bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconsidering Redundancy
Authors: VanHook Annalisa M.
Published: September 2008

The multimeric serine-threonine protein phosphatase PP2A, which has been implicated in signaling induced by transforming growth factor–β (TGF-β) superfamily ligands, is a heterotrimer composed of catalytic, structural, and regulatory subunits. The B family of mammalian regulatory subunits comprises four highly similar members that differ in tissue-specific and subcellular localization but that otherwise appear to be functionally redundant. Batut
et al.
report that two of these B subunits, Bα and Bδ, have distinct and opposite functions in mediating signaling elicited by the TGF-β superfamily ligands TGF-β, Activin, and Nodal. Bδ knockdown with morpholino antisense oligonucleotides caused an expansion of anterior structures in
Xenopus laevis
embryos, whereas Bα knockdown caused loss of anterior structures. The observed phenotypes, in combination with quantitative polymerase chain reaction (PCR) and in situ expression data for two positively regulated targets of Nodal signaling, suggested that Bα potentiated and Bδ inhibited Nodal signaling. In
Xenopus
animal cap assays, Bα knockdown blocked Activin-induced axial elongation, reduced phosphorylation of the TGF-β family signaling effector Smad2 (pSmad2), and prevented nuclear accumulation of pSmad2. In contrast, Bδ knockdown enhanced Activin-induced elongation, increased the amount of pSmad2, and increased pSmad2 nuclear accumulation, which suggested that Bα and Bδ oppositely affected Activin signaling. Similar results were seen in HeLa cells using TGF-β–induced phosphorylation and Smad2 nuclear accumulation to assay Bα and Bδ function. Both Bα and Bδ could dephosphorylate an artificial peptide and a Raf substrate in vitro, but neither dephosphorylated Smad2. Knockdown analyses in a keratinocyte cell line and in
Xenopus
animal caps indicated that Bα inhibits lysosomal degradation of ALK4 and ALK5, type I receptors that transduce signaling from TGF-β superfamily ligands, and that Bδ inhibits ALK4 receptor clustering. Thus, both subunits appear to influence the threshold ligand concentration that can elicit signaling but act on distinct processes to exert their opposing effects. Although the mechanism of neither subunit’s activity has been determined, it is intriguing that such similar subunits can exert opposing effects on a signaling pathway.

J. Batut, B. Schmierer, J. Cao, L. A. Raftery, C. S. Hill, M. Howell, Two highly related regulatory subunits of PP2A exert opposite effects on TGF-β/Activin/Nodal signalling.
Development
135
, 2927-2937 (2008).
[Abstract]
[Full Text]
A Life or Death Decision
Authors: Adler Elizabeth M.
Published: September 2008

Stimulation of lymphocyte death receptors leads to activation of the cysteine protease caspase-8, which undergoes autoproteolysis to produce a mature form that cleaves effector caspases (such as caspase-3) as part of a proteolytic cascade that ends in apoptosis. In contrast, caspase-8 activation during antigenic stimulation, which involves its association with a complex that contains Bcl10 and MALT1, is required for lymphocyte proliferation. Kawadler
et al
. found that interleukin-2 (IL-2) production was reduced in activated human T cells (stimulated with antibodies directed against CD3 and a chimeric form of CD28) in which caspase-8 was knocked down with siRNA. Caspase-8 activated by antibody stimulation underwent limited autoproteolysis and failed to cleave substrate effector caspases appreciably. Activation of the transcription factor NF-κB in response to coexpression of MALT1 and Bcl10 was attenuated in Jurkat lymphoma cells lacking caspase-8; moreover, MALT1 knockdown prevented caspase-8 activation in primary human T cells. Noting that MALT1 contains a paracaspase domain (distantly related to the caspase proteolytic domain), the authors used a controlled heterodimerization system to show that heterodimerization of MALT1 and caspase-8 led to cleavage of the latter. The MALT1 paracaspase domain bound to the caspase-8 protease domain; however, mutational analysis established that caspase-8 cleavage was autoproteolytic and did not depend on MALT1 protease activity. MALT1 failed to stimulate caspase-8–mediated proteolysis of caspase-3, although it did stimulate proteolysis of the caspase homolog c-FLIP
L
. c-FLIP
L
was cleaved after antibody stimulation of lymphocytes, and its knockdown inhibited IL-2 production. Moreover, mutational analysis revealed that MALT1-dependent activation of caspase-8 and proteolysis of c-FLIP
L
were critical to NF-κB activation and IL-2 production. Thus, MALT1 appears to activate caspase-8 in a manner that affects its processing and substrate specificity, which leads to proliferative—rather than apoptotic—signaling.

H. Kawadler, M. A. Gantz, J. L. Riley, X. Yang, The paracaspase MALT1 controls caspase-8 activation during lymphocyte proliferation.
Mol. Cell
31
, 415-421 (2008).
[PubMed]
Capable Caspase
Authors: Foley John F.
Published: September 2008

