bluuebunny/crossref_metadata_2025 huggingface dataset:
Catenalis digitata, gen. et sp.nov., a plant from the Lower Devonian (Siegenian) of Yunnan, China
Authors: Shougang Hao , Beck Charles B.
Published: December 2007

A new genus and species, Catenalis digitata, is described from two localities of the Posonchong Formation of Siegenian age in the Wenshan district of Yunnan. This small, dichotomously branched plant exhibits morphological differentiation into a vegetative region that comprises the major part of the plant and terminal fertile regions. The fertile regions consist of fan-shaped clusters of terminal branchlets that bear uniseriate sporangia on only one side. Many sporangia have a crescent-shaped dehiscence slit near the distal margin. Some terminal branchlets in fertile regions lack sporangia, but the positions from which they have apparently been lost are conspicuous as elliptical regions. In these segments a dark, carbonaceous strand is apparent in a groove along the midplane. A few tracheid-like fragments have been macerated from a segment of carbonized axis suggesting that Catenalis might have been a vascular plant, but because of a lack of detailed information on the components of these strands we cannot conclude with certainty that they were typical vascular plant tracheids. Because of a morphology intermediate between that of certain fucalean algae and typical land vascular plants, we suggest that Catenalis might represent a group ancestral to vascular plants or a new group of primitive vascular plants of algal derivation. Key words: Catenalis digitata, alga-like, dichotomous, uniseriate sporangia, Siegenian, Yunnan.
Halosarpheia minuta sp.nov., an ascomycete from submerged mangrove wood
Authors: Leong W. F. , Tan T. K. , Hyde K. D. , Jones E. B. Gareth
Published: December 2007

Halosarpheia minuta sp.nov. on submerged wood of Avicennia alba, A. lanata, Bruguiera cylindrica, and Rhizophora apiculata, from Singapore, Malaysia, and Brunei, is described and illustrated. Key words: Ascomycotina, taxonomy, marine fungi, mangrove, tropical.
Lamina architecture and anatomy in the Heliconiaceae and Musaceae (Zingiberales)
Authors: Triplett Jimmy K. , Kirchoff Bruce K.
Published: December 2007

Lamina size, thickness, venation, and anatomy are studied in 15 species of Heliconia (Heliconiaceae), 3 species of Musa, and 1 of Ensete (Musaceae). The most typical laminas of these genera are large and oblong and have an acute or irregular apex and an asymmetrical cordate base. The laminar veins are parallel and are oriented essentially perpendicular to the costa and the margin. However, there is considerable variation in lamina architecture in the Heliconiaceae. Thickness ranges considerably across the lamina, with considerable variation between species. The only pattern common to all species is that the blades are thinner at the margin than at the costa. The veins of the lamina occur in a number of size classes that are arranged into a repeating unit called a set. Set patterns are described for the species and families. Although the Heliconiaceae and Musaceae do not differ in general set pattern, variation in the Heliconiaceae tends toward simpler sets, whereas the Musaceae tends towards more complex sets. Lamina anatomy is similar to that reported in the literature for these families, with several notable exceptions. The Heliconiaceae and Musaceae may be distinguished by characteristics of their lamina anatomy and by the fact that Musaceae blades have an irregular apex. The value of these characters for taxonomic and cladistic analyses is discussed. Key words: leaves, plant anatomy, vasculature, Zingiberales, Musaceae, Heliconiaceae.
Implications of inorganic carbon utilization: ecology, evolution, and geochemistry
Authors: Raven John A.
Published: December 2007

CO2-concentrating mechanisms based on active inorganic C influx across a membrane (or membranes) are widespread in aquatic phototrophs. They are apparently absent from, or poorly developed in, taxa such as bryophytes and freshwater red algae, but are retained in some terrestrial phototrophs, i.e., some lichens and free-living algae and cyanobacteria related to the lichen photobionts. The natural occurrence of CO2-concentrating mechanisms is negatively correlated with CO2 enrichment of aquatic habitats from respiration of organic C produced elsewhere and, less clearly, with low temperatures during the growing season, with low external pH, and with rapid water movement over the plant surface. Predictions based on laboratory data and on theoretical considerations as to the influence of light, nitrogen, and iron availability on the occurrence of CO2-concentrating mechanisms have yet to be rigorously tested in the field. The evolution of CO2-concentrating mechanisms is not well understood, but clearly the location of inorganic C pumps must have been influenced by successive symbiotic events. Increasing atmospheric CO2 levels, and other anthropogenic effects (acidification, eutrophication), may influence the selective advantage (or disadvantage) associated with possession of CO2-concentrating mechanisms in particular environments. Key words: bicarbonate, CO2-concentrating mechanisms, iron, light, nitrogen, unstirred layers.
Active CO2 transport in cyanobacteria
Authors: Miller Anthony G. , Espie George S. , Canvin David T.
Published: December 2007

