bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparing the structure and dynamics of phospholamban pentamer in its unphosphorylated and pseudo‐phosphorylated states
Authors: Oxenoid Kirill , Rice Amanda J. , Chou James J.
Published: August 2007

Human phospholamban (PLN), a 30 kDa homopentamer in the sarcoplasmic reticulum (SR) membrane, controls the magnitude of heart muscle contraction and relaxation by regulating the calcium pumping activity of the SR Ca2+‐ATPase (SERCA). When PLN is not phosphorylated, it binds and inhibits SERCA. Phosphorylation of PLN at S16 or T17 releases such inhibitory effect. It remains a matter of debate whether phosphorylation perturbs the structure of PLN, which in turn affects its interaction with SERCA. Here we examine by NMR spectroscopy the structure and dynamics of PLN pentamer with a physiologically relevant, phosphorylation‐mimicking mutation, S16E. Based on extensive NMR data, including NOEs, dipolar couplings, and solvent exchange of backbone amides, we conclude that the phosphorylation‐mimicking mutation does not perturb the pentamer structure. However,15NR1andR2relaxation rates and15N(1H) NOEs suggest subtle differences in the dynamics of the extramembrane portion of the protein.
The mutability of enzyme active‐site shape determinants
Authors: Miller Brian G.
Published: August 2007

Investigations of enzyme action typically focus on elucidating the catalytic roles of hydrogen bonding interactions between polar active‐site residues and substrate molecules. Less clear is the importance of non‐hydrogen bonding contacts to enzymatic rate accelerations. To investigate the importance of such interactions in a model system, six residues that participate in van der Waals contacts with substrate glucose within the active site of Escherichia coli glucokinase were individually randomized via site‐directed mutagenesis. In vivo selection in a glucokinase‐deficient bacterium was employed to identify amino acid substitutions that were complicit with enzyme activity. The results suggest that small residues, such as alanine and glycine, are largely immutable, whereas larger amino acids are more tolerant of diverse substitution patterns. Surprisingly, a glucokinase variant that contains glycine in place of six non‐hydrogen bonding contacts retains ∼1% of the wild‐type activity. These findings establish non‐hydrogen bonding shape determinants as highly appealing targets for widespread substitution during efforts to redesign the catalytic properties of natural enzymes.
Interactive effects of keystone rodents on the structure of desert grassland arthropod communities
Authors: Davidson Ana D. , Lightfoot David C.
Published: August 2007

Certain species play particularly large roles in ecosystems, and are often referred to as keystones. However, little is known about the interactive effects of these species where they co‐occur. Prairie dogs (Cynomys spp.) and banner‐tailed kangaroo rats Dipodomys spectabilis are commonly considered keystone species of grassland ecosystems, creating a mosaic of unique habitats on the landscape through ecosystem engineering and herbivory. We examined the separate and interactive effects of these species on the structure of grassland arthropod communities. We conducted a cross‐site study at two locations in the northern Chihuahuan Desert, and evaluated the impacts of these rodents on ground‐dwelling arthropod and grasshopper communities in areas where prairie dogs and kangaroo rats co‐occurred compared to areas where each rodent species occurred alone. Our results demonstrate that prairie dogs (C. gunnisoni and C. ludovicianus) and banner‐tailed kangaroo rats had keystone‐level impacts on arthropod communities both separately and interactively. Their burrow systems provided important habitats for multiple trophic and taxonomic groups of arthropods, and increased overall arthropod abundance and species richness. Many arthropods also were attracted to the aboveground habitats around the mounds and across the landscapes where the rodents occurred. Detritivores, predators, ants, grasshoppers, and rare rodent burrow inhabitants were especially associated with prairie dog and kangaroo rat activity. The impacts of prairie dogs and kangaroo rats were unique, and the habitats they created supported different assemblages of arthropods. Where both rodent species co‐occurred, there was greater heterogeneity and arthropod diversity on the landscape. Our results suggest that the interaction of multiple keystones, especially those with engineering roles, results in unique and more diverse communities in time and space.
Transferability and model evaluation in ecological niche modeling: a comparison of GARP and Maxent
Authors: Townsend Peterson A. , Papeş Monica , Eaton Muir
Published: August 2007

We compared predictive success in two common algorithms for modeling species’ ecological niches, GARP and Maxent, in a situation that challenged the algorithms to be general – that is, to be able to predict the species’ distributions in broad unsampled regions, here termed transferability. The results were strikingly different between the two algorithms – Maxent models reconstructed the overall distributions of the species at low thresholds, but higher predictive levels of Maxent predictions reflected overfitting to the input data; GARP models, on the other hand, succeeded in anticipating most of the species’ distributional potential, at the cost of increased (apparent, at least) commission error. Receiver operating characteristic (ROC) tests were weak in discerning models able to predict into broad unsampled areas from those that were not. Such transferability is clearly a novel challenge for modeling algorithms, and requires different qualities than does predicting within densely sampled landscapes – in this case, Maxent was transferable only at very low thresholds, and biases and gaps in input data may frequently affect results based on higher Maxent thresholds, requiring careful interpretation of model results.
Importance of N‐linked glycosylation in the functional expression of murine CD1d1
Authors: Sriram Venkataraman , Willard Claire A. , Liu Jianyun , Brutkiewicz Randy R.
Published: August 2007

