bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diurnal Nitrogenase Modification in the Cyanobacterium Anabaena variabilis*
Authors: Ernst Anneliese , Liu Yong‐Ding , Reich Sabine , Böger P. 
Published: February 2014

AbstractThe nitrogen‐fixing cyanobacterium Anabaena variabilis (ATCC 29413) was cultivated as continuous culture under a 12 h: 12 h light‐dark cycle. In the light, photosynthetic activity resulted in a continuous increase in cellular glycogen content, followed by an almost complete dissimilation of the polysaccharide during the dark period. Nitrogenase activity, assayed by the acetylene reduction technique, was low at the end of the dark period and increased quickly upon illumination to reach a maximum after 4 to 6 h of light. The activity rapidly declined after darkening the culture. Increase and decrease of activity were accompanied by a change in the electrophoretic mobility of the Fe‐protein of nitrogenase (dinitrogenase reductase) indicative of enzyme modification being involved in the diurnal control of nitrogenase activity. Modification and demodification of the Fe‐protein were not coupled to the cell cycle since they followed darkening and illumination when the light or dark periods were changed. Addition of fructose increased nitrogenase activity even in darkness and caused demodification of the Fe‐protein. Ammonium chloride supplied at the onset of illumination slowed down the increase of nitrogenase activity. A delayed inhibition of the enzyme was accompanied by partial Feprotein modification only. The reaction was completed after transfer to darkness. The function of enzyme modification in maintaining a constant C: N ratio is discussed and a dominating role of carbohydrate supply in this regulation is indicated by the reported findings.
Peroxisomes in the Alga Vaucheria are Neither of the Leaf Peroxisomal Nor of the Glyoxysomal Type*,1
Authors: Backeshoff K. , Stabenau H. 
Published: February 2014

AbstractMicrobodies were isolated from the freshwater alga Vaucheria sessilis as well as from a marine Vaucheria. The organelles equilibrated on sucrose gradients at densities 1.23 g . cm−3 and 1.24g . cm−3, respectively. On electron micrographs they showed an ovoid or spheroid shape with a diameter of 0.5 to 0.8 μm.Besides catalase, the peroxisomes of both algae possess glycolate oxidase and glutamate‐glyoxylate aminotransferase, but no other leaf‐peroxisomal enzymes. Instead, the enzymes malate synthase and isocitrate lyase, which are markers of glyoxysomes in higher plants, are constituents of the peroxisomes in the marine as well as in the freshwater alga.Citrate synthase, aconitase, malate dehydrogenase and enzymes of the fatty acid β‐oxidation pathway are located exclusively in the mitochondria. Therefore, the peroxisomes from Vaucheria do not belong to either the type of leaf peroxisomes or to the type of glyoxysomes.
Oligomeric Forms of Glycolytic Enzymes in Chlorella Grown in Different Light Qualities*
Authors: Kowallik W. , Grotjohann N. , Ruyters G. 
Published: February 2014

AbstractFast protein liquid chromatography on Superose 6 of crude extracts from the green alga Chlorella kessleri cultivated autotrophically in white light reveals several peaks with phosphofructokinase (PFK, EC 2.7.1.11) or pyruvate kinase (PK, EC 2.7.1.40) activity with molecular weights larger than the usually reported ones of 320–380 and 240 kDa, respectively. All other glycolytic enzymes are eluted as one peak each with a molecular weight corresponding to data from the literature. Indirect evidence indicates that the various forms of PFK and presumably PK are oligomers. The occurrence of different PFK species depends markedly on growth conditions such as wavelength of light: Red light leads to only one rather large PFK (1,580 kDa), blue light to two smaller species (760 and 360 kDa). All species are probably present in white light‐grown cells (1,500, 1,050, 930, 700 and 440 kDa). The various light qualities do not significantly affect all other glycolytic enzymes. PK constantly exhibits four forms with molecular weights of 830, 680, 480, 305 kDa. Experiments with the chlorophyll‐free mutant no. 20 of Chlorella kessleri support the assumption that oligomerization of enzymes is characteristic of regulatory enzymes, thereby providing the cell with an additional regulatory means.
The Supramolecular Organization of Photosynthetic Membranes of the Thallus Stage of Porphyra leucosticta Thuret. (Bangiales, Rhodophyta) Visualized by Freeze‐Fracture
Authors: Tsekos I. , Reiss H.‐D. 
Published: February 2014