Cyanobacteria appear to possess an active transport system for molecular CO2. This system, first discovered by Badger and Andrews in 1982 (1982. Plant Physiol. 70: 517–523), is without reported precedence in the bacterial, animal, or plant literature. The transport system operates so efficiently that in dense cell suspensions the extracellular CO2 concentration is pulled far below the equilibrium value. This CO2 drawdown is not due to CO2 fixation but can be accounted for by a transport system that recognizes molecular CO2 and causes it to be transported into the cell. The fact that operation of the system causes a massive disequilibration of the extracellular CO2–HCO3− system means that there must be an expenditure of metabolic energy. The CO2 is actually moved against a considerable CO2 concentration gradient. In this review we discuss methods that can be used to monitor CO2 transport in cyanobacteria. We present evidence that CO2 transport is an active process. It is emphasized that little is known about the concomitant ion fluxes that must occur to ensure charge and pH regulation during CO2 transport. Key words: cyanobacteria, active CO2 transport, metabolic inhibitors, transport models.
Active HCO3− transport in cyanobacteria
Authors: Espie George S. , Miller Anthony G. , Kandasamy Ramani A. , Canvin David T.
Published: December 2007

Cyanobacteria possess systems for the active transport of both CO2 and HCO3−. While the active CO2 transport system seems to be present in cells grown on all levels of CO2 or dissolved inorganic carbon, the bicarbonate transport systems are only present in cells grown on low levels of CO2 or dissolved inorganic carbon (air levels or lower). Active bicarbonate transport can be shown to occur when the rate of photosynthesis exceeds that which could be sustained by the production of CO2 from the dehydration of bicarbonate or when CO2 transport is inhibited with carbon oxysulfide or hydrogen sulfide. Two systems for active bicarbonate transport have been identified: one is dependent on the presence of millimolar concentrations of sodium, and the other is independent of the sodium requirement. Cells grown with air bubbling normally possess the first whereas cells grown in standing culture normally possess the second. The sodium-dependent bicarbonate transport can be inhibited by omitting sodium from the reaction medium or competitively with lithium when sodium is present. Monensin and amiloride also inhibit sodium-dependent bicarbonate transport. It does not appear to be inhibited by ethoxyzolamide. The inhibition of sodium-independent bicarbonate transport is not yet established. Bicarbonate transport appears to have no effect on CO2 transport and CO2 transport appears to have no effect on bicarbonate transport. Hence, the transport systems seems to be independent. Although a number of mechanisms have been proposed for bicarbonate transport, the experimental data are not sufficient to clearly distinguish between them. Key words: cyanobacteria, active CO2 transport, active HCO3− transport, photosynthesis, sodium.
Molecular analysis of high CO2 requiring mutants: involvement of genes in the region of rbc, including rbcS, in the ability of cyanobacteria to grow under low CO2
Authors: Lieman-Hurwitz Judy , Schwarz Rakefet , Martinez Flor , Maor Zeev , Reinhold Leonora , Kaplan Aaron
Published: December 2007

Modifications of the genomic region near (and including) rbc, the operon that codes for the large and small subunits of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), resulted in cyanobacterial mutants that demand high CO2 for growth. Mutant EK6 originated from the fusion of the 3' end of rbcS (which codes for the small subunit of Rubisco) with 84 nucleotides from the 5′ flanking region of nptII (kanamycin-resistance gene), leading to a 17-kDa small subunit, as compared to 14 kDa in the wild type. Mutant D4 originated from substitution of the 1.4-kb PstI fragment, downstream of rbc, with nptII, inactivating several open reading frames in this region. Mutant O105 was obtained by chemical mutagenesis and the mutation was mapped approximately 9 kb upstream of rbc. Mutants EK6 and O105 exhibited a very low apparent photosynthetic affinity for inorganic carbon, whereas D4 had an affinity similar to that observed in wild-type cells grown under high CO2. These mutants, and the constructs used to raise them, can be used to study the role of the small subunit of Rubisco and the genomic region near rbc in cyanobacterial photosynthesis. We propose that this region contains a cluster of genes involved in the ability of cyanobacteria to grow under low ambient CO2..
Cloning and characterization of the genes required for inorganic carbon transport of Synechocystis PCC6803
Authors: Ogawa Teruo
Published: December 2007

Transformation of the high CO2-requiring mutants of Synechocystis PCC6803 defective in inorganic carbon (Ci) transport (RKa and RKb) by wild type (WT) DNA libraries restored their ability to grow under air levels of CO2. Two clones (PK-1 and HP-1), which complement RKa and RKb, respectively, were isolated from the libraries. PK-1 contained an 11.8-kilobase pair (kbp) DNA insert. The sequence of amino acid coded in the DNA in the region of the mutation showed an extensive homology to that of the ndh2 gene product of liverwort chloroplasts, which is suspected to be the subunit 2 of NADH dehydrogenase. Based on the result, we designated the gene mutated in RKa as ndh2. Inactivation of the ndh2 gene in the WT cells by inserting an aminoglycoside-3′-phosphotransferase gene generated a mutant (M57) that was unable to grow under low CO2 conditions. HP-1 contained a 5.4-kbp DNA insert. Sequencing of nucleotides in the region of the mutation revealed an open reading frame that codes a hydrophobic protein that consists of 80 amino acids. Insertional inactivation of this putative Ci transport gene, designated ictA, generated a high CO2-requiring mutant (M9). All these mutants (RKa, RKb, M9, and M57) showed very low activity of CO2 uptake into the intracellular Ci pools. The activity of HCO3− uptake was negligibly low in RKb, M9, M57 and high CO2-grown cells of RKa, and was about 10% the activity of wild type cells in low CO2-adapted cells of RKa. Key words: CO2-concentrating mechanism, inorganic carbon transport, Synechocystis PCC6803, mutant, NADH dehydrogenase, insertional inactivation.
The carboxysome, a prokaryotic organelle: a mini-review
Authors: Shively J. M. , English R. S.
Published: December 2007