T cell anergy is a state of unresponsiveness that is induced by suboptimal activation of T cells; namely, engagement of the T cell receptor (TCR) in the absence of a costimulating signal, such as stimulation of CD28. Anergic T cells do not proliferate in response to further stimulation, making the induction of anergy an effective method for inactivating self-reactive T cells. Stimulation of the TCR results in the Ca
2+
-dependent transcription of genes encoding proteins associated with anergy. The group of Puga
et al
. had previously shown that one of these proteins was the proapoptotic protein caspase-3. In the current study, the authors mixed mouse T cells expressing an ovalbumin-specific TCR with Chinese hamster ovary (CHO) cells expressing a complex of MHC class II and ovalbumin peptide (CHO-OVA) to induce T cell anergy. The abundances of
Casp3
mRNA and active caspase-3 protein were increased in these T cells compared with those of T cells mixed with non-OVA CHO cells; however, the anergic T cells did not exhibit any of the characteristics of apoptotic cells. When T cells and CHO-OVA cells were incubated with a caspase inhibitor, proliferation assays showed that the T cells did not become anergic. Similarly,
Casp3
–/–
T cells were less susceptible than cells from wild-type mice to becoming anergic after TCR stimulation in vitro. Western blotting assays showed that caspase-3 was recruited to the plasma membrane of anergic T cells, where it cleaved the adaptor protein GADS and the guanine nucleotide exchange factor Vav1, both of which are TCR signaling components. Together, these data suggest a nonapoptotic role for caspase-3 in maintaining the hyporesponsiveness of anergic T cells by inhibiting TCR signaling.

I. Puga, A. Rao, F. Macian, Targeted cleavage of signaling proteins by caspase 3 inhibits T cell receptor signaling in anergic T cells.
Immunity
29
, 193-204 (2008).
[PubMed]
RNA Interference and Plant Defenses
Authors: Riddihough Guy
Published: September 2008

RNA interference plays an important role in innate immunity in plants and in animals. Specific microRNAs have also been implicated in pathways that sense pathogen-associated molecular patterns (PAMPs). Now, Navarro
et al.
examine in more detail the role of microRNAs in innate immunity in
Arabidopsis
. MicroRNAs were found to be more broadly required for PAMP sensing. Pathogenic bacteria appear to have evolved various effectors that are secreted into the host that suppress the microRNA pathway at various points. Infection with turnip mosaic virus,

which produces a suppressor of both the small interfering RNA and microRNA pathways, promotes infection by nonpathogenic bacteria, which may explain the observed synergy between viral and bacterial pathogens seen in the field.

L. Navarro, F. Jay, K. Nomura, S. Y. He, O. Voinnet, Suppression of the microRNA pathway by bacterial effector proteins.
Science
321
, 964-967 (2008).
[Abstract]
[Full Text]
Jam the Signal
Authors: Ash Caroline
Published: September 2008

Many bacterial pathogens sense that they are in a potential host because they can detect adrenergic molecules. These organisms share a sensor kinase that picks up the signal and relays it to virulence gene loci, thus kicking in the responses needed to ensure bacterial establishment. This pathway makes a good target for broad-spectrum antibiotic development because virulence inhibition should not present a strong selective pressure for resistance. Rasko
et al
. have had some success with this approach using a nontoxic small-molecule inhibitor of the sensor kinase QseC, which blocks signaling in a sensitive and specific manner. In animal models, the inhibitor was somewhat effective against gastrointestinal infections with enterohemorrhagic
E. coli
and
Salmonella typhimurium
. Encouragingly, the lead molecule was more effective against the systemic pathogen
Francisella tularensis
: A single oral dose protected 80% of infected mice from death.

D. A. Rasko, C. G. Moreira, D. R. Li, N. C. Reading, J. M. Ritchie, M. K. Waldor, N. Williams, R. Taussig, S. Wei, M. Roth, D. T. Hughes, J. F. Huntley, M. W. Fina, J. R. Falck, V. Sperandio, Targeting QseC signaling and virulence for antibiotic development.
Science
321
, 1078-1080 (2008).
[Abstract]
[Full Text]
To Divide or Not to Divide
Authors: Ray L. Bryan
Published: September 2008

Cells can stop dividing and remain in a nonproliferative state (like most differentiated cells in an organism), but under some conditions the cells can reenter the cell division cycle and begin to proliferate again. Sang
et al.
provide evidence that a transcriptional repressor known as Hairy and Enhancer of Split1 (HES1) has an important role in determining whether a cell can resume cell division. When proliferation of human fibroblast cells in culture was inhibited, reduction of Hes1 activity prevented cells from reinitiating cell division once the block to proliferation was removed. Inappropriate reentry into the cell cycle is a property of tumor cells, and treatments that inhibited Hes1 function in skeletal muscle tumor cells also inhibited proliferation and promoted differentiation.

L. Sang, H. A. Coller, J. M. Roberts, Control of the reversibility of cellular quiescence by the transcriptional repressor HES1.
Science
321
, 1095-1100 (2008).
[Abstract]
[Full Text]
GRK Versus HDAC
Authors: Foley John F.
Published: September 2008

G protein-coupled receptor kinase 5 (GRK5) phosphorylates HDAC5, thus allowing the transcription of genes involved in cardiac hypertrophy.
Microglial Messages Modulate Neurogenesis
Authors: Adler Elizabeth M.
Published: September 2008

Microglial signaling factors are critical to inhibition of adult hippocampal neurogenesis by presenilin 1 variants associated with familial Alzheimer's disease.
Dynein Light Chain Connecting ROS to NF-κB
Authors: Gough Nancy R.
Published: September 2008

Reversible oxidation of dynein light chain contributes to activation of NF-κB by stimuli that produce reactive oxygen species.
Channel Opening
Authors: Vinson Valda J.
Published: September 2008

Circularly arrayed transmembrane helices tilt to facilitate the opening of a bacterial mechanosensitive channel.
Seeing the Signaling Forest and the Trees
Authors: Yaffe Michael B.
Published: September 2008

