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Relevant bibliographies by topics / Catalytic activities

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Academic literature on the topic 'Catalytic activities'

Author: Grafiati

Published: 4 June 2021

Last updated: 18 June 2025

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Journal articles on the topic "Catalytic activities"

1

Adeoye, Raphael I., Dunsin S. Osalaye, Theresia K. Ralebitso-Senior, et al. "Catalytic Activities of Multimeric G-Quadruplex DNAzymes." Catalysts 9, no. 7 (2019): 613. http://dx.doi.org/10.3390/catal9070613.

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G-quadruplex DNAzymes are short DNA aptamers with repeating G4 quartets bound in a non-covalent complex with hemin. These G4/Hemin structures exhibit versatile peroxidase-like catalytic activity with a wide range of potential applications in biosensing and biotechnology. Current efforts are aimed at gaining a better understanding of the molecular mechanism of DNAzyme catalysis as well as devising strategies for improving their catalytic efficiency. Multimerisation of discrete units of G-quadruplexes to form multivalent DNAzyes is an emerging design strategy aimed at enhancing the peroxidase activities of DNAzymes. While this approach holds promise of generating more active multivalent G-quadruplex DNAzymes, few examples have been studied and it is not clear what factors determine the enhancement of catalytic activities of multimeric DNAzymes. In this study, we report the design and characterisation of multimers of five G-quadruplex sequences (AS1411, Bcl-2, c-MYC, PS5.M and PS2.M). Our results show that multimerisation of G-quadruplexes that form parallel structure (AS1411, Bcl-2, c-MYC) leads to significant rate enhancements characteristic of cooperative and/or synergistic interactions between the monomeric units. In contrast, multimerisation of DNA sequences that form non-parallel structures (PS5.M and PS2.M) did not exhibit similar levels of synergistic increase in activities. These results show that design of multivalent G4/Hemin structures could lead to a new set of versatile and efficient DNAzymes with enhanced capacity to catalyse peroxidase-mimic reactions.

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Holzwarth, Arnold, and Wilhelm F. Maier. "Catalytic Phenomena in Combinatorial Libraries of Heterogeneous Catalysts." Platinum Metals Review 44, no. 1 (2000): 16–21. http://dx.doi.org/10.1595/003214000x4411621.

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Combinatorial catalysis is becoming a significant method for investigating the activities of large numbers of potential catalysts. A very important prerequisite for making use of combinatorial catalysis research is a reliable, fast and efficient technique for monitoring the catalytic activities. Emissivity-corrected infrared thermography, which monitors the heat changes resulting from the heat of reaction on catalyst surfaces, is such a technique. In this article we describe emissivity-corrected infrared thermography and demonstrate its performance, over time, in monitoring the catalytic activities of catalyst libraries. It is shown that not only can static relative activity be displayed, but also that catalyst-specific time-dependent properties, such as activation and deactivation phenomena can be demonstrated.

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MATCHAM, G. W. J., J. M. CHAPSAL, and D. GUILLOCHON. "Catalytic Activities of Bovine Hemoglobin." Annals of the New York Academy of Sciences 501, no. 1 Enzyme Engine (1987): 21–35. http://dx.doi.org/10.1111/j.1749-6632.1987.tb45680.x.

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Oba, Takae, Jun Fukushima, Masako Maruyama, Ryoko Iwamoto, and Kenji Ikehara. "Catalytic Activities Of [GADV]-Peptides." Origins of Life and Evolution of Biospheres 35, no. 5 (2005): 447–60. http://dx.doi.org/10.1007/s11084-005-3519-5.

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Sohn, Jong Rack, and Jun Seob Lim. "Catalytic Activities of Al2O3-promoted NiSO4/TiO2 for Acid Catalysis." Catalysis Letters 108, no. 1-2 (2006): 71–78. http://dx.doi.org/10.1007/s10562-006-0020-3.

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Carballares, Diego, Roberto Morellon-Sterling, and Roberto Fernandez-Lafuente. "Design of Artificial Enzymes Bearing Several Active Centers: New Trends, Opportunities and Problems." International Journal of Molecular Sciences 23, no. 10 (2022): 5304. http://dx.doi.org/10.3390/ijms23105304.

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Harnessing enzymes which possess several catalytic activities is a topic where intense research has been carried out, mainly coupled with the development of cascade reactions. This review tries to cover the different possibilities to reach this goal: enzymes with promiscuous activities, fusion enzymes, enzymes + metal catalysts (including metal nanoparticles or site-directed attached organometallic catalyst), enzymes bearing non-canonical amino acids + metal catalysts, design of enzymes bearing a second biological but artificial active center (plurizymes) by coupling enzyme modelling and directed mutagenesis and plurizymes that have been site directed modified in both or in just one active center with an irreversible inhibitor attached to an organometallic catalyst. Some examples of cascade reactions catalyzed by the enzymes bearing several catalytic activities are also described. Finally, some foreseen problems of the use of these multi-activity enzymes are described (mainly related to the balance of the catalytic activities, necessary in many instances, or the different operational stabilities of the different catalytic activities). The design of new multi-activity enzymes (e.g., plurizymes or modified plurizymes) seems to be a topic with unarguable interest, as this may link biological and non-biological activities to establish new combo-catalysis routes.

