Showing 81 - 90 of 733 Items
Measurement of gross photosynthesis, respiration in the light, and mesophyll conductance usingh2 18o labeling
Date: 2018-05-01
Creator: Paul P.G. Gauthier, Mark O. Battle, Kevin L. Griffin, Michael L. Bender
Access: Open access
- A fundamental challenge in plant physiology is independently determining the rates of gross O2 production by photosynthesis and O2 consumption by respiration, photorespiration, and other processes. Previous studies on isolated chloroplasts or leaves have separately constrained net and gross O2 production (NOP and GOP, respectively) by labeling ambient O2 with 18O while leaf water was unlabeled. Here, we describe a method to accurately measure GOP and NOP of whole detached leaves in a cuvette as a routine gas-exchange measurement. The petiole is immersed in water enriched to a d18O of ;9,000 , and leaf water is labeled through the transpiration stream. Photosynthesis transfers 18O from H2O to O2. GOP is calculated from the increase in d18O ofO2 as air passes through the cuvette. NOP is determined from the increase in O2/N2. Both terms are measured by isotope ratio mass spectrometry. CO2 assimilation and other standard gas-exchange parameters also were measured. Reproducible measurements are made on a single leaf for more than 15 h. We used this method to measure the light response curve of NOP and GOP in French bean (Phaseolus vulgaris) at 21% and 2% O2. We then used these data to examine the O2/CO2 ratio of net photosynthesis, the light response curve of mesophyll conductance, and the apparent inhibition of respiration in the light (Kok effect) at both oxygen levels. The results are discussed in the context of evaluating the technique as a tool to study and understand leaf physiological traits.
Evidence for penguin-diagram decays: First observation of B→K*(892)γ
Date: 1993-01-01
Creator: R. Ammar, S. Ball, P. Baringer, D. Coppage, N., Copty, R. Davis, N. Hancock, M. Kelly, N. Kwak, H. Lam, Y. Kubota, M. Lattery, J. K. Nelson, S. Patton, D. Perticone, R. Poling, V. Savinov, S. Schrenk, R. Wang, M. S. Alam, I. J. Kim, B. Nemati, J. J. O'Neill, H. Severini, C. R. Sun, M. M. Zoeller, G. Crawford, M. Daubenmeir, R. Fulton, D. Fujino, K. K. Gan
Access: Open access
- We have observed the decays B0→K*(892)0γ and B-→K*(892)-γ, which are evidence for the quark-level process b→sγ. The average branching fraction is (4.5±1.5±0.9) ×10-5. This value is consistent with standard model predictions from electromagnetic penguin diagrams. © 1993 The American Physical Society.
Study of D0 decays into K̄0 and K̄*0
Date: 1993-01-01
Creator: M. Procario, S. Yang, D. S. Akerib, B. Barish, M., Chadha, S. Chan, D. F. Cowen, G. Eigen, J. S. Miller, J. Urheim, A. J. Weinstein, D. Acosta, M. Athanas, G. Masek, B. Ong, H. Paar, M. Sivertz, A. Bean, J. Gronberg, R. Kutschke, S. Menary, R. J. Morrison, S. Nakanishi, H. N. Nelson, T. K. Nelson, J. D. Richman, H. Tajima, D. Schmidt, D. Sperka, M. S. Witherell, R. Ballest
Access: Open access
- Using the CLEO II detector at CESR we have studied D0 decays into final states with a K̄0 or K̄*0, and have measured branching ratios for the decay modes D0→(K̄0K̄*0)π0,η, η′. These results are compared with predictions of various charm decay models, and contributions of final-state interactions are discussed. © 1993 The American Physical Society.
Molecular and mass spectral identification of the broadly conserved decapod crustacean neuropeptide pQIRYHQCYFNPISCF: The first PISCF-allatostatin (Manduca sexta- or C-type allatostatin) from a non-insect
Date: 2010-01-01
Creator: Elizabeth A. Stemmler, Emily A. Bruns, Christopher R. Cashman, Patsy S. Dickinson, Andrew E., Christie
Access: Open access
- The PISCF-allatostatins (Manduca sexta- or C-type allatostatins) are a family of pentadecapeptides characterized by a pyroglutamine blocked N-terminus, an unamidated-PISCF C-terminus, and a disulfide bridge between two internal Cys residues. Several isoforms of PISCF-AST are known, all from holometabolous insects. Using a combination of transcriptomics and mass spectrometry, we have identified the first PISCF-type peptides from a non-insect species. In silico analysis of crustacean ESTs identified several Litopenaeus vannamei (infraorder Penaeidea) transcripts encoding putative PISCF-AST precursors. Translation of these ESTs, with subsequent prediction of their putative post-translational processing, revealed the existence of as many as three PISCF-type peptides, including pQIRYHQCYFNPISCF (disulfide bridging between Cys7 and Cys14). Although none of the predicted isoforms was detected by mass spectrometry in L. vannamei, MALDI-FTMS mass profiling identified an m/z signal corresponding to pQIRYHQCYFNPISCF (disulfide bridge present) in neural tissue from 28 other decapods, which included members of six infraorders (Stenopodidea, Astacidea, Thalassinidea, Achelata, Anomura and Brachyura). Further characterization of the peptide using SORI-CID and chemical derivatization/enzymatic digestion supported the theorized structure. In both the crab Cancer borealis and the lobster Homarus americanus, MALDI-based tissue surveys suggest that pQIRYHQCYFNPISCF is broadly distributed in the nervous system; it was also detected in the posterior midgut caecum. Collectively, our data show that members of the PISCF-AST family are not restricted to the holometabolous insects, but instead may be broadly conserved within the Pancrustacea. Moreover, our data suggest that one highly conserved PISCF-type peptide, pQIRYHQCYFN-PISCF, is present in decapod crustaceans, functioning as a brain-gut paracrine/hormone. © 2009 Elsevier Inc. All rights reserved.