Since first being isolated and named carboxysomes more than 17 years ago, these prokaryotic inclusions have been studied with great interest. Several summary statements can be made regarding the structure, composition, and function of carboxysomes. The carboxysome is composed of 7–15 peptides, of which 3–5 are shell glycoproteins. The only enzyme demonstrated to be associated with the carboxysomes is ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The carboxysome may be a dodecahedron or an icosahedron. The molecular weight of the carboxysomes from Thiobacillus neapolitanus is approximately 2.4 × 108. Rubisco may fill the carboxysome or line the inner surface of the shell. The carboxysome is active in CO2 fixation. The function of the carboxysome is related to the availability of CO2 to the cells. The molecular mechanisms of carboxysome function are not yet available. Key words: carboxysomes, review, ribulose-1,5-bisphosphate carboxylase/oxygenase, Rubisco, structure, composition.
A model for inorganic carbon fluxes and photosynthesis in cyanobacterial carboxysomes
Authors: Reinhold Leonora , Kosloff Ronnie , Kaplan Aaron
Published: December 2007

A barrier to CO2 diffusion within the cyanobacterial cell has been regarded as essential for the inorganic carbon concentrating mechanism. We present here an extension of our earlier quantitative model demonstrating that it may be unnecessary to postulate any barrier other than the ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) molecules themselves. It is proposed that carbonic anhydrase is located in the interior of the carboxysome and that the CO2 generated is largely fixed as it diffuses outwards past Rubisco sites located along the diffusion path. Equations have been developed, by combining a mass balance equation with Fick's Law and the Michaelis-Menten equation (representing CO2 fixation), estimate the value that must be assigned to the diffusion coefficient for CO2 within the carboxysome if the CO2 concentration is to be reduced to near zero at the carboxysome outer surface. A solution has been obtained for two limiting cases, that where CO2 concentration is nearly saturating and that where it is at the Km(CO2) value or below. These two estimates predict that the permeability constant for the Rubisco zone in the carboxysome would have to be 10−2–10−3 cm∙s−1, a value that we suggest is reasonable for three-dimensional diffusion through a densely packed protein layer. The concentration gradient in the inward direction, for substrates penetrating the carboxysomes from the cytoplasm, is shown to be relatively flat, owing to the concentrating effect experienced by solutes passing from the periphery to the center of a sphere. Key words: cyanobacteria, carboxysomes, inorganic carbon fluxes, photosynthesis, model.
Na+-coupled bicarbonate transport in renal proximal tubular epithelia
Authors: Grassl Steven M.
Published: December 2007

The renal proximal tubule cell is the functional unit of an epithelium that serves to maintain a normal acid–base balance by reclaiming HCO3− filtered at the glomerulus and returning it to the circulation. The proximal tubule cell performs transcellular HCO3− reabsorption by a process of H+ secretion at the luminal membrane and export of intracellular HCO3− at the basolateral membrane. The present review describes the identification and functional characterization of the major transport pathway mediating efflux of intracellular HCO3− across the basolateral membrane of the proximal tubule cell. Compelling experimental evidence obtained from investigations using isolated membrane vesicles and the perfused proximal tubule preparation is discussed that indicate this transport pathway is an electrogenic cotransport mechanism coupling transfer of Na+, HCO3−, and CO32− across the basolateral membrane. Key words: acid–base, bicarbonate reabsorption, renal epithelia.
CO2 syndrome in Chlorella
Authors: Tsuzuki Mikio , Miyachi Shigetoh
Published: December 2007

Effects of CO2 concentration on microalgae, especially on Chlorella, are discussed from the aspect of the high affinity of microalgae for inorganic carbon (Ci) in photosynthesis. Accumulation of Ci and carbonic anhydrase are the two main factors underlying the high affinity for Ci. The other factors such as development of carboxysomes and pyrenoids under low CO2 conditions may also be important. Contribution of each factor to the high affinity for Ci in photosynthesis seems to differ from species to species. Key words: Chlorella, inorganic carbon transport, carbonic anhydrase, fatty acids composition, CO2.
Changes in protein and gene expression during induction of the CO2-concentrating mechanism in wild-type and mutant Chlamydomonas
Authors: Spalding Martin H. , Winder Thomas L. , Anderson James C. , Geraghty Anne M. , Marek Laura F.
Published: December 2007

