bluuebunny/crossref_metadata_2025 huggingface dataset:
EncM, a versatile enterocin biosynthetic enzyme involved in Favorskii oxidative rearrangement, aldol condensation, and heterocycle-forming reactions
Authors: Xiang Longkuan , Kalaitzis John A. , Moore Bradley S.
Published: October 2004

The bacteriostatic natural product enterocin from the marine microbe “
Streptomyces maritimus
” has an unprecedented carbon skeleton that is derived from an aromatic polyketide biosynthetic pathway. Its caged tricyclic, nonaromatic core is derived from a linear poly-β-ketide precursor that formally undergoes a Favorskii-like oxidative rearrangement.
In vivo
characterization of the gene
encM
through mutagenesis and heterologous biosynthesis demonstrated that its protein product not only is solely responsible for the oxidative C—C rearrangement, but also facilitates two aldol condensations plus two heterocycle forming reactions. In total, at least five chiral centers and four rings are generated by this multifaceted flavoprotein. Heterologous expression of the enterocin biosynthesis genes
encABCDLMN
in
Streptomyces lividans
resulted in the formation of the rearranged metabolite desmethyl-5-deoxyenterocin and the shunt products wailupemycins D-G. Addition of the methyltransferase gene
encK
, which was previously proposed through mutagenesis to additionally assist EncM in the Favorskii rearrangement, shifted the production to the
O
-methyl derivative 5-deoxyenterocin. The
O
-methyltransferase EncK seems to be specific for the pyrone ring of enterocin, because bicyclic polyketides bearing pyrone rings are not methylated
in vivo
. Expression of
encM
with different combinations of homologous actinorhodin biosynthesis genes did not result in the production of oxidatively rearranged enterocin-actinorhodin hybrid compounds as anticipated, suggesting that wild-type EncM may be specific for its endogenous type II polyketide synthase or for benzoyl-primed polyketide precursors.
Epistatic interaction between
Arabidopsis FRI
and
FLC
flowering time genes generates a latitudinal cline in a life history trait
Authors: Caicedo Ana L. , Stinchcombe John R. , Olsen Kenneth M. , Schmitt Johanna , Purugganan Michael D.
Published: October 2004

Epistatic gene interactions are believed to be a major factor in the genetic architecture of evolutionary diversification. In
Arabidopsis thaliana
, the
FRI
and
FLC
genes mechanistically interact to control flowering time, and here we show that this epistatic interaction also contributes to a latitudinal cline in this life history trait within the species. Two major
FLC
haplogroups (

FLC
A

and

FLC
B

) are associated with flowering time variation in
A. thaliana
in field conditions, but only in the presence of putatively functional
FRI
alleles. Significant differences in latitudinal distribution of
FLC
haplogroups in Eurasia and North Africa also depend on the
FRI
genotype. There is significant linkage disequilibrium between
FRI
and
FLC
despite their location on separate chromosomes. Although no nonsynonymous polymorphisms differentiate

FLC
A

and

FLC
B

, vernalization induces the expression of an alternatively spliced
FLC
transcript that encodes a variant protein with a radical amino acid replacement associated with the two
FLC
haplogroups. Numerous polymorphisms differentiating the
FLC
haplogroups also occur in intronic regions implicated in the regulation of
FLC
expression. The features of the regulatory gene interaction between
FRI
and
FLC
in contributing to the latitudinal cline in
A. thaliana
flowering time are consistent with the maintenance of this interaction by epistatic selection. These results suggest that developmental genetic pathways and networks provide the molecular basis for epistasis, contributing to ecologically important phenotypic variation in natural populations and to the process of evolutionary diversification.
Induction in myeloid leukemic cells of genes that are expressed in different normal tissues
Authors: Lotem Joseph , Benjamin Hila , Netanely Dvir , Domany Eytan , Sachs Leo
Published: October 2004

Using DNA microarray and cluster analysis of expressed genes in a cloned line (M1-t-p53) of myeloid leukemic cells, we have analyzed the expression of genes that are preferentially expressed in different normal tissues. Clustering of 547 highly expressed genes in these leukemic cells showed 38 genes preferentially expressed in normal hematopoietic tissues and 122 other genes preferentially expressed in different normal nonhematopoietic tissues, including neuronal tissues, muscle, liver, and testis. We have also analyzed the genes whose expression in the leukemic cells changed after activation of WT p53 and treatment with the cytokine IL-6 or the calcium mobilizer thapsigargin. Of 620 such genes in the leukemic cells that were differentially expressed in normal tissues, clustering showed 80 genes that were preferentially expressed in hematopoietic tissues and 132 genes in different normal nonhematopietic tissues that also included neuronal tissues, muscle, liver, and testis. Activation of p53 and treatment with IL-6 or thapsigargin induced different changes in the genes preferentially expressed in these normal tissues. These myeloid leukemic cells thus express genes that are expressed in normal nonhematopoietic tissues, and various treatments can reprogram these cells to induce other such nonhematopoietic genes. The results indicate that these leukemic cells share with normal hematopoietic stem cells the plasticity of differentiation to different cell types. It is suggested that this reprogramming to induce in malignant cells genes that are expressed in different normal tissues may be of clinical value in therapy.
A systematic method for identifying small-molecule modulators of protein–protein interactions
Authors: Horswill Alexander R. , Savinov Sergey N. , Benkovic Stephen J.
Published: October 2004

