bluuebunny/crossref_metadata_2025 huggingface dataset:
Intra- and interobserver reproducibility of vertebral endplate signal (Modic) changes in the lumbar spine: the nordic modic consensus group classification
Authors: Jensen T. S. , Sorensen J. S. , Kjaer P.
Published: August 2007

Background: The lumbar vertebral endplate is considered a potential cause of specific low back pain. However, in relation to future research, there is need for a reliable and detailed magnetic resonance imaging (MRI) protocol to be used in the evaluation of vertebral endplate signal changes.

Purpose: To assess the intra- and interobserver reliability of the “Nordic Modic classification” protocol.

Material and Methods: MRI scans of 50 individuals representative of the general Danish population aged 40 were evaluated by two observers. Criteria for grading the changes were developed by the Nordic Modic Consensus Group. After consensus was established, all 50 MRI examinations were evaluated independently by each observer. Intraobserver reliability was assessed by re-evaluation of the 50 examinations by one of the observers. Kappa statistics were used to calculate agreement.

Results: Intra- and interobserver agreement of the evaluation of variables describing vertebral signal changes, i.e. Modic type, location, volume, maximum height, and endplate area, were all found to have substantial to almost perfect agreement. The evaluation of osteophytes was found to be reliable, whereas the evaluation of localized endplate defects and irregular endplates had only moderate agreement. The evaluation of development over time was found to have substantial intraobserver agreement but only moderate interobserver agreement. As expected, intraobserver agreement was generally better than interobserver agreement.

Conclusion: In this study, we found convincing reproducibility of a detailed evaluation protocol of vertebral endplate signal changes, the “Nordic Modic Classification.” The authors recommend that the evaluation protocol should be used in future studies investigating vertebral endplate signal changes.
Ultrasound guidance for puncture and injection in the radiocarpal joint
Authors: Lohman M. , Vasenius J. , Nieminen O.
Published: August 2007

Background: The use of intra-articular contrast agent has been shown to increase the diagnostic accuracy of wrist magnetic resonance (MR) in patients with suspected trauma of the wrist ligaments. Traditionally, the contrast agent has been applied under fluoroscopic guidance.

Purpose: To present a method based on ultrasound guidance for the injection of intra-articular contrast agent in wrist MR.

Material and Methods: One hundred eight patients (56 female and 52 male, mean age 36 years) referred for wrist MR arthrograms due to suspected ligament rupture were included in this retrospective study. The preferred injection point is about 1 cm distal to Lister's tubercle in the distal radius. A correct positioning of the injection needle can be ensured using ultrasound guidance.

Results: Using this technique, the injection was intra-articular in 93.5% of the 108 injections over a 2-year learning period.

Conclusion: Ultrasound guidance of the contrast injection in radiocarpal MR arthrograms is a cost-effective and safe alternative to fluoroscopically guided procedures. Furthermore, the use of ultrasound guidance provides clues about possible fluid collections within the joint.
Abnormal default-mode network activation in cirrhotic patients: a functional magnetic resonance imaging study
Authors: Zhang Long Jiang , Yang Guifen , Yin Jianzhong , Liu Yawu , Qi Ji
Published: August 2007

Background: Recently, increasing numbers of studies have demonstrated that, in humans, a default-mode functional network exists in the resting state. Abnormal default-mode network in various diseases has been reported; however, no report concerning hepatic cirrhosis has been published to date.

Purpose: To prospectively explore whether the resting-state network in patients with hepatic cirrhosis is abnormal or not, using functional magnetic resonance imaging (fMRI).

Material and Methods: 14 patients with hepatic cirrhosis (12 male, two female; 45±9 years) and 14 age- and gender-matched healthy volunteers (12 male, two female; 42±10 years) participated in a blocked-design fMRI study. A modified Stroop task with Chinese characters was used as the target stimulus. Statistical Parametric Mapping 99 software was employed to process the functional data. Individual maps and group data were generated for patients with hepatic cirrhosis and for healthy controls, respectively. Intergroup analysis between patients and healthy controls was also generated using the two-sample t-test model. Cluster analyses were done based on the group data, and an identical P value ⩽0.01 with continuously connected voxels of no less than 10 was defined as significant deactivation. After fMRI scanning was complete, behavioral Stroop interference tests were performed on all subjects; reaction time and error number were recorded.

Results: Functionally, deactivation of the posterior cingulate cortex (PCC) and precuneus was absent when subjects performed the incongruous word-reading task; deactivation of the PCC, precuneus, and ventral medial prefrontal cortex was increased when they performed the incongruous color-naming task.

Conclusion: The functional as well as behavioral data suggest that cirrhotic patients may have an abnormal deactivation mode. The absence of deactivation in the PCC and precuneus may be a sensitive rather than specific marker in patients with hepatic cirrhosis.
W. Zacheus Cande: Evolutionary biologist in cell biologist's clothing
Authors: Williams Ruth
Published: August 2007

Zac Cande wants to get to the roots of cell division and cytoskeletal mechanics.
Electrostatic Interaction of Internal Mg2+ with Membrane PIP2 Seen with KCNQ K+ Channels
Authors: Suh Byung-Chang , Hille Bertil
Published: August 2007