The mouse CD1d1 glycoprotein is specialized in presenting lipid antigens to a novel class of T cells called natural killer T (NKT) cells. CD1d1 is predicted to contain five potential N‐linked glycosylation sites (asparagine residues at positions 25, 38, 60, 128, and 183). Glycosylation has been shown to invariably affect the molecular and functional properties of various glycoproteins, and in the current report it was found that a conservative change of the individual endogenous asparagine residues in CD1d1 to glutamine differentially affected its functional expression. Although the maturation rate of the glycosylation mutants was comparable to that of wild type, they differed in their relative levels of surface expression and in their ability to stimulate NKT cells. Mutating all five glycosylation residues resulted in the absence of detectable CD1d1 expression, with a concomitant lack of NKT cell activation. Therefore, these results demonstrate that glycosylation plays a significant role in the functional expression of CD1d1.
Low‐temperature bitumen stiffness and viscous paraffinic nano‐ and micro‐domains by cryogenic AFM and PDM
Authors: MASSON J‐F. , LEBLOND V. , MARGESON J. , BUNDALO‐PERC S.
Published: August 2007

In an effort to better understand the structure and behaviour of bitumen in low temperature, we describe the first use of cryogenic atomic force microscopy and phase detection microscopy to characterize bitumen nano‐ and micro‐structures. The results were interpreted in light of glass transition temperatures (Tgs) for bitumen fractions. The domains visible by microscopy, the catana, peri and para phases, were attributed to domains rich in asphaltenes, naphthene and polar aromatics, and saturates, respectively. Between −10°C and −30°C, atomic force microscopy images revealed topographic features not visible in atomic force microscopy images acquired at room temperature. According to phase detection microscopy and Tgs, the features were assigned to viscous unfrozen saturates. Upon cooling to −72°C, unfrozen domains of 20–400 nm were observed. These domains were found in the paraphase rich in saturates and in the periphase rich in naphthene aromatics and polar aromatics. The findings indicate that new viscous domains form upon cooling to low temperatures owing to phase segregation, and that some bitumens are never entirely rigid in low temperatures.
The use of amphipathic polymers for cryo electron microscopy of NADH:ubiquinone oxidoreductase (complex I)
Authors: FLÖTENMEYER MATTHIAS , WEISS HANNS , TRIBET CHRISTOPHE , POPOT JEAN‐LUC , LEONARD KEVIN
Published: August 2007

In the three‐dimensional (3D) structure determination of macromolecules, cryo electron microscopy (cryo‐EM) is an important method for obtaining micrographs of unstained specimens for the single‐particle reconstruction approach. For cryo‐EM, proteins are fixed in a frozen hydrated state by quick‐freezing in a thin water layer on a holey carbon film. Cryo‐EM of detergent‐solubilized membrane proteins is hindered by the fact that detergents reduce the surface tension of water, so that it is difficult to control the ice thickness and the distribution of protein. Amphipols are a new class of amphipathic polymers designed to handle membrane proteins in aqueous solutions under particularly mild conditions. Amphipol A8‐35 stabilizes NADH:ubiquinone oxidoreductase (complex I) from Neurospora crassa and keeps it water‐soluble in the absence of free detergent. Electron microscope images of quick‐frozen complex I/A8‐35 samples were used for computer‐based single‐particle averaging and 3D reconstruction, and the reconstruction of unstained frozen‐hydrated particles compared with previous detergent‐based reconstructions. The potential of amphipols for cryo‐EM is discussed.
Recrystallization behaviour of the nickel‐based alloy 80 A during hot forming
Authors: MITSCHE S. , POELT P. , SOMMITSCH C.
Published: August 2007

The dynamic recrystallization as well as meta‐dynamic and static recrystallization of the nickel‐based alloy 80A was investigated by means of electron backscatter diffraction (EBSD). Specimens were hot compressed at a temperature of 1120°C and a strain rate of 0.1/s at varying strain and soak times to describe the recrystallization behaviour. Various approaches were tested in order to differentiate between recrystallized and deformed grains based on EBSD data. The grain orientation spread was clearly found to be the most reliable procedure. A high twinning of the recrystallized grains was observed, and as a consequence the measured grain size was strongly dependent on whether the coherent and incoherent twin boundaries were regarded as genuine boundaries or removed.
The interpretation of indexing of high Σ CSL grain boundaries from ceramics
Authors: SHIH SHAO‐JU , PARK MYUNG‐BEOM , COCKAYNE DAVID J. H.
Published: August 2007

Electron backscatter diffraction (EBSD) is a useful technique for measuring the orientation of individual grains and for determining grain boundary misorientations in polycrystals. However, its application to ceramics is more difficult than to metals, because the surface quality that can be achieved often makes the Kikuchi patterns blurred. As a consequence, it can be difficult, even for automated systems, to differentiate between different grain orientations, which have similar patterns. In this paper, we carry out EBSD analyses of SrTiO3 polycrystalline material prepared with different polishing methods, and we consider the effect of different criteria in interpreting the EBSD patterns from them. In particular, we investigate the CSL statistics using both the Palumbo and Aust and the Brandon criteria in this situation.
LEUCOCYTE ADHESION MOLECULES IN ISCHAEMIC RENAL INJURY: KIDNEY SPECIFIC PARADIGMS?
Authors: Rabb Hamid , Postler Gilbert
Published: August 2007

1. Renal ischaemic–reperfusion injury (IRI) is an important cause of acute renal failure in native kidneys and in allografts.

2. Leucocyte adhesion molecules CD11/CD18, intercellular adhesion molecule‐1 and selectins mediate cardiac, skin and muscle IRI in experimental models and recent studies have begun to evaluate their role in renal IRI.

3. The CD11/CD18 has been shown to mediate renal IRI in rat models.

4. Intercellular adhesion molecule‐1 has a more prominent role in mediating renal IRI than CD11/CD18 in both rat and mouse models. Blockade of both pathways together appears to provide synergistic protection.

5. Unlike in heart and muscle, L‐selectin does not appear to mediate leucocyte recruitment to postischaemic kidney or tubular damage.

6. Leucocyte adhesion molecules may mediate renal IRI by mechanisms other than simply leucocyte migration, such as signal transduction and cell transport.