Identification and cardiotropic actions of sulfakinin peptides in the American lobster Homarus americanus
Date: 2007-07-01
Creator: Patsy S. Dickinson, Jake S. Stevens, Szymon Rus, Henry R. Brennan, Christopher C., Goiney, Christine M. Smith, Lingjun Li, David W. Towle, Andrew E. Christie
Access: Open access
- In arthropods, a group of peptides possessing a -Y(SO3H)GHM/ LRFamide carboxy-terminal motif have been collectively termed the sulfakinins. Sulfakinin isoforms have been identified from numerous insect species. In contrast, members of this peptide family have thus far been isolated from just two crustaceans, the penaeid shrimp Penaeus monodon and Litopenaeus vannamei. Here, we report the identification of a cDNA encoding prepro-sulfakinin from the American lobster Homarus americanus. Two sulfakinin-like sequences were identified within the open-reading frame of the cDNA. Based on modifications predicted by peptide modeling programs, and on homology to the known isoforms of sulfakinin, particularly those from shrimp, the mature H. americanus sulfakinins were hypothesized to be pEFDEY(SO3H)GHMRFamide (Hoa-SK I) and GGGEY(SO3H)DDY(SO3H)GHLRFamide (Hoa-SK II). Hoa-SK I is identical to one of the previously identified shrimp sulfakinins, while Hoa-SK II is a novel isoform. Exogenous application of either synthetic Hoa-SK I or Hoa-SK II to the isolated lobster heart increased both the frequency and amplitude of spontaneous heart contractions. In preparations in which spontaneous contractions were irregular, both peptides increased the regularity of the heartbeat. Our study provides the first molecular characterization of a sulfakinin-encoding cDNA from a crustacean, as well as the first demonstration of bioactivity for native sulfakinins in this group of arthropods.
To what extent may peptide receptor gene diversity/complement contribute to functional flexibility in a simple pattern-generating neural network?
Date: 2019-06-01
Creator: Patsy S. Dickinson, J. Joe Hull, Alexandra Miller, Emily R. Oleisky, Andrew E., Christie
Access: Open access
- Peptides are known to contribute to central pattern generator (CPG) flexibility throughout the animal kingdom. However, the role played by receptor diversity/complement in determining this functional flexibility is not clear. The stomatogastric ganglion (STG) of the crab, Cancer borealis, contains CPGs that are models for investigating peptidergic control of rhythmic behavior. Although many Cancer peptides have been identified, their peptide receptors are largely unknown. Thus, the extent to which receptor diversity/complement contributes to modulatory flexibility in this system remains unresolved. Here, a Cancer mixed nervous system transcriptome was used to determine the peptide receptor complement for the crab nervous system as a whole. Receptors for 27 peptide families, including multiple receptors for some groups, were identified. To increase confidence in the predicted sequences, receptors for allatostatin-A, allatostatin-B, and allatostatin-C were cloned, sequenced, and expressed in an insect cell line; as expected, all three receptors trafficked to the cell membrane. RT-PCR was used to determine whether each receptor was expressed in the Cancer STG. Transcripts for 36 of the 46 identified receptors were amplified; these included at least one for each peptide family except RYamide. Finally, two peptides untested on the crab STG were assessed for their influence on its motor outputs. Myosuppressin, for which STG receptors were identified, exhibited clear modulatory effects on the motor patterns of the ganglion, while a native RYamide, for which no STG receptors were found, elicited no consistent modulatory effects. These data support receptor diversity/complement as a major contributor to the functional flexibility of CPGs.