Discovering small-molecule modulators of protein–protein interactions is a challenging task because of both the generally noncontiguous, large protein surfaces that form these interfaces and the shortage of high-throughput approaches capable of identifying such rare inhibitors. We describe here a robust and flexible methodology that couples disruption of protein–protein complexes to host cell survival. The feasibility of this approach was demonstrated through monitoring a small-molecule-mediated protein–protein association (FKBP12–rapamycin–FRAP) and two cases of dissociation (homodimeric HIV-1 protease and heterodimeric ribonucleotide reductase). For ribonucleotide reductase, we identified cyclic peptide inhibitors from genetically encoded libraries that dissociated the enzyme subunits. A solid-phase synthetic strategy and peptide ELISAs were developed to characterize these inhibitors, resulting in the discovery of cyclic peptides that operate in an unprecedented manner, thus highlighting the strengths of a functional approach. The ability of this method to process large libraries, coupled with the benefits of a genetic selection, allowed us to identify rare, uniquely active small-molecule modulators of protein–protein interactions at a frequency of less than one in 10 million.
Expression of antiapoptotic genes
bcl-xL
and
ced-9
in tomato enhances tolerance to viral-induced necrosis and abiotic stress
Authors: Xu Ping , Rogers Stephanie J. , Roossinck Marilyn J.
Published: October 2004

D satellite RNA (satRNA) is a strain of cucumber mosaic virus (CMV) satRNA that induces an epidemic lethal disease in tomato. No natural resistance or tolerance has ever been found. Previously, we demonstrated the involvement of programmed cell death in disease development. Here, transgenic tomato plants expressing animal antiapoptotic genes
bcl
-
xL
and
ced
-
9
were generated through agrobacterium-mediated transformation. High expression of
bcl
-
xL
or
ced
-
9
affected plant growth and seed development. Inoculation of seedlings with CMV/D satRNA at T
1
and T
2
generations resulted in delayed cell-death symptoms or absence of symptoms. The degree of symptom suppression was correlated with increasing expression levels of the transgenes. Survival rates were compared among inoculated transgenic lines expressing
bcl
-
xL, ced
-
9
, and
bcl
-
xL
(G138A), a loss-of-function mutant of
bcl
-
xL
. More than 80% of the
bcl
-
xL
and
ced
-
9
T
1
transgenic lines showed higher survival rates than the average for
bcl
-
xL
(G138A) transgenic lines. Total RNA extracted from surviving plants contained D satRNA, indicating systemic accumulation of D satRNA. Thus, expression of
bcl
-
xL
and
ced
-
9
improved tolerance to, rather than resistance to, CMV/D satRNA infection. In addition, expression of
bcl
-
xL
and
ced
-
9
specifically abrogated the formation of necrotic lesions, but not other symptoms, in tomato leaves during chilling at 4°C. At 7°C, temperature-induced leaf senescence was dramatically delayed in
bcl
-
xL
and
ced
-
9
transgenic plants, and high levels of anthocyanins accumulated, possibly limiting oxidative stress. Hence, expression of these animal antiapoptotic genes improved plant survival under abiotic or biotic stress.
The phytochrome-interacting transcription factor, PIF3, acts early, selectively, and positively in light-induced chloroplast development
Authors: Monte Elena , Tepperman James M. , Al-Sady Bassem , Kaczorowski Karen A. , Alonso Jose M. , Ecker Joseph R. , Li Xin , Zhang Yuelin , Quail Peter H.
Published: October 2004

The phytochrome (phy) family of sensory photoreceptors transduce informational light signals to selected nuclear genes, inducing plant growth and developmental responses appropriate to the environment. Existing data suggest that one signaling pathway by which this occurs involves direct, intranuclear interaction of the photoactivated phy molecule with PIF3, a basic helix-loop-helix transcription factor. Here, we provide evidence from recently identified
pif3
mutant alleles that PIF3 is necessary for early chloroplast greening and rapid phy-induced expression of nuclear genes encoding chloroplast components upon first exposure of seedlings to light. Therefore, these data indicate that PIF3 functions to transduce phy signals to genes involved in a critical facet of the early seedling deetiolation process, the generation of a functional photosynthetic apparatus. When transgenically expressed GUS:PIF3 fusion protein constructs were used, we found that PIF3 protein levels are rapidly and reversibly modulated by the photoreceptor over diurnal cycles in
Arabidopsis
seedlings. The PIF3 protein declines rapidly to a basal steady-state level upon initial light exposure, but reaccumulates to preirradiation levels in darkness during the subsequent night period. These data suggest that PIF3 may function in early phy signaling at the dark-to-light transition, not only during initial seedling deetiolation, but daily at dawn under diurnal light-dark cycles.
Important Roles for E Protein Binding Sites within the Immunoglobulin κ Chain Intronic Enhancer in Activating Vκ Jκ
Rearrangement
Authors: Inlay Matthew A. , Tian Hua , Lin Tongxiang , Xu Yang
Published: October 2004

The immunoglobulin κ light chain intronic enhancer (iEκ) activates κ rearrangement and is required to maintain the earlier or more efficient rearrangement of κ versus lambda (λ). To understand the mechanism of how iEκ regulates κ rearrangement, we employed homologous recombination to mutate individual functional motifs within iEκ in the endogenous κ locus, including the NF-κB binding site (κB), as well as κE1, κE2, and κE3 E boxes. Analysis of the impacts of these mutations revealed that κE2 and to a lesser extent κE1, but not κE3, were important for activating κ rearrangement. Surprisingly, mutation of the κB site had no apparent effect on κ rearrangement. Comparable to the deletion of the entire iEκ, simultaneous mutation of κE1 and κE2 reduces the efficiency of κ rearrangement much more dramatically than either κE1 or κE2 mutation alone. Because E2A family proteins are the only known factors that bind to these E boxes, these findings provide unambiguous evidence that E2A is a key regulator of κ rearrangement.
Well-approximable angles and mixing for flows on 𝕋² with nonsingular fixed points
Authors: Kochergin A.
Published: October 2004

We consider special flows over circle rotations with an asymmetric function having logarithmic singularities. If some expressions containing singularity coefficients are different from any negative integer, then there exists a class of well-approximable angles of rotation such that the special flow over the rotation of this class is mixing.
The role of immigrants in the assembly of the South American rainforest tree flora
Authors: Pennington R. Toby , Dick Christopher W.
Published: October 2004