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Cao, Liang, Le Niu, and Tim Mueller. "Computationally generated maps of surface structures and catalytic activities for alloy phase diagrams." Proceedings of the National Academy of Sciences 116, no. 44 (2019): 22044–51. http://dx.doi.org/10.1073/pnas.1910724116.

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To facilitate the rational design of alloy catalysts, we introduce a method for rapidly calculating the structure and catalytic properties of a substitutional alloy surface that is in equilibrium with the underlying bulk phase. We implement our method by developing a way to generate surface cluster expansions that explicitly account for the lattice parameter of the bulk structure. This approach makes it possible to computationally map the structure of an alloy surface and statistically sample adsorbate binding energies at every point in the alloy phase diagram. When combined with a method for predicting catalytic activities from adsorbate binding energies, maps of catalytic activities at every point in the phase diagram can be created, enabling the identification of synthesis conditions likely to result in highly active catalysts. We demonstrate our approach by analyzing Pt-rich Pt–Ni catalysts for the oxygen reduction reaction, finding 2 regions in the phase diagram that are predicted to result in highly active catalysts. Our analysis indicates that the Pt3Ni(111) surface, which has the highest known specific activity for the oxygen reduction reaction, is likely able to achieve its high activity through the formation of an intermetallic phase with L12 order. We use the generated surface structure and catalytic activity maps to demonstrate how the intermetallic nature of this phase leads to high catalytic activity and discuss how the underlying principles can be used in catalysis design. We further discuss the importance of surface phases and demonstrate how they can dramatically affect catalytic activity.

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Yuan, Zeqin, Jun Liao, Hao Jiang, Peng Cao, and Yang Li. "Aldehyde catalysis – from simple aldehydes to artificial enzymes." RSC Advances 10, no. 58 (2020): 35433–48. http://dx.doi.org/10.1039/d0ra06651f.

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Aogaki, R., R. Morimoto, M. Asanuma, et al. "Chiral catalytic activities in magnetoelectrochemical etching." Magnetohydrodynamics 51, no. 2 (2015): 353–60. http://dx.doi.org/10.22364/mhd.51.2.20.

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Chen, Kai, and Frances H. Arnold. "Engineering new catalytic activities in enzymes." Nature Catalysis 3, no. 3 (2020): 203–13. http://dx.doi.org/10.1038/s41929-019-0385-5.

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Dissertations / Theses on the topic "Catalytic activities"

1

Tamura, Tomoki. "Functionalization of ribonucleopeptide receptors for sensing and catalytic activities." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225707.

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Jurado-Gonzalez, Magdalena. "Metal phosphonates modified silicas : synthesis, characterisation and catalytic activities." Thesis, Queen Mary, University of London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409511.

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Agboola, Bolade Oyeyinka. "Catalytic activities of Metallophthalocyanines towards detection and transformation of pollutants /." Thesis, Rhodes University, 2007. http://eprints.ru.ac.za/873/.

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Aidam, Edward Kwaku. "Preparation, characterisation and catalytic activities of supported Pd-Ce systems." Thesis, Brunel University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303208.

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Suzuki, Toshiaki. "Syntheses, Structures, and Catalytic Activities of Novel Zerovalent Ruthenium Complexes." Kyoto University, 2000. http://hdl.handle.net/2433/180929.

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Mehmood, Zahid. "Catalytic activities of heterologously expressed human cytochrome P450 3A4 in yeast." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245538.

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Nambukara, Wellala Nadeesha P. "Synthesis and Catalytic Activities of Nickel Complexes Bearing Flexible Tridentate Ligands." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1491561548324255.

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Ghosh, A. "Synthesis, characterization and catalytic activities of organic-inorganic hybrid mesoporous materials." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2004. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2409.

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Ishchenko, Olga. "Elaboration of plasmonic nano-composites and study of their specific catalytic activities." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAF042/document.