Presented at the Experimental Biology Symposium on the Role of Integrins in Acute Renal Failure, New Orleans, Louisiana, USA, 1997.
DIFFERENT MECHANISMS FOR [Ca2+]i OSCILLATIONS INDUCED BY CARBACHOL AND HIGH CONCENTRATIONS OF [Ca2+]o IN THE RAT VENTRICULAR MYOCYTE
Authors: Wang Hong‐Xin , Ouyang Ming , Zhang Wei‐Min , Sheng Jian‐Zhong , Wong Tak‐Ming
Published: August 2007

1. The purpose of the present study was to explore the different mechanisms of [Ca2+]i oscillations induced by high concentrations of either carbachol (CCh) or extracellular Ca2+ ([Ca2+]o). First, we compared the oscillations induced by CCh at concentrations of 100–300 μmol/L and [Ca2+]o (5 mmol/L) in the single rat ventricular myocyte. Second, we studied CCh‐ and [Ca2+]o‐induced [Ca2+]i oscillations following either interference with the production of inositol trisphosphate (IP3), reductions in cytosolic Ca2+ ([Ca2+]i), inhibition of Ca2+ influx and Na+–Ca2+ exchange or depletion of Ca2+ from its intracellular store.

2. The [Ca2+]i oscillations induced by CCh were frequent and were superimposed on [Ca2+]i transients in electrically stimulated cells, whereas those induced by high [Ca2+]o were occasional and occurred in quiescent cells and between [Ca2+]i transients in electrically stimulated cells. In both cases, [Ca2+]i oscillations were preceded by an increase in resting levels of [Ca2+]i.

3. Carbachol‐induced [Ca2+]i oscillations were accompanied by an increase in amplitude and prolongation of the time of decline to 80% of the peak of the [Ca2+]i transient, while high [Ca2+]o‐induced [Ca2+]i oscillations were the opposite.

4. A reduction of [Ca2+]o to 0.1 mmol/L and treatment with Ni2+ or ryanodine or 1,2‐bis(2‐aminophenoxy)ethane‐N,N,N',N'‐tetraacetic acid AM (BAPTA‐AM) abolished the [Ca2+]i oscillations induced by both CCh and high [Ca2+]o.

5. The calcium channel blockers verapamil and nifedipine and inhibitors of phospholipase C (neomycin and U‐73122) abolished the [Ca2+]i oscillations induced by CCh; Li+ accelerated the onset of the [Ca2+]i oscillations induced by CCh.

6. These observations suggest that the mechanisms responsible for the [Ca2+]i oscillations induced by CCh and high [Ca2+]o are different from each other. Other than an increase in extracellular Ca2+ influx as a mechanism common for both CCh‐ and high [Ca2+]o‐induced [Ca2+]i oscillations, the CCh‐induced [Ca2+]i oscillations involve influx of Ca2+ via L‐type Ca2+ channels, Na+–Ca2+ exchange, mobilization of intracellular Ca2+ and IP3 production.
GLUCURONIDATION OF DIHYDROCODEINE BY HUMAN LIVER MICROSOMES AND THE EFFECT OF INHIBITORS
Authors: Kirkwood Lynette C , Nation Roger L , Somogyi* Andrew A
Published: August 2007

1. Glucuronidation is the major route of metabolism of dihydrocodeine (DHC) and accounts for 25–30% of an oral dose in urine. The kinetics of DHC‐6‐glucuronide formation in liver microsomes from five human donors and the effect of a number of potential inhibitor drugs were examined using a newly developed and validated HPLC assay.

2. The formation of DHC‐6‐glucuronide exhibited atypical kinetics that conformed to the Hill equation. The mean intrinsic dissociation constant (Ks) and maximum velocity (Vmax) values were 1566 μmol/L and 0.043 μmol/min per g, respectively. The Ks and Vmax values varied 1.5‐ and 3.5‐fold, respectively.

3. Seven drugs were tested for inhibitory effects on DHC glucuronidation at low (50 μmol/L) and high (500 μmol/L) concentrations. At 50 μmol/L, only diclofenac produced greater than 50% inhibition, while at concentrations of 500 μmol/L inhibition was greater than 35% for diclofenac, amitriptyline, oxazepam, naproxen, chloramphenicol and probenecid, but not paracetamol.

4. The present study found little interindividual variation in the activity of human liver microsomes for glucuronidation of DHC. Comparison of the results from the inhibition studies with those reported previously for codeine and morphine suggest that the UDP‐glucuronosyltransferase isoform UGT2B7 is involved in the glucuronidation of DHC.
THERAPEUTIC EFFECT OF ARGININE–GLYCINE–ASPARTIC ACID PEPTIDES IN ACUTE RENAL INJURY
Authors: Goligorsky Michael S , Noiri Eisei , Kessler Horst , Romanov Victor
Published: August 2007

1. Previous studies from our laboratory have suggested that arginine–glycine–aspartic acid (RGD) peptides, serving as a decoy, may prevent tubular obstruction in the ischaemic model of acute renal failure. Specifically, we have demonstrated that: (i) stressed tubular epithelial cells reverse the polarity of integrin receptors from the predominantly basolateral location to the apical cell membrane as a part of a more generalized process of the loss of epithelial cell polarity; (ii) depletion of integrins expressed on the basal cell surface leads to the loss of anchorage to the basement membrane and cell desquamation; (iii) expression of integrin receptors on the apical cell membrane leads to indiscriminate interactions (e.g. the adhesion of desquamated cells to the cells remaining in situ), thus initiating the process of tubular obstruction; and (iv) conglomeration of the desquamated cells via integrin receptors further aggravates tubular obstruction.