The Amazon lowland rainforest flora is conventionally viewed as comprising lineages that evolved in biogeographic isolation after the split of west Gondwana (ca. 100 Myr ago). Recent molecular phylogenies, however, identify immigrant lineages that arrived in South America during its period of oceanic isolation (ca. 100–3 Myr ago). Long–distance sweepstakes dispersal across oceans played an important and possibly predominant role. Stepping–stone migration from Africa and North America through hypothesized Late Cretaceous and Tertiary island chains may have facilitated immigration. An analysis of inventory plot data suggests that immigrant lineages compriseca. 20% of both the species and individuals of an Amazon tree community in Ecuador. This is more than an order of magnitude higher than previous estimates. We also present data on the community–level similarity between South American and palaeotropical rainforests, and suggest that most taxonomic similarity derives from trans–oceanic dispersal, rather than a shared Gondwanan history.
SEASONAL FLUCTUATIONS IN TISSUE NITROGEN, PHOSPHORUS, AND N:P FOR FIVE MACROALGAL SPECIES COMMON TO THE PACIFIC NORTHWEST COAST1
Authors: Wheeler Patricia A. , Björnsäter Bo R.
Published: October 2004

Variations in tissue nitrogen (N) and phosphorus (P) were examined over a complete seasonal cycle for five macroalgae common in Oregon coastal water. Tissue N ranged from 2.0 to 5.5% dry weight (dry wt) in leafy macroalgae (Enteromorpha intestinalis (Linnaeus) Link. Ulva fenestrata Postels et Ruprecht, and Porphyra sp.) and from 0.9 to 2.6% drt wt in branched macroalgae (Codium fragile (Suringar) Hariot and Pelvetiopsis limitata Setchell). Tissue P ranged from 0.32 to 0.86% dry wt in leafy macroalgae and from 0.27 to 0.50% dry wt in branched macroalgae, Ulva fenestrata, C. fragile, and P. limitata appeared to be N limited during part of the year based on tissue N levels. Variations in N:P showed a more distinct seasonal pattern than either tissue N and tissue P. All macroalgae examined appeared to be N limited at least part of the year based on N:P composition, and P limitation occurred for all macroalgae examined except C. fragile. Our results suggest that tissue N:P ratio for macroalgae may be a good index for evaluating in situ nutrient status.
PHOTOSYNTHETIC RESPONSE OF NATURAL ASSEMBLAGES OF MARINE BENTHIC MICROALGAE TO SHORT‐AND LONG‐TERM VARIATIONS OF INCIDENT IRRADIANCE IN BAFFIN BAY, TEXAS1
Authors: Blanchard Gérard F. , Montagna Paul A.
Published: October 2004

This study was designed to understand the high variability characterizing primary production rates of microphytobenthos. The photosynthetic efficiency (αB) and photosynthetic capacity (PBmax) of the microphytobenthos were measured at different times of the day on two different dates (8 May and 7 July 1990). In July, unusually low light conditions were caused by the development of a brown tide (chrysophytes). Both light‐limited and light‐saturated photosynthesis changed at hourly and monthly scales. There was a linear relationship between αB and PBmax, suggesting a common response to environmental factors [αB= 0.0075(±0.00063)·PBmax+ 0.00097(±0.0071), R2= 0.94]. Incident irradiance at the sediment‐water interface was the primary physical factor that explained variability of both αB (84%) and PBmax (92%). Temperature had a negative but minor effect that explained an extra 8% and 2% of the variance, respectively. There was no diel rhythm of αB and PBmax and incident irradiance was regulated by wind‐induced currents. Therefore, microphytobenthos photosynthesis seemed to be primarily controlled by wind events in Baffin Bay.
SIMAZINE‐INDUCED INHIBITION IN PHOTOACCLIMATED POPULATIONS OF ANABAENA CIRCINALIS (CYANOPHYTA)1
Authors: Millie David F. , Hersh C. Mark , Dionigi Christopher P.
Published: October 2004

The effects of the triazine herbicide, simazine, on photosynthetic oxygen evolution and growth rate in photoacclimated populations of Anabaena circinalis Rabenhorst were investigated. Chemostat populations were acclimated to photon flux densities (PFDs) of 50, 130, and 230 μmol·m−2·s−1 of photosynthetic active radiation (PAR), Decreases in chlorophyll a (Chl a). c‐phycocyanin (CPC), and total carotenoid (TCar) contents and CPC: Chl a and CPC: TCar ratios of populations coincided with increasing PFD, Polynomial regression models that characterize inhibition of photosynthesis for populations acclimated to 50 and 130 μmol photons·m−2·s−1 PAR were distinct from the model for populations acclimated to 230 μmol photons·m−2·s−1 PAR. Simazine concentrations that, depressed oxygen evolution 50% compared to controls decreased with increasing PFD. Increases and decreases in both biomass and growth rate coincided with increasing PFD and simazine concentration, respectively. Simazine concentrations that depressed growth rate 50% compared to controls increased with decreasing PFD. The differences in photosynthetic and growth inhibition among photoacclimated populations indicate that sensitivity to photosystem II inhibitors is affected by alterations in pigment contents.
PHOTOSYNTHETIC PIGMENTS OF PSEUDOSCOURFIELDIA MARINA AND SELECT GREEN FLAGELLATES AND COCCOID ULTRAPHYTOPLANKTON: IMPLICATIONS FOR THE SYSTEMATICS OF THE MICROMONADOPHYCEAE (CHLOROPHYTA)1
Authors: Fawley Marvin W.
Published: October 2004