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L’objective est d’améliorer l’activité photocatalytique de TiO2 sous irradiations UV et Visible. Pour contourner les limites de TiO2 intrinsèque nous envisageons une fabrication de nanocomposite plasmonique à base de nanofils de TiO2 périodiquement organisés et assemblés avec des nanoparticules plasmoniques. Pour la fabrication des nanofils de TiO2 mécaniquement stables, deux approches ont été réalisées. La première approche est basée sur la croissance sélective en phase vapeur, la deuxième approche consiste en l’utilisation d’un moule de membranes AAO et d’un dépôt de films conformes par ALD. En parallèle les films de TiO2déposés par ALD sont assemblés avec les nanoparticules plasmoniques d’or. Les différentes architectures de TiO2 sont valorisées par des tests photocatalytiques (UV et Visible) sur les polluants modèles. Une nouvelle approche de la fabrication des films mesoporeux d’H-TiO2 avec efficacité photocatalytique à la fois sous irradiation UV et Visible est développée<br>The objective of this thesis is to improve the photo-response of well-known photocatalytic material such as TiO2, which is usually only active in the UV range. The basic idea is to assemble several approaches within one device to improve the photocatalytic properties: fabrication of periodically-organised TiO2 nanostructures and their assembly with plasmonic nanoparticles. Two fabrication strategies were investigated for these purposes. The first approach consists of selective vapour phase growth. The second approach implements the use of an AAO template. In parallel, TiO2 films deposited by ALD and assembled with plasmonic gold nanoparticles are investigated. The photocatalytic measurements on various TiO2 architectures were performed in both irradiation ranges UV and Vis. A new fabrication approach of mesoporous H-TiO2 films was developed giving promising results of photocatalytic efficiency improvement in both UV and Visible ranges

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Wilson, Daniel Bernard. "The effects of zinc on the multi-catalytic activities of acetylcholinesterase and butyrylcholinesterase." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0030/NQ27472.pdf.

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Books on the topic "Catalytic activities"

1

Aidam, Edward Kwaku. Preparation charaterisation and catalytic activities of supported Pd-Ce systems. Brunel University, 1986.

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Metal Oxidesupported Gold Nanoparticles Sizedependence Of Catalytic Activities. LAP Lambert Academic Publishing, 2012.

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Demartis, Salvatore. A strategy for the isolation of catalytic activities from repertoires of enzymes displayed on phage. 2000.

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4

Aegerter, Paul A. Thiophene hydrodesulfurization over alumina-supported molybdenum carbide nitride catalysts: Adsorption sites, catalytic activities and nature of the active surface. 1996.

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5

Netzer, Falko P., and Claudine Noguera. Oxide Thin Films and Nanostructures. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198834618.001.0001.

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Nanostructured oxide materials ultra-thin films, nanoparticles and other nanometer-scale objects play prominent roles in many aspects of our every-day life, in nature and in technological applications, among which is the all-oxide electronics of tomorrow. Due to their reduced dimensions and dimensionality, they strongly interact with their environment gaseous atmosphere, water or support. Their novel physical and chemical properties are the subject of this book from both a fundamental and an applied perspective. It reviews and illustrates the various methodologies for their growth, fabrication, experimental and theoretical characterization. The role of key parameters such as film thickness, nanoparticle size and support interactions in driving their fundamental properties is underlined. At the ultimate thickness limit, two-dimensional oxide materials are generated, whose functionalities and potential applications are described. The emerging field of cation mixing is mentioned, which opens new avenues for engineering many oxide properties, as witnessed by natural oxide nanomaterials such as clay minerals, which, beyond their role at the Earth surface, are now widely used in a whole range of human activities. Oxide nanomaterials are involved in many interdisciplinary fields of advanced nanotechnologies: catalysis, photocatalysis, solar energy materials, fuel cells, corrosion protection, and biotechnological applications are amongst the areas where they are making an impact; prototypical examples are outlined. A cautious glimpse into future developments of scientific activity is finally ventured to round off the treatise.

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Book chapters on the topic "Catalytic activities"

1

Sinohara, H., and K. Matsuura. "Catalytic Activities and Functional Effects of Bence Jones Proteins." In Catalytic Antibodies. KARGER, 2000. http://dx.doi.org/10.1159/000058799.

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2

Klotz, I. M. "Synzymes: Synthetic Polymers with Enzymelike Catalytic Activities." In Advances in Chemical Physics. John Wiley & Sons, Inc., 2007. http://dx.doi.org/10.1002/9780470142585.ch3.

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Snell, Esmond E. "Tryptophanase: Structure, Catalytic Activities, and Mechanism of Action." In Advances in Enzymology - and Related Areas of Molecular Biology. John Wiley & Sons, Inc., 2006. http://dx.doi.org/10.1002/9780470122877.ch6.

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Sternfeld, Meira, Shlomo Seidman, Rachel Beeri, and Hermona Soreq. "Catalytic and Non-Catalytic Activities of Acetylcholinesterase Implied from Transgenic ACHE Expression in Vertebrates." In Neutrotransmitter Release and Uptake. Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/978-3-642-60704-2_22.