Science Signaling
launches primary research to meet the needs of the signal transduction community.
What Are Dimers Good For?
Authors: Foley John F.
Published: September 2008

The assembly of scaffold proteins and ERK dimers is required for the activation of cytoplasmic, but not nuclear, substrates.
Signaling from the Right Place
Authors: Adler Elizabeth M.
Published: September 2008

Type IV collagens influence localization of the morphogen Dpp in
Drosophila
embryos and ovaries.
Wnt Receptor Signaling
Authors: Ray L. Bryan
Published: September 2008

The interaction of the signaling molecule Wnt with its receptor triggers accumulation of a lipid regulator, which stimulates phosphorylation of the receptor and cellular responses.
Quantity, Not Just Quality, Matters
Authors: Kiberstis Paula A.
Published: September 2008

In patients with colorectal cancer, one allele of the transforming growth factor–β gene produces less mRNA and thus less protein, a likely contributor to disease risk.
Multifunctional SH2 Domains
Authors: Ray L. Bryan
Published: September 2008

Crystal structures reveal how SH2 protein interaction domains can both enhance and inhibit activity of cytoplasmic tyrosine kinases.
Smad Signaling Dynamics: Insights from a Parsimonious Model
Authors: Shankaran Harish , Wiley H. Steven
Published: September 2008

Computational modeling of protein localization dynamics yields new information about Smad signaling.
A Surprising Partner
Authors: Adler Elizabeth M.
Published: September 2008

The p75 neurotrophin receptor interacts with ephrin-As to mediate their reverse signaling.
Open and Closed Case
Authors: Hurtley Stella M.
Published: September 2008

The synaptic vesicle protein that mediates membrane fusion during exocytosis also regulates the rate and extent of this process by controlling vesicle tethering.
A Two-Way Street
Authors: Adler Elizabeth M.
Published: September 2008

Tumorigenesis in hedgehog-secreting cancers depends on reciprocal signals between the cancer cells and their stromal environment.
Creating Force from Destruction
Authors: VanHook Annalisa M.
Published: September 2008

Apoptosis creates mechanical force that helps drive morphogenesis in
Drosophila.
Points of Recombination in Epstein-Barr Virus (EBV) Strain P3HR-1-Derived Heterogeneous DNA as Indexes to EBV DNA Recombinogenic Events In Vivo
Authors: Ikuta Kazufumi , Srinivas Shamala K. , Schacker Tim , Miyagi Jun-ichi , Scott Rona S. , Sixbey John W.
Published: September 2008

Deletions and rearrangements in the genome of Epstein-Barr virus (EBV) strain P3HR-1 generate subgenomic infectious particles that, unlike defective interfering particles in other viral systems, enhance rather than restrict EBV replication in vitro. Reports of comparable heterogeneous (het) DNA in EBV-linked human diseases, based on detection of an abnormal juxtaposition of EBV DNA fragments BamHI W and BamHI Z that disrupts viral latency, prompted us to determine at the nucleotide level all remaining recombination joints formed by the four constituent segments of P3HR-1-derived het DNA. Guided by endonuclease restriction maps, we chose PCR primer pairs that approximated and framed junctions creating the unique BamHI M/B1 and E/S fusion fragments. Sequencing of PCR products revealed points of recombination that lacked regions of extensive homology between constituent fragments. Identical recombination junctions were detected by PCR in EBV-positive salivary samples from human immunodeficiency virus-infected donors, although the W/Z rearrangement that induces EBV reactivation was frequently found in the absence of the other two. In vitro infection of lymphoid cells similarly indicated that not all three het DNA rearrangements need to reside on a composite molecule. These results connote a precision in the recombination process that dictates both composition and regulation of gene segments altered by genomic rearrangement. Moreover, the apparent frequency of het DNA at sites of EBV replication in vivo is consistent with a likely contribution to the pathogenesis of EBV reactivation.
Cell-Restricted Immortalization by Human Papillomavirus Correlates with Telomerase Activation and Engagement of the hTERT Promoter by Myc
Authors: Liu Xuefeng , Dakic Aleksandra , Chen Renxiang , Disbrow Gary L. , Zhang Yiyu , Dai Yuhai , Schlegel Richard
Published: September 2008

The high-risk human papillomaviruses (HPVs) are the causative agents of nearly all cervical cancers and are etiologically linked to additional human cancers, including those of anal, oral, and laryngeal origin. The main transforming genes of the high-risk HPVs are E6 and E7. E6, in addition to its role in p53 degradation, induces hTERT mRNA transcription in genital keratinocytes via interactions with Myc protein, thereby increasing cellular telomerase activity. While the HPV type 16 E6 and E7 genes efficiently immortalize human keratinocytes, they appear to only prolong the life span of human fibroblasts. To examine the molecular basis for this cell-type dependency, we examined the correlation between the ability of E6 to transactivate endogenous and exogenous hTERT promoters and to immortalize genital keratinocytes and fibroblasts. Confirming earlier studies, the E6 and E7 genes were incapable of immortalizing human fibroblasts but did delay senescence. Despite the lack of immortalization, E6 was functional in the fibroblasts, mediating p53 degradation and strongly transactivating an exogenous hTERT promoter. However, E6 failed to transactivate the endogenous hTERT promoter. Coordinately with this failure, we observed that Myc protein was not associated with the endogenous hTERT promoter, most likely due to the extremely low level of Myc expression in these cells and/or to differences in chromatin structure, in contrast with hTERT promoters that we found to be activated by E6 (i.e., the endogenous hTERT promoter in primary keratinoctyes and the exogenous hTERT core promoter in fibroblasts), where Myc is associated with the promoter in either a quiescent or an E6-induced state. These findings are consistent with those of our previous studies on mutagenesis and the knockdown of small interfering RNA, which demonstrated a requirement for Myc in the induction of the hTERT promoter by E6 and suggested that occupancy of the promoter by Myc determines the responsiveness of E6 and the downstream induction of telomerase and cell immortalization.
RNA Interference Inhibits Respiratory Syncytial Virus Replication and Disease Pathogenesis without Inhibiting Priming of the Memory Immune Response
Authors: Zhang Wenliang , Tripp Ralph A.
Published: September 2008

