bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of Photosynthesis and Resistance to Photoinhibition in Cyanobacteria within Biological Desert Crust
Authors: Harel Yariv , Ohad Itzhak , Kaplan Aaron
Published: October 2004

Filamentous cyanobacteria are the main primary producers in biological desert sand crusts. The cells are exposed to extreme environmental conditions including temperature, light, and diurnal desiccation/rehydration cycles. We have studied the kinetics of activation of photosynthesis during rehydration of the cyanobacteria, primarily Microcoleus sp., within crust samples collected in the Negev desert, Israel. We also investigated their susceptibility to photoinhibition. Activation of the photosynthetic apparatus, measured by fluorescence kinetics, thermoluminescence, and low temperature fluorescence emission spectra, did not require de novo protein synthesis. Over 50% of the photosystem II (PSII) activity, assembled phycobilisomes, and photosystem I (PSI) antennae were detected within less than 5 min of rehydration. Energy transfer to PSII and PSI by the respective antennae was fully established within 10 to 20 min of rehydration. The activation of a fraction of PSII population (about 20%–30%) was light and temperature-dependent but did not require electron flow to plastoquinone [was not inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea]. The cyanobacteria within the crusts are remarkably resistant to photoinhibition even in the absence of protein synthesis. The rate of PSII repair increased with light intensity and with time of exposure. Consequently, the extent of photoinhibition in high-light-exposed crusts reached a constant, relatively low, level. This is in contrast to model organisms such as Synechocystis sp. strain PCC 6803 where PSII activity declined continuously over the entire exposure to high illumination. Ability of the crust's organisms to rapidly activate photosynthesis upon rehydration and withstand photoinhibition under high light intensity may partly explain their ability to survive in this ecosystem.
Carbon Status Constrains Light Acclimation in the Cyanobacterium Synechococcus elongatus
Authors: MacKenzie Tyler D.B. , Burns Robert A. , Campbell Douglas A.
Published: October 2004

Acclimation to one environmental factor may constrain acclimation to another. Synechococcus elongatus (sp. PCC7942), growing under continuous light in high inorganic carbon (Ci; approximately 4 mm) and low-Ci (approximately 0.02 mm) media, achieve similar photosynthetic and growth rates under continuous low or high light. During acclimation from low to high light, however, high-Ci cells exploit the light increase by accelerating their growth rate, while low-Ci cells maintain the prelight shift growth rate for many hours, despite increased photosynthesis under the higher light. Under increased light, high-Ci cells reorganize their photosynthetic apparatus by shrinking the PSII pool and increasing Rubisco pool size, thus decreasing the photosynthetic source-to-sink ratio. Low-Ci cells also decrease their reductant source-to-sink ratio to a similar level as the high-Ci cells, but do so only by increasing their Rubisco pool. Low-Ci cells thus invest more photosynthetic reductant into maintaining their larger photosystem pool and increasing their Rubisco pool at the expense of population growth than do high-Ci cells. In nature, light varies widely over minutes to hours and is ultimately limited by daylength. Photosynthetic acclimation in S. elongatus occurs in both high and low Ci, but low-Ci cells require more time to achieve acclimation. Cells that can tolerate low Ci do so at the expense of slower photosynthetic acclimation. Such differences in rates of acclimation relative to rates of change in environmental parameters are important for predicting community productivity under variable environments.
The Roles of Ethylene, Auxin, Abscisic Acid, and Gibberellin in the Hyponastic Growth of Submerged Rumex palustris Petioles
Authors: Cox Marjolein C.H. , Benschop Joris J. , Vreeburg Robert A.M. , Wagemaker Cornelis A.M. , Moritz Thomas , Peeters Anton J.M. , Voesenek Laurentius A.C.J.
Published: October 2004

Rumex palustris responds to complete submergence with upward movement of the younger petioles. This so-called hyponastic response, in combination with stimulated petiole elongation, brings the leaf blade above the water surface and restores contact with the atmosphere. We made a detailed study of this differential growth process, encompassing the complete range of the known signal transduction pathway: from the cellular localization of differential growth, to the hormonal regulation, and the possible involvement of a cell wall loosening protein (expansin) as a downstream target. We show that hyponastic growth is caused by differential cell elongation across the petiole base, with cells on the abaxial (lower) surface elongating faster than cells on the adaxial (upper) surface. Pharmacological studies and endogenous hormone measurements revealed that ethylene, auxin, abscisic acid (ABA), and gibberellin regulate different and sometimes overlapping stages of hyponastic growth. Initiation of hyponastic growth and (maintenance of) the maximum petiole angle are regulated by ethylene, ABA, and auxin, whereas the speed of the response is influenced by ethylene, ABA, and gibberellin. We found that a submergence-induced differential redistribution of endogenous indole-3-acetic acid in the petiole base could play a role in maintenance of the response, but not in the onset of hyponastic growth. Since submergence does not induce a differential expression of expansins across the petiole base, it is unlikely that this cell wall loosening protein is the downstream target for the hormones that regulate the differential cell elongation leading to submergence-induced hyponastic growth in R. palustris.
Unique and Overlapping Expression Patterns among the Arabidopsis 1-Amino-Cyclopropane-1-Carboxylate Synthase Gene Family Members
Authors: Tsuchisaka Atsunari , Theologis Athanasios
Published: October 2004

