium dust treated plots were observed.
Displacement and Return Movement of Chloroplasts in the Marine Dinophyte Pyrocystis noctiluca. Experiments with Optical Tweezers
Authors: Leitz G. , Greulich K. O. , Schnepf E. 
Published: February 2014

AbstractInfrared laser traps (optical tweezers) were used to study laser‐induced organelle movements in the marine alga Pyrocystis noctiluca (Dinophyta). These cells are highly suitable for optical micromanipulation due to their large size and extensive vacuole. Experiments were done with plastids held by optical tweezers and moved from the nuclear area into the vacuole. The subsequent retraction movement was analysed for speed. The displaced organelles remained connected to their original position by a thin cytoplasmic strand, often less than 1 μm in diameter. When the organelles were released they rapidly returned at an initial rate of 81.7 ± 7.8 μm . s−1 (overall displacement 50 μm, measured distance 20 μm, 25 °C ± 1 °C, number of cells 22), slowing down with progressive retraction of the connecting strand. The return movement was reduced to 4.2 ± 0.2 μ .s−1 (n = 10) when the organelles were displaced and held for 1 min. Displacement to a longer distance increased the rate of return movement. A change from a high to a low environmental temperature significantly reduced movement from 94.5 ± 9.0 . s−1 (30 °C ± 1 °C, n = 22) to 34.5 ± 2.7 μm .s−1 (5°C ± 1 °C, n = 22). Nocodazole and N‐ethylmaleimide (NEM), inhibitors of microtubules and acto‐myosin, respectively, did not affect the retraction of the connecting strand, but at high concentrations of NEM it became increasingly difficult to move organelles away from the nuclear area. We suggest that the return movement of organelles within laser‐induced artificial strands mainly depends on the viscoelastic properties of the tonoplast. The quantification of these properties by optical tweezers allows determination of reactions of plant cells to temperature changes.
The Non‐Ionic Detergent Brij 58 Conserves the Structure of the Tonoplast H+‐ATPase of Mesembryanthemum crystallinum L. During Solubilization and Partial Purification
Authors: Ratajczak R. 
Published: February 2014

AbstractThe effects of solubilization with Triton X‐100 or Brij 58 on the polypeptide composition and the substrate affinity of the tonoplast H+‐ATPase of plants of Mesembryanthemum crystallinum performing C3 photosynthesis or crassulacean acid metabolism (CAM) have been compared. Although all known subunits of the tonoplast H+‐ATPase were present in the fraction of solubilized proteins after treatment with Brij 58 or Triton X‐100, with Triton X‐100 the apparent KM value for ATP hydrolysis was increased by a factor of 1.8 and 1.5 in preparations from C3 and CAM plants, respectively, even at low concentrations in contrast to treatment with Brij 58. This is explained by structural changes of the tonoplast H+‐ATPase due to the Triton X‐100 treatment.After solubilization with Brij 58 the tonoplast H+‐ATPase was partially purified by Superose‐6 size‐exclusion FPLC. When Brij 58 was present, addition of lipids to the chromatography buffer was not necessary to conserve enzyme activity in contrast to previously described purification methods using Triton X‐100. The substrate affinity of the partial purified H+‐ATPase was similar to the substrate affinity obtained for ATP‐hydrolysis of native tonoplast vesicles, indicating that the enzyme structure during partial purification was conserved by using Brij 58. The results underline that the lipid environment of the tonoplast H+‐ATPase is important for enzyme structure and function.
High Molecular Weight Organic Compounds in the Xylem Sap of Mangroves: Implications for Long‐Distance Water Transport
Authors: Zimmermann U. , Zhu J. J. , Meinzer F. C. , Goldstein G. , Schneider H. , Zimmermann G. , Benkert R. , Thürmer F. , Melcher P. , Webb D. , Haase A. 
Published: February 2014