Respiratory syncytial virus (RSV) is a major cause of morbidity in infants, young children, and the elderly worldwide. Currently, there is no effective vaccine, and antiviral drugs to control infection are limited. RNA interference is a powerful tool amenable to development of antiviral drugs. Using small interfering RNA (siRNA) targeting the RSV P gene (siRNA-P), RSV replication can be silenced both in vitro and in a BALB/c model of RSV infection. In this study, we examine the effect of siRNA prophylaxis on the primary and memory immune response to RSV infection in mice. We show that mice prophylactically treated with siRNA-P to decrease but not eliminate RSV replication exhibit reduced pulmonary inflammation and lung pathogenesis and produce a robust anti-RSV memory response when subsequently challenged with RSV. The pulmonary T-cell memory response was characterized by high numbers of CD44hiCD62LloCD4+and CD8+T cells, M2 peptide tetramer+CD8+T cells expressing gamma interferon, and an RSV-specific antibody response. The results support the hypothesis that siRNAs can be developed as effective antiviral drugs that can be used to reduce the viral load and parameters of pathogenesis without limiting the induction of the memory immune response.
Is tendon pathology a continuum? A pathology model to explain the clinical presentation of load-induced tendinopathy
Authors: Cook J L , Purdam C R
Published: September 2008

Overuse tendinopathy is problematic to manage clinically. People of different ages with tendons under diverse loads present with varying degrees of pain, irritability, and capacity to function. Recovery is similarly variable; some tendons recover with simple interventions, some remain resistant to all treatments.

The pathology of tendinopathy has been described as degenerative or failed healing. Neither of these descriptions fully explains the heterogeneity of presentation. This review proposes, and provides evidence for, a continuum of pathology. This model of pathology allows rational placement of treatments along the continuum.

A new model of tendinopathy and thoughtful treatment implementation may improve outcomes for those with tendinopathy. This model is presented for evaluation by clinicians and researchers.
The effects of choline derivatives on the growth and lipid content of continuously cultured Chlorella vulgaris
Authors: Orcutt D. M. , Davis G. A. , Moore L. D.
Published: September 2008

(2-Chloroethyl)trimethylammonium chloride (CCC), (2-hydroxyethyl)trimethylammonium chloride (CC), and (2-hydroxyethyl)trimethylammonium chloride phosphate (PCC) were studied relative to their effects on the growth and lipid composition of Chlorella vulgaris grown in continuous culture. Each chemical was added to a culture in the following sequence of concentrations: 10−6, 10−5, and 10−4 M. CC was the most effective inhibitor of cell growth and caused sequential growth reductions at increasing concentrations. CCC and PCC at 10−6 M initially inhibited cell growth, but growth recovery occurred with subsequent addition of higher concentrations of these chemicals. The polar lipid fatty acid (PL-FA), free fatty acid (FFA), triacylglycerol fatty acid (TAG-FA), and paraffinic hydrocarbon (PH) composition was determined for cells treated with each chemical. CCC at 10−5 and 10−4 M caused significant increases in TAG-FA. CC at 10−4 M stimulated TAG-FA, FFA, and PH production but inhibited PL-FA levels. PCC at 10−6 M significantly inhibited PL-FA concentrations but was stimulatory at 10−4 M. The reverse was true for the FFA concentrations relative to PCC treatments. Qualitative changes were also observed in the unsaturated fatty acid composition of the PL-FA and FFA lipid classes.
Peroxidase activity and induced lignification in rusted flax interactions varying in their degree of incompatibility
Authors: Coffey M. D. , Cassidy D. S. M.
Published: September 2008

A histological comparison of the L9, K, P, P1, P2, and P3 genotypes in flax revealed differences in their expression of incompatibility. K and P1 were only moderately incompatible, whereas P, P2, and P3 were highly incompatible, restricting fungal development completely by the 4th day after inoculation. Host cell necrosis was delayed until day 3 in P3 and day 2 in P2; it was present at day 1 in P. Peroxidase, using guaiacol as a proton donor, was detected in P after 2 days, in K at 5 days, and in L9 after 7 days. Soluble peroxidase activity increased in the rusted P genotype from day 3 and from day 7 in K. Gel electrophoresis of infected P revealed a new peroxidase isozyme at 6 days after inoculation. Three new protein bands were also detected at this stage. In 3- and 4-day-old rusted P, peroxidase was detected in the host cell walls of tissue surrounding necrotic infection sites. It was not located in the host cell walls of the compatible L9 genotype at this stage. Lignin was detected histochemically in P after 2 days, in K after 5 days, and in L9 after 9 days. The Wiesner, Maiile, and KMnO4 tests gave equivalent results. Suberin was detected in P, K, and L9 at the same time that lignin became observable.
The influence of nitrogen sources on root-mediated changes in substrate pH
Authors: Weinberger Pearl , Yee Dennis
Published: September 2008