1-Aminocyclopropane-1-carboxylate synthase (ACS) catalyzes the rate-limiting step in the ethylene biosynthetic pathway in plants. The Arabidopsis genome encodes nine ACS polypeptides that form eight functional (ACS2, ACS4-9, and ACS11) homodimers and one nonfunctional (ACS1) homodimer. Transgenic Arabidopsis lines were constructed expressing the β-glucuronidase (GUS) and green fluorescence protein (GFP) reporter genes from the promoter of each of the gene family members to determine their patterns of expression during plant development. All genes, except ACS9, are expressed in 5-d-old etiolated or light-grown seedlings yielding distinct patterns of GUS staining. ACS9 expression is detected later in development. Unique and overlapping expression patterns were detected for all the family members in various organs of adult plants. ACS11 is uniquely expressed in the trichomes of sepals and ACS1 in the replum. Overlapping expression was observed in hypocotyl, roots, various parts of the flower (sepals, pedicle, style, etc.) and in the stigmatic and abscission zones of the silique. Exogenous indole-3-acetic acid (IAA) enhances the constitutive expression of ACS2, 4, 5, 6, 7, 8, and 11 in the root. Wounding of hypocotyl tissue inhibits the constitutive expression of ACS1 and ACS5 and induces the expression of ACS2, 4, 6, 7, 8, and 11. Inducers of ethylene production such as cold, heat, anaerobiosis, and Li+ ions enhance or suppress the expression of various members of the gene family in the root of light-grown seedlings. Examination of GUS expression in transverse sections of cotyledons reveals that all ACS genes, except ACS9, are expressed in the epidermis cell layer, guard cells, and vascular tissue. Similar analysis with root tip tissue treated with IAA reveals unique and overlapping expression patterns in the various cell types of the lateral root cap, cell division, and cell expansion zones. IAA inducibility is gene-specific and cell type-dependent across the root tip zone. This limited comparative exploration of ACS gene family expression reveals constitutive spatial and temporal expression patterns of all gene family members throughout the growth period examined. The unique and overlapping gene activity pattern detected reveals a combinatorial code of spatio-temporal coexpression among the various gene family members during plant development. This raises the prospect that functional ACS heterodimers may be formed in planta.
Airborne Ethylene May Alter Antioxidant Protection and Reduce Tolerance of Holm Oak to Heat and Drought Stress
Authors: Munné-Bosch Sergi , Peñuelas Josep , Asensio Dolores , Llusià Joan
Published: October 2004

Plant-emitted ethylene has received considerable attention as a stress hormone and is considered to play a major role at low concentrations in the tolerance of several species to biotic and abiotic stresses. However, airborne ethylene at high concentrations, such as those found in polluted areas (20–100 nL L−1) for several days, has received far less attention in studies of plant stress tolerance, though it has been shown to alter photosynthesis and reproductive stages (seed germination, flowering, and fruit ripening) in some species. To assess the potential effects of airborne ethylene on plant stress tolerance in polluted areas, the extent of oxidative stress, photo- and antioxidant protection, and visual leaf area damage were evaluated in ethylene-treated (approximately 100 nL L−1 in air) and control (without ethylene fumigation) holm oak (Quercus ilex) plants exposed to heat stress or to a combination of heat and drought stress. Control plants displayed tolerance to temperatures as high as 50°C, which might be attributed, at least in part, to enhanced xanthophyll de-epoxidation and 2-fold increases in α-tocopherol, and they suffered oxidative stress only when water deficit was superimposed on temperatures above 45°C. By contrast, ethylene-treated plants showed symptoms of oxidative stress at lower temperatures (35°C) than the controls in drought, as indicated by enhanced malondialdehyde levels, lower α-tocopherol and ascorbate concentrations, and a shift of the redox state of ascorbate to its oxidized form. In addition, ethylene-treated plants showed higher visual leaf area damage and greater reductions in the maximum efficiency of the PSII photochemistry than controls in response to heat stress or to a combination of heat and drought stress. These results demonstrate for the first time that airborne ethylene at concentrations similar to those found in polluted areas may reduce plant stress tolerance by altering, among other possible mechanisms, antioxidant defenses.
Quantification of Compartmented Metabolic Fluxes in Developing Soybean Embryos by Employing Biosynthetically Directed Fractional 13C Labeling, Two-Dimensional [13C, 1H] Nuclear Magnetic Resonance, and Comprehensive Isotopomer Balancing
Authors: Sriram Ganesh , Fulton D. Bruce , Iyer Vidya V. , Peterson Joan Marie , Zhou Ruilian , Westgate Mark E. , Spalding Martin H. , Shanks Jacqueline V.
Published: October 2004

Metabolic flux quantification in plants is instrumental in the detailed understanding of metabolism but is difficult to perform on a systemic level. Toward this aim, we report the development and application of a computer-aided metabolic flux analysis tool that enables the concurrent evaluation of fluxes in several primary metabolic pathways. Labeling experiments were performed by feeding a mixture of U-13C Suc, naturally abundant Suc, and Gln to developing soybean (Glycine max) embryos. Two-dimensional [13C, 1H] NMR spectra of seed storage protein and starch hydrolysates were acquired and yielded a labeling data set consisting of 155 13C isotopomer abundances. We developed a computer program to automatically calculate fluxes from this data. This program accepts a user-defined metabolic network model and incorporates recent mathematical advances toward accurate and efficient flux evaluation. Fluxes were calculated and statistical analysis was performed to obtain sds. A high flux was found through the oxidative pentose phosphate pathway (19.99 ± 4.39 μmol d−1 cotyledon−1, or 104.2 carbon mol ± 23.0 carbon mol per 100 carbon mol of Suc uptake). Separate transketolase and transaldolase fluxes could be distinguished in the plastid and the cytosol, and those in the plastid were found to be at least 6-fold higher. The backflux from triose to hexose phosphate was also found to be substantial in the plastid (21.72 ± 5.00 μmol d−1 cotyledon−1, or 113.2 carbon mol ±26.0 carbon mol per 100 carbon mol of Suc uptake). Forward and backward directions of anaplerotic fluxes could be distinguished. The glyoxylate shunt flux was found to be negligible. Such a generic flux analysis tool can serve as a quantitative tool for metabolic studies and phenotype comparisons and can be extended to other plant systems.
Recurrent preeclampsia and perinatal outcome: a study of women with recurrent preeclampsia compared with women with preeclampsia who remained normotensive during their prior pregnancies
Authors: Mendilcioglu Inanc , Trak Bilal , Uner Mine , Umit Selda , Kucukosmanoglu Mesut
Published: October 2004

Objective.  To evaluate the impact of preeclampsia recurrence on perinatal outcome.