2. Importantly, these integrin‐based interactions can be blocked by synthetic RGD peptides. The linear RGD peptide injected into the renal artery upon release of the renal artery clamp prevented the elevation of proximal tubular hydrostatic pressure characteristically seen in animals with renal ischaemia that received injection of the vehicle of an inactive peptide.

3. In vivo study of RGD peptides in ischaemic acute renal failure in rats demonstrated attenuation of renal injury and accelerated recovery of renal function.

4. Using linear RGD peptide labelled with 99mTc, we have shown that this probe was retained in ischaemic kidneys.

5. To visualize RGD binding sites at the cellular level, we performed a mapping using fluorescent derivatives of two RGD peptides, a cyclic biotinylated (Bt)‐RGD peptide and a linear Rhodamine green‐labelled (RhoG)‐RGD peptide.

6. The findings suggest that the binding sites for RGD peptide are represented by the αVβ3 integrin in the vasculature and some desquamated cells, whereas the majority of the desquamated cells bind Bt‐RGD via β1 integrins.

7. These findings were further tested using cultured endothelial cells co‐incubated with leucocytes. When co‐incubation experiments were performed in the presence of cyclic RGD pentapeptide, the adhesion of HL‐60 cells to both control and hypoxic endothelial monolayers was significantly reduced.

Presented at the Experimental Biology Symposium on the Role of Integrins in Acute Renal Failure, New Orleans, Louisiana, USA, 1997.
BATHTUB‐TYPE CURVES IN RELIABILITY AND BEYOND
Authors: Bebbington Mark , Lai Chin‐Diew , Zitikis Ričardas
Published: August 2007

Finding optimal, or at least good, maintenance and repair policies is crucial in reliability engineering. Likewise, describing life phases of human mortality is important when determining social policy or insurance premiums. In these tasks, one searches for distributions to fit data and then makes inferences about the population(s). In the present paper, we focus on bathtub‐type distributions and provide a view of certain problems, methods and solutions, and a few challenges, that can be encountered in reliability engineering, survival analysis, demography and actuarial science.
NONPARAMETRIC METHOD FOR ESTIMATING THE SIZE OF AN OPEN POPULATION USING MARGINAL DATA FROM REPEATED MULTIPLE LISTS
Authors: Liu Danping , Yip Paul S. F. , Huggins Richard M.
Published: August 2007

Kernel smoothing methods are used to extend the Poisson log‐linear approach to the estimation of the size of population using multiple lists to an open population when the multiple lists are recorded at each time point. The data is marginal as only the lists at each time point are available and the transitions of individuals between lists at different time points are not observable. Our analysis is motivated by and applied to data on the number of drug addicts in the Hong Kong Special Administrative Region.
Who Needs Immigrant Farm Workers? A South African Case Study
Authors: JOHNSTON DEBORAH
Published: August 2007

Recent writing on migration in Southern Africa focuses on the experiences and desires of migrants themselves. While it gives valuable insights, this article argues that it can obscure the role of employers in structuring migration opportunities. In the case of female migrants from Lesotho working in South African agriculture, farmer demand has clearly impacted on the spectrum of both legal and illegal employment opportunities available, with the boundaries between legal and illegal migration appearing more porous than often imagined. The demand for foreign farm workers is complex and cannot be reduced to a simple story of wage differentials with local workers. The conclusion is that if we wish to understand migration flows, and particularly the use of immigrant labour in South African agriculture, we must retain an analytical role for employers’ demand.
Labour Process and Workers’ Bargaining Power in Export Grape Production, North East Brazil
Authors: SELWYN BEN
Published: August 2007

This article uses the Global Commodity Chain (GCC) framework to investigate labour regimes in export grape production in the São Francisco (SF) valley, North East Brazil. A combination of strict northern retailer requirements and producers’ ability to target export windows leads to an increasingly complex labour process. Whilst much GCC literature focusing on export agriculture concludes that labour is relatively powerless, this article presents a rather different case. The need to upgrade production continually in response to retailers’ demands gives workers strategic leverage which, together with a strong and continuing tradition of rural trade union organization, means that they have been able to extract significant concessions from exporting farms.
Land Reform, Rural Social Relations and the Peasantry
Authors: AKRAM‐LODHI A. HAROON
Published: August 2007

A new book, Promised Land: Competing Visions of Agrarian Reform, edited by Peter Rosset, Raj Patel and Michael Courville is considered. This book, via both general analytical treatment and a series of case studies set in Latin America, Asia and Africa, offers a powerful critique of the World Bank's market‐led agrarian reform (MLAR) and provides an alternative model of agrarian reform, the ‘food sovereignty movement’, that has been articulated by La Via Campesina. Food sovereignty requires that priority be allocated to the domestic production of food and that a right to land be given to small farmers and their families. It is a vision of agrarian reform, with an emphasis on smallholder farming and the transformative power of rural social movements, that has truly emerged ‘from below’. The critique of MLAR is compelling. It is argued in this essay, however, that two crucial questions are abstracted from. The first is that of the vastly differing sets of social relations that exist (compare, say, socialist Cuba and capitalist Brazil) and their implications. It is not clear that food sovereignty can, in effect, offer a coherent political economy of an alternative global agrarianism. The second relates to the implicit assumption, found throughout the book, that the peasantry is a homogeneous, undifferentiated social group. This is manifestly not so, and what the existence of socially differentiated peasantries implies requires careful examination.
ETHEPHON (2‐CHLOROETHYLPHOSPHONIC ACID) EFFECTS ON SCENEDESMUS QUADRICAUDA (CHLOROPHYCEAE)1,2
Authors: Chapman Richard W. , Vance B. Dwain
Published: August 2007