The relationship between nutritional nitrogen (nitrate, ammonium, and urea) and changes in rhizosphere pH was established using axenic cultures of seedlings grown on nutrient agar. A nutrient-related rhizosphere pH was obtained which was modulated by the source of nitrogen in the medium. After 3 weeks of growth, a pH of 8.5–9.5 was generated by wheat seedlings fertilized with Hoagland's nutrient solution No. 2. A comparable degree of alkalization was observed in nitrate-fertilized plants. A rhizosphere pH less than 4.0 was obtained in plants fertilized with ammonium salts while no significant change was detected in wheat seedlings provided with urea as the sole source of nitrogen. These results are consistent with the concept of cation–anion uptake balance, maintenance of electroneutrality across the root surface, uptake by cotransporters, and chemiosmotic principles.
Fine structure of the giant cells induced by Meloidogyne javanica in lima bean
Authors: Fattah F. , Webster J. M.
Published: September 2008

Giant cells associated with egg-laying females of Meloidogyne javanica in lima bean, Phaseolus lunatus cv. L-136, were examined by light and electron microscopy. These giant cells have characteristics that are typical of nematode-induced giant cells in a wide range of hosts, but they differ in that they (i) are less closely associated with xylem vessels, (ii) contain a very large number of plastids which are devoid of starch grains, and (iii) contain several different forms of cytoplasmic crystals. One form of the crystal is associated with a large number of "spiny" vesicles. The possible role of these features, especially the crystals, in the giant cell response of lima bean is discussed.
Shoot development in Betula papyrifera. III. Long-shoot organogenesis
Authors: Macdonald Alastair D. , Mothersill D. H. , Caesar J. C.
Published: September 2008

Buds and developing branches of Betula papyrifera were collected weekly from mature trees during three successive growing seasons. Material was prepared to show stages of bud inception, development, flushing, shoot expansion, and male inflorescence inception and early development. Stages of bud development were correlated with axillant leaf and subjacent internodal extension. Long-shoot buds develop in the axils of distal late leaves of the previous season's long shoot. The bud contains one rudimentary leaf with prominent stipules, two or three embryonic foliage leaves which flush as early leaves, and about five smaller primordia which expand in the spring as late leaves. Preformed primordia are produced in mid-May through to early August. A pause in the inception sequence occurs in June, corresponding to the period of rapid late-leaf and internodal expansion of axillant leaves and subjacent internodes. Long-shoot bud determination occurs in mid-July. True late leaves may form during shoot extension. Male inflorescence induction, which occurs before bud break, restricts late leaf production and results in the last-formed leaf primordia maturing as transitional leaves instead of foliage leaves. Male induction limits crown expansion by reducing sites for axillary bud formation. This reduces the photosynthetic potential of the shoot.
Stomatal and anatomical leaf characteristics of 10 Populus clones
Authors: Ceulemans R. , Impens I. , Steenackers V.
Published: September 2008

Stomatal characteristics (frequency and length of stomata on adaxial and abaxial leaf surface) and anatomical characteristics (thickness of epidermal, palisade, and spongy layers) of field-grown plants of Populus clones, six of American, two of European, and two of Euramerican origin, were studied. All clones except one were amphistomatous and all clones had most stomata on the abaxial leaf surface. In all clones the spongy parenchyma layer was thicker than the palisade layer. Stomatal and anatomical characteristics varied significantly among clones. Both cluster analysis and principal-component analysis, utilizing mean clonal values of stomatal and anatomical characters as independent variables, indicated that these characteristics were related to place of origin and to parentage. Different groupings of the clones were observed on the basis of abaxial stomatal length and total stomatal frequency. Abaxial and mean stomatal length were significantly correlated with yield (represented by stem volume data), but relationships between other characteristics and yield were not significant.
A visual indicator of heterokaryosis in Fusarium oxysporum from celery
Authors: Puhalla John E.
Published: September 2008

Wild-type isolates of Fusarium oxysporum f. sp. apii (celery pathogens) were white or pale pink. Ultraviolet-light (UV) treatment of conidia, however, yielded stable orange mutants, which in turn gave rise to yellow and white mutants after a second UV treatment. Some pairings between these yellow and white mutants developed an orange line where they touched. This orange line developed only if the two mutants formed heterokaryons with each other. In contrast, attempts to demonstrate heterokaryons between complementary auxotrophic mutants on minimal medium failed. The color heterokaryon was a mosaic of homokaryotic and heterokaryotic cells, the latter being confined to the area of anastomosis between the two mutants. Genetic complementation was also confined to this area. In pairings among color mutants of five wild-type strains two vegetative (heterokaryon) compatibility (VC) groups were defined. VC groups in other formae spéciales of F. oxysporum should also be detectable by this method.
Chromosome numbers and sexual compatibility in North America of Rorippa sylvestris (Cruciferae)
Authors: Mulligan Gerald A. , Munro Derek B.
Published: September 2008

Tetraploid (2n = 32), pentaploid (2n = 40), and hexaploid (2n = 48) plants of Rorippa sylvestris (L.) Besser (Cruciferae) and a natural pentaploid (2n = 40) interspecific hybrid, R. sylvestris × R. palustris (L.) Besser, are recorded for North America. These counts are compared with published information on European plants. Tetraploids are most common in Europe (68 vs. 20%), whereas hexaploids are most common in North America (65 vs. 29%). Although self-incompatible R. sylvestris rarely sets seed in nature, indicating that plants within most sites are genetically the same clone, intraspecific crossing data, chromosome information, and field observations indicate that North American R. sylvestris results from the vegetative introduction of many different genotypes.
Interactions of growth regulators, explant age, and culture environment controlling organogenesis from lettuce cotyledons in vitro
Authors: Webb David T. , Torres Luis D. , Fobert Pierre
Published: September 2008