Materials and methods.  A case‐controlled study was performed in multiparous women who developed preeclampsia in index pregnancy (n = 64). Among these, women who had preeclampsia in previous pregnancies (n = 21) were compared to those who remained normotensive during their prior pregnancies (n = 43). Maternal and fetal variables were compared. Multivariate logistic analyses were performed to examine the impact of preeclampsia recurrence on fetal loss, preterm delivery, small for gestational age (SGA) occurrence and respiratory distress syndrome adjusted for confounding variables.

Results.  No statistical significant difference was observed between the two groups in terms of age, delivery weeks, steroid use and laboratory markers. Fetal loss was higher in women with recurrent preeclampsia (19.0%) than in women with preeclampsia who had a normotensive pregnancy history (4.7%), with adjusted odds ratio (OR) of 5.77 [95% confidence interval (CI) 0.84–39.54].

Conclusion.  Women with recurrent preeclampsia had a higher rate of perinatal loss compared to women with preeclampsia who were normotensive in their prior pregnancies.
Neonatal outcome in a Danish national cohort of 8602 children born after in vitro fertilization or intracytoplasmic sperm injection: the role of twin pregnancy
Authors: Pinborg Anja , Loft Anne , Andersen Anders Nyboe
Published: October 2004

Background.  In Denmark, 4% of all infants are born after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) and 40% of these children are twins.

Methods.  We investigated neonatal outcome in a complete Danish IVF/ICSI birth cohort including 8602 infants born between 1995 and 2000: 3438 twins (40%) and 5164 singletons (60%). Births conceived after IVF or ICSI were identified by record linkage with the Danish IVF Registry and the National Medical Birth Registry. Data on neonatal outcome were collected from the National Patient Registry.

Results.  IVF/ICSI twins had a 10‐fold increased age‐ and parity‐adjusted risk of delivery before 37 completed weeks [odds ratio (OR) 9.9, 95% confidence interval (95% CI) 8.7–11.3] and a 7.4‐fold increased risk of delivery before 32 completed weeks (OR 7.4, 95% CI 5.6–9.8) compared with singletons. Correspondingly, ORs of birthweight <2500 g and birthweight <1500 g in twins were 11.8 (95% CI 10.3–13.6) and 5.4 (95% CI 4.1–7.0), respectively. The stillbirth rate was doubled in twins (13.1/1000) compared with singletons (6.6/1000) (p = 0.002). The risk of cesarean section and of admittance to a neonatal intensive care unit (NICU) was 4.6‐ and 1.8‐fold higher in IVF/ICSI twins than in singletons. The rate of major malformations was 40.4/1000 in twins and 36.8/1000 in singletons (p = 0.4), whereas the total malformation rate (major + minor) was higher in twins (73.7/1000) than in singletons (55.0/1000) (p = 0.001). After exclusion of patent ductus arteriosus (PDA), which is strongly associated with preterm birth, no significant differences in any malformation rates were observed between twins and singletons. Apart from the frequency of ICSI children with hypospadias, which reached a significance level of p = 0.05, malformation rates in ICSI children were similar to those in IVF children.

Conclusions.  This study indicates that neonatal outcome in IVF/ICSI twins is considerably poorer than in singletons. Thus, the impact is to draw the attention of clinicians to the benefit of elective single embryo transfer (eSET).
Management of ovarian cysts
Authors: Knudsen Ulla Breth , Tabor Ann , Mosgaard Berit , Andersen Erik Soegaard , Kjer Jens Joergen , Hahn‐Pedersen Suzanne , Toftager‐Larsen Kim , Mogensen Ole
Published: October 2004

Background.  The treatment of an ovarian cyst relies on its nature, and accurate preoperative discrimination of benign and malignant cysts is therefore of crucial importance. This study was undertaken to review the literature concerning the preoperative diagnosis and treatment of ovarian cysts.

Methods.  Articles concerning ovarian cysts from a medline literature search during the period 1985–2003 were included in addition to articles found as references in the initial publications.

Results.  Different methods for discriminating between benign and malignant ovarian cysts are discussed. The diagnosis and the treatment are assessed in relation to age, menopausal status, pregnancy, and whether the cyst is presumed to be benign or malignant. In general, expectant management is the choice in premenopausal and pregnant women with non‐suspicious cysts and normal levels of CA‐125. In postmenopausal women, unilocular, anechoic cysts less than 5 cm in diameter together with a normal CA‐125 may be followed up. Operation is recommended in women with cysts larger than 5 cm and/or elevated levels of CA‐125. Women with symptoms should be operated regardless of age, menopausal status, or ultrasound findings.

Conclusions.  The preoperative discrimination between benign and malignant ovarian cysts is a challenge. Multimodal methods improve the results of single modalities, but we still need improved preoperative diagnostic tools. Furthermore, these methods should be validated in consecutive patient populations large enough to give a reliable estimate of the method's sensitivity and specificity.
Perinatal outcome of twin pregnancies after in vitro fertilization
Authors: Manoura Antonia , Korakaki Eftyhia , Hatzidaki Eleftheria , Bikouvarakis Stylianos , Papageorgiou Maria , Giannakopoulou Christine
Published: October 2004

Background.  There are conflicting data concerning perinatal outcome of twin, in vitro fertilization (IVF) pregnancies. The aim of this study was to evaluate and compare perinatal and neonatal outcomes in twin IVF pregnancies to those of spontaneously conceived twin gestations.