Activity of KCNQ (Kv7) channels requires binding of phosphatidylinositol 4,5-bisphosphate (PIP2) from the plasma membrane. We give evidence that Mg2+ and polyamines weaken the KCNQ channel–phospholipid interaction. Lowering internal Mg2+ augmented inward and outward KCNQ currents symmetrically, and raising Mg2+ reduced currents symmetrically. Polyvalent organic cations added to the pipette solution had similar effects. Their potency sequence followed the number of positive charges: putrescine (+2) < spermidine (+3) < spermine (+4) < neomycin (+6) < polylysine (≫+6). The inhibitory effects of Mg2+ were reversible with sequential whole-cell patching. Internal tetraethylammonium ion (TEA) gave classical voltage-dependent block of the pore with changes of the time course of K+ currents. The effect of polyvalent cations was simpler, symmetric, and without changes of current time course. Overexpression of phosphatidylinositol 4-phosphate 5-kinase Iγ to accelerate synthesis of PIP2 attenuated the sensitivity to polyvalent cations. We suggest that Mg2+ and other polycations reduce the currents by electrostatic binding to the negative charges of PIP2, competitively reducing the amount of free PIP2 available for interaction with channels. The dose–response curves could be modeled by a competition model that reduces the pool of free PIP2. This mechanism is likely to modulate many other PIP2-dependent ion channels and cellular processes.
Green’s formulas for cone differential operators
Authors: Witt Ingo
Published: August 2007

Green’s formulas for elliptic cone differential operators are established. This is achieved by an accurate description of the maximal domain of an elliptic cone differential operator and its formal adjoint; thereby utilizing the concept of a discrete asymptotic type. From this description, the singular coefficients replacing the boundary traces in classical Green’s formulas are deduced.
Filament sets, aposyndesis, and the decomposition theorem of Jones
Authors: Prajs Janusz , Whittington Keith
Published: August 2007

Applications of the work introduced by the authors in a recent article, Filament sets and homogeneous continua, are given to aposyndesis and local connectedness. The aposyndetic decomposition theorem of Jones is generalized to spaces with the property of Kelley.
Généralisation du critère de Beurling-Nyman pour l’hypothèse de Riemann
Authors: de Roton Anne
Published: August 2007

Nous généralisons dans cet article le critère de Beurling-Nyman, qui concerne la fonction

ζ
\zeta

de Riemann, à une large classe de séries de Dirichlet. Nous établissons donc une correspondance entre la densité d’un certain sous-espace de fonctions dans

L
2

(
0
,
1
)

L^2(0,1)

et la localisation des zéros d’une série de Dirichlet. Nous utilisons pour obtenir ce résultat la structure de l’espace de Hardy du demi-plan. Abstract. We generalise Beurling-Nyman’s criterion, already known for the Riemann

ζ
\zeta

function, to a larger class of Dirichlet series. We reveal a link between the density of some subspace of functions in

L
2

(
0
,
1
)

L^2(0,1)

and the localization of the zeros of a Dirichlet series. To do so, we use the structure of the Hardy space of the half-plan.
Clusters, Coxeter-sortable elements and noncrossing partitions
Authors: Reading Nathan
Published: August 2007

We introduce Coxeter-sortable elements of a Coxeter group 

W
.

W.

For finite

W
,

W,

we give bijective proofs that Coxeter-sortable elements are equinumerous with clusters and with noncrossing partitions. We characterize Coxeter-sortable elements in terms of their inversion sets and, in the classical cases, in terms of permutations.
Stable and Unstable Cadherin Dimers: Mechanisms of Formation and Roles in Cell Adhesion
Authors: Troyanovsky Regina B. , Laur Oscar , Troyanovsky Sergey M.
Published: August 2007

Numerous attempts to elucidate the strength of cadherin dimerization that mediates intercellular adhesion have produced controversial and inconclusive results. To clarify this issue, we compared E-cadherin dimerization on the surface of living cells with how the same process unfolds on agarose beads. In both cases, dimerization was monitored by the same site-specific cross-linking assay, greatly simplifying data interpretation. We showed that on the agarose surface under physiological conditions, E-cadherin produced a weak dimer that immediately dissociated after the depletion of calcium ions. However, either at pH 5 or in the presence of cadmium ions, E-cadherin produced a strong dimer that was unable to dissociate upon calcium depletion. Both types of dimers were W156-dependent. Remarkably, only the strong dimer was found on the surface of living cells. We also showed that the intracellular cadherin region, the clustering of which through catenins had been proposed as stabilizer of weak intercadherin interactions, was not needed, in fact, for cadherin junction assembly. Taken together, our data present convincing evidence that cadherin adhesion is based on high-affinity cadherin–cadherin interactions.
Analgesic Action of Acupuncture and Moxibustion: A Review of Unique Approaches in Japan
Authors: Okada Kaoru , Kawakita Kenji
Published: August 2007

The mechanism of acupuncture analgesia (AA) is one of the most widely researched topics in complementary and alternative medicine (CAM) based on modern medical methodology. Endogenous opioid‐mediated mechanisms of acupuncture have been well established since the 1970s. In this review, we have covered the progress of AA research by Japanese investigators. In particular, we have reviewed the physiological basis of analgesic effects induced by acupuncture and moxibustion, including the actions of endogenous opioid and diffuse noxious inhibitory controls (DNICs), and the afferent fibers participating in acupuncture and moxibustion stimuli are discussed.
Amplified fragment length polymorphism analysis of Mycobacterium avium complex isolates recovered from southern California
Authors: Pfaller Stacy L. , Aronson Timothy W. , Holtzman Alan E. , Covert Terry C.
Published: August 2007