Several changes occur in wild-type Chlamydomonas reinhardtii upon exposure to limiting CO2, including induction of several polypeptides. Polypeptide induction was previously shown to correlate with appearance of the active CO2-concentrating mechanism (CCM) of this alga. In this paper induction of polypeptides by limiting CO2 was investigated in mutants with lesions in the CCM. Mutants with lesions in the ca-1 and pmp-1 loci exhibited alterations in polypeptide induction, but it was concluded that the alterations probably do not represent their primary genetic lesions. Other changes that occur in this alga in response to limiting CO2 were also investigated. Based on a lack of significant change in the transcript abundance of ribulose-1,5-bisphosphate carboxylase/oxygenase large and small subunit genes in the wild type, it was concluded that the previously reported transient decline in synthesis of both subunits is controlled at the translational level. A transient increase in the activity of the photorespiratory enzyme phosphoglycolate phosphatase was observed in the wild type but not in a mutant, cia-5, that lacks induction of the CCM. In addition, changes in expression of genes encoding periplasmic carbonic anhydrase, a 36-kDa membrane-associated protein and a chlorophyll-binding protein occurred in the wild type but not in cia-5 in response to limiting CO2. The absence of these changes in cia-5 was attributed to a lack of either the signal itself or transduction of the signal responsible for adaptation to limiting CO2, which led to speculation that a larger range of responses are regulated by the same signal than was previously recognized. Key words: photosynthesis, photorespiration, algae, inorganic carbon transport, transcription, translation.
The role of the chloroplast in inorganic carbon acquisition by Chlamydomonas reinhardtii
Authors: Moroney James V. , Mason Catherine B.
Published: December 2007

The role of the chloroplast in algal inorganic carbon acquisition is reviewed. Unicellular green algae possess the ability to grow photoautotrophically at very low CO2 concentrations. The presence of a CO2-concentrating system that elevates the CO2 level within the cell can account for the algae's ability to reduce photorespiration and grow under these conditions. The mechanism of this inorganic carbon transport is unclear at present, although both the plasmalemma and the chloroplast have been implicated in this process. Three aspects of the role of the chloroplast in Chlamydomonas reinhardtii inorganic carbon uptake are discussed in this review. First, the present models of inorganic carbon uptake are summarized. Second, the purity and integrity of intact chloroplast preparations are discussed. Third, an evaluation of the published data on inorganic carbon uptake by isolated intact chloroplasts is presented. Key words: Chlamydomonas reinhardtii, carbonic anhydrase, chloroplast, active CO2 uptake.
Inorganic carbon transport in some marine microalgal species
Authors: Merrett M. J.
Published: December 2007

Inorganic carbon transport was investigated in a range of marine microalgae. A small-celled strain of Stichococcus bacillaris, containing appreciable carbonic anhydrase activity, showed a high affinity for CO2, while measurement of the internal inorganic carbon pool by the silicone oil layer centrifugal filtering technique showed cells concentrated inorganic carbon up to 20-fold in relation to the external medium at pH 5.0 but not pH 8.3. The addition of 14CO2 or H14CO3− to cells in short-term kinetic experiments at pH 8.3 confirmed that only CO2 provides the exogenous substrate for substantial inorganic carbon accumulation within the cell. High-affinity HCO3− transport in Phaeodactylum tricornutum and Porphyridium purpureum is dependent on sodium ions, while intracellular carbonic anhydrase increased the steady-state flux of CO2 from inside the plasmalemma to Rubisco. In the presence of HCO3− the intracellular pH in cells of P. purpureum is 7.1 but on carbon starvation the pH falls to 6.0. Ethoxyzolamide blocks bicarbonate-dependent alkalinization of the cytosol, confirming a central role for carbonic anhydrase–bicarbonate in cytosolic pH regulation. Carbonic anhydrase activity is pH dependent in P. purpureum so synergistic interaction between CO2 uptake and bicarbonate transport may occur.
The catalytic mechanism of carbonic anhydrase
Authors: Silverman David N.
Published: December 2007

Water as a ligand of the zinc in carbonic anhydrase has a pKa of 7 or less and the zinc-bound hydroxide is enhanced as a nucleophile for attack on CO2. The product of catalysis is HCO3− and a proton, and the catalytic pathway as determined for vertebrate isozymes I, II, and III occurs in two separate and distinct stages. The first stage includes the hydration of CO2 and ends with the release of HCO3− from its binding site as a ligand of the zinc; its position is replaced by a water molecule. This process is described by the ratio kcat/Km; for hydration catalyzed by isozyme II, the most efficient of the carbonic anhydrases, kcat/Km is close to diffusion controlled at 108 M−1∙s−1. The second stage is the regeneration of the zinc-bound hydroxide by protolysis of water and release of a proton to the surrounding medium. For carbonic anhydrase II, this proton transfer is rate determining for the maximal turnover number kcat of 106 s−1. Its pathway includes intramolecular proton transfer from the zinc-bound water to His64 in the active-site cavity followed by proton transfer to buffer in solution. For the least efficient of the carbonic anhydrases, isozyme III, kcat/Km near 3 × 105 M−1∙s−1 is not diffusion controlled; nevertheless, proton transfer from zinc-bound water to solution is still rate limiting for a maximal turnover of 104 s−1. Carbonic anhydrase isolated from spinach chloroplasts is quite similar to vertebrate isozyme II in catalytic properties, although it has been found to have almost no sequence homology with the vertebrate carbonic anhydrases. Key words: carbonic anhydrase, CO2, catalytic mechanism, proton transfer, bicarbonate.
Extracellular carbonic anhydrase of Chlamydomonas reinhardtii: localization, structural properties, and catalytic properties
Authors: Husic H. David
Published: December 2007