Methods.  The medical files of 73 IVF and 148 naturally conceived twin pregnancies were studied retrospectively. Data concerning maternal characteristics, obstetric complications, and neonatal outcome were recorded and compared by χ2 test. The one‐way analysis of variance (anova) was used to compare the means of groups.

Results.  Mean maternal age, the proportion of nulliparous women, and the incidence of premature rupture of membranes, cesarean section, and premature delivery were significantly higher in the study group. The mean birthweight was significantly lower, the frequency of admission to the intensive care unit and the duration of hospitalization were significantly higher in the study group. The incidence of intaventricular hemorrhage was significantly higher in the IVF group. The number of perinatal deaths was similar.

Conclusion.  IVF twin pregnancies are at greater risk for obstetric complications and adverse neonatal outcome in comparison with naturally conceived twin gestations.
THE 1929 STOCK MARKET: IRVING FISHER WAS RIGHT*
Authors: McGrattan Ellen R. , Prescott Edward C.
Published: October 2004

Many stock market analysts think that in 1929, at the time of the crash, stocks were overvalued. Irving Fisher argued just before the crash that fundamentals were strong and the stock market was undervalued. In this article, we use growth theory to estimate the fundamental value of corporate equity and compare it to actual stock valuations. Our estimate is based on values of productive corporate capital, both tangible and intangible, and tax rates on corporate income and distributions. The evidence strongly suggests that Fisher was right. Even at the 1929 peak, stocks were undervalued relative to the prediction of theory.
ESTIMATING THE GENERAL EQUILIBRIUM BENEFITS OF LARGE CHANGES IN SPATIALLY DELINEATED PUBLIC GOODS*
Authors: Sieg Holger , Smith V. Kerry , Banzhaf H. Spencer , Walsh Randy
Published: October 2004

The purpose of this article is to report a new approach for measuring the general equilibrium willingness to pay for large changes in spatially delineated public goods such as air quality. We estimate the parameters of a locational equilibrium model and compute equilibria for alternative scenarios characterizing the availability of public goods within a system of communities. Welfare measures take into consideration the adjustments of households in equilibrium to nonmarginal changes in public goods. The framework is used to analyze willingness to pay for reductions in ozone concentrations in Southern California between 1990 and 1995.
ANALYTICAL EVALUATION OF VOLATILITY FORECASTS*
Authors: Andersen Torben G. , Bollerslev Tim , Meddahi Nour
Published: October 2004

Estimation and forecasting for realistic continuous‐time stochastic volatility models is hampered by the lack of closed‐form expressions for the likelihood. In response, Andersen, Bollerslev, Diebold, and Labys (Econometrica, 71 (2003), 579–625) advocate forecasting integrated volatility via reduced‐form models for the realized volatility, constructed by summing high‐frequency squared returns. Building on the eigenfunction stochastic volatility models, we present analytical expressions for the forecast efficiency associated with this reduced‐form approach as a function of sampling frequency. For popular models like GARCH, multifactor affine, and lognormal diffusions, the reduced form procedures perform remarkably well relative to the optimal (infeasible) forecasts.
THE PRICING OF JOB CHARACTERISTICS WHEN MARKETS DO NOT CLEAR: THEORY AND POLICY IMPLICATIONS*
Authors: Lang Kevin , Majumdar Sumon
Published: October 2004

This article examines nonsequential search when jobs vary with respect to nonpecuniary characteristics. In the presence of frictions in the labor market, the equilibrium job distribution need not show evidence of compensating wage differentials. The model also generates several pervasive features of labor markets: unemployment and vacancies, apparent discrimination, and market segmentation. When workers are homogeneous, restrictions on the range of job offers decrease welfare and cannot reduce unemployment. However, when workers have heterogeneous preferences, such restrictions may lower unemployment, and can even lead to a Pareto improvement in welfare. We consider the impact of policies banning discrimination and regulating working conditions.
ON THE POLITICAL ECONOMY OF IMMIGRATION AND INCOME REDISTRIBUTION*
Authors: Dolmas Jim , Huffman Gregory W.
Published: October 2004

In this article, we analyze an economy in which agents vote over immigration policy and redistributive tax policy. We show that natives' preferences over immigration are influenced by the prospect that immigrants will be voting over future tax policy. We also show that changes in the degree of international capital mobility, the distribution of initial capital among natives, the wealth or poverty of the immigrant pool, and the future voting rights and entitlements of immigrants can have dramatic effects on equilibrium immigration and tax policies. Finally, we provide some empirical support for the model's predictions.
MISERY LOVES COMPANY: EQUILIBRIUM PORTFOLIOS WITH HETEROGENEOUS CONSUMPTION EXTERNALITIES*
Authors: Gollier Christian
Published: October 2004

The present article extends the Arrow–Debreu portfolio model to consumption externalities. It is assumed that each investor has a von Neumann–Morgenstern utility that is a function of her own consumption and of the average consumption in the group to which she belongs. Individual degrees of risk aversion and conformism are heterogeneous within each group and between the different groups in the economy. We show that, under some conditions on the degree of conformism in the economy, the optimal portfolio and consumption choices observed at equilibrium in each group with consumption externalities are equivalent to those that are optimal without any externality, but with an adjusted degree of risk aversion. If these conditions are not fulfilled, groups have no representative agent and the demand for pure zero‐mean lotteries may be positive, thereby showing that not all diversifiable risks are washed away at equilibrium. We characterize the relationship between the distribution of conformism in the economy to the competitive allocation of risk and to the equity premium. We provide conditions for the two‐fund separation property to hold.
COLLUSION IN LOCAL PUBLIC WORKS*
Authors: Besfamille Martin
Published: October 2004

