Polar Diatoms Research Articles

Long-Term Temperature Acclimation of Photosynthesis in Steady-State Cultures of the Polar Diatom Fragilariopsis cylindrus

Cultures of the obligate psychrophilic diatom Fragilariopsis cylindrus (Grunow) were grown for 4 months under steady-state conditions at -1 degrees C and +7 degrees C (50 micromol photons m(-2) s(-1)) prior to measurements in order to investigate long-term acclimation of photosynthesis to both temperatures. No differences in maximum intrinsic quantum yield of PS II (F(V)/F(M)) and relative electron transport rates could be detected at either temperature after 4 months of acclimation. Measurements of photosynthesis (relative electron transport rates) vs. irradiance (P vs. E curves) revealed similar values for relative light utilization efficiency (alpha = 0.57 at -1 degrees C, alpha = 0.60 at +7 degrees C) but higher values for irradiance levels at which photosynthesis saturates (E(K)) at -1 degrees C and, therefore, higher maximum photosynthesis (P(MAX) = 54 (relative units) at -1 degrees C, P(MAX) = 49 at +7 degrees C). Nonphotochemical quenching (NPQ) measurements at 385 mumol photons m(-2) s(-1) indicated higher (37%) NPQ for diatoms grown at -1 degrees C compared to +7 degrees C, which was possibly related to a 2-fold increase in the concentration of the pigment diatoxanthin and a 9-fold up-regulation of a gene encoding a fucoxanthin chlorophyll a,c-binding protein. Expression of the D1 protein encoding gene psbA was ca. 1.5-fold up-regulated at -1 degrees C, whereas expression levels of other genes from Photosystem II (psbC, psbU, psbO), as well as rbcL, the gene encoding the Rubisco large subunit were similar at both temperatures. However, a 2-fold up-regulation of a plastid glyceraldehyde-P dehydrogenase at -1 degrees C indicated enhanced Calvin cycle activity. This study revealed for the first time that a polar diatom could efficiently acclimate photosynthesis over a wide range of polar temperatures given enough time. Acclimation of photosynthesis at -1 degrees C was probably regulated similarly to high light acclimation.

Collisional quantum interference on rotational energy transfer: (II) in a polar diatom–diatom system

A model of collisional quantum interference was derived in an atom–diatom system [Chem. Phys. Lett. 339 (2001) 413]. In this Letter, a theoretical model of CQI is derived in a polar diatom–diatom system, based on the first order Born approximation of time dependent perturbation theory and taken into account of the multipolar interaction potential. The key factors in the determination of the differential and integral interference angles are obtained. CO A 1Π(v=0)– e 3Σ −(v=1) system in collision with HCl is calculated. The changing tendency of the interference angles with the experimental temperatures is obtained.

Fiberoptic Array Spectroscopy of NH \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $_{2}$ \end{document} in Comet Hale‐Bopp: Nature of the Rotational Energy Distributions

Moderate-resolution spectra of the 030 band of NH2 near 6300 A were recorded in Comet Hale-Bopp near 2.6 and 1.0 AU with the HYDRA array spectrometer on the WIYN telescope. The spectra from beyond the collision sphere were examined with respect to the relative rotational energy distributions in NH2. The relative rotational profiles could be consistently fitted at both heliocentric positions by a photostationary state model that follows optical pumping and fluorescence in the 2A1(Πu)- 2B1 band and radiative rotational relaxation in the ground state. The behavior of the spectra with regard to the relative weakness of lines from K = even states at large heliocentric distances is explained by this model, where only the solar flux changes. The general heliocentric dependence of the rotational excitation temperature of collision-free NH2, and, to a first-order approximation, polar diatomic radicals are predicted. The form of the heliocentric dependence is coincidentally similar to that of CO in the collision sphere as observed by others. Species that can undergo optical pumping will show a heliocentric dependence of the rotational excitation temperature of the form Texc(rh) = T1 AU/r. The NH2 radical and diatomic hydrides will have flatter rh dependence than the polar first row diatomics. The rh dependence is largely controlled by the ratio of the fluorescence excitation rate and the rate of radiative rotational relaxation.

Creation of polar and nonpolar ultra-long-range rydberg molecules

We predict the existence of a ubiquitous class of long-range molecular Rydberg states, whose Born-Oppenheimer potential curves are oscillatory in nature. These oscillations reflect the nodal structure of the atomic Rydberg state wave functions. The temperature and density of atoms in a Bose-Einstein condensate are particularly favorable for the laser excitation of ultra-long-range vibrational bound states localized at internuclear distances in the range 10(3)- 10(5) a.u. A surprising trilobitelike class of polar homonuclear diatomics should exhibit electric dipole moments in the kilodebye range.

INFLUENCE OF ULTRAVIOLET RADIATION ON GROWTH AND PHOTOSYNTHESIS OF TWO COLD OCEAN DIATOMS1

ABSTRACTThe 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.