Fine-scale genotyping methods are necessary in order to identify possible sources of human exposure to opportunistic pathogens belonging to the Mycobacterium avium complex (MAC). In this study, amplified fragment length polymorphism (AFLP) analysis was evaluated for fingerprinting 159 patient and environmental MAC isolates from southern California. AFLP analysis accurately identified strains belonging to M. avium and Mycobacterium intracellulare and differentiated between strains within each species. The method was also able to differentiate strains that were presumed to be genetically identical in two previous studies using large RFLP analysis with PFGE, or PCR-amplification of DNA segments located between insertion sequences IS1245 and IS1311. For M. avium, drinking-water isolates clustered more closely with each other than with patient or food isolates. Patient isolates were more genetically diverse. None of the environmental isolates shared identical AFLP patterns with patient isolates for either species. There were, however, environmental isolates that shared identical patterns, and patient isolates that shared identical patterns. A subset of the isolates, which are referred to as MX isolates due to their ambiguous identification with the Gen-Probe system, produced AFLP patterns similar to those obtained from M. intracellulare isolates. Sequence analysis of 16S rDNA obtained from the MX isolates suggests that they are strains of M. intracellulare that were not correctly identified by the M. intracellulare AccuProbe from Gen-Probe.
Racemoside A, an anti-leishmanial, water-soluble, natural steroidal saponin, induces programmed cell death in Leishmania donovani
Authors: Dutta Avijit , Ghoshal Angana , Mandal Debayan , Mondal Nirup B. , Banerjee Sukdeb , Sahu Niranjan P. , Mandal Chitra
Published: August 2007

Leishmaniasis remains a major health problem of the tropical and subtropical world. The visceral form causes the most fatalities if left untreated. Dramatic increases in the rates of infection and drug resistance and the non-availability of safe vaccines have highlighted the need for identification of novel and inexpensive anti-leishmanial agents. This study reports that racemoside A, a water-soluble steroidal saponin purified from the fruits of Asparagus racemosus, is a potent anti-leishmanial molecule effective against antimonial-sensitive (strain AG83) and -unresponsive (strain GE1F8R) Leishmania
donovani promastigotes, with IC50 values of 1.15 and 1.31 μg ml−1, respectively. Incubation of promastigotes with racemoside A caused morphological alterations including cell shrinkage, an aflagellated ovoid shape and chromatin condensation. This compound exerts its leishmanicidal effect through the induction of programmed cell death mediated by the loss of plasma membrane integrity as detected by binding of annexin V and propidium iodide, loss of mitochondrial membrane potential culminating in cell-cycle arrest at the sub-G0/G1 phase, and DNA nicking shown by deoxynucleotidyltransferase-mediated dUTP end labelling (TUNEL). Racemoside A also showed significant activity against intracellular amastigotes of AG83 and GE1F8R at a 7–8-fold lower dose, with IC50 values of 0.17 and 0.16 μg ml−1, respectively, and was non-toxic to murine peritoneal macrophages up to a concentration of 10 μg ml−1. Hence, racemoside A is a potent anti-leishmanial agent that merits further pharmacological investigation.
Development of a simple model for studying the effects of antifungal agents on multicellular communities of Aspergillus fumigatus
Authors: Mowat Eilidh , Butcher John , Lang Sue , Williams Craig , Ramage Gordon
Published: August 2007

Aspergillus fumigatus is an increasingly prevalent opportunistic fungal pathogen of various immunocompromised individuals. It has the ability to form filaments within the lungs, producing dense intertwined mycelial balls, which are difficult to treat. The aim of this study was to develop a suitable model of A. fumigatus to examine the effects of antifungal challenge on these intertwined filamentous communities. A. fumigatus NCPF 7367 growth conditions were optimized on both Thermanox coverslips and on flat-bottomed microtitre plates to establish optimal conidial seeding densities. Isolates were treated with itraconazole, voriconazole, amphotericin B and caspofungin and their overall killing efficiency was measured using an XTT formazan metabolic dye assay. This was compared with the CLSI (formerly NCCLS) methodology of broth microdilution of moulds (standard M38-A). It was shown that 1×105 conidia ml−1 in RPMI 1640 was the optimum concentration of spores for biofilm formation. Filamentous growth characteristics were not observed until 10 h incubation, followed by an exponential increase in the biofilm biomass (hyphae and extracellular material) and cellular activity (metabolism). When susceptibility testing of biofilms was compared with that of planktonic cells by CLSI broth microdilution testing, all antifungal drugs were at least 1000 times less effective at reducing the overall metabolic activity of 90 % of the cells. Overall, this study showed that A. fumigatus has the ability to form coherent multicellular biofilm structures that are resistant to the effects of antifungal drugs.
ULTRASTRUCTURE OF THE GREEN ALGA DICHOTOMOSIPHON TUBEROSUS WITH SPECIAL REFERENCE TO THE OCCURRENCE OF STRIATED TUBULES IN THE CHLOROPLAST1
Authors: Moestrup Øjvind , Hoffman Larry R.
Published: August 2007

The ultrastructure of the siphonous green alga Dichotomosiphon tuberosus (A. Br.) Ernst is compared with that of other siphonous plants. There is a characteristic association between the Golgi bodies and endoplasmic reticulum, but. the mitochondria are not involved in the association as they are in Vaucheria and the phycomycete Saprolegnia. An unusual structure and arrangement of the chloroplasts is described as well as a previously unreported type of “striated tubule” which occurs in most if not all chloroplasts, and amyloplasts. The structure of these tubules is compared with that of other tubules recently found in green algae and higher plants. In addition, cytoplasmic microtubules arranged in the longitudinal direction of the siphon suggest a function in cytoplasmic streaming.
A CONTINUOUS CULTURE STUDY OF PHOSPHATE UPTAKE, GROWTH RATE AND POLYPHOSPHATE IN SCENEDESMUS SP.1
Authors: Rhee G‐Yull
Published: August 2007

The kinetics of phosphate uptake and growth in Scenedesmus sp. have been studied in continuous culture with particular reference to the shifts in the cellular P compounds as a function of growth rate.