A hierarchical model of collusion in local public works is presented. A local authority plans to undertake a project, delegating its construction to a construction firm. Both of them know the project's cost. However, the federal government decides whether to subsidize the project without knowing its cost. Therefore, the local authority and the constructor may agree to misreport their private information, in order to benefit from the allocation of federal grants. We show that different collusive behaviors may emerge. Then, we characterize the optimal federal grant policy. Finally, we investigate when constructing (shutting down) useless (valuable) projects is optimal.
LACK‐OF‐RECALL AND CENTRALIZED MONETARY TRADE*
Authors: Temzelides Ted , Yu Jialin
Published: October 2004

We introduce lack‐of‐recall of past transactions as an alternative assumption to anonymity in a model where trade is centralized. In environments where there is an intertemporal lack‐of‐double‐coincidence of wants problem and lack‐of‐commitment, lack‐of‐recall can give rise to monetary equilibria that dominate nonmonetary outcomes in terms of welfare.
INTERNATIONAL DEVIATIONS FROM THE LAW OF ONE PRICE: THE ROLE OF SEARCH FRICTIONS AND MARKET SHARE*
Authors: Alessandria George
Published: October 2004

This article examines the size and persistence of international deviations from the law of one price in an industry with search frictions. Cost differences lead foreign and domestic firms to price differently within countries. When local firms are more common in each country, there are large and persistent price differences across countries. Large and persistent changes in international relative costs lead to large and persistent changes in international relative prices. Dynamic considerations imply that the amount of a cost shock firms pass through to prices is U‐shaped in the market share of firms receiving the shock.
Integrable Equations in Nonlinear Geometrical Optics
Authors: Konopelchenko B. , Moro A.
Published: October 2004

Geometrical optics limit of the Maxwell equations for nonlinear media with the Cole–Cole dependence of dielectric function and magnetic permeability on the frequency is considered. It is shown that for media with slow variation along one axis such a limit gives rise to the dispersionless Veselov–Novikov equation for the refractive index. It is demonstrated that the Veselov–Novikov hierarchy is amenable to the quasiclassical ‐dressing method. Under more specific requirements for the media, one gets the dispersionless Kadomtsev–Petviashvili equation. Geometrical optics interpretation of some solutions of the above equations is discussed.
On a Nonlinear Discretized LKR System: Reductions and Underlying Virasoro Symmetry Algebras
Authors: Lou S. Y. , Rogers C. , Schief W. K.
Published: October 2004

A differential‐difference version of the Loewner–Konopelchenko–Rogers (LKR) system is constructed by discretization of the spatial variables in the continuous LKR system. The differential‐difference LKR system admits a diversity of significant reductions. The symmetry algebras of the discrete LKR system and its reductions are shown to possess underlying Kac–Moody–Virasoro type structure. A discrete dromion‐like solution of the LKR system is constructed via finite symmetry group transformation.
Dipole and Quadrupole Solitons in Optically Induced Two‐Dimensional Photonic Lattices: Theory and Experiment
Authors: Yang Jianke , Makasyuk Igor , Bezryadina Anna , Chen Zhigang
Published: October 2004

Dipole and quadrupole solitons in a two‐dimensional photorefractive optical lattice are investigated both theoretically and experimentally. It is shown theoretically that out‐of‐phase dipole solitons and quadrupole solitons exist and are linearly stable in the intermediate‐intensity regime. In‐phase dipole and quadrupole solitons, however, are always linearly unstable, but their instabilities are rather weak in the low‐intensity regime. Experimentally, both types of dipole solitons are observed, and the experimental results agree qualitatively with the theoretical predictions. In addition, we have observed the anisotropic effect of the photorefractive crystal in the dipole‐soliton formation.
AKINETE GERMINATION IN ANABAENA CIRCINALIS (CYANOPHTA)
Authors: van Dok Wendy , Hart Barry T.
Published: October 2004

Akinetes of a clonal culture of Anabaena circinalis Rabenhorst from Mt. Bold reservoir (eutrophic), South Australia, were isolated and the effects of light, phosphorus, and nitrogen availability on their germination were investigated. Light was required but there was no significant difference in percentage of germination after 72 h if akinetes were incubated in ASM‐1 medium at irradiances of 15, 30, or 50 μmol.m‐2.s‐1. Maximum akinete germination occurred by 48 h. Nitrogen was not required, as 88% of akinetes germinated in the flasks without combined nitrogen added to the medium and without N2 in the air. NH4+‐N at 28 mg N.L‐1 completely suppressed germination, whereas 28 mg NO3 N.L‐1 had no effect relative to the controls without nitrogen. Phosphorus was required, and at 48 h percentage of germination in the flasks with 0.6 mg P.L‐1 added (78%) was significantly greater than in the flasks with 0.06 P.L‐1 (58%) and 0 mgP.L‐1 (24%) added. Germlings in the 0 mg P.L‐1 flasks were only 2–4 cells long and stunted in appearance, whereas germlings at all other P concentrations were 8–16 cells long. It is likely that the isolation process exposed some akinetes to intracellular phosphorus released from lysing vegetative cells, but this was insufficient to allow normal development in the 0 mg P.L‐1 flasks. The plot of percentage of germination vs. initial phosphorus concentration, in the medium showed a relationship analogous to Michaelis‐Menten nutrient uptake kinetics, suggesting that a specific membrane‐bound enzyme system(s) is involved, with phosphorus as the substrate. The half saturation value (KS) for germination was 50 μg P.L‐1.
LIGHT‐DEPENDENT GROWTH, DARK SURVIVAL, AND GLUCOSE UPTAKE BY CRYPTOPHYTES ISOLATED FROM A FRESHWATER CHEMOCLINE
Authors: Gervais Frank
Published: October 2004