Growth of Scenedesmus quadricauda (Turp.) Bréb. was significantly increased when the cultures were grown in Ethephon 68–241 (2‐chloroethylphosphonic acid) at concentrations of 0.001–1.0 μg · ml−1. At 0.1 μg · ml−1, Ethephon caused a significant increase in RNA levels on a dry weight basis. Total protein and DNA levels increased but not significantly. These data indicate that ethylene, the decomposition product of Ethephon at physiological pH, has some effect on the metabolism of algae.
PHYLOGENETIC RELATIONSHIPS OFCAULERPA(CHLOROPHYTA) BASED ON COMPARATIVE CHLOROPLAST ULTRASTRUCTURE1,2
Authors: Calvert Harry E. , Dawes Clinton J. , Borowitzka Michael A.
Published: August 2007

The ultrastructure of chloroplasts from 28 of the 73 species ofCaulerpaLamouroux (Chlorophyta, Caulerpales) has been studied to aid in interpreting phylogenetic relationships among the 12 recognized sections. Variations of systematic value include pyrenoid occurrence and fine structure, thylakoid architecture and amount of photosynthate storage. Comparisons of field and culture specimens indicate these characters are consistent. Chloroplast thylakoids are grouped into bands, with the distribution of bands differing among species. In the most common arrangement, bands are evenly distributed throughout the chloroplast. A few species show lateral displacement of bands whereas others have a majority of bands arranged at one end of the chloroplast. Starch is stored cither as one or two large grains (> 1 μm diam.) or numerous small grains (< 0.5 μm diam.). Electron‐transparent regions are common in other species in which chloroplasts rarely store starch. Simple, embedded pyrenoids are present in several species of section Sedoideae. An opaque region occurs in chloroplasts ofC. elongatawhich may represent an intermediate stage in the evolutionary loss of the pyrenoid. It is suggested that the chloroplast ofCaulerpaevolved, from a large, complex, pyrenoid‐containing organelle housing both photosynthetic and amylogenic functions, to a small, structurally simpler one, specialized for photosynthesis alone. A phylogeny of the 12 sections ofCaulerpais constructed, based on chloroplast evolution which agrees with an earlier morphology‐based hypothesis on the origin and evolution ofCaulerpa.
PHASED DIVISION OF PERIDINIUM CINCTUM F. WESTII (DINOPHYCEAE) AND DEVELOPMENT OF THE LAKE KINNERET (ISRAEL) BLOOM1,2
Authors: Pollingher Utsa , Serruya Colette
Published: August 2007

The yearly bloom of Peridinium cinctum f. westii (Lemm.) Lef. in Lake Kinneret is described and compared with the distribution of dinoflagellates in other freshwater bodies. The physical conditions required by the Wyatt and Horwood model do not fit the actual physical events accompanying the onset of the bloom. In situ measurements of the percentage of cells in division were undertaken to clarify various points about the internal dynamics of the population. The exponential increase of the population occurs when the diurnal percentage of cells in division is not higher than 10–15%. This percentage increases up to 45% in late February–March, but does not cause any increase of population. At this period, the loss rate is nearly equal to the rate of cell increase and is interpreted as massive mortality.
CACHONINA ILLDEFINA SP. NOV. (DINOPHYCEAE): CHLOROPLAST TUBULES AND DEGENERATION OF THE PYRENOID1
Authors: Herman Eliot Mark , Sweeney Beatrice M.
Published: August 2007

A new species of the dinoflagellate genus Cachonina, C. illdefina sp. nov., was isolated from a red tide off El Capitan State Park, Santa Barbara County, California, in October 1973. The organism is light yellowgreen in color with deeply incised girdle and sulcal grooves. Electron microscopy of the organism, revealed a typical dinokaryotic nucleus. The chloroplasts of the organism are connected, and often contain microtubule‐like elements, 25 nm diam. The pyrenoids are characterized as excluding chloroplast thylakoids and ribosomes, although containing an amorphous matrix and numerous tubular invaginations from the cytoplasm. The pyrenoids become detached from the chloroplasts and degenerate into small vesicles. C. illdefina is not bioluminescent.
LONG‐TERM EFFECTS OF MANIPULATING LIGHT INTENSITY AND NUTRIENT ENRICHMENT ON THE STRUCTURE OF A SALT MARSH DIATOM COMMUNITY1,2
Authors: Michael J. Sullivan
Published: August 2007

The long‐term effects of manipulating light intensity and nutrient enrichment on the structural characteristics of a diatom community inhabiting the sediments beneath a pure stand of dwarfSpartina alternifloraLoisel. were investigated over a yearly cycle. Clipping or shading the cord grass cover, or phosphorus enrichment caused significant decreases in both species diversity (H') and the number of diatom species, whereas nitrogen enrichment only significantly decreased the latter parameter. Of the 105 diatom taxa identified, only 10 were restricted to certain of the 12 study areas; and of these, 8 occurred exclusively in the clipped habitats. An analysis of variance (light × nutrient × collection date) involving 19 of the most abundant taxa revealed that certain experimental treatments had significant effects on the relative abundances of each and every taxon. However, attempts to group taxa with similar response patterns proved unsuccessful because of the frequent significance of the 3‐way interaction term. Synthesis of these results with earlier work by the author showed that differences in structure of diatom communities inhabiting the sediments beneath the 3 dominant marsh grasses were not primarily caused by differences in reduction of light intensity by their grass canopies, and that clipping of the cord grass produced a shift in community structure towards that characteristic of a salt panne algal mat.
KINETICS OF SILICIC ACID UPTAKE AND RATES OF SILICA DISSOLUTION IN THE MARINE DIATOM THALASSIOSIRA PSEUDONANA1,2
Authors: Nelson David M. , Goering John J. , Kilham Susan S. , Guillard Robert R. L.
Published: August 2007