Uptake velocity is a function of both internal and external substrate concentrations and can be described by the kinetics of noncompetitive enzyme inhibition. The concentrations of polyphosphates (alkali‐extractable or 7‐min) can he substituted as inhibitors in the kinetic equation. The apparent half‐saturation constant of uptake. Km, is 0.6 μM. The apparent half‐saturation concentration for growth is less than Km, by 1 order of magnitude. Growth is a function of cellular P concentrations, and the polyphosphates (alkali‐extractable or 7‐min) appear to regulate growth rate directly or indirectly. To understand P limitation, therefore, it is necessary to measure both external P and internal polyphosphate levels. Evidence indicates that alkali‐extractable polyphosphates, which can be quantitatively determined by a simple method of measuring surplus P, are involved in cell division process find that a maintenance concentration of functional phosphate exists in the form of poly phosphates. Alkaline phosphatase activity has an inversely linear relationship to growth rate and to the reciprocals of both polyphosphates and surplus P. Changes in lipid P, RNA P, and presumably all other forms except DNA are related to changes in growth rate.
UTILIZATION OF SEM AND FREEZE‐ETCH TECHNIQUES IN THE STUDY OF HYPNOSPORES1
Authors: Archibald Patricia A. , Teigler Dian J.
Published: August 2007

Hypnospores, a type of sculptured‐walled resting spore formed by some zoosporic chlorophycean and chrysophycean algae, have been viewed at the ultrastructural level using thin section, SEM, and freeze‐etch techniques. The “spiny” wall of the hypnospore, as seen in the light microscope, appears as a raised, scalloped surface at the ultrastructural level. The PAS‐positive wall is composed of 2 distinct layers. Prior to the formation of the wall, vacuoles form in the cytoplasm, lipid deposits are detectable, and typical cytoplasmic organelles apparently degenerate. The entire process is completed in less than 24 hr.
NITROGEN ASSIMILATION OF AN OCEANIC DIATOM IN NITROGEN‐LIMITED CONTINUOUS CULTURE1
Authors: Eppley Richard W. , Renger Edward H.
Published: August 2007

The oceanic diatomThalassiosira pseudonanaHasle and Heimdal (formerlyCyclotella nana) was grown with 12L:12D illumination cycles in nitrogen‐limited continuous culture with a mixture of ammonium and nitrate as the N source. Measurements included, at 3 different growth rates (degrees of N limitation), cell concentration, cell carbon, nitrogen, and chlorophyllacontents, cell volume, photosynthetic carbon assimilation vs. irradiance, short‐term uptake of ammonium and nitrate vs. their ambient concentrations, andin vitroactivities of the assimilatory enzymes nitrate reductase and glutamic dehydrogenase.

The various parameters showed either an increase (patterna) or a decrease (patternb) with increasing N limitation. Those following patternawere nitrate reductase activity and the capacity to assimilate nitrate and ammonium. Those following patternbwere glutamic dehydrogenase activity, photosynthetic rate, nitrogen:carbon and chlorophylla:carbon composition ratios. Results are discussed in terms of the interpretation such measurement for natural phytoplankton and effects of circadian periodicity.
THE BENTHIC ALGAE OF SOUTHERN BAFFIN ISLAND. I. EPIPELIC COMMUNITIES IN RIVERS1
Authors: Moore J. W.
Published: August 2007

The epipelic algae found in 9 rivers of southern Baffin Island were investigated during the 1972 growing season. The overall assemblage consisted of 240 taxa, of which 200 belonged to the Bacillariophyta and, only 17 to the Chlorophyta. Members of the Bacillariophyta accounted for S7–100% by numbers and 44–100% by volume of the algae at most localities. The dominant taxa were Achnanthes kriegeri Krasske, A. marginulata Grun., and Tabellaria flocculosa (Roth.) Kütz. The Chlorophyta comprised. 0–7% by numbers and 0–30% by volume of the algae, with Cosmarium tinctum Ralfs, Cylindrocystis spp., and Mougeotia sp. being most common.

The standing crop in the different rivers commonly exceeded 8 × 106 cells/cm2 (8 × 109μ3/cm2), and a maximum growth rate of 3.2 × 105 cells/cm2/day (3.2 × 108μ/cm2/day) was observed. Temperature and light are considered important, factors in the regulation of algal numbers, while nutrient supply in the overlying water, grazing by herbivores, wave action, and flooding appeared to have little effect.
RHAMNOCHRYSIS AESTUARINAE, A NEW MONOTYPIC GENUS OF BENTHIC MARINE CHRYSOPHYTES1
Authors: Wilce Robert T. , Markey Donald R.
Published: August 2007

Rhamnochrysis aestuarinae from Ipswich, Massachusetts, is a new species of benthic marine chrysophyta. Details are given describing its gross and fine structure morphology, its reproductive life history as understood from, both field and culture studies, and its ecology and probable systematic position in the Chrysomeridaceae (Sarcinochrysidales).
DNA SYNTHESIS IN CRYPTOTHECODINIUM COHNII1
Authors: Franker Colin K. , Sakhrani Lahki M. , Prichard Candyce D. , Lawden Carol A.
Published: August 2007

Thermal denaturation profiles of 32P‐labeled DNA obtained from synchronous cultures of Cryptothecodinium cohnii were examined by elution from hydroxyapatite over a temperature range of 65 to 99 C. The profile of uniformly labeled DNA from this organism shows at least 4 discrete components which elute after a temperature of 83 C is reached. These components from the “high melt” region of the profile appear to be synthesized during the latter one‐third of the S phase in synchronous culture.
THE FEEDING OF AMEBAE ON ALGAE IN CULTURE1
Authors: Ho Theresa S.‐S. , Alexander Martin
Published: August 2007