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Klotz, Irving M., and Junghun Suh. "Evolution of Synthetic Polymers with Enzyme-like Catalytic Activities." In Artificial Enzymes. Wiley-VCH Verlag GmbH & Co. KGaA, 2006. http://dx.doi.org/10.1002/3527606645.ch3.

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Saraswathi, S., and M. H. Keyes. "A Systematic Approach to Induce New Catalytic Activities in Proteins." In Polymeric Materials in Medication. Springer US, 1985. http://dx.doi.org/10.1007/978-1-4899-2245-8_21.

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Liu, Yu. "Mesostructured and Mesoporous Aluminosilicates with Improved Stability and Catalytic Activities." In Mesoporous Zeolites. Wiley-VCH Verlag GmbH & Co. KGaA, 2015. http://dx.doi.org/10.1002/9783527673957.ch4.

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Yamamoto, Yasuhiko, and Atsuya Momotake. "Structures and Catalytic Activities of Complexes Between Heme and DNA." In Handbook of Chemical Biology of Nucleic Acids. Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-1313-5_12-1.

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Yamamoto, Yasuhiko, and Atsuya Momotake. "Structures and Catalytic Activities of Complexes Between Heme and DNA." In Handbook of Chemical Biology of Nucleic Acids. Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-19-9776-1_12.

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Tate, Suresh S., and Alton Meister. "L-Aspartate-β-Decarboxylase; Structure, Catalytic Activities, and Allosteric Regulation." In Advances in Enzymology - and Related Areas of Molecular Biology. John Wiley & Sons, Inc., 2006. http://dx.doi.org/10.1002/9780470122808.ch9.

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Conference papers on the topic "Catalytic activities"

1

Verma, Divya, Vikash Sharma, Sarita Parmar, Gunadhor Singh Okram, and Shubha Jain. "Synthesis, characterizations and catalytic activities of CoFe2O4 nanoparticles." In 2ND INTERNATIONAL CONFERENCE ON CONDENSED MATTER AND APPLIED PHYSICS (ICC 2017). Author(s), 2018. http://dx.doi.org/10.1063/1.5032845.

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Pálinkó, István, Adrien Ordasi, János T. Kiss, Imre Labádi, V. K. Vaidyan, and V. S. Jayakumar. "Immobilized Cu (II)—Amino Acid Complexes as Prospective Highly Efficient Catalytic Materials: Synthesis, Structural Characterization and Catalytic Activities." In PERSPECTIVES IN VIBRATIONAL SPECTROSCOPY: Proceedings of the 2nd International Conference on Perspectives in Vibrational Spectroscopy (ICOPVS 2008). AIP, 2008. http://dx.doi.org/10.1063/1.3046201.

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Kokai, Fumio, T. Kameshima, T. Miyazaki, et al. "Catalytic activities of metals for single-wall carbon nanotube growth during CO2 laser vaporization." In High-Power Lasers and Applications, edited by Kouichi Murakami, David B. Geohegan, and Frank Traeger. SPIE, 2002. http://dx.doi.org/10.1117/12.459731.

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Petersen, L. C., M. Johannessen, D. Foster, A. Kumar, and E. Mulvihill. "CATALYTIC ACTIVITIES OF ONE-CHAIN tPA AS REVEALED BY AN ANALOGUE RESISTANT TO PLASMIN CLEAVAGE." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643845.

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Substitution of Arg275 with Gly in the activation site of tPA provides a one-chain recombinant analogue, tPA-Gly275, which is very resistant to cleavage by plasmin. The amidolytic activity of tPA-Gly275 with simple synthetic substrates was investigated and compared to the kinetics obtained with authentic one- and two-chain tPA. Both one-chain (zymogen) forms possess enzymatic activity, however, in the absence of fibrin it is much lower than that of two-chain tPA. Fibrin enhances the activity of the one-chain tPA forms, but not of two-chain tPA.A chromogenic assay was developed for measurement of plasminogen activation. Due to the presence of a high affinity plasmin substrate (D-Val-Phe-Lys-pNA) and aprotinin in the reaction mixture, the assay ensures a low steady-state concentration of free plasmin during the measurement. With this assay and with tPA-Gly275 it is possible to measure plasminogen activation kinetics of one-chain tPA without any significant two-chain tPA formation even in the presence of fibrin. The intactness of tPA-Gly275 was confirmed by direct measurement of the one-/two-chain tPA content by means of reduced SDS-PAGE combined with Western blotting after exposure to plasmin digestion in the presence and absence of fibrin. The results suggest that one-chain tPA possesses enzymatic activity also with plasminogen as the substrate, however, the activity is much lower than that of two-chain tPA. Addition of fibrin profoundly enhances the plasminogen activation rate of both tPA-Gly275, one-chain, and two-chain authentic tPA to approx. the same maximal level. Taken together these observations indicate that fibrin binding can induce an activated state of the intact tPA ‘zymogen’

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Ahmad, Amirah, Karimah Kassim, and Hamizah Md Rasid. "Synthesis and characterization of thiourea complex encapsulated into functionalized-MCM41 and their catalytic activities for oxidation reaction." In 2012 IEEE Colloquium on Humanities, Science and Engineering (CHUSER). IEEE, 2012. http://dx.doi.org/10.1109/chuser.2012.6504429.