In the unicellular green alga Chlamydomonas reinhardtii, a form of the enzyme carbonic anhydrase that is localized outside of the plasma membrane is an inducible component of a system that is involved in inorganic carbon acquisition and concentration from the growth medium. This article contains a review and analysis of the current literature regarding the extracellular carbonic anhydrase from Chlamydomonas reinhardtii and presents some new studies on its extracellular localization, physiological role in inorganic carbon acquisition, and some of the structural and catalytic properties of the enzyme. Key words: carbonic anhydrase, Chlamydomonas reinhardtii, inorganic carbon utilization.
cDNA cloning and gene expression of carbonic anhydrase in Chlamydomonas reinhardtii
Authors: Fukuzawa Hideya , Ishida Sarami , Miyachi Shigetoh
Published: December 2007

cDNA and genes encoding periplasmic carbonic anhydrase (CA) polypeptides of Chlamydomonas reinhardtii have been isolated and characterized. Nucleotide sequence analysis of cDNA clones revealed that the large subunit (35 kDa or 36.5 kDa) and the small subunit (4 kDa) are cotranslated as a precursor polypeptide (41 626 Da) with a NH2-terminal hydrophobic signal peptide of 20 amino acids. The amino acid sequence of Chlamydomonas CA showed 20–22% identity with animal CA isozymes (CAI, CAII, CAIII, and CAVII). Three zinc-liganded histidine residues and those forming the hydrogen-bond network to zinc-bound solvent molecules were highly conserved. No significant sequence similarity was observed between Chlamydomonas CA and chloroplast CAs of spinach and pea. Two copies of structurally related CA genes (CAH1 and CAH2) were tandemly clustered in Chlamydomonas nuclear genome and regulated by external CO2 concentration in a reverse manner. The 5′ upstream gene CAH1 encodes the major periplasmic CA whose mRNA level is induced under low CO2 condition in light. Photosynthesis is absolutely required for the accumulation of the CAH1 mRNA. The 3′ downstream gene CAH2 is possibly a gene for another periplasmic CA isozyme, which is induced under high CO2 conditions. Light has an inhibitory effect on the accumulation of the CAH2 mRNA. Key words: photosynthesis, light regulation, zinc, CO2-concentrating mechanism, intracellular processing.
Sequence analysis and regulation of expression of a gene coding for carbonic anhydrase in Chlamydomonas reinhardtii
Authors: Coleman J. R. , Luinenburg Irene , Majeau Nathalie , Provart Nicholas
Published: December 2007

Using immunological and molecular biological techniques, we studied the localization, gene organization, and regulation of expression of the extracellular carbonic anhydrase in the eukaryotic green alga Chlamydomonas reinhardtii. Electron microscopy data using immunogold labelling suggest an association of the protein with the inner face of the cell wall. The same polyclonal antibody was previously used to select an immunoreactive 2.5-kb genomic DNA fragment coding for a portion of the carbonic anhydrase monomer. Using the known carbonic anhydrase cDNA sequence and sequence analysis of the genomic DNA fragment, we have deduced the exon–intron organization of the genomic clone. The similarities between Chlamydomonas and higher plant carbonic anhydrase amino acid sequences and the effect of photoheterotrophic growth on the expression of the algal carbonic anhydrase are also examined. Key words: carbonic anhydrase, Chlamydomonas, immunogold labelling, sequence, expression.
Influence of protein synthesis inhibitors on the extracellular current pattern and electrophysiological properties of internodal cells of Chara corallina
Authors: Mimura Tetsuro , Frost-Shartzer Stacey A. , Lucas William L.
Published: December 2007

Internodal cells of Chara corallina exhibit a spatially controlled pattern of alternating acid and alkaline regions along their surface, corresponding to regions of outward and inward current density, respectively. Incubation of isolated cells in either 25 μg∙mL−1 cycloheximide or 50 μM 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide resulted in a 70–90% reduction in current density and a 50% decrease in the magnitude of the dark-induced membrane hyperpolarization. When cells were supplied with dissolved inorganic carbon, in the form of either CO2 or HCO3−, 25 μg∙mL−1 cycloheximide caused a minimal and 30% reduction in photosynthetic O2 evolution, respectively. In vivo protein synthesis, measured by [3H]-leucine incorporation, showed an 11% decrease in the presence of cycloheximide, while chloramphenicol caused a 91.5% inhibition. It is interesting to note that although exposure to chloramphenicol elicited only a slight decrease in current density, the dark-induced membrane hyperpolarization was inhibited by 50%. All treatments failed to perturb the regions on the cell surface, of zero current, giving stable band location, even though the current density was reduced. The effect of these protein synthesis inhibitors is discussed in terms of the cellular control mechanism involved in regulating the supply of inorganic carbon for photosynthesis. Key words: Chara corallina, extracellular currents, cycloheximide, protein synthesis inhibitors, proton transport, membrane potential.
pH-dependent proton permeability of the plasma membrane is a regulating mechanism of polar transport through the submerged leaves of Potamogeton lucens
Authors: Miedema H. , Prins H. B. A.
Published: December 2007