Evolution of the diatoms (Bacillariophyta). II. Nuclear-encoded small- subunit rRNA sequence comparisons confirm a paraphyletic origin for the centric diatoms

A phylogeny of the diatoms was inferred from comparisons of nuclear-encoded small subunit ribosomal RNA coding regions using maximum likelihood, weighted maximum parsimony, and neighbor-joining distance methods with Jukes and Cantor, Kimura, Gamma, van de Peer, and LogDet evolutionary models. Analyses of 30 taxa in 11 orders recovered two clades (Clades I and II). Neither of these clades correspond to the three classes of diatoms presently recognized or to the traditionally recognized radially symmetrical centric diatoms or bilaterally symmetrical pennate diatoms. All analyses show that the centric diatoms are a paraphyletic lineage. Tests of alternative phylogenies that address existing hypotheses regarding diatom systematics with the maximum likelihood and maximum parsimony methods support the two clades. Clade I is defined by centric diatom orders with specialized tubes, termed labiate processes, located peripherally in the cell wall. Clade II contains (1) bi(multi)polar centric diatoms with centrally located labiate processes, (2) centric diatoms with other central tubes termed strutted processes, and (3) pennate diatoms. Morphological evidence from fossil assemblages and cytological architecture support the results of the molecular analyses, whereas morphological features of extant diatoms are too derived to resolve the deeper branches in the tree.

Carbon acquisition and growth of Antarctic sea ice diatoms in closed bottle incubations

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 135:169-177 (1996) - doi:10.3354/meps135169 Carbon acquisition and growth of Antarctic sea ice diatoms in closed bottle incubations Gleitz M, Kukert H, Riebesell U, Dieckmann GS Mixed cultures of 4 polar diatoms regularly found in Antarctic pack ice were grown over 20 d in closed bottles at high light (200 to 250 umol photons m-2 s-1) and at 0*C in order to investigate growth physiology and biomass production under conditions simulating the sea ice habitat during summer. Species tested were: Chaetoceros cf. neogracile, Fragilariopsiscylindrus, Thalassiosiraantarctica and Porosira pseudodenticulata i>. Initially, all species grew exponentially, but exponential growth ceased for P. pseudodenticulata and T.antarctica after 6 d, for F.cylindrus after 8 d, and for C. cf. neogracile after 10 d. Slight increases in cell number were observed for all species 2 d later. Peak biomass amounted to 140 ug chl a (850 umol particulate organic carbon, POC) l-1. At the same time, concentrations of dissolved inorganic carbon (DIC) were reduced by 1000 uM, oxygen concentrations increased to 1400 uM, and pH increased to 10.5. At this stage, a substantial decline in plasma-containing cells was recorded for F.cylindrus. C. cf. neogracile accounted for 80%, and C. cf. neogracile and F.cylindrus accounted for &GT95% of total carbon biomass. The carbon isotope composition of POC (expressed as delta13C) increased from -24 to -9 during the experiment. Model calculations showed that diffusive uptake of dissolved CO2 satisfied cellular carbon demand for all species except P. pseudodenticulata at CO2(aq) concentrations &GT0.5 uM, whereas direct HCO3- utilization was observed for C. cf. neogracile below this concentration. Our data confirm that intense photosynthetic carbon assimilation may lead to profound chemical changes in isolated interstitial brine solutions, with significant consequences for sea ice biota. We propose that the capacity to efficiently utilize ambient DIC, possibly mediated by virtue of favorable surface to volume ratios as well as active pathways of inorganic carbon acquisition, favors growth of small diatoms, and may be an important factor driving ice algal species succession during summer blooms. Since only 2 species continued to grow in fresh medium following experimental incubation (C. cf. neogracile and P. pseudodenticulata), differential tolerance to chemical variations may influence the seeding potential of ice algae following release into the open water. Antarctica . Sea ice microalgae . Carbon uptake . Growth . Dissolved inorganic carbon . pH . Oxygen Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 135. Publication date: May 17, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

On the application of the EXP-like approximation for the description of the site-site ion-molecular models

The site-site radial distribution functions for model ion-molecular systems within the framework of the exponential (EXP)-like approximation are presented and analysed. The ions and molecules are taken to be oppositely charged hard spheres and symmetrical polar hard diatomics or tetraatomics, respectively. The density-controlled ordering as well as the solvation and molten salt regions are discussed in terms of the site-site radial distribution functions. The characteristic features of the short-range order in these regions are determined by the interplay between the short-range and long-range ion-ion, ion-site and site-site interactions. The influence of the molecular shape and moleclar distribution of charge on the system short-range structure is shown. The reference hypernetted chain-like and the reference Percus-Yevick-Allnatt-like integral equations are proposed.

Effects of altered photic regimes on diel patterns of species-specific photosynthesis

Diel patterns of photosynthesis were measured for two polar diatoms (Coscinodiscus sp. and Porosira pseudodenticulata) collected in September 1985 from McMurdo Sound, Antarctica, and four temperate dinoflagellates (Gonyaulax hyalina, Gymnodinium splendens, Dinophysis caudata, and Glenodinium sp.) collected in July 1985 and January 1986 from the Southern California Bight, California, USA. For phytoplankton incubated under three combinations of photoperiod and irradiance, distinct diel patterns of light-saturated (Pmax) and light-limited (PL) photosynthesis were found for (i) different species isolated from the same environment, and (ii) polar diatoms and temperate dinoflagellates. The time of day when the maximum rate of Pmax occurred was influenced by both irradiance and daylength for the polar diatoms but not by daylength for three out of four temperate dinoflagellates. The range of values of the ratio of maximum to minimum rates of photosynthesis (Pmax:Pmin) was similar for polar diatoms and temperate dinoflagellates. The results of this study suggest that changes in irradiance or photoperiod could influence species-specific patterns of photosynthesis in nature. As a consequence, in light-limited environments differential reproductive success could result from these diel patterns, and ultimately be reflected in temporal and spatial differences in community structure.