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Susanti, Y. D., N. Afifah, and R. Saleh. "Comparison between photo- and sono- catalytic activities of LaMnO3/Fe3O4/NGP to remove methylene blue from wastewater." In PROCEEDINGS OF THE 3RD INTERNATIONAL SYMPOSIUM ON CURRENT PROGRESS IN MATHEMATICS AND SCIENCES 2017 (ISCPMS2017). Author(s), 2018. http://dx.doi.org/10.1063/1.5064033.

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Park, Seokju, Octia Floweri, and Naesung Lee. "CNT paste emitters with minimal damage during high temperature vacuum brazing fabricated using fillers having low catalytic activities." In 2016 29th International Vacuum Nanoelectronics Conference (IVNC). IEEE, 2016. http://dx.doi.org/10.1109/ivnc.2016.7551512.

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Kwong, C. W., C. Y. H. Chao, and K. S. Hui. "Recycling Biomass Co-Combustion Fly-Ash Products for an Integrated Solar-Assisted Ventilation System." In ASME 2009 3rd International Conference on Energy Sustainability collocated with the Heat Transfer and InterPACK09 Conferences. ASMEDC, 2009. http://dx.doi.org/10.1115/es2009-90128.

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The potential use of biomass co-combustion derived fly-ash products and zeolite 13X for the elimination of volatile organic compounds (VOCs) using ozone was investigated for an integrated solar-assisted air purification and desiccant cooling system. Fly-ash products from rice husk-coal co-combustion at different biomass blending ratios were used as the adsorbent/catalyst materials. The material characteristics of the adsorbent/catalyst materials such as metal content and surface area were compared and correlated with the catalytic activities. It was found that the surface area and the metal constitutes have made the catalytic activities over the fly-ash products from biomass co-combustion superior to that from coal-only combustion. The elevated reaction temperatures from 25°C to 75°C also have significant effects on the removal of VOCs. The apparent activation energies of the reaction path over the fly-ash products with the addition of ozone to the air were reduced, when compared with the use of air as an oxidant. On the other hand, the potential synergy to Zeolite 13X was explored. The combined catalytic ozonation and adsorption enhanced the VOCs removal and at the same time reduced the intermediates emission. Furthermore, the hydrophilic properties of zeolite 13X could be utilized to handle the latent load of the solar-assisted ventilation system for energy conservations.

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Kelm, S., W. Jahn, E. A. Reinecke, J. Baggemann, and H. J. Allelein. "CFD Simulation of Passive Auto-Catalytic Recombiner Operational Behaviour." In 17th International Conference on Nuclear Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/icone17-75831.

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In order to mitigate the impact of a possible hydrogen combustion and to avoid containment failure, passive auto-catalytic recombiners (PAR) are used for hydrogen removal in an increasing number of European nuclear power plants. Hydrogen and oxygen react exothermally even below conventional flammability limits on the catalytic surfaces inside a PAR generating steam and heat. Modelling of the operational behaviour of PAR is one part of development issues in order to achieve reliable predictions of local atmosphere conditions. International research activities, e.g. in the European FP-6/FP-7 Network of Excellence SARNET (Severe Accident Research NETwork), investigate these aspects. At Forschungszentrum Ju¨lich, two strategies are pursued. First, the detailed evaluation of the reaction kinetics and heat and mass transport phenomena on a single catalyst element is performed by a direct implementation of the transport and kinetic approaches in ANSYS CFX-11. Second, in order to model the interaction of PAR with the containment, REKO-DIREKT, a detailed user model of the relevant processes inside a PAR based on Fortran 90 will be implemented in CFX. At present, validation against the available experimental database is performed. The validity of the numerical models strongly depends on the experimental data available. For this purpose, detailed experiments are performed at Ju¨lich. In the small-scale test facility REKO-3, representing a recombiner section, detailed investigations of the reaction kinetics under well-defined and steady-state conditions have been performed. In co-operation with RWTH Aachen University, a new test vessel REKO-4 is currently under preparation for testing PAR behaviour under natural convection conditions. It will provide various possibilities for instrumentation to measure temperatures and gas compositions and in particular it will be equipped with particle image velocimetry (PIV) for measuring the flow field around the PAR.