Recently it has been hypothesized that light-induced polarity in leaves of the submerged angiosperms Potamogeton and Elodea results in part from a pH-dependent change in the permeability of the plasma membrane for protons. It is assumed that the proton permeability increases at high pH. In this paper we studied the effects on polarity of pH buffers, applied to just one side of the leaf. An experimental set up was used in which the solutions in contact with either side of the leaf surface were separated. The above hypothesis was partly confirmed, in that acidification, normally observed at the morphological lower side, was strongly suppressed by the application of a low-pH buffer at the upper side. Apparently, the low pH at the upper epidermis reduced the proton permeability, and as a result the proton pumps at the lower side were inactivated by a lack of substrate or by an effect on cytoplasmic pH. However, increasing the apoplastic pH at the lower side indicated that the proton permeability of the plasma membrane of these ceils did not change significantly. Hence both cell types seem to behave differently concerning the pH dependent proton permeability of the plasma membrane. This may explain why in the polar leaves of the angiosperms acidification always occurs at the lower and alkalinization always at the upper side. Key words: plasma membrane, proton permeability, pH polarity, Potamogeton, Elodea.
Effects of nutritional status on cyanobacterial buoyancy, blooms, and dominance, with special reference to inorganic carbon
Authors: Klemer Andrew R.
Published: December 2007

Evidence from correlative studies suggesting that nutrient deficiency is responsible for cyanobacterial surface blooms is contrasted with evidence from lake and laboratory experiments suggesting that the ability of cyanobacterial populations to monopolize light in the surface layers of stratified water columns depends on the availability of nutrients required for gas-vesicle synthesis as well as for growth. A resolution of the paradoxical roles of inorganic carbon in cyanobacterial buoyancy regulation is advanced and is used to explain the success of different types of cyanobacteria in environments that differ greatly in bicarbonate content. Key words: cyanobacteria, gas vesicles, buoyancy, blooms, dominance, bicarbonate.
The inorganic carbon requirements for nitrogen assimilation
Authors: Turpin David H. , Vanlerberghe Greg C. , Amory Alan M. , Guy Robert D.
Published: December 2007

In the green alga Selenastrum minutum (Naeg.) Collins the assimilation of NH4+ into the full suite of protein amino acids requires at least three separate and distinct inorganic carbon fixing reactions, catalyzed by the enzymes ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC), and carbamoyl phosphate synthetase. In this paper we examine the requirements for CO2 fixation of NH4+ assimilation in this organism. When grown under N-sufficient conditions, NH4+ assimilation is directly dependent upon photosynthetic CO2 fixation to provide carbon skeletons for amino acid synthesis. When cultured under N-limited conditions, the cells accumulate starch, which is then available for amino acid synthesis. This alleviates the requirement of photosynthetic CO2 fixation for NH4+ assimilation. N-limited cells, however, still exhibit a nonphotosynthetic CO2 requirement for N assimilation that is mediated through PEPC. This activity of PEPC increases during N assimilation to replenish TCA cycle intermediates consumed during amino acid synthesis. The in vivo activity of this enzyme is tightly regulated so that there are ~0.3 moles C fixed per mole N assimilated. In S. minutum PEPC is regulated primarily by the ratio of glutamine/glutamate, thus providing a mechanism by which primary NH4+ assimilation modulates the supply of carbon for amino acid biosynthesis. Activation of PEPC during NH4+ assimilation occurs in both the light and the dark. Key words: dissolved inorganic carbon, nitrogen assimilation, phosphoenolpyruvate carboxylase, photosynthesis, amino acid synthesis, respiration.
Somatic embryogenesis in conifers
Authors: Tautorus T. E. , Fowke L. C. , Dunstan D. I.
Published: December 2007

Substantial progress has been made towards the development of systems for in vitro embryogenesis in conifers. Since the first report of somatic embryogenesis from zygotic embryos of Picea abies in 1985, cultured explants of at least 18 different coniferous species have been induced to produce somatic embryos. Somatic embryos have been cryopreserved, grown in liquid suspensions, and matured into plants. In addition, plantlets have been regenerated from protoplasts isolated from embryogenic suspensions of Picea glauca and Larix ×eurolepis, permitting studies into direct gene transfer and somatic hybridization. Currently however, it is only possible to obtain somatic embryogenesis from embryonic and juvenile explants. Furthermore, for most species the efficiency of plantlet production from somatic embryos is poor and remains a problem for the commercial utilization of this technology. Biochemical, cytological, and physiological studies of conifer somatic embryogenesis have resulted in improved knowledge concerning the origin of somatic embryos, storage product accumulation during embryo development, and similarities with zygotic embryos. Furthermore, the technique of indirect immunofluorescence microscopy has permitted investigations of the cytoskeleton in conifer cells and protoplasts, providing insights into cell division and morphogenesis. In this review, emphasis is placed on the more fundamental aspects of conifer somatic embryogenesis. Where possible, comparisons between zygotic and somatic embryogenesis are made. Key words: somatic embryogenesis, zygotic embryogenesis, conifers, review.
Recovery of Cochliobolus sativus and Fusarium graminearum from living and dead wheat and nongramineous winter crops in southern Brazil
Authors: Fernandez Myriam R.
Published: December 2007

Wheat and several nongramineous plant species, commonly used in rotation with wheat in southern and central Brazil, were examined for the presence of the wheat pathogens Cochliobolus sativus and Fusarium graminearum. Both fungi were isolated from residues of all the plant species, artificially inoculated and grown in a growth chamber, or grown outdoors exposed to inoculum in the form of infested sorghum grains. After harvest of outdoor plants, recovery was lower in 4-month-old residues than in 5-week-old residues. These fungi were also recovered from healthy and lesioned parts of many of these plant species collected in the field. Artificially inoculated nongramineous plants did not show any symptoms of infection and microscopic examination of inoculated leaves showed a resistant reaction to C. sativus.
Somatic embryogenesis and plant regeneration from immature embryos of Carica papaya × Carica cauliflora cultured in vitro
Authors: Chen M. H. , Chen C. C. , Wang D. N. , Chen F. C.
Published: December 2007

