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Science Highlights, January 21, 2015

Bioscience

Understanding how plants have resistance to fungus

Researchers have investigated the nature of resistance of tomato plants to a fungal infection. The tomato is one of the most economically important crops and a model system for fruit development. Strains of the ascomycete fungus Fusarium oxysporum are ubiquitous soil inhabitants. F. oxysporum acts as a pathogen to cause disease in vegetables, fruit trees, wheat, corn, cotton and ornamental crops. The fungus invades plant roots to infect vascular bundles in the plant host, leading to wilt symptoms. Cliff Han (Bioenergy and Biome Sciences, B-11) and Katherine Borkovich (University of California-Riverside, UCR) led a team that examined why the tomato cultivar Moneymaker is susceptible to the fungus Fusarium oxysporum while the near-isogenic tomato cultivar Motelle is resistant to the same fungus. The journal Plos Pathogens published the work.

The team explored a possible role for tomato miRNAs in the differential resistance of Moneymaker and Motelle to F. oxysporum. The researchers conducted a genome-wide microRNA (miRNA) expression analysis to determine the differential miRNA profiles induced upon fungal infection in susceptible and resistant tomato plants. The miRNAs are single-stranded RNA molecules of approximately 20–24 nucleotides in length that are endogenously transcribed from single-stranded non-coding RNA species. miRNAs are the negative regulators of specific messenger RNAs (mRNAs) that code proteins, which determine functions of human and plant cells.

The study provides a platform for differentially expressed miRNAs in tomato after F. oxysporum infection and demonstrates that plant miRNAs are involved in defense against the fungus. The results indicate that two different miRNAs contribute to plant immunity in tomato by influencing mRNA stability or translation of at least three nucleotide-binding site domain-containing proteins distinct from the I-2 gene, the only known resistance gene for F. oxysporum in tomato. The team observed that the miRNAs that down-regulate the expression of tm-2 (a resistance protein) are underexpressed in resistant tomato and overexpressed in susceptible tomato. It is the first report of the involvement of the tm-2 protein in the fungal resistance in tomato. The authors suggest that the potential resistance of the susceptible cultivar is insufficiently expressed due to the action of miRNAs. The findings support roles for resistance genes, in addition to the I-2 gene, in the plant’s immune response.

This combination of plant pathology and microbiology expertise of UCR and the next-generation functional genomics capability in LANL made this important discovery possible. These findings provide insight on how a pathogen subverts host defense through the down-regulation of an important tomato resistance gene. Identification of such mechanisms will be important in developing novel preventive measures, which in this case would imply up-regulation of the resistance gene.

Reference: “MicroRNAs Suppress NB Domain Genes in Tomato That Confer Resistance to Fusarium oxysporum,” Plos Pathogens 10 (10), e1004464 (2014); doi: 10.1371/journal.ppat.1004464. Authors include Shouqiang Ouyang, Gyungsoon Park, and Hagop S. Atamian (University of California-Riverside); Cliff S. Han (Bioenergy and Biome Sciences, B-11); Jason E. Stajich, Isgouhi Kaloshian, and Katherine A. Borkovich (UC-R).

The research was part of a special collaboration was between the Laboratory’s Bioscience Division and the University of California - Riverside Plant Science. The University of California Office of President funded the work to focus on the biology, diagnosis, and therapy of plant diseases. The research supports the Laboratory’s Global Security mission area and the Materials for the Future science pillar through the development of pathogen-resistant crops. Technical contact: Cliff Han

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Earth and Environmental Sciences

Scientists support Comprehensive Nuclear-Test-Ban Treaty field inspection exercise

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is an agreement that bans all signatory nations from conducting nuclear tests. The CTBT has been signed by more than 180 nations, but for entry into force, all 44 countries that possessed nuclear technology in 1996 must sign and ratify the Treaty. The Treaty has not yet entered into force because a number of countries have not ratified it. In preparation for eventual ratification and entry into force, the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) conducted the 2014 Integrated Field Exercise (IFE14), a simulated On-Site Inspection, which took place in Jordan from November 3 - December 9, 2014. Lab geologist Ward Hawkins (Geophysics, EES-17) chaired the Scenario Development Group for the integrated field exercise, and other Lab scientists supported the activity.