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Jeevetha, T. "A Review on Smart and Eco-Friendly Building Material." In Sustainable Materials and Smart Practices. Materials Research Forum LLC, 2022. http://dx.doi.org/10.21741/9781644901953-14.

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Abstract. Due to industrialization and man-made activities in and around the world, Day by day pollution levels are drastically increasing. This being said, building materials in the present context can be produced using novel techniques by applying advanced pollution reduction coatings/strategies. The self-cleaning and de-air polluting concept is emphasized in concrete structures using nanotechnology. Photo-catalytic treatment will be a promising approach as it alleviates structural and aesthetic damages on building materials. Finally, the risk exposure due to pollutants can be computed for better treatment of the same.

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Reports on the topic "Catalytic activities"

1

Schuster, Gadi, and David Stern. Integrated Studies of Chloroplast Ribonucleases. United States Department of Agriculture, 2011. http://dx.doi.org/10.32747/2011.7697125.bard.

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Gene regulation at the RNA level encompasses multiple mechanisms in prokaryotes and eukaryotes, including splicing, editing, endo- and exonucleolytic cleavage, and various phenomena related to small or interfering RNAs. Ribonucleases are key players in nearly all of these post-transcriptional mechanisms, as the catalytic agents. This proposal continued BARD-funded research into ribonuclease activities in the chloroplast, where RNase mutation or deficiency can cause metabolic defects and is often associated with plant chlorosis, embryo or seedling lethality, and/or failure to tolerate nutrient stress. The first objective of this proposal was to examined a series of point mutations in the PNPase enzyme of Arabidopsis both in vivo and in vitro. This goal is related to structure-function analysis of an enzyme whose importance in many cellular processes in prokaryotes and eukaryotes has only begun to be uncovered. PNPase substrates are mostly generated by endonucleolytic cleavages for which the catalytic enzymes remain poorly described. The second objective of the proposal was to examine two candidate enzymes, RNase E and RNase J. RNase E is well-described in bacteria but its function in plants was still unknown. We hypothesized it catalyzes endonucleolytic cleavages in both RNA maturation and decay. RNase J was recently discovered in bacteria but like RNase E, its function in plants had yet to be explored. The results of this work are described in the scientific manuscripts attached to this report. We have completed the first objective of characterizing in detail TILLING mutants of PNPase Arabidopsis plants and in parallel introducing the same amino acids changes in the protein and characterize the properties of the modified proteins in vitro. This study defined the roles for both RNase PH core domains in polyadenylation, RNA 3’-end maturation and intron degradation. The results are described in the collaborative scientific manuscript (Germain et al 2011). The second part of the project aimed at the characterization of the two endoribonucleases, RNase E and RNase J, also in this case, in vivo and in vitro. Our results described the limited role of RNase E as compared to the pronounced one of RNase J in the elimination of antisense transcripts in the chloroplast (Schein et al 2008; Sharwood et al 2011). In addition, we characterized polyadenylation in the chloroplast of the green alga Chlamydomonas reinhardtii, and in Arabidopsis (Zimmer et al 2009). Our long term collaboration enabling in vivo and in vitro analysis, capturing the expertise of the two collaborating laboratories, has resulted in a biologically significant correlation of biochemical and in planta results for conserved and indispensable ribonucleases. These new insights into chloroplast gene regulation will ultimately support plant improvement for agriculture.

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Handa, Avtar K., Yuval Eshdat, Avichai Perl, Bruce A. Watkins, Doron Holland, and David Levy. Enhancing Quality Attributes of Potato and Tomato by Modifying and Controlling their Oxidative Stress Outcome. United States Department of Agriculture, 2004. http://dx.doi.org/10.32747/2004.7586532.bard.