Clones of Cryptomonas phaseolus Skuja, Cryptomonas rostratiformis (Skuja) Skuja in Huber‐Pestalozi, and Cryptomonas undulata Gervais were isolated from the deep chlorophyll maximum near the oxic/anoxic boundary layer of the mesoeutrophic lake Schlachtensee, Germany. Different autecological features of these species were studied in batch culture experiments. Cryptomonas cf. ovata Ehrenberg and Chroomonas sp. that never dominated in the deep chlorophyll layer were also isolated from Schlachtensee to study their light‐dependent growth in comparison to the deep‐living species. Cryptomonas undulata, C. cf. ovata, and C. phaseolus had a very low light compensation point (5–7 μmol.m‐2.s‐1),whereas the growth rate of Chroomonas sp. and C. rostratiformis was positive above 16 and 24 μmol.m‐2.s‐1. Cryptomonas phaseclus and Chroomonas sp. became photoinhibited above photon flux densities of 92 and 116 μmol.m‐2.s‐1. Cryptomonas rostratiformis, C. cf. ovata, and C. undulata reached a maximum growth rate at a considerably higher photon flux density (198–250 μmol.m‐2.s‐1). Cryptomonas phaseolus grew fastest under light‐limiting conditions. Chyptomonas phaseolus and C. undulata were best able to suruive prolonged periods of darkness. Cryptomonas phaseolus, C. rostratiformis, and C. undulata did not show any uptake of fluorescent latex beads. When labeled glucose was provided in naturally occurring concentrations, carbon uptake by C. phaseolus, C. rostratiformis, and C. undulata was negligibly small in comparison to cellular carbon content. I suggest that the adaptation to a low‐light environment is an important preadaptation for the dominance of C. phaseolus and C. undulata near the freshwater chemocline.
INTRASPECIFIC VARIATION IN THE DINOFLAGELLATEGAMBIERDIZSCUS TOXICUS(DINOPHYCEAE). I. ISOZYME ANALYSIS
Authors: Chinain Mireille , Germain Michel , Sako Yoshihiko , Pauillac Serge , Legrand Anne‐Marie
Published: October 2004

Intraspecific variation among 19 isolates of the ciguatera‐causing dinoflagellateGambierdiscus toxicusAdachi & Fukuyo (Dinophyceae) collected from French Polynesia, New Caledonia, and the French West Indies was investigated by isozyme analysis. Comparison of their cell sizes and growth rates revealed that significant variation exists among these clones. Comparison of electrophoretic patterns for seven enzyme systems indicated thatG. toxicusis comprised of numerous biochemically distinct strains. Isolates from Tubuai and Hao appeared to be the most distantly related. Tahitian strains ofG. toxicusalso showed a remarkably low degree of similarity with the Tubuai isolates. The latter, which were taken from the same locale in Tubuai, also exhibited highly heterogeneous electrophoretic Profiles when compared to each other, suggesting a multiclonal origin. The single isolate analyzed from the Atlantic Ocean was most closely related to Tahitian isolates, despite their geographic separation. Finally, no clear relationship was found between the electrophoretic profiles of these isolates and their capacity to produce ciguatoxic compounds.
FUNGAL CELLWALL POLYSACCHARIDES ELICIT AN ANTIFUNGAL SECONDARY METABOLITE (PHYTOALEXIN) IN THE CYANOBACTERIUM SCYTONEMA OCELUTUM2
Authors: Patterson Gregory M. L. , Bolis Christine M.
Published: October 2004

The addition of fungal cell‐wall homogenates of Penicillium notatum and Cylindrocladium spathiphylli markedly stimulated the accumulation of tolytoxin, an antifungal secondary metabolite, in cultures of the cyanobacterium Scytonema ocellatum Lyngbye ex Bornet et Flahault. Evaluation of polysaccharides, proteins, and other polymers established that a limited range of polysaccharides, especially chitin and carboxymthylcellulose, selectively elicited enhanced tolytoxin accumulation in S. ocellatum. The elicitor activity of fungal cell‐wall preparations could be correlated with the chitin content of the preparation. Polymeric chitin was half‐maximally effective at a concentration (EC50) of 19 mg.L‐1, whereas chitin oligoments were more effective (EC50= 3.3 mg.L‐1) in eliciting enhanced tolytoxin accumulation. The elicitor activity of either purified chitin or an elicitor‐active fungal cell‐wall preparation could be destroyed by treatment with chitinase. The results suggest an ecological role for tolytoxin as an inducible chemical defense agent (phytoalexin) capable of protecting S. ocellatum against fungal invasion.
AGLAOTHAMNION HALLIAE COMB. NOV. AND A. COLLINSII SP. NOV. (CERAMIALES, RHODOPHYTA): RESOLUTION OF NOMENCLATURAL AND TAXONOMIC CONFUSION
Authors: Aponte Nilda E. , Ballantine David L. , Norris James N.
Published: October 2004