AbstractThe supramolecular organization of the thylakoid membranes of the thallus stage in the red alga Porphyra leucosticta is studied in replicas of rapidly frozen and fractured cells. Freeze‐fractured thylakoid membranes exhibit only two types of fracture faces (EF and PF), because the lamellae in red algal chloroplasts are not stacked. The PF reveals numerous, tightly packed, but randomly distributed particles (density range from 2970 to 3550 particles/μm2). In contrast, the EF particles appear organized into parallel rows, the spacing of which is about 60–70 nm (about 8–9 particles occur along 100 nm of the line that is formed). Significant numbers of single EF particles are randomly distributed between the EF particle rows. The particles on both fracture faces (PF and EF) fall into two size classes: 10 to 11 nm (major size class) and 14 to 15 nm (minor size class).
Sequence Characteristics and Transcripts of rbcS Genes from Brassica napus: Temporal and Spatial Expression During Crucifer Seedling Morphogenesis*
Authors: Fiebig C. , Kretzschmar F. , Sprenger I. , Link G. 
Published: February 2014

AbstractThe small subunit of ribulose‐1,5‐bisphosphate carboxylase/oxygenase is encoded by a nuclear multigene family (rbcS genes). We have cloned and characterized three rbcS cDNA sequences from Brassica napus. These cDNA clones all appear to encode the same protein, but they differ in their nucleotide sequence, which has been exploited in the construction of clone‐specific oligonucleotides as selective hybridization probes. By using a nonselective RNA probe, the temporal expression of the entire rbcS gene family was analyzed during seedling development of Brassica napus and of Sinapis alba. In both crucifer species, rbcS transcripts show transient peak levels and then decrease, although to a different degree. Only a moderate (twofold) difference in transcript pool sizes is observed in light‐grown versus dark‐grown seedlings at the time of peak levels, while a much higher light/dark ratio is found in late‐stage seedlings. The oligonucleotide probes reveal three subsets of transcripts which differ in their accumulation kinetics and light/dark ratio. Assessment of the spatial distribution by using in situ hybridization indicates that rbcS transcripts are uniformly localized in cross‐sections of cotyledons from either light‐grown or dark‐grown seedlings, whereas they are undetectable in root sections.
Phosphate Activates the Phosphoenolpyruvate Carboxylase from the C4 Plant Amaranthus viridis L.
Authors: Podestá F. E. , Andreo C. S. , Iglesias A. A. 
Published: February 2014

AbstractPhosphoenolpyruvate carboxylase from Amaranthus viridis leaves was activated by inorganic orthophosphate in a concentration‐ and pH‐dependent manner. Maximal activation at pH 7.0 was achieved at phosphate concentrations above 20 mM, and a positive cooperativity was observed for the binding of the anion at this pH. At pH 8.0 the maximum of activity was achieved at 10 mM phosphate; higher concentrations reduced the activation. KM for phosphoenolpyruvate‐Mg at pH 7.0 was lowered by phosphate in all concentrations tested up to 30 mM. While at pH 8.0 the KM values were lower than that of the control up to 10 mM phosphate; higher anion concentrations raised the minimum value of KM at this pH. VMAX increased at pH 7.0, and remained unchanged at pH 8.0. A KA value of 0.41 mM was calculated for phosphate at the alkaline pH. The phosphate analogue arsenate also behaved as an activating agent, while other anions (e.g. nitrate, nitrite, sulfate, tetraborate) were ineffective. The phosphate‐activated enzyme was shown to be insensitive to glucose‐6‐phosphate, but was inhibited by l‐malate to the same extent as the control.
Distribution and δ 13C Values of Portulacaceae Species of the High Andes in Northern Chile
Authors: Arroyo Mary Kalin , Medina E. , Ziegler H. 
Published: February 2014