Amebae differed greatly in their ability to prey on algae. Species of Chlamydomonas, Pandorina, Anabaena, Ourococcus, Ankistrodesmus, and Gloeocystis were utilized by 3 or all 4 of the test protozoa, while strains of Staurastrum and Chlorella would not support growth of the predators. Heating the cells of Chlorella sp. rendered them available to the 4 amebae and made Pandorina morum a better nutrient for some of the protozoa. Heating Chlamydomonas oblonga had no effect on its availability to Tetramituis rostratus and reduced its suitability as a food source for Amoeba discoides. The rate of protozoan feeding was also influenced by temperature, pH, and age of the algal prey.
MITOSIS, CYTOKINESIS, AND COLONY FORMATION IN THE GREEN ALGASORASTRUM1
Authors: Marchant Harvey J.
Published: August 2007

Synchronous mitotic divisions produce multi‐nucleate cells ofSorastrum. Perinuclear envelopes of endoplasmic reticulum and a virtually intact nuclear envelope enclose mitotic nuclei. Cytoplasmic cleavage, which shirts before the last round of Synchronous mitoses, gives rise to uninucleate fragments which differentiate to form zoospores. These zoospores are released into a spherical vesicle, presumably derived from the inner layer of the parental cell wall, in which they swarm actively before aggregating as a spherical colony. The roughly conical shaped zoospores apparently adhere laterally before withdrawing their flagella and extending horns and a stipe, which, following wall deposition, interconnects the cells at the center of the colony. The probable role of the microtubules, which underlie the plasmalemma of aggregating cells, in determining the shape of both the cells and the colony itself is discussed.
TOXICITY OF THE PESTICIDE ZECTRAN ON PHOTOSYNTHESIS, RESPIRATION, AND GROWTH IN FOUR ALGAE1,2
Authors: Snyder C. E. , Sheridan R. P.
Published: August 2007

The insecticide Zectran decreased both respiration and photosynthesis in Oscillatoria terebriformis and Synechococcus lividus at concentrations between 0.5 and 12.5 ppm, whereas Navicula pelliculosa and Scenedesmus quadricauda were, relatively unaffected by these, same concentrations in the short‐term, manometric experiments. In long‐term growth experiments all 4 species exhibited a toxicity threshold between 1 and 10 ppm Zectran.
CELL DIVISION INBULBOCHAETE.II. HAIR CELL FORMATION1
Authors: Pickett‐Heaps Jeremy D.
Published: August 2007

Most vegetative cells ofBulbochaete, and all those ofOedogonium, possess an apical, circular discontinuity in the structure of their secondary wall. Rupture of the wall at this precise site permits expansion of the ring during cell division and release of the zoospore following zoosporogenesis. Certain cells ofBulbochaete(always the apical daughter cell of a division pair) lack this type of discontinuity. Instead, the apical wall is thinned out on one side, so that the cell bulges asymmetrically. In the middle of the bulge is a wall discontinuity which extends only part way around the cell. The wall will rupture here, too, for zoospore release, but if a cell having such a wall, divides, it invariably does so asymmetrically, with one pole of the spindle located in the bulge. Cytokinesis then cuts off a small, colorless daughter cell. The wall ruptures at the discontinuity, and this daughter cell emerges through the slit and differentiates into a hair.

The creation of hairs in such cells commences with the deposition of a pad of primary wall lining the bulge. Golgi bodies are involved in its secretion, but not in that of a secondary wall layer which forms next in the premitotic cell and covers the primary wall. The cell becomes polarized; the nucleus migrates toward this region as the chloroplast moves aside. After the asymmetric mitosis, a curved phycoplast cuts off the hair cell nucleus and prevents the chloroplast from moving back into the future hair, whose cytoplasm soon loses much of its affinity for heavy metal stains. Following rupture of the parental wall, the phycoplast moves some distance past the limits of the newly deposited secondary wall layer and then forms a cross wall under the hair.

The secondary wall of the hair isnotcontinuous with the secondary wall structure of the parental cell; the circular discontinuity that arises around the base of the bulging parental wall is then perpetuated and accentuated as the hair's secondary wall thickens. This wall weakening becomes the dislocation that will predetermine the site of the ring and consequently the direction of cell expansion in the next normal division of the cell subtending the hair. Abnormal ring formation and the creation of terminal twin hairs have also been examined. The lip of the growing hair contains a characteristic organization of membranes and other components which may be related to the organization of the hair's numerous longitudinally oriented microtubules.

These results are discussed in terms of the morphology of the wall in the Oedogionales generally. The creation of the special wall morphology that leads to hair cell formation is considered to be ontogenetically related to a similar wall morphology that is involved in formation of the fertilization pore of the oogonium.
NUTRIENT UPTAKE KINETICS IN PHYTOPLANKTON: A BASIS FOR NICHE SEPARATION1
Authors: Stross R. G. , Pemrick S. M.
Published: August 2007

Daily patterns of incorporation of carbon dioxide and inorganic phosphate were measured in phytoplankton from Lake George, New York, in January and February 1972. Rates of photosynthesis oscillated in phase for the entire assemblage and for individual cells of the diatoms Asterionella, Tabellaria, and Fragilaria. The photosynthetic capacity was maximal in the early afternoon.

Daily patterns of phosphate uptake were also rhythmic. At ambient concentrations the assemblage takes up phosphate maximally in the morning while individual cells of the large diatom take it up maximally in the evening.

A kinetic analysis of phosphate uptake indicated 2 velocities of uptake for cells of Tabellaria and Fragilaria: a hyperbolic function at small and an apparently linear relationship at relatively large concentrations. The large diatoms, in contrast to the total assemblage, functioned maximally at 2 separate times of the day: in the evening at ambient levels and in the morning at 0.4 μM and larger concentrations.