Photosynthetic pigments of the green flagellate Pseudoscourfieldia marina (Throndsen) Manton (Micromonadophyceae) are similar to those of the coccoid Pycnococcus provasolii Guillard; prasinoxanthin is the predominant carotenoid. Other organisms that possess prasinoxanthin also possess additional pigments not found in either P. marina or P. provasolii. Uriolide, a xanthophyll previously described from the coccoid done URI 266G, was also found in Mantoniella squamata (Manton et Parke) Desikachary, Micromonas pusilla Manton et Parke and Mamiella gilva (Parks et Rayns) Moestrup, all flagellate members of the Mamiellales, and the coccoid clone IV E5G. Other unidentified carotenoids were also present in M. squamata, M. pusilla, and M. gilva. These results suggest that P. marina and the coccoid organisms URI 266G and IV E5G may be related to the Mamiellales, and that P. provasolii may be more closely related to P. marina than to M. squamata, M. pusilla, and M. gilva.
FATTY ACID CONTENT AND CHEMICAL COMPOSITION OF FRESHWATER MICROALGAE1
Authors: Ahlgren Gunnel , Gustafsson Inga‐Britt , Boberg Merike
Published: October 2004

Fatty acid (FA), total lipid, protein, amino acid, carbon, nitrogen, and phosphorus content was analyzed in 24 samples of freshwater microalgae. The samples originated from batch, continuous, or mass cultures in various growth phases and from net samples from lakewater. FA were analyzed quantitatively by using an internal standard in a GLC system and expressed as mg·g−1 dry weight (DW). The FA of one group of blue‐greens (e.g. Oscillatoria and Microcystis) were similar to those of the greens with higher amounts of 18C acids of the ω3 type compared to the ω6 type, whereas the other group (e.g. Anabaena and Spirulina) contained mostly ω6 acids. The flagellates, a taxonomically diverse group, were characterized by high amounts of long‐chained (20–22 C) polyunsaturated FA (PUFA), particularly of the ω3 type. The ω3/ω6 ratio appears to be highest in algae in the exponential growth phase. The increased lipid content in stressed algae was mostly due to increased saturated fatty acids and ω6 acids, whereas the valuable ω3 acids were unchanged or even decreased.

Amino acid composition (% of total amino acids) did not vary much betaken species, but when analyzed quantitatively (mg‐g−1 DW), varied considerably between species and within species in different growth phases. The nitrogen and phosphorus contents were variable in all three algal groups. The relationship between PUFA and phosphorus content differed among the algal groups. The data suggest that PUFA in the phospholipids consist mostly ω3 acids.
AMPHIESMAL ULTRASTRUCTURE OF DINOFLAGELLATES: A REEVALUATION OF PELLICLE FORMATION1
Authors: Höhfeld Ingo , Melkonian Michael
Published: October 2004

The ultrastructure of the amphiesma during pellicle formation was investigated in two species of Dinophyceae,Amphidinium rhynchocephalumAnissimowa andHeterocapsa niei(Loeblich) Morrill & Loeblich using thin sections. In both species the amphiesma consists of an outermost membrane (i.e. the plasma membrane) underlain by amphiesmal vesicles. InA. rhynchocephalumthe latter appear empty whereas each amphiesmal vesicle inH. nieicontains a thecal plate and a thin, amorphous layer (dark‐staining layer) located between, the thecal plate and the inner amphiesmal vesicle membrane. When cells of both taxa are carefully fixed, amphiesmal vesicles are always separate entities (i.e. the sutures are undisrupted). During ecdysis the following amphiesmal components are shed: the plasma membrane, the outer amphiesmal vesicle membrane, and inH. nieithe thecal plates. The inner membranes of the amphiesmal vesicles then fuse with each other and form a continuous membrane (termed pellicle membrane) that remains tightly oppressed to an underlying amorphous layer (pellicular layer). InA. rhynchocephalumthe pellicular layer is already present in vegetative non‐ecdysed cells, whereas inH. nieiit forms during ecdysis beneath the pellicle membrane. During ecdysis inH. niei, material from the dark‐staining layer precipitates on the outer surface of the pellicle membrane, where it forms a characteristic honeycomb pattern. The new observations are incorporated into a revised model of pellicle formation in dinoflagellates and contrasted with earlier proposals.
A MOLECULAR AND MORPHOLOGICAL ANALYSIS OF THE GYMNOGONGRUS DEVONIENSIS (RHODOPHYTA) COMPLEX IN THE NORTH ATLANTIC1
Authors: Maggs Christine A. , Douglas Susan E. , Fenety John , Bird Carolyn J.
Published: October 2004

The Gymnogongrus devoniensis (Greville) Schotter complex in the North Atlantic Ocean was elucidated by comparative molecular, morphological, and culture studies. Restriction fragment length patterns and hybridization data on organellar DNA revealed two distinct taxa in samples from Europe and eastern Canada. Nucleotide sequences for the intergenic spacer between the large and small subunit genes of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), and the adjoining regions of both genes, differed by 12.5–13.4% between the two taxa. One of the taxa, which included material from the type locality of G. devoniensis at Torbay, Devon, England, was taken to represent authentic G. devoniensis. Within this taxon, samples from Ireland, England, northern France, northern Spain, and southern Portugal showed great morphological variation, particularly in habit, but their Rubisco spacer sequences were identical or differed by only a single nucleotide. Constant morphological features included the development, from a single auxiliary cell, of the spherical cystocarp with a thick mucilage sheath that appears to be typical of Gymnogongrus species with internal cystocarps. Two life‐history types were found. Northern isolates underwent a direct‐type life history, recycling apomictic females by carpospores, whereas the Portuguese isolate followed a heteromorphic life history in which carpospores gave rise to a crustose tetrasporophyte.