Somatic embryos were induced directly on immature embryos of Carica papaya × Carica cauliflora hybrids cultured on modified Murashige and Skoog's medium. When transferred to medium supplemented with abscisic acid, individual somatic embryos proliferated numerous daughter embryos through repeated embryogenesis. Light microscopic study of the repeatedly embryogenic cultures showed that daughter embryos arose from single superficial cells of parent embryos. Plant regeneration occurred following transfer of somatic embryos to medium devoid of plant growth regulators. Regenerated plants were intermediate between C. papaya and C. cauliflora in several morphological respects and showed isozyme patterns specific to both species as well as some new bands, indicating that they are indeed interspecific hybrids. Key words: Carica, interspecific hybrid, embryo culture, somatic embryogenesis.
Genetic variations of ectomycorrhizal fungi: extramatrical phase of Pisolithus sp.
Authors: Lamhamedi Mohammed S. , Fortin J. André
Published: December 2007

The ability of 28 monokaryons and 78 reconstituted dikaryons of Pisolithus sp. from South Africa to form mycelial strands in association with Pinus pinaster was tested under aseptic and non-aseptic conditions. All monokaryotic and some dikaryotic cultures failed to form mycelial strands either on agar medium or in growth pouches. The remaining dikaryotic cultures showed wide genetic variation in the development of mycelial strands and in the extension of their extramatrical phase. The exploration of the surrounding environment by the extramatrical phase from synthesized Pinus pinaster – dikaryotic cultures of the Pisolithus sp. depended largely upon the type of medium used, being more extensive in soil than on nutrient agar medium. Microscopic observation showed that mycelial strands were formed by aggregations of hyphae. Large central hyphae with disorganized cytoplasm were observed in some strands. The results are discussed in relation to nutrient and water absorption. Key words: Pisolithus sp., Pinus pinaster, genetic, extramatrical phase, mycelial strands.
The development of cauliflory in redbud, Cercis canadensis (Fabaceae)
Authors: Owens Shirley A. , Ewers Frank W.
Published: December 2007

Cauliflory, flowering on older branches or trunks of woody plants, in Cercis canadensis was studied using light and scanning electron microscopy and macroscopic bud counts. A linear series of up to 10 floral buds are initiated in the axil of the foliage leaf before stem elongation is completed. These buds sequentially mature into first-order inflorescences over a 5-year period. Although an individual inflorescence flowers only once, second-order reproductive buds are formed in the axils of the basal bud scales of the inflorescence and can produce third-order reproductive buds. Buds and the bases of abscised inflorescences form wens, which are macroscopic swollen areas along the stem, corresponding to the original orthodistichous phyllotaxy. Branching of primary vascular tissue in a wen indicates a continuum of vascular connections between reproductive buds and the vascular traces to the inflorescences can be followed to the pith. The wens often produce epicormic shoots that are themselves cauliflorous with first-order reproductive buds formed in their leaf axils. The shoots usually abscise above the first-order reproductive buds at their base. These buds, along with the higher order reproductive buds, perpetuate the cauiflorous condition throughout the life of the plant. Key words: axillary buds, cauliflory, Cercis canadensis, epicormic shoots, wens.
Phylogeny of anaerobic rumen Chytridiomycetes inferred from small subunit ribosomal RNA sequence comparisons
Authors: Dore J. , Stahl D. A.
Published: December 2007

The 18S-like rRNA sequences of four recently isolated strains of rumen anaerobic phycomycetes (Neocallimastix frontalis MCH3, Piromonas communis FL, Sphaeromonas communis FG, and Neocallimastix joyonii NJ1) were analyzed and compared to examine the phylogenetic relatedness of the four isolates to each other and to other eukaryotes. The rumen chytrids characterized demonstrated very high 18S-like rRNA sequence similarities (97–99%). They are more closely related to the true fungi than to any other eukaryotes. Key words: phylogeny, anaerobic fungi, rumen, chytrids, Chytridiomycetes, Neocallimastix.
Mechanisms of seed dormancy in an annual population of Zostera marina (eelgrass) from The Netherlands
Authors: Harrison Paul Garth
Published: December 2007

Mechanisms of dormancy of seeds from an annual population of the seagrass Zostera marina L. (eelgrass) in the SW Netherlands were investigated in the laboratory. Both physiological dormancy (a requirement for reduced salinity for germination) and physical dormancy (imposed by the seed coat) existed in recently shed seeds. Physiological seed dormancy was partly released in the seed bank by early winter, but physical dormancy lasted longer. By March seeds germinated quickly in the dark in full-strength seawater without artificial weakening of the seed coat. Viable seeds were released with coats that ranged from green (easily ruptured by the embryo) to brown (not easily ruptured); this variation may account for the occasional seedlings that appear during winter. No significant effects of temperature or light on germination were detected. A reexamination of the literature suggests that the observed variation in timing of germination in eelgrass populations may be a result of hitherto overlooked aspects of dormancy. Key words: eelgrass, seagrass, seed coat, seed dormancy, seed germination, Zostera marina.
A multivariate comparison of the seagrasses Zostera marina and Zostera japonica in monospecific versus mixed populations
Authors: Nomme Kathy M. , Harrison Paul G.
Published: December 2007