Temporal stratification of the nutrient niche may be achieved by several uptake mechanisms in the algal cell that function at different times of the day or with a variable uptake velocity.
THE EFFECT OF LIGHT QUALITY ON THE CARBON METABOLISM AND EXTRACELLULAR RELEASE OF CHLAMYDOMONAS REINHARDTII DANGEARD1
Authors: Brown T. J. , Geen G. H.
Published: August 2007

The influence of red, blue, green, and white light on growth and photosynthetic rates, carbon metabolism, and rates of release of extracellular compounds in the freshwater alga Chlamydomonas reinhardtii Dangeard was examined. Relative growth constants were 0.28, 0.32, 0.40, and 0.41 in green, white, blue, and red light, respectively. Photosynthetic rates were higher in white, blue, or red than in green light of the same intensity.

More than 66% of the 14CO2 assimilated by cells grown under blue or green light was incorporated into the ethanol‐insoluble fraction, compared with about 50% in cells grown under white or red light. The percentage of sugars in this fraction was significantly higher in cells grown under green or red light than in cells cultured in white or blue light, while the percentage of proteins was highest in blue light. Light quality also influenced the composition of the ethanol‐soluble fraction. The percentage of organic acids was highest in cells grown in green and white light, while amino acids were highest in blue and green cultures. The percentage of ethanol‐soluble sugars was greatest in cultures grown in blue and red light.

The percentage release of dissolved organic carbon into the medium was highest in white light and lowest in blue or red light. The nature of the extracellular products varied according to the quality of light under which the cells were cultured, but had no consistent relation to the nature or concentration or components in the ethanol‐soluble fraction.
AN IMPROVED METHOD FOR OBTAINING AXENIC CLONES OF PLANKTONIC BLUE‐GREEN ALGAE1,2
Authors: Carmichael Wayne W. , Gorham Paul R.
Published: August 2007

Axenic clones from 5 isolates of Anabaena flosaquae, 1 isolate of Microcystis acruginosa, and 1 isolate of Aphanizomenon flos‐aquae were obtained by a combination of steps that provided a 1000‐fold reduction in the bacteria‐algae ratio and permitted bacteria‐free filaments or cells to be isolated and grown from agar pour plates. The first step consisted of the addition of phenol to a dark‐treated culture to selectively reduce the numbers of actively growing bacteria while leaving the resting algal cells viable. The next steps involved washing the treated algal suspension on a Millipore filter pad or membrane followed by plating in washed agar containing buffered mineral medium plus vitamins and soil extract. The final steps consisted of incubating the agar pour plates, coring bacteria‐free filaments or cells, culturing the agar cores in a buffered mineral medium, and rigorously testing the resulting cultures for bacteriological contamination. Between 50 and 90% of the cores grew, and of these about 50% were judged axenic. The method, with appropriate adaptations, should be suitable for obtaining axenic clones of other freshwater and marine algae.
GROWTH OF VITAMIN B12‐REQUIRING MARINE DIATOMS IN MIXED LABORATORY CULTURES WITH VITAMIN B12‐PRODUCING MARINE BACTERIA12
Authors: Haines Kenneth C. , Guillard Robert R. L.
Published: August 2007

The vitamin B12requirement of several marine diatoms can be satisfied in B12−limited laboratory cultures by heterotrophic marine bacteria isolated from the same waters and from sediments. The bacteria can utilize diatom excretory products, or the remains of dead diatom cells, in the production of the vitamin.

The growth of 12 B121− requiring diatoms (7 genera) in mixed cultures with 14 different bacteria (without added B12) was compared to the growth of those same diatoms in axenic cultures with excess added B12. Diatom growth was generally rapid in the first few days, followed by sustained, slower growth. The diatom yields in mixed cultures ranged from 0.8 to 84% of the yields in axenic cultures with added B12.

In a detailed study of one mixed culture, increases in diatom densities were paralleled by increases in cell densities of the bacterium during the first few days of exponential diatom growth. During the period of slow diatom growth, when diatom densities oscillated but steadily increased, the decreases in diatom densities were associated with increased bacterial growth. This suggests that death of a fraction of the B12‐limited diatom population releases sufficient organic matter to stimulate growth of the bacteria and their subsequent excretion of B12; this B12in turn stimulates further growth of the diatoms.

Diatom‐bacteria interactions leading to the production of B12may be important in maintaining viable populations of B12‐requiring diatoms in nutrient‐poor waters during periods between blooms, when conditions are unfavorable for rapid growth.
OCCURRENCE OF CHOLINE ESTERS IN THE MARINE DINOFLAGELLATE AMPHIDINIUM CARTERI12
Authors: Taylor Richard F. , Ikawa Miyoshi , Sasner John J. , Thurberg Frederick P. , Andersen Kenneth K.
Published: August 2007

Acrylylcholine, choline O‐sulfate, and a yet unidentified choline ester have been isolated from cells of Amphidinium carteri. Natural and synthetic acrylyl choline had approximately 1/4,000 the activity of acetylcholine and choline O‐sulfate about 1/20,000 the activity on isolated Mercenaria mercenaria heart.
SOME ASPECTS OF PHOTOSYNTHESIS IN CLADOPHORA GLOMERATA1
Authors: Mantai Kenneth E.
Published: August 2007

Photosynthetic rates in field‐collected samples of Cladophora glomerata were measured using the oxygen electrode technique. Rates observed were three‐ to fourfold higher than literature values obtained with the light and dark bottle method. The discrepancy appears to be due to light‐limiting conditions prevailing in the bottles. It was also found that photosynthesis in Cladophora does not saturate at low light intensities as reported by other workers.
LE PLASTIDOME CHEZ EUGLENA GRACILIS Z1
Authors: et R. Calvayrac A.‐M. Orcival‐Lafont
Published: August 2007