The second group of samples, from Nova Scotia and Northern Ireland, provisionally referred to as Gymnogongrus sp., showed little morphological variation. The life history in both areas consists of apomictically reproducing diploid female gametophytes and diploid crustose bisporophytes and tetrasporophytes. Rubisco spacer sequences of the samples were identical, and the plasmid previously described in the Nova Scotian samples was also present in the Northern Ireland population. This species is widely distributed in the western Atlantic, from Newfoundland to Massachusetts. In Europe, gametophytes are known only at one site, but crusts are distributed from Denmark, Scotland (and probably Norway) to France. It is very likely that this species was introduced from one side of the North Atlantic to the other by shipping during the early nineteenth century. Several morphological features are unusual within the genus but are shared with G. leptophyllus J. Agardh from the eastern Pacific Ocean, and further work is necessary to determine whether Gymnogongrus sp. and G. leptophyllus are conspecific.
DISTRIBUTION AND SYSTEMATICS OFBATRACHOSPERMUM(BATRACHOSPERMALES, RHODOPHYTA) IN NORTH AMERICA. 1. SECTIONCONTORTA1
Authors: Sheath Robert G. , Vis Morgan L. , Cole Kathleen M.
Published: October 2004

Multivariate morphometrics and image analysis were used to determine the number of well‐distinguished infra‐generic taxa in the sectionContortaof the freshwater red algal genusBatrachospermumin North America. Five groupings were distinguished from 29 populations examined from New Mexico to Costa Rica. These entities were statistically related to 12 type specimens reported from or similar to North American populations. The following taxa were recognized:B. ambiguumMontagne (syn.B. bicudoiNecchi andB. basilareFlint et Skuja)B. globosporumIsraelson (syn.B. cipoenseKumano et Necchi andB. jolyiNecchi),B. intortumJao,B. louisianaeSkuja andB. procarpumSkuja var.americanumvar. nov. The new variety differs from the nominate variety in having significantly larger whorls and smaller carpogonia.Batrachospermum ambiguum, B. louisianae, andB. procarpumvar.americanumoccur in low ion waters (10–187 μS·cm−1), whereasB. intortumandB. globosporumare found in high ion waters (260–1760 μS·cm−1). Detailed descriptions and a key to the five taxa are given.
VALVE AND BAND MORPHOLOGY OF SOME FRESHWATER DIATOMS. V. VARIATIONS IN THE CINGULUM OF PLEUROSIRA LAEVIS (BACILLARIOPHYCEAE)1
Authors: Johnson Lisa M. , Rosowski James R.
Published: October 2004

Frustule ultrastructure of Pleurosira laevis (Ehr.) Compère from an epilithon sample collected from the Missouri River was examined using scanning electron microscopy. Valve characteristics were similar to those found by other authors, whereas certain features of the cingulum were new. The cingulum consists primarily of three girdle bands (a valvocopula and two pleurae). The valvocopula can be complete but open at one end, below the ocellus. However, it is more commonly bisegmented, with two narrow and severable connecting points located in the pars interior region underlapping the mantle. The first and second pleurae are either biligulate or uniligulate and closed, but the former, when uniligulate, may be an open band as well. The second pleura is narrower and more delicate than the first. When a natural cleavage of a band subtends a ligula, the band is prone to break along the cleavage during specimen preparation, thus making difficult the assessment of band form and cingulum arrangement. Regions of band overlap have smooth poreless edges, whereas those of underlap are rimmed with either fine fimbriae or, occasionally, a coarser comblike fringe. The variability of the bands results in a cingulum that can be assembled in at least four different arrangements.
RELATIONSHIP BETWEEN PHOTOSYNTHETIC OXYGEN CYCLING AND CARBON ASSIMILATION IN SYNECHOCOCCUS WH7803 (CYANOPHYTA)1
Authors: Kana Todd M.
Published: October 2004

Mass spectrometric analysis of oxygen uptake and evolution in the light by marine Synechococcus WH7803 indicated that the respiration rate was near zero at low irradiance levels but increased significantly at high irradiances. The light intensity (Ir) at which oxygen uptake began to increase with increasing light intensity depended on the growth irradiance of the culture. In each case, Ir coincided with the minimum light intensity for saturation of carbon assimilation (Ik). At irradiances >Ir, net oxygen evolution rates paralleled carbon assimilation rates. Oxygen uptake at high light intensities was inhibited by DCMU, indicating that oxygen uptake was due to Mehler reaction activity. The onset of Mehler activity at Ik supports the idea that oxygen becomes an alternative sink for electrons from photosystem I when NADPH turnover is limited by the capacity of the dark reactions to utilize reductant.
ULTRASTRUCTURE AND IMMUNOLOCALIZATION OF PHYCOBILIPROTEINS AND RIBULOSE 1,5‐BISPHOSPHATE CARBOXYLASE/OXYGENASE IN THE MARINE CYANOBACTERIUM TRICHODESMIUM THIEBAUTII1
Authors: Siddiqui Pirzada J. A. , Carpenter Edward J. , Bergman Birgitta
Published: October 2004

Trichodesmium thiebautii Gomont, a marine planktonic diazotrophic cyanobacterium, has an unusual subcellular arrangement. To identify subcellular structures related to photosynthesis, antibodies against phycoerythrin, phycocyanin, and ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco) were used together with an immuno‐gold labeling technique and electron microscopy. Thylakoid membranes, identified by transmission electron microscopy and phycobiliprotein labeling, were arranged as a loose network throughout all cells. Rubisco showed a particularly intense localization in medium electron‐dense polyhedral bodies, therefore identified as carboxysomes. The average density of the carboxysomal Rubisco label was about five times higher than that in the cytoplasm. The carboxysomes (4–11 per cell section) were scattered throughout the cytoplasm. These data, together with those obtained from double immunolabeling experiments using nitrogenase (Fe‐protein) and Rubisco antibodies, revealed that Trichodesmium contains both N2‐ and CO2‐fixing proteins within the same cell. This is in contrast to the previous concept of a spatial segregation of the two processes in Trichodesmium and demonstrate that nitrogenase‐containing cells are not comparable to heterocysts in this context.
POLYCLONAL ANTIBODIES AGAINST IRON‐SUPEROXIDE DISMUTASE FROM ESCHERICHIA COLI B CROSS‐REACT WITH SUPEROXIDE DISMUTASES FROM SYMBIODINIUM MICROADRIATICUM (DINOPHYCEAE)1
Authors: Matta Jaime L. , Govind Nadathur S. , Trench Robert K.
Published: October 2004