Organogenesis in cultured Lactuca sativa L. cv. Grand Rapids cotyledons was controlled by growth regulators and influenced by explant age as well as culture environment. Control explants formed roots with a low frequency. Exposure to indoleacetic acid (IAA) greatly stimulated root initiation. Kinetin (K) applied singly or in combination with IAA induced bud formation. Benzylaminopurine (BA) also caused bud initiation. Root and shoot initiation was optimal with 4-day-old explants. Organogenesis declined with older explants. More buds formed in light than in darkness. Other environmental variables tested had no marked effect on K-induced bud initiation. Control explants on medium containing no growth regulator never formed buds.
Hybridization of the seedling-infecting Ustilago spp. pathogenic on barley and oats, and a study of the genotypes conditioning the morphology of their spore walls
Authors: Huang H.-Q. , Nielsen J.
Published: September 2008

The Ustilago spp. pathogenic on barley, U. nigra and U. hordei, were successfully hybridized with the species pathogenic on oats, U. avenae and U. kolleri, using the common host Agropyron tsukushiense var. transiens. The genetic relationship of these species was studied based on their crossability and the distribution of genes for spore wall morphology. The echinulation of the spore walls of U. nigra was conditioned by the two dominant and complementary genes E1 and E2 that had previously been identified in U. avenae. Ten collections of U. hordei from 10 countries of five continents had genotype E1e2, resulting in smooth spores. The 11 collections of U. kolleri from seven countries had smooth walls, and their genotypes were either e1e2 (Canada), e1E2 (Spain, Morocco, Tunisia, Turkey, and Australia), or E1e2 (Portugal). Hybrids between genotypes e1E2 and E1e2 of U. kolleri had echinulate spores, and would thus belong to another taxon: U. avenae. Similarly, hybrids between U. hordei genotype E1e2, and U. kolleri genotype e1E2 had echinulate spores. Intra- and inter-specific crosses of U. avenae and U. kolleri showed that incompatibility between collections can occur within as well as between these species. The suggested causes of such incompatibility are multigene differences or chromosomal rearrangement, an effect of long-term isolation of populations of these species. The results are discussed in view of proposals of how to taxonomically delimit the four seedling-infecting Ustilugo species parasitic on barley and oats.
Localisation par autoradiographie de l'acide [5-3H]indole-3-acétique dans le bourgeon terminal du Lycopersicum esculentum
Authors: Driss-Ecole D. , Perbal G. , Leroux Y.
Published: September 2008

[3H]indoleacetic acid (AIA) was applied to the shoot tip of intact young plants of Tomato (Lycopersicum esculentum Mill.) for 10, 60, or 120 min. Autoradiograms of whole plants were prepared and liquid scintillation counts of stem segments and principal root segments were performed. Chromatographic analysis showed that 66% of the radioactivity was associated with AIA after 120 min of contact with [3H]AIA. Autoradiographs of semithin and ultrathin sections were prepared after treatment by DCC (1-(3-dimethyl-aminopropyl)-3-ethylcarbodiimide hydrochloride). The quantity of label per cell and the density of label were determined for all tissues of the apical bud. The density of label was greater for meristematic cells than for differentiated cells. The observed homogeneity of label distribution in the apical meristem shows that auxin levels do not play a prominent role in distinguishing between its lateral and axial zones. The density of label was similar in the apical and in the axillary bud of leaf 4. The cells of the rib meristem, which elongate to produce pith, were more intensely labelled than the other meristematic cells. The percentage of label was calculated for each tissue in a transverse section of the stem just below the apex. The amount of auxin was greatest in the parenchyma (axial and cortical) with lesser amounts in the procambium, phloem parenchyma, and xylem parenchyma. Vessels, which had the greatest density of label, did not contain more than about 3% of total radioactivity of the stem section, while sieve tubes had only 0.5%. Pathways of auxin transport and the role of AIA in regulating meristematic activity in the apical bud are discussed.
Predetermination of lateral shoot characteristics in grand fir
Authors: Worrall John
Published: September 2008

The terminal bud and all but one subterminal bud were removed from the terminal leaders of shade-grown 15-year-old grand fir plants at monthly intervals during the season of their formation. The growth of shoots from the remaining subterminal bud was assessed in August of the following growing season and compared with control shoots. These latter displayed marked plagiotropy and distichy under the conditions of the experiment. In treated plants, compensatory growth occurred, with respect to both number of leaves and internode length. The shoots assumed a more vertical position, earlier treatment being more effective. The distichous positioning of leaves on these shoots, however, was not affected, causing leaves to be oriented in a manner inefficient for light interception. Plagiotropy seemed to have been imposed on the shoot gradually, during the season prior to its growth, whereas distichy was perhaps imposed close to the time of inception of the shoot's apical meristem. Possible reasons for this are discussed.
Cadmium-binding protein in roots of maize
Authors: Rauser Wilfried E. , Glover John
Published: September 2008