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General The final goal and overall objective of the current research has been to modify lipid hydroperoxidation in order to create desirable phenotypes in two important crops, potato and tomato, which normally are exposed to abiotic stress associated with such oxidation. The specific original objectives were: (i) the roles of lipoxygenase (LOX) and phospholipids hydroperoxide glutathione peroxidase (PHGPx) in regulating endogenous levels of lipid peroxidation in plant tissues; (ii) the effect of modified lipid peroxidation on fruit ripening, tuber quality, crop productivity and abiotic stress tolerance; (iii) the effect of simultaneous reduction of LOX and increase of PHGPx activities on fruit ripening and tuber quality; and (iv) the role of lipid peroxidation on expression of specific genes. We proposed to accomplish the research goal by genetic engineering of the metabolic activities of LOX and PHGPx using regulatable and tissue specific promoters, and study of the relationships between these two consecutive enzymes in the metabolism and catabolism of phospholipids hydroperoxides. USA Significant progress was made in accomplishing all objectives of proposed research. Due to inability to regenerate tomato plants after transforming with 35S-PHGPx chimeric gene construct, the role of low catalase induced oxidative stress instead of PHGPx was evaluated on agronomical performance of tomato plant and fruit quality attributes. Effects of polyamine, that protects DNA from oxidative stress, were also evaluated. The transgenic plants under expressing lipoxygenase (LOX-sup) were crossed with catalase antisense (CAT-anti) plants or polyamine over producing plants (SAM-over) and the lines homozygous for the two transgenes were selected. Agronomical performance of these line showed that low catalase induced oxidative stress negatively affected growth and development of tomato plants and resulted in a massive change in fruit gene expression. These effects of low catalase activity induced oxidative stress, including the massive shift in gene expression, were greatly overcome by the low lipoxygenase activity. Collectively results show that oxidative stress plays significant role in plant growth including the fruit growth. These results also for the first time indicated that a crosstalk between oxidative stress and lipoxygenase regulated processes determine the outcome during plant growth and development. Israel Regarding PHGPx, most of the study has concentrated on the first and the last specific objectives, since it became evident that plant transformation with this gene is not obvious. Following inability to achieve efficient transformation of potato and tomato using a variety of promoters, model plant systems (tobacco and potato cell cultures, tobacco calli and plantlets, and Arabidopsis) were used to establish the factors and to study the obstacles which prohibited the regeneration of plants carrying the genetic machinery for overproduction of PHGPx. Our results clearly demonstrate that while genetic transformation and over-expression of PHGPx occurs in pre-developmental tissue stage (cell culture, calli clusters) or in completed plant (Arabidopsis), it is likely that over-expression of this enzyme before tissue differentiation is leading to a halt of the regeneration process. To support this assumption, experiments, in which genetic engineering of a point-mutated PHGPx gene enable transformation and over-expression in plants of PhSPY modified in its catalytic site and thus inactive enzymatically, were successfully carried out. These combined results strongly suggest, that if in fact, like in animals and as we established in vitro, the plant PHGPx exhibits PH peroxidase activity, these peroxides are vital for the organisms developmental process.

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Sessa, Guido, and Gregory Martin. A functional genomics approach to dissect resistance of tomato to bacterial spot disease. United States Department of Agriculture, 2004. http://dx.doi.org/10.32747/2004.7695876.bard.

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The research problem. Bacterial spot disease in tomato is of great economic importance worldwide and it is particularly severe in warm and moist areas affecting yield and quality of tomato fruits. Causal agent of spot disease is the Gram-negative bacterium Xanthomonas campestris pv. vesicatoria (Xcv), which can be a contaminant on tomato seeds, or survive in plant debris and in association with certain weeds. Despite the economic significance of spot disease, plant protection against Xcvby cultural practices and chemical control have so far proven unsuccessful. In addition, breeding for resistance to bacterial spot in tomato has been undermined by the genetic complexity of the available sources of resistance and by the multiple races of the pathogen. Genetic resistance to specific Xcvraces have been identified in tomato lines that develop a hypersensitive response and additional defense responses upon bacterial challenge. Central goals of this research were: 1. To identify plant genes involved in signaling and defense responses that result in the onset of resistance. 2. To characterize molecular properties and mode of action of bacterial proteins, which function as avirulence or virulence factors during the interaction between Xcvand resistant or susceptible tomato plants, respectively. Our main achievements during this research program are in three major areas: 1. Identification of differentially expressed genes during the resistance response of tomato to Xcvrace T3. A combination of suppression subtractive hybridization and microarray analysis identified a large set of tomato genes that are induced or repressed during the response of resistant plants to avirulent XcvT3 bacteria. These genes were grouped in clusters based on coordinate expression kinetics, and classified into over 20 functional classes. Among them we identified genes that are directly modulated by expression of the type III effector protein AvrXv3 and genes that are induced also during the tomato resistance response to Pseudomonas syringae pv. tomato. 2. Characterization of molecular and biochemical properties of the tomato LeMPK3MAP kinase. A detailed molecular and biochemical analysis was performed for LeMPK3 MAP kinase, which was among the genes induced by XcvT3 in resistant tomato plants. LeMPK3 was induced at the mRNA level by different pathogens, elicitors, and wounding, but not by defense-related plant hormones. Moreover, an induction of LeMPK3 kinase activity was observed in resistant tomato plants upon Xcvinfection. LeMPK3 was biochemically defined as a dual-specificity MAP kinase, and extensively characterized in vitro in terms of kinase activity, sites and mechanism of autophosphorylation, divalent cation preference, Kₘand Vₘₐₓ values for ATP. 3. Characteriztion of molecular properties of the Xcveffector protein AvrRxv. The avirulence gene avrRxvis involved in the genetic interaction that determines tomato resistance to Xcvrace T1. We found that AvrRxv functions inside the plant cell, localizes to the cytoplasm, and is sufficient to confer avirulence to virulent Xcvstrains. In addition, we showed that the AvrRxv cysteine protease catalytic core is essential for host recognition. Finally, insights into cellular processes activated by AvrRxv expression in resistant plants were obtained by microarray analysis of 8,600 tomato genes. Scientific and agricultural significance: The findings of these activities depict a comprehensive and detailed picture of cellular processes taking place during the onset of tomato resistance to Xcv. In this research, a large pool of genes, which may be involved in the control and execution of plant defense responses, was identified and the stage is set for the dissection of signaling pathways specifically triggered by Xcv.