Assays for superoxide dismutases (SODs) were performed using cell‐free extracts of the symbiotic dinoflagellate Symbiodinium microadriaticum Freudenthal (emend Trench and Blank) after separation in undenatured polyacrylamide gels. Using appropriate inhibitors (KCN and H2O2) we detected the presence of Cu/Zn‐, Mn‐, and Fe‐SODs. In immunoblot assays, polyclonal antibodies against Fe‐SOD from Escherichia coli B cross‐reacted with two major polypeptides in the water‐soluble fraction and one polypeptide in the Triton X‐100‐solubilized pellet fraction. The polypeptide common to both fractions, with a relative molecular mass of 43.5 kDa, was identified as Mn‐SOD. In S. microadriaticum, FeSOD, found only in the water‐soluble fraction, appears to be monomeric, with a relative molecular mass of 49.5 kDa.
DNA NUCLEOSIDE COMPOSITION AND METHYLATION IN SEVERAL SPECIES OF MICROALGAE1
Authors: Jarvis Eric E. , Dunahay Terri G. , Brown Lewis M.
Published: October 2004

Total DNA was isolated from 10 species of microalgae, including representatives of the Chlorophyceae (Chlorella ellipsoidea, Chlamydomonas reinhardtii, and Monoraphidium minutum), Bacillariophyceae (Cyclotella cryptica, Navicula saprophila, Nitzschia pusilla, and Phaeodactylum tricornutum), Charophyceae (Stichococcus sp.), Dinophyceae (Crypthecodinium cohnii), and Prasinophyceae (Tetraselmis suecica). Control samples of Escherichia coli and calf thymus DNA were also analyzed. The nucleoside base composition of each DNA sample was determined by reversed‐phase high performance liquid chromatography. All samples contained 5‐methyldeoxycytidine, although at widely varying levels. In M. minutum, about one‐third of the cytidine residues were methylated. Restriction analysis supported this high degree of methylation in M. minutum and suggested that methylation is biased toward 5′‐CG dinucleotides. The guanosine + cytosine (GC) contents of the green algae were, with the exception of Stichococcus sp., consistently higher than those of the diatoms. Monoraphidium minutum exhibited an extremely high GC content of 71%. Such a value is rare among eukaryotic organisms and might indicate an unusual codon usage. This work is important for developing strategies for transformation and gene cloning in these algae.
CONCORDANCE OF MOLECULAR AND ULTRASTRUCTURAL DATA IN THE STUDY OF ZOOSPORIC CHLOROCOCCALEAN GREEN ALGAE1
Authors: Lewis Louise A. , Wilcox Lee W. , Fuerst Paul A. , Floyd Gary L.
Published: October 2004

Alternative evolutionary hypotheses generated from features of vegetative cell morphology and motile cell ultra‐structure were investigated using a molecular data set. Complete nuclear‐encoded small subunit (18S) ribosomal RNA (rRNA) gene sequences were determined for six species (three each) of the chlorococcalean green algae “Neo chloris” andCharacium. Based on motile cell ultra‐structure, it was previously shown that both genera could be separated into three distinct groups possibly representing three separate orders and two classes of green algae. 18S rRNA gene sequences were also obtained for three additional taxa,Dunaliella parvaLerche,Pediastrum duplexMeyen, andFriedmannia israelensisChantanachat and Bold. These organisms were selected because each, in turn, is a representative of one of the three ultrastructural groups into which theNeochlorisandCharaciumspecies are separable. Phylogenetic analyses utilizing the molecular data fully support the ultrastructural findings, suggesting that the similar vegetative cell morphologies observed in these organisms have resulted from convergence.
ASSESSING THE RELATIONSHIPS OF AUTOSPORIC AND ZOOSPORIC CHLOROCOCCALEAN GREEN ALGAE WITH 18S rDNA SEQUENCE DATA1
Authors: Wilcox Lee W. , Lewis Louise A. , Fuerst Paul A. , Floyd Gary L.
Published: October 2004

We examined the relationships of autosporic and zoosporic taxa in the Chlorococcales by analyzing available complete nuclear‐encoded small‐subunit (18S) rRNA gene sequences along with two new sequences fromHydrodictyon reticulatum(L.) Lagerh. andNeochloris vigenisArchibald. Some autosporic taxa grouped with the coenobial hydrodictyacean algae and related unicellular organisms having directly opposed basal bodies. These includeScenedesmus obliquus(Turp.) Kütz. andChlorella fuscavar. vacuolata Shihira et Krauss. Other autosporic organisms, includingChlorella kessleriFott et Novakova,C. minutissimaFott et Novakova,C. pro‐tothecoidesKrug.,C. vulgarisBeij.,Nanochlorum eucaryotumWilhelm, Eisenbeis, Wild, et Zahn, andPrototheca wickerhamiiSoneda et Tubaki, form a separate group. Of the zoosporic taxa examined, this group would appear to have the greatest affinity to organisms having a counterclockwise displacement of basal bodies, the Pleurastrophyceae. Beyond the fact thatAnkistrodesmus stipitatus(=A. falcatusvar.stipitatus(Chodat) Lemm.) does not group with the latter organisms, its position remains in doubt. None of the autosporic taxa appear to be closely related to chlorophycean organisms possessing a clockwise basal body displacement.
AXENIC CULTURES OF ACETABULARIA (CHLOROPHYTA): A DECONTAMINATION PROTOCOL WITH POTENTIAL APPLICATION TO OTHER ALGAE1
Authors: Hunt Brenda E. , Mandoli Dina F.
Published: October 2004