Chloroplast morphology changes cyclically during each cell generation of synchronous photoheterotrophic cultures of Euglena gracilis Z; these cycles persist until the transition to stationary phase. Structural modifications, development of pyrenoids, and increase in chloroplast volume accompany the cessation of cell division. Chloroplasts of stationary phase heterotrophic cells resemble those of exponential phase autotrophic cells, suggesting a relationship between chloroplast morphology and available carbon.
CHLOROPLAST INCLUSIONS IN ZOOSPORES OF OEDOCLADIUM1
Authors: Markowitz Melvin M. , Hoffman Larry R.
Published: August 2007

Chloroplast inclusions have been studied in zoospores of Oedocladium carolinianum and their ultrastructure compared with the same inclusions previously described in the related genera Oedogonium and Bulbochaete. Structure of the mature pyrenoids is consistent in all 3 genera; the pyrenoid matrix is penetrated by branched cytoplasmic channels delimited by a double membrane system continuous with the chloroplast envelope. Pyrenoids typically arise de novo in zoospores of O. carolinianum. No evidence for the bipartition of a parent pyrenoid has been observed. The incipient pyrenoids of Oedocladium are similar to those found in zoospores of Oedogonium and Bulbochaete, but they frequently demonstrated a crystalline matrix. However, a crystalline matrix was never observed in any mature pyrenoid, even those immediately adjacent to incipient pyrenoids with crystalline structure. Other chloroplast inclusions typical of Oedogonium and Bulbochaete zoospores are the eyespot and striated microtubules. Although the zoospores of O. carolinianum possess striated microtubules, the presence of an eyespot has not been observed.
MITOSIS AND CYTOKINESIS IN THE CHLOROMONADOPHYCEAN ALGAGONYOSTOMUM SEMEN1
Authors: Heywood Peter
Published: August 2007

Mitosis and cytokinesis inGonyostomum semen(Ehrenberg) Diesing have been investigated with the light microscope. During prophase nucleoli disappear and the chromatid structure of the chromosomes becomes apparent. Separation of chromatids at anaphase is accompanied by progressive fusion of the progeny chromosomes. This process continues into telophase by which stage the progeny nuclei consist of dense masses of chromatin with occasional chromosomes extending from their equatorial surfaces. By the end of telophase, nucleoli are reforming and the interphase nuclear morphology is reestablished. Mitosis is followed by cytokinesis, which is a relatively lengthy phase. In early cytokinesis the 2 interphase nuclei are present, and there is no indication of the forthcoming division of the cytoplasm. Later in cytokinesis a membrane is formed between the 2 nuclei. Final separation of the progeny individuals is accomplished by vigorous movements of swimming cells or, in the case of palmelloid cells, by the deposition of a mucilaginous layer.
VAUCHERIAE OF NORTH CAROLINA. I. MARINE AND BRACKISH WATER SPECIES1
Authors: Ott Donald W. , Hommersand Max H.
Published: August 2007

Marine Vaucheriae of North Carolina were investigated in the field and in culture for 4 years. Of the 11 species collected, 4 are new records for North Carolina and 2 are previously unreported species. A new section is established, Acrandrae, to contain Vaucheria acrandra sp. nov. and Vaucheria adela sp. nov. The diagnostic character of the new section is the production of androphores directly from the terminal portion of the main filament rather than from a special cell produced laterally on the filament as in the section Androphorae.
GROWTH OF VITAMIN B12‐LIMITED CULTURES: THALASSIOSIRA PSEUDONANA, MONOCHRYSIS LUTHERI, AND ISOCHRYSIS GALBANA1,2
Authors: Swift Dorothy G. , Taylor W. Rowland
Published: August 2007

The growth rates of 3 species of phytoplankton were found to be dependent on the vitamin B12 concentrations in the media. In batch cultures, the vitamin B12 half‐saturation constants and standard errors were 0.39 ± 0.042 μμg/ml for Thalassiosira pseudonana (clone 3H), 1.69 ± 0.24 μμg/ml for Isochrysis galbana, and 2.77 ± 1.65 μμg/ml for Monochrysis lutheri. A chemostat was used to grow T. pseudonana with vitamin B12 as the controlling factor. In the chemostat the yield and standard deviation, 102 ± 21 × 104 cells/μμg vitamin B12, was the same as in the batch culture, 126 ± 13 ± 104 cells/μμg. The chemostat half‐saturation constant, 0.26 ± 0.068 μμg/ml vitamin B12, and maximum growth rate were in agreement with those obtained in batch cultures. Vitamin concentrations for maximum growth, rates were greater than those calculated necessary from yield data to give observed population densities similar to those in natural waters. In the sea the effect of vitamin B12 concentration on growth rates may be complicated by low concentrations of other nutrients or the presence of inhibitors.
STUDIES ON THE MARINE ALGAL FLORA OF VENEZUELA. V. PSEUDOGLOIOPHLOEA HALLIAE1,2
Authors: Ganesan E. K.
Published: August 2007

Details of structure and reproduction, particularly pre‐ and postfertilization development, are given for the first time in Pseudogloiophloea halliae. In general, the author's observations agree with what is known for most species of the genus. Some remarks on the identity of 3 species of Pseudogloiophloea in the tropical and subtropical American Atlantic shores are also included.
DENSITY‐DEPENDENT VERTICAL MIGRATION IN THE FRESHWATER DINOFLAGELLATEPERIDINIUM PENARDII(LEMM.) LEMM. FO.CALIFORNICUMJAVORN.1,2
Authors: Sibley Thomas H. , Herrgesell Perry L. , Knight Allen W.
Published: August 2007

The freshwater dinoflagellatePeridininm penardii(Lemm.) Lemm. fo.californicumJavorn. has a positively phototactic diel migration. The extent of migration seems to vary with population density.
THE FINE STRUCTURE OF THE FLAGELLAR APPARATUS OF CARTERIA1,2
Authors: Lembi Carole A.
Published: August 2007