Measurement of the τ-lepton mass
Date: 1993-01-01
Creator: R. Balest, M. Daoudi, W. T. Ford, D. R. Johnson, K., Lingel, M. Lohner, P. Rankin, J. G. Smith, J. P. Alexander, C. Bebek, K. Berkelman, D. Besson, T. E. Browder, D. G. Cassel, H. A. Cho, D. M. Coffman, P. S. Drell, R. Ehrlich, R. S. Galik, M. Garcia-Sciveres, B. Geiser, B. Gittelman, S. W. Gray, D. L. Hartill, B. K. Heltsley, K. Honscheid, C. D. Jones, J. Kandaswamy, N. Katayama, P. C. Kim, D. L. Kreinick
Access: Open access
- Using data from the CLEO II detector at CESR, we measure the τ-lepton mass by exploiting the unique kinematics of events in which both τ's decay hadronically. The result is mτ=1777.8±0.7±1.7 MeV/c2. By comparing our result with other measurements near τ-pair threshold, we extract an upper limit on the τ-neutrino mass of 75 MeV/c2 at 95% confidence level. © 1993 The American Physical Society.
Coordination of distinct but interacting rhythmic motor programs by a modulatory projection neuron using different co-transmitters in different ganglia
Date: 2013-05-01
Creator: Molly A. Kwiatkowski, Emily R. Gabranski, Kristen E. Huber, M. Christine Chapline, Andrew E., Christie, Patsy S. Dickinson
Access: Open access
- While many neurons are known to contain multiple neurotransmitters, the specific roles played by each co-transmitter within a neuron are often poorly understood. Here, we investigated the roles of the co-transmitters of the pyloric suppressor (PS) neurons, which are located in the stomatogastric nervous system (STNS) of the lobster Homarus americanus. The PS neurons are known to contain histamine; using RT-PCR, we identified a second co-transmitter as the FMRFamide-like peptide crustacean myosuppressin (Crust-MS). The modulatory effects of Crust-MS application on the gastric mill and pyloric patterns, generated in the stomatogastric ganglion (STG), closely resembled those recorded following extracellular PS neuron stimulation. To determine whether histamine plays a role in mediating the effects of the PS neurons in the STG, we bath-applied histamine receptor antagonists to the ganglion. In the presence of the antagonists, the histamine response was blocked, but Crust-MS application and PS stimulation continued to modulate the gastric and pyloric patterns, suggesting that PS effects in the STG are mediated largely by Crust-MS. PS neuron stimulation also excited the oesophageal rhythm, produced in the commissural ganglia (CoGs) of the STNS. Application of histamine, but not Crust-MS, to the CoGs mimicked this effect. Histamine receptor antagonists blocked the ability of both histamine and PS stimulation to excite the oesophageal rhythm, providing strong evidence that the PS neurons use histamine in the CoGs to exert their effects. Overall, our data suggest that the PS neurons differentially utilize their co-transmitters in spatially distinct locations to coordinate the activity of three independent networks. © 2013. Published by The Company of Biologists Ltd.
A hydrophobic, carboxy-proximal region of a light-harvesting chlorophyll a/b protein is necessary for stable integration into thylakoid membranes.
Date: 1989-01-01
Creator: B. D. Kohorn, E. M. Tobin
Access: Open access
- Proteins synthesized as soluble precursors in the cytoplasm of eukaryotic cells often cross organellar membrane barriers and then insert into lipid bilayers. One such polypeptide, the light-harvesting chlorophyll a/b-binding protein (LHCP), must also associate with pigment molecules and be assembled into the photosystem II light-harvesting complex in the chloroplast thylakoid membrane. A study of the import of mutant LHCPs into isolated chloroplasts has shown that a putative alpha-helical membrane-spanning domain near the carboxy terminus (helix 3) is essential for the stable insertion of LHCP in the thylakoid. Protease digestion experiments are consistent with the carboxy terminus of the protein being in the lumen. This report also shows that helix 3, when fused to a soluble protein, can target it to the thylakoids of isolated, intact chloroplasts. Although helix 3 is required for the insertion of LHCP and mutant derivatives into the thylakoid, the full insertion of helix 3 itself requires additionally the presence of other regions of LHCP. Thus, LHCP targeting and integration into thylakoid membranes requires a complex interaction involving a number of different domains of the LHCP polypeptide.
Nonlinear excitations in magnetic lattices with long-range interactions
Date: 2019-06-24
Creator: Miguel Molerón, C. Chong, Alejandro J. Martínez, Mason A. Porter, P. G., Kevrekidis, Chiara Daraio
Access: Open access
- We study - experimentally, theoretically, and numerically - nonlinear excitations in lattices of magnets with long-range interactions. We examine breather solutions, which are spatially localized and periodic in time, in a chain with algebraically-decaying interactions. It was established two decades ago (Flach 1998 Phys. Rev. E 58 R4116) that lattices with long-range interactions can have breather solutions in which the spatial decay of the tails has a crossover from exponential to algebraic decay. In this article, we revisit this problem in the setting of a chain of repelling magnets with a mass defect and verify, both numerically and experimentally, the existence of breathers with such a crossover.