A partially purified cadmium (Cd) binding protein was isolated from roots of maize (Zea mays L.). Proteins were first separated on the anion exchanger QAE-Sephadex A-25. The major Cd fraction, comprising as much as 85% of the buffer-soluble Cd, was then chromatographed on Sephadex G-75 in 1 M KCl buffer. The resulting partially purified protein preparation was dark brown, had an apparent molecular weight of 3100, and bound 2 g atoms Cd/mol. The cysteine content was 40%; the Cd:cysteine ratio was 1:6. The Cd–thiolate chromophore was evident from spectroscopic measurements. The roots produced the metallothioneinlike protein after they were exposed to 3 μM Cd for 4 days.
Influence of time of sowing, photoperiod, and temperature on supernumerary spikelet expression in wheat (Triticum)
Authors: Pennell Annabel L. , Halloran G. M.
Published: September 2008

Three tetraploid (Triticum turgidum L. emend, gr. turgidum and gr. durum) and six hexaploid wheats (Triticum × aestivum L. emend aestivum) with reported tendencies for "branched" heads (supernumerary spikelets) exhibited variation for this character when grown under different photoperiod and temperature regimes. Wheats with a weak vernalization response under short photoperiod in an outdoor (low temperature) environment and those with a strong vernalization response under a long-photoperiod outdoor (low temperature) environment developed more supernumerary spikelets than under other photoperiods and temperatures. There was a variation among the nine wheats in the level and stability of supernumerary spikelet expression and in their fertility and grain number per head over the different times of sowing. This indicates the feasibility for selecting high and stable expression of supernumerary spikelets in breeding to increase spikelet number per head in wheat.
Population variation in Sorghum halepense, Johnson grass, at the northern limits of its range
Authors: Warwick S. I. , Thompson B. K. , Black L. D.
Published: September 2008

Thirteen populations of Sorghum halepense, Johnson grass, were sampled from fields in Ontario, Canada, and Ohio and New York, United States. Only four of these populations were reported to overwinter as rhizomes. The morphology, phenology, resource allocation patterns, and growth of seedling and mature plants of the overwintering and the non-overwintering populations were compared. Field-collected specimens from the nonoverwintering populations had wider culms and leaves and larger seeds and inflorescences. Analysis of material grown in a 5-month greenhouse trial indicated similar differences. Greenhouse plants from the nonoverwintering populations were also characterized by greater percent emergence, larger and faster growing seedlings, earlier flowering, larger culms and seeds, greater reproductive dry weight per plant, and about 1/10th the rhizome dry weight of overwintering plants. Differences between populations within a biotype were evident for both biotypes, although there was little within-population variation, except in rhizome production, where certain individuals of some nonoverwintering populations did not produce extended rhizomes. Among the five enzymes which were examined electrophoretically, only one, phosphoglucomutase (PGM), showed variable isozyme patterns. No differences in enzyme patterns were apparent between the overwintering and the nonoverwintering biotypes. The relationship of the nonoverwintering populations to the cultivated species, Sorghum bicolor and S. almum, an introgressant between S. halepense and S. bicolor, is discussed.
Additional Agaricales on wetland Monocotyledoneae in Canada
Authors: Redhead S. A.
Published: September 2008

Coprinus phaeosporus Karst., Hypholoma subericaceum (Fr.) Kühner, Mycena tubarioides (Maire) Kühner, and Stropharia pseudocyanea (Desm.) comb. nov. are documented from North America for the first time. Agaricus albocyaneus Desm. ex Fr. is shown to be an error for A. pseudocyaneus Desm. Agrocybe paludosa (Lange) Kühner & Romagnesi, Coprinus martinii Favre ex Orton and C. subimpatiens Lange & Smith are reported from Canada. Range extensions or new host records are noted for Coprinus stercoreus Fr., C. urticicola (Berk. & Br.) Buller, Marasmius limosus Quél., Melanotus caricicola (Orton) Guz., Mycena juncicola (Fr.) Gillet, Pholiota graminis (Quél.) Singer, and Resinomycena saccharifera (Berk. & Br.) comb. nov. Resinomycena kalalochensis subsp. saccharifera in Europe and subsp. kalalochensis (Smith) comb. nov. in western North America are vicariant taxa.
The taxonomic value of using epidermal characteristics in the Canadian rough fescue complex (Festuca altaica, F. campestris, F. hallii, "F. scabrella")
Authors: Aiken S. G. , Lefkovitch L. P.
Published: September 2008

Epidermal peels were made from specimens chosen from a wide range of different locations selecting 10 collections of each of the three species recognized by J. Looman and K. F. Best as being in the Canadian rough fescue complex. Cell measurements and observations on wall shape were made on cells from the intercostal zones. The results of this study are consistent with the suggestion that there are three taxa in the rough fescue complex. The mean values for cell length and wall shape showed that, statistically, the taxa differ significantly from each other; in a single specimen the characters showed a wide range of variation and none could be used reliably to confirm identification.
Ascospore germination, mycelial growth, and microconidial anamorphs of Encoelia pruinosa in culture
Authors: Juzwik Jennifer , Hinds T. E.
Published: September 2008

Germination of ascospores, morphology and growth rate of colonies, and production of microconidial anamorphs of Encoelia pruinosa (Ell. & Everh.) Torkelson & Eckblad were investigated. Rate of germination was high (95–99% within 24 h) on 2% water agar and 2% malt extract agar. Growth rate ranged from medium (3.5–6.4 mm/day) to moderately rapid (>6.4 mm/day) on four media; the colonial morphology of different isolates varied with the media tested. Spherical micro-conidia were produced three ways: by ascospores functioning as phialides, by an Acreinoitium-like anamorph, and by a Myrioconium-like anamorph. The taxonomic implications of these anamorphic associations are discussed.
Comparative morphology and fine structure of a group of Umbilicaria lichens
Authors: Scott Martha G. , Larson Douglas W.
Published: September 2008