Specimens from the exsiccatae Phycotheca BorealiAmericana number 698 are shown to represent two distinct species. One of them, formerly known as Callithamnion halliae, is transferred to Aglaothamnion on the basis of its uninucleate cells. The specimens exhibit distichous branching and are ecorticate. A lectotype is proposed for one of the P.B.‐A. #698 specimens displaying these characters. Aglaothamnion halliae (Collins) comb. nov. is an earlier name for Aglaothamnion westbrookiae Rueness et L'Hardy‐Halos. The second species, together with specimens of P.B.‐A. #1896, has radial branching and corticated axes and is described herein as a new species, Aglaothamnion collinsii. The binomial Aglaothamnion boergesenii (Aponte et Ballantine)L'Hardy‐Halos et Rueness in Aponte, Ballantine, et J. Norris is validated. A key to the tropical and warm‐temperate western Atlantic species of Aglaothamnion is presented.
THE NEW GENUS AND SPECIESOSSIELLA PACIFICA(GRIFFITHSIEAE, RHODOPHYTA) FROM HAWAII AND NORFOLK ISLAND, PACIFIC OCEAN
Authors: Millar Alan J. K. , Abbott Isabella A.
Published: October 2004

Ossiella pacificagen. et sp. nov. is described from sub tidal habitats (5–19 m) in the central (Hawaiian Islands) and southwestern (Norfolk Island) Pacific Ocean. Plants consist of limited prostrate axes that rapidly become erect and form ecorticate, subdichotomously branched axes bearing up to seven (mostly six) di‐/to trichotomously branched, pigmented, determinate, quickly caducous whorled laterals from subapical axial cells. Two to five tetrasporangza are borne directly on the inflated basal cells of pigmented determinate laterals. One to two spermatangial fascicles are similarly placed in male plants. Subapical procarps are borne on a three‐celled fertile axis, which occupies the same position as an indeterminate branch, being itself displaced laterally by the continued growth of the indeterminate axis. Procarps are bicarpogonial, the sterile cell normally associated with the supporting cell in procarps of the Griffithsieae being converted into a functional four‐celled carpogonial branch. Ossiellais compared with the other membus of the tribe, and a dichotomous key to the genera is offered. On morphological grounds, Ossiellaseemingly forms a perfect intermediary link along the phylogenetic lineage between the eastern Australian genusBaldockiaA. Millar, the eastern American genusCalliclavulaG. W. Schneid, and the widespreadAnotrichiumNägeli.
CHARACTERIZATION OF MYHOGRAMME LNIDA, MYRIOGRAMMEAE TRIB. NOV (DELESSEIUACEAE, FWODOPHYTA)
Authors: Hommersand Max H. , Fredericq Suzanne
Published: October 2004

The Myriogramme group of Kylin was found to contain two distinct clusters of genera that merit recognition at the tribal level. In this paper, we establish the tribe Myriogrammae based on a study of the type species of Myriogramme, M. livida, from the Southern Hemisphere. The Myriogrammae is characterized by 1) marginal and diffuse intercalary meristems; 2) nuclei arranged in a ring bordering the side walls of vegetative cells; 3) microscopic veins absent; 4) procarps scattered, formed opposite one another on both sides of the blade posterior to one or more vegetative pericentral cells (cover cells) and consisting of a carpogonial branch, a one‐/to two‐celled lateral sterile group and a one‐celled basal sterile group; 5) auxiliary cell diploidized by a connecting cell cut off posteriolaterally from the fertilized carpogonium; 6) gonimoblast initial cut off distally from the auxiliary cell, generating one distal and one to two lateral gonimoblast filaments that branch in the plane of the expanding cystocarp cavity and later fuse to from an extensive, branched fusion cell; 7) spermatangial and tatrasporangial sori formed inside the margin on both sides of the blade by resumption of meristematic activity; and 8) tetrasporangia produced primarily from the central cells. The Myriogrammae currently includes Myriogramme Kylin, Gonimocolax Kylin, Haraldiophyllum A. Zinova, Hideophyllum A. Zinova, and a possible undescribed genus from Pacific North and South America. Genera are separated based primarily on features of gonimoblast and carposporangial development.
CYANOBACTERIAL DOMINANCE OF POLAR FRESHWATER ECOSYSTEMS: ARE HIGH‐LATITUDE MAT‐FORMERS ADAPTED TO LOW TEMPERATURE?1
Authors: Tang Evonne P. Y. , Tremblay Roxanne , Vincent Wanuick F.
Published: October 2004

Although it is generally believed that cyanobacteria have high temperature optima for growth (> 20° C), mat‐foming cyanobacteria are dominant in many types of lakes, streams, and ponds in the Arctic and Antarctic. We studied the effect of temperature on growth (μ) and relative pigment composition of 27 isolates of cyanobacteria (mat‐forming Oscillatoriaceae) from the Arctic, subarctic, and Antarctic to investigate whether they are a) adapted to the low temperature (i.e. psychrophilic) or b) tolerant of the low temperature of the polar regions (i.e. psychrotrophic). We also derived a parabolic function that describes both the rise and the decline of cyanobacterial growth rates with increasing temperature. The cyanobacteria were cultured at seven different temperatures (5°‐35° C at 5° C intervals), with continuous illumination of 225 μmol photons.m−2.s−1. The parabolic function fits the μ‐temperature data with 90% confidence for 75% of the isolates. Among the 27 isolates of cyanobacteria studied, the temperature optima (Topt) for growth ranged from 15° to 35° C, with an average of 19.9° C. These results imply that most polar cyanobacteria are psychrotrophs, not psychrophiles. The cyanobacteria grew over a wide temperature range (typically 20° C) but growth rates were low men at Topt (average μmax of 0.23 ± 0.069 d−1). Extremely slow growth rates at low temperature and the high temperature for optimal growth imply that the cyanobacteria are not adapted genetically to cold temperatures, which characterize their ambient environment. Other competitive advantages such as tolerance to desiccation, freeze—thaw cycles, and bright, continuous solar radiation may contribute to their dominance in polar aquatic ecosystems.
OCCURRENCE OF PHYIWATED CHLOROPHYLLcINISOCHRYSIS GALBANAANDISOCHRYSISSP. (CLONE T‐ISO) (PRYMNESIOPHYCEAE)1
Authors: Zapata Manuel , Garrido José L.
Published: October 2004