AbstractThe rise of sap in mangroves has puzzled plant physiologists for many decades. The current consensus is that negative pressures in the xylem exist which are sufficiently high to exceed the osmotic pressure of seawater (2.5 MPa). This implies that the radial reflection coefficients of the mangrove roots are equal to unity. However, direct pressure probe measurements in xylem vessels of the roots and stems of mangrove (Rhizophora mangle) grown in the laboratory or in the field yielded below‐atmospheric, positive (absolute) pressure values. Slightly negative pressure values were recorded only occasionally. Xylem pressure did not change significantly when the plants were transferred from tap water to solutions containing up to 1700 mOsmol kg−1 NaCl. This indicates that the radial reflection coefficient of the roots for salt, and therefore the effective osmotic pressure of the external solution, was essentially zero as already reported for other halophytes. The low values of xylem tension measured with the xylem pressure probe were consistent with previously published data obtained using the vacuum/leafy twig technique. Values of xylem tension determined with these two methods were nearly two orders of magnitude smaller than those estimated for mangrove using the pressure chamber technique (−3 to −6MPa). Xylem pressure probe measurements and staining experiments with alcian blue and other dyes gave strong evidence that the xylem vessels contained viscous, mucilage‐ and/or protein‐related compounds. Production of these compounds resulting from wound or other artifactual reactions was excluded. The very low sap flow rates of about 20–50 cm h−1 measured in these mangrove plants were consistent with the presence of high molecular weight polymeric substances in the xylem sap. The presence of viscous substances in the xylem sap of mangroves has the following implications for traditional xylem pressure measurement techniques, development of xylem tension, and longdistance water transport: (1) high external balancing pressures in the pressure chamber are needed to force xylem sap to the cut surface of the twig; (2) stable tensions much larger than 0.1 MPa can be developed only occasionally because viscous solutions provide nucleation sites for gas bubble formation; (3) the frequent presence of small gas bubbles in viscous solutions allows water transport by interfacial, gravity‐independent streaming at gas/water interfaces and (4) the increased density of viscous solutions creates (gravity‐dependent) convectional flows. Density‐driven convectional flows and interfacial streaming, but also the very low radial reflection coefficient of the roots to NaCl are apparently the means by which R. mangle maintains water transport to its leaves despite the high salinity of the environment.
Water Relations, CO2 Exchange, Water‐use Efficiency and Growth of Welwitschia mirabilis Hook. fil. in three Contrasting Habitats of the Namib Desert1
Authors: VON Willert D. J. , Wagner‐Douglas Ute 
Published: February 2014

Summary:CO2 exchange, transpiration and leaf water potential of Welwitschia mirabilis were measured in three contrasting habitats of the Namib desert. From these measurements stomatal conductance, internal CO2concentration and WUE were calculated. In two of the three habitats photosynthetic CO2 uptake decreased and transpiration increased with increasing leaf age while in the third habitat CO2 uptake increased and transpiration decreased with leaf age. Except for the stomata of young leaf sections in this habitat, stomata closed with increasing δw leading to a pronounced midday depression of CO2 uptake. The high stomatal limitation of photosynthetic CO2 uptake of glasshouse‐grown plants was verified in the natural habitat. Photosynthetic CO2 uptake saturated between 800 and 1300 μmol photons m−2 s−1depending on leaf age and habitat. CO2 uptake had a broad temperature optimum declining significantly beyond 32 °C. Predawn leaf water potential reflected water availability and atmospheric conditions in the three habitats and ranged from − 2.5 to − 6.2 MPa. There was a pronounced diurnal course of leaf water potential in all habitats. During the day a gradient in water potential developed along the leaf axis with the lowest potential at the leaf's tip. With respect to whole plant balances of CO2 exchange and transpiration, there were marked differences between Welwitschias in the three habitats. Despite a negative CO2 balance over a period of five months, leaves in the driest habitat grew constantly at the expense of carbon reserves in the plant. Only at the wettest site did carbon gain exceed carbon demand for growth. The WUE of whole plants was insignificant in all habitats. The results were as contrasting as the habitats and plants and did not allow generalisations about adaptational features of Welwitschia mirabilis.
Functional Analysis of the N‐Terminal Prepeptides of Watermelon Mitochondrial and Glyoxysomal Malate Dehydrogenases*
Authors: Lehnerer M. , Keizer‐Gunnik L. , Veenhuis M. , Gietl C. 
Published: February 2014

AbstractMitochondrial and glyoxysomal malate dehydrogenase (mMDH; gMDH; L‐malate: NAD+ oxidoreductase; EC 1.1.1.37) of watermelon (Citrullus vulgaris) cotyledons are synthesized with N‐terminal cleavable presequences which are shown to specify sorting of the two proteins. The two presequences differ in length (27 or 37 amino acids) and primary structure. Precursor proteins of the two isoenzymes with site‐directed mutations in their presequences and hybrid precursor proteins with reciprocally exchanged presequences were analyzed for proper import using two approaches, namely in vitro using isolated watermelon organelles or in vivo after synthesis in the heterologous host, Hansenula polymorpha.The mitochondrial presequence is essential and sufficient to target the mature glyoxysomal isoenzyme into mitochondria (Gietl et al., 1994). As to the function of the mitochondrial presequence a substitution of −3R (considered important for one step precursor cleavage in yeast and mammals) with −3L permitted import into mitochondria but cleavage of the transit peptide and conversion into active mature enzyme was impeded. Substitution of −13R−12S (in a sequence reminiscent of the octapeptide motif serving as a substrate for the mammalian and yeast intermediate peptidase) into −13L12F permitted mitochondrial import and processing like the wild type transit peptide. Purified rat mitochondrial processing protease, which can effect single step cleavage of mitochondrial protein precursors, cleaves in vitro translated watermelon mMDH precursor into its mature form.The glyoxysomal presequence is essential and sufficient to target the mature mitochondrial isoenzyme into peroxisomes of Hansenula polymorpha, but these peroxisomes lack a processing enzyme to cleave the presequence (Gietl et al., 1994). We here show that isolated watermelon organelles also import the hybrid proteins in vitro and process the glyoxysomal presequence. Site directed mutations within the conserved RI‐X5‐HL‐motif impede efficiency of import and cleavage by watermelon organelles.
Visualization by Freeze‐Fracture Electron Microscopy of Intramembraneous Particles corresponding to the Tonoplast H+‐Pyrophosphatase and H+‐ATPase of Kalanchoë daigremontiana Hamet et Perrier de la Bâthie*
Authors: Mariaux J.‐B. , Becker Andrea , Kemna Inge , Ratajczak R. , Fischer‐Schliebs Elke , Kramer D. , Lüttge U. , Marigo G. 
Published: February 2014