The gross morphology and fine structure of tissue layers in five Umbilicaria species (U. vellea, U. mammulata, U. papulosa, U. muhlenbergii, and U. deusta) were examined using bright-field and transmission electron microscopy. Differences in the surface topography of the upper and lower cortexes of the five species were found. Four of the species contained an osmiophilic banding material on the walls of the outermost file of living upper cortical hyphae. Although the fine structure of phycobiont cells was basically similar for all species, U. vellea was found to have smaller amounts of stored starch and peripheral lipid in cells of the algal zone than the other four species. Algal–fungal contacts were not haustorial, although aplanospore clusters were penetrated by wedge-shaped intrusive hyphae. Senescent algal cells accumulated large numbers of starch grains. Hyphae in the medullary zones were found to be similar for all species with the exception of U. muhlenbergii, which had an extrahyphal, gel-like matrix. Extensive, sheetlike lamellae were also present in the lower cortex of this species. It would appear that many aspects of thallus fine structure and morphology have a direct effect on gas exchange and water relations responses previously reported in the literature.
Seasonal variation in nitrogen fixation, associated microbial populations, and carbohydrates in roots and rhizomes of Typha latifolia (Typhaceae)
Authors: Biesboer David D.
Published: September 2008

Seasonal changes in nitrogen fixation, numbers of nitrogen-fixing bacteria associated with the roots, and rhizome–root carbohydrates were studied for the broad-leaved cattail, Typha latifolia L. Populations of anaerobic and aerobic diazotrophic bacteria were present on the root surface. Anaerobic bacteria predominated in the diazotrophic association, were more active in the acetylene reduction assay, and generally outnumbered aerobic bacteria by 2 to 1 during maximum rates of seasonal nitrogen fixation. The observed maximum nitrogen fixation rate coincided closely with reproductive development in Typha and peak microbial populations. Starch levels in rhizomes were nearly depleted during the middle of the growing season, whereas free sugar concentrations remained stable. Sugar concentrations in the roots increased rapidly during rhizome–root growth and decreased rapidly prior to peak nitrogenase activity.
Culm anatomy in barley (Hordeum vulgare)
Authors: Cenci C. A. , Grando S. , Ceccarelli S.
Published: September 2008

Four barley varieties and four F8 lines derived by divergent selection for culm length were studied for a number of anatomical characteristics of the culm. Significant differences were observed in length and width of epidermal cells, culm thickness, thickness of sclerenchyma, and thickness of sclerenchyma cell walls. Except for the thickness of the sclerenchyma cell walls, the differences in the anatomical characteristics of the culm were not correlated with those in culm length caused by selection. Although it was not possible to determine the genetic basis of the association between culm length and thickness of the sclerenchyma cell walls because of the type of material used, this result does have implications in relation to breeding for lodging resistance. It is suggested that a higher lodging resistance could be obtained by combining in the same genotype a short culm with thick-walled sclerenchyma cells.
Microscale pattern of vascular plant distribution in two high arctic plant communities
Authors: Sohlberg E. H. , Bliss L. C.
Published: September 2008

Microscale pattern is of crucial importance in determining the distribution of vascular plants in the extreme environments of the High Arctic. Point-quadrat analysis of the distribution of the vascular plants in a mesic cryptogam–herb meadow and a xeric Puccinellia barren found a nonrandom distribution of vascular species. Most species were found growing in moss turfs versus crustose lichen or bare soil surfaces in the meadow and in desiccation cracks in the barren. Two species showed an opposite distribution pattern in the meadow indicating that incipient niche differentiation occurs in the High Arctic. Quadrat sampling showed that seed distribution was random in the meadow and only slightly skewed toward cracks in the barren. Microsites appeared to be crucial to the seedling establishment and adult distribution pattern for Papaver radicatum but less important for Ranunculus sabinei. Microclimate analyses showed that soil temperatures were higher, wind speeds were lower, soil moisture content was greater, and nitrate levels were higher in the microsites usually preferred by plants.
Regulation of ATP-sulfurylase by various nitrogen and sulfur sources in cultured Ipomoea sp.
Authors: Zink M. W.
Published: September 2008

ATP-sulfurylase of Ipomoea sp. (morning glory) grown in suspension culture on a chemically defined medium is incompletely repressed by a readily assimilated sulfur source such as sulfate. The developmental pattern of the enzyme shows two peaks of activity, one peak before the onset and the other at the end of the logarithmic phase of growth. However, when ammonium plus nitrate is replaced by ammonium or casein hydrolysate as a nitrogen source in the medium, one peak of enzyme activity is observed. The enzyme is derepressed during growth of the cells on a slowly assimilated sulfur source such as L-djenkolate or cysteic acid or under conditions of sulfur starvation. Cysteic acid derepresses the enzyme even in the presence of repressible levels of sulfate in the medium. The enzyme also is derepressed when Ipomoea is grown on cysteine or methionine at a concentration of sulfur equivalent to that present in 1 mM sulfate. These amino acids repress ATP-sulfurylase only when added to the medium containing derepressing levels of sulfate (0.1 mM). Cells grown on a slowly assimilated nitrogen source such as proline, histidine, or nitrate form lower levels of ATP-sulfurylase than cells grown on readily assimilated nitrogen such as ammonium, ammonium plus nitrate, or casein hydrolysate. Thus, sulfate assimilation is subject to positive control by nitrogen metabolism and negative control by sulfur sources such as cysteine and methionine.