Tracer techniques using the stable isotope 30Si were used to measure rates of silicic acid uptake and silica dissolution in silicon replete and silicon depleted populations of 2 clones of the marine diatom Thalassiosira pseudonana Hasle & Heimdal. Uptake kinetics were describable using the Michaelis‐Menten equation for enzyme kinetics, and no threshold concentration for uptake was evident. The maximum specific uptake rate of the estuarine clone 3H (0.062–0.092 · h−1) was higher than that of the Sargasso Sea clone 13‐1 (0.028–0.031 · h−1), but half‐saturation constants for uptake by the 2 clones were not measurably different (0.8–2.3 μM for 3H; 1.4–1.5 μM for 13‐1). There was little or no light dependence of uptake in populations grown under optimal light conditions prior to the experiment. Exponentially growing populations released silicic acid to the medium by dissolution of cellular silica at rates ranging from 6.5 to 15% of the maximum uptake rate.
SEXUAL ISOLATION BETWEEN A EUROPEAN AND AN AMERICAN POPULATION OF ECTOCARPUS SILICULOSUS (PHAEOPHYTA)1
Authors: Müller Dieter G.
Published: August 2007

Sexual plants of Northeastern American Ectocarpus siliculosus (Dilhw.) Lyngb. have been isolated and cultured. Female gametes produce a volatile sex hormone acting on male gametes. Combination of American and European gametes shows that the initial step of the sexual reaction (attraction of male gametes) works normally, whereas interaction of cell surfaces and fusion of gametes is prevented.
KINETICS OF EXTRACELLULAR RELEASE IN AXENIC ALGAE AND IN MIXED ALGAL‐BACTERIAL CULTURES: SIGNIFICANCE IN ESTIMATION OF TOTAL (GROSS) PHYTOPLANKTON EXCRETION RATES1
Authors: Nalewajko C. , Dunstall T. G. , Shear H.
Published: August 2007

In axenic Chlorella pyrenoidosa Chick cultures, extracellular release was linear with time, but plateau‐type curves were obtained in cultures with added bacteria. Initial rates of excretion were identical in both, systems. Kinetics of extracellular release in axenic Anabaena flos‐aquae (Lyng.) Bréb. cultures were more complex than in Chlorella but the initial excretion rates were identical in axenic and mixed algal‐bacterial cultures. In lakewater, extracellular release kinetics resemble the pattern in mixed Chlorella‐bacteria cultures. An explanation is an initial lag in bacterial utilization of algal extracellular products. As a result, both in situ and in the laboratory, consecutive short, experiments give higher excretion rates than single long incubations. It is suggested that the former are close to total or gross extracellular release rates whereas the latter give net values, detecting only substances not, removed by heterotrophs.
A NEW HOMOTHALLIC VARIETY OF CHLAMYDOMONAS MOEWUSH (CHLOROPHYCEAE)1
Authors: Deason Temd R. , Ratnasabapathy M.
Published: August 2007

A new homothallic variety of Chlamydomonas moewusii Gerloff var. monoica is described. When first isolated, the alga exhibited a very strong mating reaction (80–90% zygotes on 2 wk BBM agar slants), but after 2 mo in axenic culture, the reaction was significantly reduced in intensity. Attempts were made to restore the initial mating intensity by varying environmental conditions, but met with limited success. The alga did not grow heterotrophically in carbon‐supplemented BBM medium.
EFFECT OF THE SINKING RATE OF TWO DIATOMS (THALASSIOSIRA SPP.) ON UPTAKE FROM LOW CONCENTRATIONS OF PHOSPHATE1
Authors: Canelli Edmondo , Fuhs G. Wolfgang
Published: August 2007

The effect of the sinking rate, or rate of medium flow (φ) on the rate of phosphate incorporation (V) by the planktonic diatoms Thalassiosira fluviatilis Hust. and T. pseudonana Hasle & Heimdal in batch and chemostat cultures was determined by passing medium at defined flow rates (0.5–25.0 mm·min−1) over algae on membrane filters. At concentrations from 1 to 100 μg phosphorus·l−1 V, increases with increasing velocity of flow, approaching a maximum value (Vm) as described by the empirical relationship:
image

where Kφ is the sinking rate value when V = 1/2 Vm+ Vo and Vo is the uptake at 0 rate of flow. By comparing uptake at controlled flow with uptake in a vigorously stirred medium, the phosphate concentration in the cell boundary layer can be determined. The sinking rate that reduces the phosphate concentration in the boundary layer to half of nominal concentration in the medium is much lower for the larger T. fluviatilis than for T. pseudonana. For both diatoms, it is inversely related to the nominal concentration.
SPORELING COALESCENCE IN CHONDRUS CRISPUS (RHODOPHYCEAE)1
Authors: Tveter Eleanor , Mathieson Arthur C.
Published: August 2007

Coalescence of developing sporelings of Chondrus crispus Stackhouse was observed. Juvenile tetra‐sporophytes showed a higher proportion of coalescence than developing gametophytes. Stages of complete coalescence between different sporelings are illustrated. Coalesced sporelings exhibit vertical and horizontal alignment of cells, as well as “cuticular” continuity and secondary pit connections between adjacent, coalesced sporelings. Ultimately the cells in the center of the coalesced sporelings produce upright, multiaxial fronds that grow more rapidly than fronds of non‐coalesced sporelings. Other red algae, such as Gracilaria verrucosa (Hudson) Papenfuss and Gigartina stellata (Stackhouse) Batters also show a similar sequence of sporeling coalescence and enhanced growth. The ecological significance of sporeling coalescence is discussed.
ECOLOGY AND NATURAL HISTORY OF IRIDAEA CORDATA (RHODOPHYTA; GIGARTINACEAE): POPULATION STRUCTURE1
Authors: Hansen Judith E. , Doyle William T.
Published: August 2007