The fine structure of the flagellar apparatus of 5 species of the green quadriflagellate alga Carteria is described. The 5 species can be morphologically separated into 2 groups on the bases of cell shape and ultrastructure of the pyrenoid and flagellar apparatus. Group I cells are spherical, possess many pyrenoid thylakoids, and retain a flagellar apparatus similar to that of Chlamydomonas reinhardi. The flagellar bases are oriented at approximately 90° to one another, have distal and proximal fibers, and are associated with 4 cruciately arranged microtubule bands. Cells of group II are ellipsoid, possess few pyrenoid thylakoids, and show a complex system of microtubule bands and sigmoid‐shaped, electron dense rods which extend between opposite pairs of basal bodies. The basal bodies of group II cells are directed inward in a circular pattern rather than outward as in group I cells. Unlike Chlamydomonas, the distal fiber of the Carteria species is nonstriated. The proximal fiber is striated, and both distal and proximal fibers are composed of 60–80 Å diameter microfibrils.
l‐THREONINE DEAMINASE IN MARINE PLANKTONIC ALGAE. V. KINETIC EVALUATION OF FEEDBACK EFFECTS FROM STRUCTURAL ANALOGS OF l‐ISOLEUCINE ON THE DEAMINASE ACTIVITY OF SEVEN UNICELLULAR SPECIES AND ELUCIDATION OF THE ALLOSTERIC BASIS FOR ANOMALOUS FEEDBACK CONTROL SHOWN BY A DIATOM AND A CRYPTOMONAD1,2
Authors: Antia Naval J. , Kripps Robert S. , Desai Indrajit D.
Published: August 2007

The biosynthetic l‐threonine deaminase of 2 cyanophytes, 1 rhodophyte, 2 cryptomonads, and 1 chlorophyte showed sensitive and powerful feedback inhibition from l‐isoleucine, which effect was closely duplicated by its isosteric structural analog l‐O‐methylthreonine. The l‐isoleucine inhibition was maximal in the pH range 7.0–8.5 and was rapidly weakened with more alkaline pH. Glycine, l‐alanine, and d‐isoleucine had no effect, while l‐α‐amino‐n‐butyric acid, l‐norvaline, l‐leucine, and l‐valine caused insensitive partial inhibitions detectable only at high concentration (100‐fold greater than l‐isoleucine). Tests of these analogs at low concentration revealed the specific capacity of l‐valine to invoke sensitive stimulation of enzyme activity from all the algal strains, and this effect was markedly enhanced by decrease in substrate concentration. Valine also counteracted the inhibitory influence of isoleucine. It was concluded from the reaction kinetics observed with these effectors that the algal threonine deaminases conform to Monad's K system of allosteric enzymes. The activity from the cryptomonad Hemiselmis virescens was exceptional in showing 2 closely spaced pH optima, which were related to marked difference in effects from isoleucine and valine at these pH values. It was inferred from various pH‐related tests that this cryptomonad may contain 2 enzymes basically similar in biosynthetic function but differing only in pH optima and sensitivity to feedback regulation.

The enzyme of the diatom Cyclotella nana was unique in showing insignificant feedback reaction from l‐isoleucine and its structural analogs, excepting l‐valine, which caused the strongest stimulation among the algae surveyed. It was concluded from the reaction kinetics that this deaminase is also of the biosynthetic type but that its feedback‐inhibition site is modified or unavailable, presumably from having this site already filled by endogenous isoleucine from the diatom.
THE ULTRASTRUCTURE OFSCENEDESMUS(CHLOROPHYCEAE). II. CELL DIVISION AND COLONY FORMATION1
Authors: Pickett‐Heaps Jeremy D. , Staehelin L. Andrew
Published: August 2007

Cell division in Scenedesmus is fairly typical of other chlorococcalean genera. The closed spindle has centrioles at polar fenestrae and apparently a series of nuclear divisions precedes cytokinesis. The phycoplast system of cytokinetic microtubules predicts the path of cleavage furrows whose mode of formation is obscure. Before and during cell division, the endoplasmic reticulum invariably accumulates granular material which later, during cytokinesis, appears to he secreted via the golgi bodies. Similar dense granular material then at accumulates outside the forming daughter cells but inside the parental wall, as the latter begins eroding away. By the end of colony formation, the cellulosic parental wall has disappeared, leaving its outer sheath and attached ornamentative features (spines, combs, reticulate or warty layer, etc.) intact as a “ghost.”

The spines and combs of new colonies appear to condense out of the extracellular aggregate; their precise mode of formation is obscure. As they form, the daughter cells, having become rearranged within the parental wall, stick to one another apparently at specific sites on their outer surface. A trilaminar (sporopollenin‐containing) layer arises first in each cell at these adhesive sites and immediately afterwards, dense material aggregates between the adjacent layers to give rise to the coenobial adhesive. Plaques of the trilaminar layer later appear over the rest of the cell's surface; they grow and fuse so that eventually each cell is enclosed by one continuous Trilaminar Sheath (TLS). While the plaques are forming, another dense layer materializes around the whole coenobium. Depending on the species, this layer turns into either the warty layer, in which instance it is applied directly on to the surface of the TLS except near the coenobial adhesive, or else it becomes the reticulate layer, in which instance it remains entirely separate from the TLS, soon acquiring the complex system of propping spikelets which suspend it from the coenobial surface.

When fully farmed, the daughter coenobium is tightly compressed within the parental TLS, with its spines folded lengthwise along the daughter cells. Release of the colony follows a quite explosive rupturing of the parental TLS, and immediately upon release, the daughter colony flattens out and erects its spines.