We developed an easy, reliable decontamination protocol for caps of Acetabularia acetabulum (L.) Silva; with minimal labor hundreds of caps can be decontaminated. In addition, cysts isolated from these caps do not exhibit dormancy and can be used immediately to establish large populations of axenic cell cultures. This method consists of three successive incubations: 1) proteinase K/sodium dodecyl sulfate/1,3‐bis[tris(hydroxymethyl)‐methylamino]propane for 1 h, 2) mild silver protein for 5 min, and 3) an antibiotic solution (neomycin, chloramphenicol, nystatin, ampicillin, streptomycin)for 3 days. This protocol eliminates bacterial, algal, fungal, and yeast contaminants. It is useful for decontaminating caps from lab cultures and caps collected from the wild and may also be effective in decontaminating the reproductive structures of other algae. Cyst dormancy was reduced from 15 weeks to less than 1 week, which represents a 40% reduction of the life cycle of A. acetabulum. We routinely obtained 90‐100% gamete release from cysts 3‐14 days after they were made axenic. The component of our culturing methods that allows gamete release without a “dormant” period is unknown.
PHYSIOLOGICAL INDICATORS OF NUTRIENT DEFICIENCY IN CLADOPHORA (CHLOROPHYTA) IN THE CLARK FORK OF THE COLUMBIA RIVER, MONTANA1
Authors: Lohman Kirk , Priscu John C.
Published: October 2004

Cellular nutrient concentrations and nutrient uptake rates of Cladophora glomerata (L.) Kuetzing were determined during summer and fall in 1989–1990 at a site on the upper Clark Fork of the Columbia River, Montana. Both physiological tests indicated that Cladophora growth is likely to be limited by nitrogen during late summer‐early fall. Maximum uptake rates of ammonia‐N and nitrate‐N were 5935–6991 and 507–984 μg · g DW−1· h−1, respectively, during July–October when dissolved inorganic nitrogen (DIN) concentrations in the river were less than 10 μg · L−1. During November‐December, when DIN was 72–376 μg · L−1, maximum ammonia‐N uptake was 1137–1633 μg · g DW−1· h−1 and maximum nitrate‐N uptake was 0–196 μg · g DW−1· h−1. Cellular nitrogen during summer–early fall was 0.78–1.80% of Cladophora dry weight, frequently at or below 1.1%, a level suggested as a critical minimum N concentration for maximum growth. In contrast, cellular P was 0.18–0.36% of dry weight, 3–6 times the suggested critical P concentration of 0.06%. Molar ratios of cellular N:P (< 16:1) and DIN: SRP (< 4:1) during late summer‐early fall also indicated potential N limitation. Cellular N and P from Cladophora collected from a second site influenced by a municipal wastewater discharge in 1990 displayed similar seasonal trends. At both sites, seasonal fluctuations in DIN were closely tracked by changes in cellular N, Cellular P, however, increased through the growing season despite declining levels of SRP in the river.
OCCURRENCE OF OCTADECAPENTAENOIC ACID IN LIPIDS OF A COLD STENOTHERMIC ALGA, PRYMNESIOPHYTE STRAIN B1
Authors: Okuyama Hidetoshi , Morita Naoki , Kogame Kazuhiro
Published: October 2004

The fatty acid composition of the prymnesiophyte strain B, a cold stenothermic microalga, was examined. The major fatty acids derived from the total lipids in this strain were myristic (14:0), palmitic (16:0), oleic (18:1ω9), linoleic (18:2ω6), octadecatetraenoic (18:4ω3), octadecapentaenoic (18:5ω3), and docosahexaenoic (22:6ω3) acids. Octadecapentaenoic acid (18:5ω3) was an unusual component and was characterized by mass spectrometry, infrared absorption spectrometry, and proton nuclear magnetic resonance spectrometry. Saturated fatty acids (14:0 and 16:0) and 18:5ω3 were distributed at significant levels in the major classes of galactolipids (monogalacto‐syldiacylglycerol, digalactosyldiacylglycerol, and sulfoqui‐novosyldiacylglycerol), phospholipids (phosphatidylcholine, phosphatidylglycerol, and phosphatidylethanolamine), and neutral lipids with the exception that phosphatidylethanolamine contained only trace amounts of 14:0. By contrast, 22:6ω3 was distributed in phospholipids and neutral lipids.

A decrease in growth temperature from 5°C to 2°C was accompanied by a significant increase in levels of 18: 5ω3 and 18:4ω3 with a concomitant decrease in the level of saturated fatty acids, whereas the level of 22:6ω3 was scarcely changed. These results suggest that, in prymnesiophyte strain B, eighteen‐carbon polyunsaturated fatty acids with more than three double bonds, 18:5ω3 in particular, serve as modulators of membrane fluidity. The potential role of 18:5ω3 as a specific marker for prym‐nesiophytes is also discussed.
EFFECTS OF VARIATION IN TEMPERATURE. II. ON THE FATTY ACID COMPOSITION OF EIGHT SPECIES OF MARINE PHYTOPLANKTON1
Authors: Thompson Peter A. , Guo Ming‐xin , Harrison Paul J. , Whyte John N. C.
Published: October 2004

Eight species of marine phytoplankton showed significant variation in the relative amount of some fatty acids (FAs) in response to variation in temperature. Large changes in relative amounts of certain FAs occurred as a result of a 15° C change in growth temperature. For example, 14:0 increased from ≃4% of total FAs at 10° C to > 20% at 25° C for Chaetoceros simplex and Isochrysis aff. galbana but decreased for Phaeodactylum tricornutum. The percentage of the polyunsaturated fatty acid (PUFA) 16:ω1 was consistently greater at 10° C than at 25° C, and the converse was usually true for 16: 4ω3. Calculated over all eight species, there was a modest but significant inverse relationship between the percentage of PUFAs and temperature. Only for Thalassiosira pseudonana was the percentage of either of the PUFAs and nutritionally essential fatty acids (EFAs) also an inverse function of temperature. For T. pseudonana, the percentage of the EFA 22:6ω3 decreased linearly with increasing temperature over the range from 10 to 25° C.