AbstractThe distribution of species of Portulacaceae in the northern Andes of Chile was recorded during the late growing season along altitudinal transects from 1500 m up to the vegetation limit. The transects were located towards the east of the towns of Arica (18 °S) and Vallenar (28 °S). Whole plants were analysed for δ 13C values to examine the occurrence of different photosynthetic pathways. Three species of Calandrinia (C. thyrsoidea, C. spicata and C. grandiflora) and two species of Philippiamra (P. amaranthoides and P. celosioides) were found to have δ 13C values indicative of CAM. Portulaca philippi was the only C4 plant in the sample. The CAM species tend to occupy the lower altitudinal levels, which are also relatively drier. All the C3 species occur in the Andean belt, with more favourable water supply. Their δ 13C values averaged −25.1 ‰, a value significantly lower than the average of lowland C3 Calandrinia species reported elsewhere or the general average for lowland C3 plants of −28.8 ‰. CAM species are also limited to the western slope of the Andean range, while C3 species occur at both sides, but often have discontinuous distributions north or south of the driest section of the Andes (21–24 °S) indicating that their migration along the western side has probably been prevented by extreme aridity. The C3 species occurring on both sides of the aridity barrier are also annual in habit.
Effect of Lateral Root Formation on the Vascular Pattern of Barley Roots
Authors: Luxová M. 
Published: February 2014

AbstractThe vascular pattern in the root of barley (Hordeum vulgare L.), characterized by discontinuous xylem, is markedly affected by its branching. The roots become divided into unbranched segments alternating with branched segments with a more complex vascular pattern, formed by two systems differing in origin and age: the primary vascular system derived from the procambium and ontogenetically younger connective vascular system derived from stelar parenchyma.Adjacent to the sites of the lateral root initiation, reprogramming of parent stelar parenchyma for connective vascular elements occurs. The connecting phloem is represented by small sieve elements and companion cells, the connecting xylem is composed of small vessel elements with reticulate or scalariform‐reticulate wall thickenings and simple perforations. Development of the connective vascular system secures continuous lateral and axial vascular connection between lateral root and parent root. The extent of the vascular connection in the parent root increases in an acropetal direction.Hydraulic effects of connective vascular tissue formation and parent root segmentation are discussed.
The Localization of Lead in the Lichen Ramalina duriaei (De Not.) Bagl.
Authors: Garty J. , Theiss Heide‐Birgitt 
Published: February 2014

AbstractIn an attempt to ascertain whether the lichen Ramalina duriaei could be employed to biomonitor atmospheric lead pollution, specimens of this lichen were exposed to Pb (NO3)2 solutions and a buffered solution (tartaric acid/sodium bitartrate, pH 2.8) of sodium rhodizonate (C6O6Na2) was used to locate lead in their thalli. The procedure entailed exposure of the lichen to 0, 5, 50 and 100 ppm Pb for 5 min and 1 h and the subsequent determination of the lead contents from photographs of the thalli. Distribution of lead in different parts of the thallus was assessed after exposure of the lichens to 2 ppm Pb (9 h or three d), 50 ppm (45 min) or 200 ppm (4d). Cross sections of vegetative parts of the thallus and of the apothecia revealed that lead penetrated into the cortical cells of the thallus but not into the algal cells of the phycobiont nor the ascospores or medullary cells. The observed massive penetration of lead into cortical cells supports the notion that Ramalina duriaei is sensitive to atmospheric lead pollution.
Flowers and Beetles in the South American Tropics
Authors: Gottsberger G. 
Published: February 2014

AbstractExamples of beetle pollination in the South American tropics are given. The case histories refer to representatives of the families Cyclanthaceae, Annonaceae, and Araceae. In most cases the cantharophilous syndrome does not seem to be the result of coevolution but of a one‐sided adaptation of flowers to the behavior, necessities, and sense‐capacities of beetle species. It is emphasized that cantharophily may not necessarily be an indication of ancientness of a flower/insect relationship. Besides primitive angiosperms, there are derived and modern groups which, in their pollination, are specialized for beetles.Carludovica palmata (Cyclanthaceae) is pollinated by small curculionids which are attracted by odors in the early morning hours. Annona coriacea (Annonaceae) and Philodendron selloum (Araceae) are pollinated by large dynastid scarab beetles in the evening hours. In all three species thermogenesis occurs. Although belonging to widely separate systematic groups, Annona flowers and Philodendron inflorescences have a similar pollination biology, which indicates that their adaptations to beetles are the result of convergent evolutionary developments.
Bird‐Flowers: Hovering Versus Perching Exploitation
Authors: Westerkamp Chr 
Published: February 2014