AbstractThe H+‐PPase and the H+‐ATPase of the vacuolar membrane were separated during purification of tonoplast proteins of Kalanchoë daigremontiana Hamet et Perrier de la Bǎthie. Three membrane protein fractions prepared contained firstly, the H+‐PPase protein without any subunits of the H+‐ATPase, secondly, the H+‐PPase protein with only minute traces of the intramembraneous 16 kDa c‐subunit of the H+‐ATPase, and thirdly, the H+‐ATPase subunits without H+‐PPase peptides as verified by SDS‐PAGE. These three preparations were reconstituted into soybean (Glycine max L.)‐phospholipid vesicles, and compared with proteoliposomes obtained by reconstitution of total solubilized tonoplast proteins as well as with native tonoplast vesicles. Analysis of freeze‐fracture replicas prepared from these five different types of vesicles showed that there are two populations of intramembraneous particles, one with a diameter of 6.7‐7.2 nm corresponding to the H+‐PPase, and one with an average diameter of 9.1 nm belonging to the H+‐ATPase. Thus, freeze‐fracture electron microscopy allows one to visualize H+‐PPase particles in addition to H+‐ATPase particles in the tonoplast of Kalanchoë daigremontiana.
Phenotypic Adaptation to Elevated Temperatures of Tonoplast Fluidity in the CAM Plant Kalanchoë daigremontiana is Caused by Membrane Proteins*
Authors: Schomburg M. , Kluge M. 
Published: February 2014

AbstractComparative electron paramagnetic resonance spectroscopic studies on spin‐labeled native and protein‐free purified tonoplast membranes in the CAM plant Kalanchoë daigremontiana showed that the phenotypic decrease in tonoplast fluidity occurring upon acclimation to elevated temperature is brought about by specific protein‐lipid interaction. However, there are indications that, to some extent, the properties of the bulk tonoplast lipids may also be affected by acclimation to high temperature. In contrast to heat acclimated individuals and for still unknown reasons, in plants grown at normal temperature depletion of the tonoplast membrane of its proteins had no effect on membrane fluidity. The results are considered as evidence for the occurrence of homeoviscous adaptation in the tonoplast of CAM plants towards changes in the temperature climate during growth.
K+ Gradients in the Pulvinus of Phaseolus coccineus during Leaf Movement*
Authors: Ruge W. A. , Hampp R. 
Published: February 2014

AbstractWe used quantitative histochemistry to investigate the tissue‐specific compartmentation of potassium in the laminar pulvinus of Phaseolus coccineus L. at day and night positions of diurnal leaf movement. The assay was based on the potassium‐dependent activation of pyruvate kinase. Total potassium levels of pulvini were higher in the light than in the dark [0.88 and 0.57mol (kg dry weight)−1, respectively]. Transverse compartmentation of potassium was studied on three tissue slices, representing the middle part, petiolar and laminar sides of individual pulvini. These were dissected further into 10 distinct subsamples (bundle; motor tissues: extensor, flexor; flanks). In the day position the amount of potassium in the extensor was higher than in the night position [1.92 and 1.50 mol (kg dry weight)−1, respectively]. Flexor changes were opposite [1.13 and 1.65 mol (kg dry weight)−1, respectively]. In the day position there was a steep and consistent increase in potassium content from the innermost to the outermost zones of the extensor. In the night position this was much more variable. Comparable gradients were not detected in flexor samples. Here highest amounts of potassium were recovered from the middle of the motor tissue. The data specify distinct tissue regions involved in osmotic adjustment during leaf movement in Phaseolus coccineus.