The population structure of 4 California Iridaea cordata (Turner) Bory populations was studied. Random sampling procedures were used to measure seasonal variations in standing crops, density and size‐class distribution of life history stages. The results describe aspects of the in situ life history; a prerequisite to realistically considering the distribution, ecology or life history expressions of an alga. Seasonal fluctuations in density occur only in the juvenile stage, which is initiated during the winter (November to January) predominantly from the basal perennial crusts. Both the gametangial and tetrasporangial stages are present throughout the year. The tetrasporangial stage is dominant in relation to the sexual stages in both density and biomass during most of the year, except spring when the new crop in just maturing and all stages are abundant. Density in nearly constant and observable changes in the populations are due to biomass fluctuations. Seasonal lows in biomass occur during the winter with the majority of thalli in the smaller size‐classes. Growth and maturation culminate in peak summer crops and dominance of the tetrasporangial stage, followed by autumnal senescence and die‐back in winter. Carrageenans analyzed from immature thalli showed a predominance of lambda‐type, previously determined as specific for tetrasporangial plants. This indirect evidence for the tetrasporangial nature of immature plants suggests that dominance of the diploid stage occurred prior to blade development and most likely at the spore level. Alternatively, field results indicate a major contribution and possible replacement of alternation of gametangial and tetrasporangial stage by thallus perennation and vegetative reproduction.
THE OCCURRENCE OF CHLOROPHYLL C1 AND C2 IN ALGAE1
Authors: Jeffrey S. W.
Published: August 2007

Forty‐two species of chlorophyll c‐containing algae (diatoms, dinoflagellates, chrysomonads, haptophytes, cryptomonads and xanthophytes) were examined for their content of chlorophyll c1 and c2. This work, and recent studies on c1/c2 distribution in the literature (total 86 species), show that chlorophyll c2 is universal to all algae examined. Chlorophyll c1 occurs in addition to c2 in brown seaweeds, diatoms, chrysomonads, haptophytes (coccolithophorids) xanthophytes and the, fucoxanthin‐containing dinoflagellates; c2 only occurs in dinoflagellates and cryptomonads. Two exceptions to the generalizations are one dinoflagellate and one cryptomonad containing c1 in addition to c2 No explanation can be offered on present knowledge for these exceptions. No alga was found containing only chlorophyll c1.

Chlorophyll c, far from being a minor accessory chlorophyll, occurred in amounts almost equal to chlorophyll a(some diatoms and dinoflagellates) or ranged from 50 to 20% of the chlorophyll a (diatoms, dinoflagellates, chrysomonads, cryptomonads, browns). Xanthophytes, however, contained only trace amounts of chlorophyll c with ratios of chlorophyll a:c ranging from 55:1 to 116:1 on a weight basis.

In those algae with both chlorophyll c components, c1 and c2, occurred either in equal amounts, or chlorophyll c2was twice the c1 content.
AUXIN, AN ENDOGENOUS REGULATOR OF GROWTH IN ALGAE?1,2
Authors: Buggeln Richard G.
Published: August 2007

The effects of 5 pairs of synthetic auxins and chemically related, but biologically inactive, derivatives (e.g., 2,4‐ and 3,5‐dichlorophenoxyacetic acid, respectively) on blade growth of the brown alga, Alaria esculenta (L.) Grev.(Laminariales) were studied. The significant result was the inability to divide the growth responses into auxin and non‐auxin groups. At high concentrations (10−3 M) 9 test substances inhibited blade growth; lower concentrations (<10−3 M) were either slightly inhibitory or showed no effect.

The data suggest that a higher plant auxin‐specific recognition mechanism is lacking in this alga. As this mechanism is central to higher plant concepts of growth control by auxin, the role of auxin as an endogenous regulator of growth in Alaria, and perhaps other algae as well, seems unlikely. This interpretation is consistent with recent negative biochemical data from auxin binding studies using subcellular preparations from algae.
LEAD INHIBITION OF CHLOROPHYCEAN MICROALGAE1
Authors: Monahan Thomas J.
Published: August 2007

The effects of lead on the growth of 9 microalgae representing 4 chlorophycean genera were investigated in axenic laboratory cultures. Variations in sensitivity to lead existed among the algae tested with availability of phosphate often limiting growth. Under conditions in which phosphate was growth limiting at pH 6.2, Chlorella pyrenoidosa Chick, C. ellipsoidea Gerneck, C. vulgaris Beij. Scenedesmus sp. (IUCC 1591).Sc. Obtusiusculus Chodat and Selenastrum capricornutum Printz first showed toxicity at 0.5 mg·l−1 pb. Two planktonic Scenedesmus spp. And an Ankistrodesmus sp. Were more tolerant, developing toxicity at 1 mg· l−1 Pb. The relationship of phosphate supply to Pb toxicity was investigated with S. capricornutum and Sc. Obtusiusculus. Al pH 8.0, Selenastrum developed toxicity at 3 mg·l−1 pb either with or without phosphate. When phosphate supply was growth‐limiting, 6 times as much pb (i.e., 3 vs. 0.5 mg l−1 was required to demonstrate toxicity with Selenastrum at pH 8.0 as opposed to pH 6.2 Sc. Obtusiusculus was inhibited at 0.5 mg· l−1 pb in phosphate‐limiting medium and developed toxicity at 1 mg·l−1 in media containing phosphate. Control of colonial morphology with Sc. Obtusiusculus was inhibited. Phosphate availability as well as pH would seem to be important factors determining lead toxicity with some algae.
ALGAL COMPETITION IN AN EPILITHIC RIVER FLORA1
Authors: Klotz Richard Larry , Cain Jerome R. , Trainor Francis R.
Published: August 2007