For three species, the ratio of unsaturated/saturated FAs was correlated with growth rate when growth rate was controlled by variation in irradiance and temperature. Only for Thalassiosira pseudonana was the ratio of unsaturated/saturated FAs also an inverse function of temperature alone.
PIGMENT TURNOVER IN THE MARINE DIATOM THALASSIOSIRA WEISSFLOGII. I. THE 14CO2‐LABELING KINETICS OF CHLOROPHYLL a1
Authors: Goericke Ralf , Welschmeyer Nicholas A.
Published: October 2004

The turnover of chlorophyll a (chl a) was investigated in the diatom Thalassiosira weissflogii (Grunow) Fryxell and Hasle using a new method based on the incorporation of 14C into chl a. The alga was maintained in its exponential growth phase under continuous light; 14C was supplied as bicarbonate. The time course of label accumulation into the tetrapyrrole ring and the phytol side chain was determined for time periods equivalent to 1–2 cell doublings. The labeling kinetics of the tetrapyrrole ring and the phytol side chain were described satisfactorily by a simple precursor‐pigment model with two free parameters, the precursor turnover rate and the pigment turnover rate, both having dimensions of time−1. The model was fit to the experimental data to determine the values of these two free parameters. The turnover rates of the tetrapyrrole ring and the phytol side chain were not significantly different, ranging from 0.01 to 0.1 per day. These rates are equivalent to turnover times ranging from days to weeks. Growth rate‐normalized turnover rates did not vary with irradiance (7.5–825 μE · m−2· s−1). The precursor turnover rates of the tetrapyrrole ring and the phytol side chain differed by an order of magnitude. These results indicate that chl a is not degraded significantly in cultures of T. weissflogii grown under continuous light. Neither irradiance nor growth rate affected growth rate‐normalized chlorophyll turnover rates. Our results are inconsistent with the hypothesis that steady‐state cellular concentrations of chl a are maintained by a dynamic equilibrium between rates of synthesis and degradation.
NUCLEOTIDE SEQUENCES OF THE SMALL‐SUBUNIT RIBOSOMAL RNA GENES FROM SELECTED LAMINARIALES (PHAEOPHYTA): IMPLICATIONS FOR KELP EVOLUTION1
Authors: Saunders Gary W. , Druehl Louis D.
Published: October 2004

The entire small‐subunit (SSU) ribosomal ribonucleic acid sequence was inferred for kelp representing seven genera: Alaria marginata Postels and Ruprecht (1824 bp), Egregia menziesii (Turner) Areschoug (1825 bp), Lessoniopsis littoralis (Tilden) Reinke (1825 bp), Macrocystis integrifolia Bory (1825 bp), Nereocystis leutkeana (Mertens) Postels and Ruprecht (1824 bp), Postelsia palmaeformis Ruprecht (1826 bp), and Pterygophora californica Ruprecht (1825 bp). We obtained a partial sequence for Eisenia arborea Areschoug (1669 bp) from a single clone of polymerase chain reaction‐amplified product. The SSU sequence was too conserved among these morphologically distinct taxa to permit phylogenetic analysis. The divergence between the most distant taxa was only 0.66%. This value was used in a SSU molecular clock to suggest that the most distantly related kelp investigated in this study diverged between 16 and 30 (more probably 16 and 20) million years ago.
CONFIRMATION OF DOMOIC ACID PRODUCTION BY PSEUDONITZSCHIA AUSTRALIS (BACILLARIOPHYCEAE) CULTURES1
Authors: Garrison David L. , Conrad Steve M. , Eilers Paul P. , Waldron Ellen M.
Published: October 2004

Single done isolates of Pseudonitzschia australis Frenguelli (= Nitzschia pseudoseriata Hasle) isolated from a toxic bloom in Monterey Bay, California produced domoic acid in culture. Although long‐term historical records do not indicate previous blooms of this species on the Pacific coast, this is probably because it has been often misidentified as Nitzschia seriata Hasle; previous evidence for toxicity is lacking. Hydrographic data suggest that areas such as Monterey Bay might be “hot spots” for domoic acid‐producing blooms.
AUXOSPORULATION IN CYCLOTELLA OCELLATA (BACILLARIOPHYCEAE) UNDER NATURAL AND EXPERIMENTAL CONDITIONS1
Authors: Pérez‐Martínez Carmen , Cruz‐Pizarro Luis , Sánchez‐Castillo Pedro
Published: October 2004

Growth and sexual reproduction in a population of Cyclotella ocellata Pantocseck were studied during one annual cycle in a reservoir and in short‐term enclosure experiments performed in situ involving different nutrient conditions and concentrations of zooplankton species. Three phases of auxosporulation in this diatom were distinguishable morphologically: 1) preauxospore, from the beginning of zygote formation until the valves were longitudinally separated, 2) primary auxospore, when the zygote grew too large to fit inside the valves and before it reached its full size, and 3) mature auxospore, characterized by a well‐developed, markedly scalloped edge. Under experimental and natural conditions, sexual reproduction was associated with changes in cell size. In the natural system, the auxospore appeared to act as a resting structure during conditions adverse for population growth. A threshold population of small cells appeared to be necessary for sexual reproduction in the natural system, whereas auxosporulation was associated with phosphorus fertilization in the enclosures. In both environments only cells smaller than 9.5 μm in diameter were capable of auxospore formation. Our results suggest that, once having reached the critical cell size, the factors that trigger sexual reproduction may depend on ambient environmental conditions.