The pigment composition of two clones ofIsochrysis galbanaParke (CCMP 1323 and CCAP 927/1), andIsochrysissp. (clone T‐ISO) was analyzed by high‐performance liquid chromatography using a polymeric octadecylsilica column. Fluorescent peaks with retention times higher than chlorophyllawere detected for all three clones. The corresponding pigments were isolated and characterized in terms of their visible absorbance and fluorescence spectra. The pigments were similar to phytol‐substituted chlorophyllc,previously isolated from Emiliania huxleyi (Lohm.) Hay and Mohler and other species containing chlmophyll c3. The presence of phytol‐substituted chlorophyllcinI. galbanawhich lacked chlorophyll c3, increases the diversity of chlorophyll patterns for the Haptophyta, which can be grouped, at present, into six different pigment types. This is the jrst observation of a haptophyte containing the apolar phytylated chlorophyll c‐like pigment but lacking chlorophyll c3.
INFLUENCE OF ULTRAVIOLET RADIATION ON GROWTH AND PHOTOSYNTHESIS OF TWO COLD OCEAN DIATOMS1
Authors: Nilawati Jusri , Greenberg Bruce M. , Smith Ralph E. H.
Published: October 2004

The influence of chronic exposure to UV‐B and UV‐A radiation on growth and photosynthesis of two polar marine diatoms (Pseudonitzschia seriata and Nitzschia sp.) was investigated in cultures exposed to moderate photon fluences for 3–7 days. Population growth rates were diminished 50% by UV‐B. Fluorescence induction kinetics of photo‐system II (PSII) revealed that UV‐B caused lower Fv/Fm ratios and half‐rise times, indicating damage to the reaction center of PSII and to related elements of the photosynthetic electron transport chain. Carbon assimilation rates per cell and per chlorophyll a were nonetheless highest for UV‐B—exposed populations, which also had the highest chlorophyll a content per cell. The UV‐B—exposed cells were, however, more vulnerable to visible light‐induced photoinhibition. Exposure to UV‐A in the absence of UV‐B had little effect on growth, fluorescence induction of PSII, or chlorophyll a contents but did have some inhibitory effects on carbon assimilation per chlorophyll a and per cell. The increased photosynthetic capacity of UV‐B‐exposed cells suggested some ability to compensate for damage to the photosynthetic apparatus.
EFFECT OF IRON NUTRITION ON THE MARINE CYANOBACTERIUM SYNECHOCOCCUS GROWN ON DIFFERENT N SOURCES AND IRRADIANCES1
Authors: Kudo Isao , Harrison Paul J
Published: October 2004

The effects of Fe deficiency on the marine cyanobacterium Synechococcus sp. were examined in batch cultures grown on nitrate or ammonium as a sole nitrogen source under two different irradiances. Fe‐stressed cells showed lower chlorophyll a content and cellular C and N quotas. Light limitation increased the critical iron concentration below which both suppression of growth rate and changes in cellular composition were observed. At a limiting irradiance (26 μmol.m−2.s−1), this critical value was ∼10 nM, a 10 times increase compared to high‐light cultures. Moreover, at low light the cellular chlorophyll a concentration was higher than at saturating light (110 μmol.m−2.s−1), this difference being most pronounced under Fe‐stressed conditions. Cells grown on ammonium showed a lower half‐saturation constant for Fe (Ks) compared to cells grown on nitrate, indicating Synechococcus sp. has the ability to grow faster on ammonium than on nitrate in a low Fe environment at high light. Consequently, in high‐nutrient and low‐chlorophyll regions where Fe limits new production, cyanobacteria most likely grow on regenerated ammonium, which requires less energy for assimilation. The Ks for growth on Fe at low light was significantly higher than at high light compared with the cells grown on the same N source, suggesting the cells require more Fe at low light. Therefore, if cells that are already Fe‐limited also become light‐limited, their iron stress level will increase even more. For cyanobacteria this is the first report of a study combining the interactions of Fe limitation, light limitation, and nitrogen source (NO3− vs. NH4+).
THE CYTOSKELETON OF THE NAKED GREEN FLAGELLATESPERMATOZOPSZS SIMILIS(CHLOROPHYTA): ANALYSIS OF ISOLATED BASAL APPARATUSES IN THE PARALLEL CONFIGURATION1,2
Authors: Geimer Stefan , Lechtreck Karl‐Ferdinand , Melkonian Michael
Published: October 2004

The biflagellate green algaSpermatozopsis similisis demonstrated to be a model organism for the biochemical and functional analysis of the basal apparatus. Basal apparatuses were isolated in the presence of 10−6M Ca2+, which induces the reorientation of the basal bodies into the parallel state. Serial thin sectioning of enriched basal apparatuses stained with tannic acid reveals several novel details of the structure of the basal bodies, the distal connecting fiber, and the striated microtubule‐associated fibers. We observed a pronounced difference in size of a striated fiber connecting the basal bodies to the five‐stranded microtubular roots depending on its association with the developmentally older or younger basal body. Instead of a proximal connecting fiber, the proximal end of each basal body is associated with a striated triangular plate; these plates appear to serve as spacers for the basal bodies in the parallel and antiparallel configurations. We suggest that the plates play a role in maintaining basal body orientation during forward and backward swimming. The results are summarized in representative drawings of the basal apparatus.