Field and laboratory procedures demonstrate that the effluent from the Willimantic, Connecticut, sewage treatment plant changes the numerical composition of the dominant epilithic algae in the Shetucket River. This effect is due to the effluent altering the competitive balance between chlorella sp. and Achnanthes deflexa Reim. The chlorella completely dominates highly polluted stretches of the river, and shares dominance with A. deflexa in other areas. The degree of river pollution can be estimated by enumerating the natural standing crops of these 2 algae. A 2‐membered assay utilizing these organisms is a sensitive laboratory pollution monitor and a useful predictive tool. Dominant stands of these epilithic species develop in polluted and unpolluted zones in this river due to competition for the limited area on the cobbles.
AN AUTORADIOGRAPHIC AND HISTOCHEMICAL LOCALIZATION OF SULFATED POLYSACCHARIDES IN EUCHEUMA NUDUM (RHODOPHYTA)1
Authors: La Claire John W. , Dawes Clinton J.
Published: August 2007

The predominant sulfated polysaccharide, ˛‐carrageenan, was localized in the middle lamella of epidermal, cortical and medullary cells of Eucheumanudum J. Agardh. Autoradiographic studies with 35SO4= indicated that the label was first incorporated in the inner wall and ultimately deposited in the middle lamella of all cells, and in an outer wall layer of the epidermal cells. There was no evidence for cytoplasmic incorporation of the label. The middle lamella stained with alcian blue, was γ‐metachromatic with toluidina blue O and bound diaminobenzidine‐osmium tetroxide. This region was also positive with periodic acid‐Schiff's (PAS) ragent, possibly demonstrating cellulose and/or a nonsulfated precursor of ˛‐carrageenan.

A proposed model for extracellular sulfation includes production and secretion of a nonsulfated polygalactan and sulfotransferase enzyme(s) by the golgi apparatus and endoplasmic reticulum, respectively. Free sulfate in the wall would be bound to the precursor polysaccharide, with much of the resulting carrageenan migrating to the middle lamella facilitating mutual cell growth.
THE RELATIONSHIP BETWEEN PHOTOSYNTHESIS AND LIGHT FOR NATURAL ASSEMBLAGES OF COASTAL MARINE PHYTOPLANKTON1
Authors: Platt Trevor , Jassby Alan D.
Published: August 2007

In a series of 188 experiments on the, light‐saturation curve for natural assemblages of phytoplankton at 3 stations in Nova Scotia coastal waters, it was found that both the initial slope (α) of the curve and the assimilation number (PmB) varied about 5‐fold throughout the year. No differences could be detected between stations, but both α and PmB decreased with depth. The mean value of α for all the experiments was 0.21 mg C[mg Chl a]−1· h−1· W−1· m2 with a range from 0.03 to 0.63. An explanation is offered for the nonconstancy of a in terms of the effect of cell‐size and shape on self‐shading. An estimate is made from first principles of the physiological maximum‐attainable value of α. This estimate corresponds, within the limits of experimental error, to the highest values of α observed in the study. It is deduced that on the average the phytoplankton were photosynthesizing at only 44% maximum capacity. The mean value of PmB for all experiments was 4.9 mg C[mg Chl a]−1· h−1, with a range from 0.73 to 24.8. In the matrix of partial correlation coefficients, α and PmB were positively correlated with each other; α was correlated with mean solar radiation averaged over the 3 days prior to the experiment, but uncorrelated with temperature; PmB was correlated strongly with temperature but uncorrelated with recent solar radiation. The results show that PmB could be estimated from α and temperature using an empirical multiple regression equation, independent of depth. It is suggested that α and PmB are both correlated with some other factor not measured in the study, perhaps the mean cell‐size of the populations, or the nutrient status of the cells. The predictability of primary production is discussed in the light of this evidence.
PEDINOMONAS NOCTILUCAE (PRASINOPHYCEAE), THE FLAGELLATE SYMBIOTIC IN NOCTILUCA (DINOPHYCEAE) IN SOUTHEAST ASIA1
Authors: Sweeney Beatrice M.
Published: August 2007

The small green flagellate symbiotic in the Noctiluca miliaris Suriray from Southeast Asia has been examined by light and electron microscopy. The flagellate is very similar to Pedinomonas minor Korschikoff. The deeper flagellar depression and the habitat distinguish this species of Pedinomonas from P. minor. It is not a euglenoid as originally proposed, since it contains starch. Characters distinguishing it from Micromonas are described. The new combination Pedinomonas noctilucae (Subrahmanyan) comb, nov. is proposed for this flagellate.
OBSERVATIONS ON CELL DEVELOPMENT INCHLAMYDOMONAS SEGNIS(CHLOROPHYCEAE) AT LOW AND HIGH CARBON DIOXIDE TENSION1
Authors: Badour Samir S. , Tan Cheng K. , Waygood Ernest R.
Published: August 2007

Some cell cycle events were compared inChlamydomonas segnisEttl during its development in synchronous cultures (12:12 LD) supplied with air and air enriched with 5% CO2. In cultures bubbled with air, growth resulted in production of 2 relatively small zoospores. In cultures provided with 5% CO2, 4 large zoospores were formed but not released in darkness unless the cultures were bubbled with CO2‐free air and/or exposed to light. Respiration in zoospores was inhibited by high CO2tension. In cultures maintained under continuous illumination for one cell cycle, provision of 5% CO2led to enhanced growth, a relatively long S‐phase and a 4 h delay of the second cell division. In such cultures, the DNA content of parental cells (12 h L) was insufficient to support two cell divisions. The RNA/DNA ratio of the resulting zoospores was 10 compared to 4 in air cultures. These results provided evidence that the delay of the second cell division was a consequence of the delay in DNA production.