AbstractUsually, bird‐flowers are classified into New World flowers (used by hovering hummingbirds) and Old World species (adapted to perching birds). Since there are many observations which violate this classification the proposal is made to distinguish between blossoms adapted to hovering birds and those providing a well‐defined perch. Characters and examples are given for both groups including the different ways a perch is provided by the plant and the distinct methods of hover‐flight in birds. The diverse adaptive solutions for bird pollination within some taxa are exemplified. To understand bird‐flowers the actual functioning of flowers must be in focus, and not the geographic distribution nor the systematic affiliation of their visitors.
Exchange of Metabolites in Cyanophora paradoxa and its Cyanelles*
Authors: Schlichting R. , Zimmer W. , Bothe H. 
Published: February 2014

AbstractThe flagellate Cyanophora paradoxa contains blue‐greenish, organelle‐like inclusions termed cyanelles which perform photosynthetic CO2‐fixation in place of chloroplasts. By the use of the HPLC‐technique, Cyanophora was shown to form glucose, sucrose, maltose, mannitol, ribose, glycerol and trehalose. Extracts from the whole organism and from the eucaryotic host, but not from the cyanelles, convert 14C‐labelled UDP‐glucose to polyglucan. Synthesis of sucrose from UDP‐glucose and fructose‐6‐P or fructose could not be demonstrated in any extract from Cyanophora. The transfer of metabolites into cyanelles was monitored by the silicone oil filtering technique. The solute spaces for 14C‐labelled sorbitol and 3H2O were the same indicating that sorbitol freely penetrated the plasma membrane of cyanelles in contrast to the situation found in chloroplasts. The measurements of the solute spaces for the different compounds showed that maltose and sucrose were not accumulated by isolated cyanelles. Other compounds like fructose, fucose, glutamine or glycine had intermediate sizes of their solute spaces. Cyanelles apparently possess a rapidly transporting glucose carrier and not a malate/oxaloacetate shuttle and also not an ATP/ADP translocator. The carrier composition at the plasma membrane of cyanelles and at the inner envelope membrane of chloroplasts seems to be totally different.
Malate Uptake into Isolated Vacuoles from Catharanthus roseus Cells: Role of the Membrane Potential
Authors: Marigo G. , Bouyssou Huguette 
Published: February 2014

AbstractThe mechanisms involved in the transport of malate into isolated vacuoles of Catharanthus roseus (L.) cells were investigated with special reference to the effects of induced changes in membrane potential and surface charges of the tonoplast. For this purpose, thiocyanate (SCN−), a highly permeant anion often used as a membrane potential probe, was extensively exploited. In the absence of Mg‐ATP, the low accumulation ratio of 14C SCN− could be related to the presence of negative charges at the outer surface of the tonoplast exerting a screening effect on the displacement of lipophilic anionic species. Nevertheless, malate was taken up continuously by vacuoles supporting the concept of a transport component which facilitates its transfer through the tonoplast. From experiments showing the pH dependence of malata uptake, it is suggested that the protonated form of the transporter is implicated in this process. Moreover, when the vacuoles are energized by Mg‐ATP, the study of the equilibrium distribution of 14C SCN− indicated an inside positive membrane potential difference. Advantage was taken of these results to modulate the membrane potential with high levels of thiocyanate. The data obtained demonstrate that malate uptake results from electrophoretic movement in response to the positive potential difference.
X‐Ray Microprobe Analyses of Vacuoles of Spruce Needle Mesophyll, Endodermis and Transfusion Parenchyma Cells at Different Seasons of the Year*
Authors: Stelzer R. , Lehmann H. , Kramer D. , Lüttge U. 
Published: February 2014

AbstractThe needles of an outdoor‐grown healthy Picea abies (L.) Karst. tree were routinely investigated from bud break up to 16 months thereafter. Transmission electron microscopical (TEM) and cryoscanning electron microscopical (CSEM) techniques were used for structural observations. Energy dispersive microanalyses (EDX) on bulk‐frozen hydrated specimens served for direct determination of element levels in the vacuoles of the mesophyll, endodermis and transfusion parenchyma cells.Both, CSEM and TEM micrographs show comparable seasonal variations e.g. in chloroplast structure and in vacuolar inclusions. EDX‐analyses clearly point out that high Mg concentrations are characteristic of mature endodermis cells. Conversely, K concentrations incline to become lower in the maturing endodermis than in the surrounding tissues. The elements P and S represent the major part of the potentially inorganic counterions for Mg and K. It is concluded that the endodermis cells serve as a storage buffer for maintaining homeostasis of Mg and S levels in the adjacent cells throughout the year.
Import of 14C‐Photosynthate by Developing Leaves of Sugarcane
Authors: Robinson‐Beers Kay , Sharkey Th. D. , Evert R. F. 
Published: February 2014