The seagrasses Zostera marina and Zostera japonica coexist along a portion of a gradual intertidal gradient at Roberts Bank, British Columbia. Individual comparisons of 11 morphological and 2 population characters for Z. marina did not reveal consistently significant differences between the deeper water monospecific population and the population in mixed vegetation. Similar comparisons between the shallow-water monospecific Z. japonica and the mixed vegetation indicated a suppression of Z. japonica shoot production (density) under a canopy of Z. marina. Principal components analysis was used to summarize the original data into a new set of multivariate characters that were then compared using ANOVA and MANOVA. With these analyses, the subtle differences between Z. marina populations became significant at various times. Similar analyses for Z. japonica indicated that morphological differences between the monospecific and mixed populations persisted throughout the sample period. The multivariate characters provide summaries of populations that are useful in detecting subtle responses to varied environments. Key words: Zostera marina, Zostera japonica, seagrass morphology, multivariate analysis, MANOVA, intertidal zone.
Isolation and partial purification of phytotoxins from liquid cultures of Leucostoma cincta and Leucostoma persoonii
Authors: Svircev A. M. , Biggs A. R. , Miles N. W.
Published: December 2007

Phytotoxins from Leucostoma persoonii and Leucostoma cincta were isolated by sequential ultrafiltration of cell-free culture filtrates through a series of exclusion membranes. Phytotoxic activity, characterized by stem necrosis and leaf wilt, chlorosis, and necrosis, was evident when a cold acetone precipitate from the < 1000-Da fraction was tested in a peach shoot tip bioassay. Analytical polyacrylamide isoelectrofocusing of the < 1000-Da fraction in the pH range 3.5–6.0 identified two peptide bands at pH 4.0 and 6.0. Preparative granulated bed isoelectric focusing in the same pH range yielded two fractions with phytotoxic activity against peach shoots. Preliminary characterization studies indicate that the two fractions with toxin activity contain small polypeptides. Key words: Cytospora spp., cytospora canker, Prunus persica, peach.
Evidence for interaction between the seagrasses Zostera marina and Zostera japonica on the Pacific coast of Canada
Authors: Nomme Kathy M. , Harrison Paul G.
Published: December 2007

Experiments were undertaken to differentiate between abiotic and biotic factors affecting seagrass growth. Monospecific patches of both Zostera marina and Zostera japonica were transplanted into one shallow subtidal and three intertidal sites at Roberts Bank, British Columbia. In transplanted patches, initiated in 1988, neither Z. marina nor Z. japonica showed any consistent differences in either population growth or mean shoot length among the sites. Abiotic environmental conditions could therefore not be considered responsible for the differences observed between the natural vegetation of the respective monospecific zones and the zone of naturally mixed seagrass vegetation. In a manipulation experiment, opaque and clear plastic seagrass canopies were imposed on Z. japonica vegetation and the resulting growth was compared with treatments of a natural Z. marina canopy and removal of the natural canopy. The artificial seagrasses combined with the patch layout of the experiment did not create the shade conditions intended and may have facilitated the loss of shoots. The results were not conclusive, but there were consistently higher densities of Z. japonica in the treatment where Z. marina had been removed. Interactions between these two seagrasses in their vegetative phase may contribute to the observed differences in population and morphological characters, but the dispersal and establishment phases remain to be studied. Key words: Zostera marina, Zostera japonica, seagrass, competition, transplants, artificial seagrass.
Analysis of vegetative compatibility groups in nonpathogenic populations of Fusarium oxysporum isolated from symptomless tomato roots
Authors: Elias Karol S. , Schneider R. W. , Lear M. M.
Published: December 2007

A collection of 471 isolates of Fusarium oxysporum was obtained from symptomless tomato roots of plants grown at eight locations in Louisiana. Isolates that produced nitrate metabolism mutants (317 isolates) were included in an analysis of vegetative compatibility groups. One hundred and eighty-six isolates were assigned to 48 vegetative compatibility groups (2015–2062) containing 2–15 members from one to three different collection sites. Even though each site contained sub-populations of F. oxysporum common to other sites, only about half of the vegetative compatibility groups (21 groups) contained isolates from more than one site. In addition, there were 131 isolates of F. oxysporum that formed single-member vegetative compatibility groups. This diverse population composition is probably the result of several factors, including breeding strategies for resistance to fusarium wilt and tomato production practices in Louisiana. Resistance genes and horticultural traits from several sources (Lycopersicon spp.) have been incorporated into commercial tomato cultivars currently being grown. In addition, the long growing season in Louisiana allows several tomato cultivars containing different genes for resistance to be grown consecutively in the same field in a single year. Furthermore, other vegetable crops may be alternated with the tomato crops. Thus, the selection pressures that influence the composition of the nonpathogenic populations of F. oxysporum are in a constant state of flux. Key words: Fusarium oxysporum, genetic diversity, nonpathogens, vegetative compatibility groups.