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Sessa, Guido, та Gregory Martin. MAP kinase cascades activated by SlMAPKKKε and their involvement in tomato resistance to bacterial pathogens. United States Department of Agriculture, 2012. http://dx.doi.org/10.32747/2012.7699834.bard.

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The research problem: Pseudomonas syringae pv. tomato (Pst) and Xanthomonas campestrispv. vesicatoria (Xcv) are the causal agents of tomato bacterial speck and spot diseases, respectively. These pathogens colonize the aerial parts of the plant and cause economically important losses to tomato yield worldwide. Control of speck and spot diseases by cultural practices or chemicals is not effective and genetic sources of resistance are very limited. In previous research supported by BARD, by gene expression profiling we identified signaling components involved in resistance to Xcvstrains. Follow up experiments revealed that a tomato gene encoding a MAP kinase kinase kinase (MAPKKKe) is required for resistance to Xcvand Pststrains. Goals: Central goal of this research was to investigate the molecular mechanisms by which MAPKKKεand associated MAP kinase cascades regulate host resistance. Specific objectives were to: 1. Determine whether MAPKKKεplays a broad role in defense signaling in plants; 2. Identify components of MAP kinase cascades acting downstream of MAPKKKε; 3. Determine the role of phosphorylation-related events in the function of MAPKKKε; 4. Isolate proteins directly activated by MAPKKKε-associatedMAPK modules. Our main achievements during this research program are in the following major areas: 1. Characterization of MAPKKKεas a positive regulator of cell death and dissection of downstream MAP kinase cascades (Melech-Bonfil et al., 2010; Melech-Bonfil and Sessa, 2011). The MAPKKKεgene was found to be required for tomato resistance to Xcvand Pstbacterial strains and for hypersensitive response cell death triggered by different R gene/effector gene pairs. In addition, overexpression analysis demonstrated that MAPKKKεis a positive regulator of cell death, whose activity depends on an intact kinase catalytic domain. Epistatic experiments delineated a signaling cascade downstream of MAPKKKεand identified SIPKK as a negative regulator of MAPKKKε-mediated cell death. Finally, genes encoding MAP kinase components downstream of MAPKKKεwere shown to contribute to tomato resistance to Xcv. 2. Identification of tomato proteins that interact with MAPKKKεand play a role in plant immunity (Oh et al., 2011). We identified proteins that interact with MAPKKKε. Among them, the 14-3-3 protein TFT7 was required for cell death mediated by several R proteins. In addition, TFT7 interacted with the MAPKK SlMKK2 and formed homodimersin vivo. Thus, TFT7 is proposed to recruit SlMKK2 and MAPKKK client proteins for efficient signal transfer. 3. Development of a chemical genetic approach to identify substrates of MAPKKKε-activated MAP kinase cascades (Salomon et al., 2009, 2011). This approach is based on engineering the kinase of interest to accept unnatural ATP analogs. For its implementation to identify substrates of MAPKKKε-activated MAP kinase modules, we sensitized the tomato MAP kinase SlMPK3 to ATP analogs and verified its ability to use them as phosphodonors. By using the sensitized SlMPK3 and radiolabeled N6(benzyl)ATP it should be possible to tag direct substrates of this kinase. 4. Development of methods to study immunity triggered by pathogen-associated molecular patterns (PAMPs) in tomato and N. benthamiana plants (Kim et al., 2009; Nguyen et al. 2010). We developed protocols for measuring various PTI-associatedphenotypes, including bacterial populations after pretreatment of leaves with PAMPs, induction of reporter genes, callose deposition at the cell wall, activation of MAP kinases, and a luciferase-based reporter system for use in protoplasts. Scientific and agricultural significance: Our research activities discovered and characterized a signal transduction pathway mediating plant immunity to bacterial pathogens. Increased understanding of molecular mechanisms of immunity will allow them to be manipulated by both molecular breeding and genetic engineering to produce plants with enhanced natural defense against disease. In addition, we successfully developed new biochemical and molecular methods that can be implemented in the study of plant immunity and other aspects of plant biology.

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