AbstractSink‐to‐source transition was studied in developing sugarcane (Saccharum interspecific variety L62–96) leaves. Fully‐expanded, mature sugarcane leaves were fed 14CO2 for 20 minutes, incorporating about 617 Bq. After five hours the leaves of each plant were cut into 1‐cm‐length segments that were weighed and then placed in scintillation cocktail for counting. All leaves younger than the leaf fed 14CO2 imported labeled photoassimilate. Three to four leaves had both importing and non‐importing regions within the blade and a distinct transition region between them. A transition region was observed in leaves which had expanded to between 30 and 90 % of final blade length. Radioactivity per gram fresh weight was calculated as a measure of sink strength. Sink strength was greatest in the youngest leaf and declined with leaf age. The results of this study indicate that 1) import of photosynthate by developing sugarcane leaves occurs over a longer span of developmental ages than in dicotyledonous leaves and 2) the actual tissue region undergoing transition within such a leaf can be resolved as narrow zone between the importing and non‐importing regions.
Salt Tolerance of Ectocarpus siliculosus (Dillw.) Lyngb.: Comparison of Gametophytes, Sporophytes and Isolates of Different Geographic Origin
Authors: Thomas D. N. , Kirst G. O. 
Published: February 2014

AbstractForty Ectocarpus siliculosus isolates from a wide geographical range, including gametophyte and sporophyte plants, have all been acclimated to the same salinity for several years. Their salinity tolerances in respect of cell viability, photosynthesis and dark respiration were evaluated over the salinity range: 8 to 96 ‰. Significant differences in the physiological tolerances to salt stress compared with viability measurements were evident. Genotypic differences in salt tolerances between groupings of the isolates, and also differences in responses of gametophyte and sporophyte generations were found. However, diploid and haploid sporophyte material had similar tolerances. Triploid and tetraploid sporophytes did not have improved tolerances over those of diploid plants. Culture plants originating from low salinities in the Baltic Sea had broader tolerances than field material collected from Baltic waters of similar salinity.
Carbon and Hydrogen Isotope Ratios in Bromeliads Growing under Different Light Environments in Natural Conditions
Authors: Medina E. , Lüttge U. , Leal F. , Ziegler H. 
Published: February 2014

AbstractWild Ananas species in northern South America occur in shady environments and appear to be relatively intolerant to droughts associated with growth under full sun exposure. This behaviour contrasts with the higher productivity of commercial varieties of Ananas comosus when grown under full sun exposure. Such differentiation within the genus offers an opportunity to study the process of adaptation of apparently high light avoiding species into true sun plants. As a first approximation, the analysis of nitrogen content and carbon and hydrogen isotope ratios of bromeliads growing under natural conditions was undertaken to test the following hypotheses: 1. Leaf nitrogen content of plants grown under partial shade is higher than that of the same species in the same habitat growing under full sun exposure, due to the higher availability to nitrogen in the under‐canopy, but also to the lower proportion of structural carbohydrates in shade leaves; 2. δ13C values are usually more negative in CAM bromeliads growing under partial shade because of the lower contribution of CAM to total carbon gain, and the probable fixation of CO2 originating from soil respiration; 3. δD values of CAM bromeliads are less negative than those of C3 bromeliads, but CAM bromeliads grown in shady habitats tend to have more negative δD values because of the lower relative accumulation of deuterium in leaf tissue water, and also because of their relatively lower CAM activity. The results show a clear differentiation between CAM and C3 bromeliads based on δ13C values, and in general δD values are less negative in CAM bromeliads. However, in several species overlapping δD values between C3 and CAM bromeliads were observed. The analysis of paired samples of the same species grown under contrasting light intensity usually conformed with the expectations. A number of deviations from the hypotheses were observed which appeared to be related to particular environmental conditions. The interpretation of δD values obtained from total organic matter is made difficult by the local variation of hydrogen/deuterium ratios in water available to the plant.