Organic carbon in sediments underlying the Ross Ice Shelf

Percentages (mean = 0.36) and δ 13C values ( mean = −25.4‰ vs PDB ) for organic carbon in 13 samples in the top meter of sediments, of Miocene age, underlying the Ross Ice Shelf at Site J9 indicate organic carbon deposition during the Miocene much like that of Recent time, i.e. a mixture of organic carbon-rich polar diatom ooze with δ 13C signature of about −27‰ and older kerogen contained in indurated shale fragments with percent and δ 13C of about 0.1 and −22‰, respectively.

Physiology of sea ice diatoms. II. Dark survival of three polar diatoms

Three polar sea ice diatoms were exposed to 5 months of darkness at −2 °C to simulate polar winter conditions. Cells were tested monthly for the ability to initiate growth of a population. A critical percentage (~1–100%) of a nonaxenic population of each diatom remained viable after 5 months of dark incubation. Survival was generally enhanced by preconditioning cells with a simulated summer–winter transition (decreasing light and temperature, increasing salinity) or a simple light–dark transition; however, preconditioning was not essential to the survival of sea ice diatom cultures under winter conditions.

Physiology of sea ice diatoms. I. Response of three polar diatoms to a simulated summer-winter transition

Physiology of sea ice diatoms. I. Response of three polar diatoms to a simulated summer-winter transition

PHYSIOLOGY OF SEA ICE DIATOMS. I. RESPONSE OF THREE POLAR DIATOMS TO A SIMULATED SUMMER‐WINTER TRANSITION1

ABSTRACTThree axenic polar sea ice diatom cultures were subjected to a 30 day simulated summer‐winter transition in which light and temperature were decreased and salinity was increased to mimic seasonal changes previously reported for ice‐covered polar seas. The diatoms responded to these changes by a reduction in cellular metabolism as indicated by: 1) A decline in growth rate and photosynthetic rate; 2) a decrease in cellular ATP; and 3) the storage and subsequent utilization of endogenous carbon reserves. In addition, heterotrophic potential of the three clones increased by as much as 60‐fold. In some cases, the decrease in light intensity characteristic of the onset of polar winter was alone sufficient to trigger these physiological changes.

Bond dependence of dipole polarisabilities in HF and HCl molecules

Ab initio calculations, within a perturbation treatment of the coupled Hartree-Fock equations are reported for the static dipole polarisability components of polar diatomics. Their dependence on internuclear-separation values around the molecule equilibrium positions is also computed and discussed. The relevance of the present results for vibrationally inelastic collisions of slow electrons pointed out in its relation with previous empirical estimates of the polarisability first derivatives.

Selection and Focusing of Polar Diatomics in States of Positive Induced Electric Dipole Moment Using a Ten-Pole Field

Using a ten-pole electric field (with two-pole symmetry) it has been possible to select and focus the rotational states J, M = 0, 0; 1, ±1; and 2, ±2 for velocity-selected thermal molecular beams of CsF and RbCl. However, because of the nonideality of this focusing field, the enhancement in intensity of the separated states (focusing effect) over the thermal population is only about a factor of 2.

ENHANCED PHOTOSYNTHETIC ASSIMILATION RATIOS IN ANTARCTIC POLAR FRONT (CONVERGENCE) DIATOMS1

Diatom populations from the Antarctic Polar Front (convergence) in the Drake Passage area exhibited relatively high : chlorophyll a ratios at light saturation.The permanent water column instability and the adverse meteorological conditions observed in the central Drake Passage area seem to produce a light‐color stress on the physiology of convergence diatoms that are restricted to a blue‐green light environment during their life cycle.The enhanced photosynthesis: chlorophyll a ratios that were determined in experiments with Antarctic Polar Front diatoms when exposed to white (fluorescent) light sources, may be related to the short‐wavelength light background of these diatoms.

Sudden Approximation Applied to Rotational Excitation of Molecules by Atoms. II. Scattering of Polar Diatomics

The sudden approximation is applied to the computation of rotational transition probabilities and inelastic total cross sections for the scattering of polar and nonpolar diatomic molecules (rigid rotors) by atoms. The calculations are based upon an interaction potential which includes both short- and long-range anisotropies. At thermal energies the long-range attractive parts of the potential are of principal importance in determining the inelasticity, with a significant contribution arising from the quadrupole interaction term (varying as R−7 cos3Θ). The computations show the rapid onset of ``dominant-coupling'' behavior (randomization of transition probability among all close-coupled states) for impact parameters below about (S/π)½, where S is the total inelastic cross section.