During an On-Site Inspection, a detailed search over an area up to 1000 km2 gathers evidence to determine whether or not a nuclear explosion has occurred. Because On-Site Inspections are the final verification measure to ensure States’ compliance with the CTBT, it is essential to test operations, procedures, and technologies before the Treaty enters into force. The IFE14 tested 15 of the 17 On-Site Inspection activities and techniques allowed by the Treaty. More than 200 technical experts from more than 40 countries conducted a mock on-site inspection in the Dead Sea area for evidence of a nuclear explosion. Jordan has a rich variety of geological features including sinkholes and landslides, which allow the testing of On-Site Inspection aspects under realistic conditions. IFE14 was the largest and most technologically advanced field exercise that the CTBTO has ever conducted. 

Experts from DOE national laboratories, including Sandia, Los Alamos, Lawrence Livermore, and Pacific Northwest National Laboratory supported the activity. LANL researchers participated in the development and implementation of IFE14. Over the past few years, Earth and Environmental Sciences employees Ward Hawkins, Ken Wohletz, and Aviva Sussman (EES-17); Emily Schultz-Fellenz, Rick Kelley, and Liz Miller (Earth System Observations, EES-14) planned, organized, and prepared various aspects of the exercise. Hawkins chaired the Scenario Development Group and served as the Control Team Leader in Jordan for the exercise. Ken Wohletz and Rick Kelley provided support in Jordon to the Control Team and the notional Inspected State Party during the exercise, Aviva Sussman and Emily Schultz-Fellenz served as Control Team members at the Operational Support Center in Vienna, and Liz Miller supported the exercise from Los Alamos as a Control Team Member. The EES-14 and EES-17 employees developed the scenario and oversaw the actual exercise to make sure that the goals of the exercise were met. Gordon MacLeod (Nuclear Nonproliferation and security, GS-NNS) worked for the CTBTO Preparatory Commission.

The conduct of IFE14 is a major step in the further development of the On-Site Inspection regime of the CTBT and will provide valuable information for preparing for future exercises and actual On-Site Inspections after entry into force. Inspection exercises such as IFE14 play a critical role in improving the mechanics of the inspection process and ensuring the operational capability and readiness for entry into force of the Treaty. More information: http://nnsa.energy.gov/blog/doennsa-participates-large-scale-ctbt-site-inspection-exercise-jordan

DOE NA-24 funded the work, which supports the Lab’s Global Security mission area and the Science of Signatures science pillar through development of methods to detect clandestine nuclear explosions. Technical contact: Ward Hawkins

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Materials Physics and Applications

Using ultrashort optical pulses to control magnetoelectric materials

Materials in which magnetic and electric order coexist have great potential for novel magnetoelectric devices, including applications in data storage, photovoltaics, and magnetic sensing. However, such materials are scarcely found in nature. Researchers at the Center for Integrated Nanotechnologies (CINT) aim to unravel key microscopic mechanisms that could advance a more abundant alternative—the engineering of artificial multiferroic composites at useful temperatures. The team successfully demonstrated a new approach to detect and control the coupling between electric and magnetic order on ultrafast timescales. The work reveals the dynamic properties of multiferroics, a rarely explored aspect that affects their potential applications. Nature Communications published the findings.

The team used femtosecond optical pulses to explore and optically manipulate the coupling between ferroelectric (FE) and ferromagnetic (FM) order in an oxide heterostructure for the first time. They discovered that the timescale dominating the magnetoelectric response is governed by demagnetization of the ferromagnetic layer through spin–lattice relaxation. Optically perturbing magnetic order in the ferromagnetic layer imposes lateral stress on the ferroelectric layer through magnetostriction, modifying ferroelectric order within tens of picoseconds. This finding demonstrates that femtosecond optical pulses can provide insight into the microscopic mechanisms underlying magnetoelectric coupling in complex oxide heterostructures and to manipulate the magnetoelectric response in these systems on ultrafast timescales.

Reference: “Using Ultrashort Optical Pulses to Couple Ferroelectric and Ferromagnetic Order in an Oxide Heterostructure,” Nature Communications 5, 5832 (2014); doi: 10.1038/ncomms6832. Authors include Yu-Miin Sheu (formerly with MPA-CINT), Stuart Trugman (Physics of Condensed Matter and Complex Systems, T-4), Li Yan (formerly with MPA-CINT), Quanxi Jia and Rohit Prasankumar (MPA-CINT), and Toni Taylor (Materials Physics and Applications, MPA-DO),

This work was performed at CINT, a DOE Office of Basic Energy Sciences user facility. The Laboratory’s Directed Research and Development (LDRD) program provided funding. The work supports the Lab’s Energy security mission area and the Materials for the Future science pillar. Multiferroics have potential applications, such as reducing the energy required to switch hard drives in computers. Technical contact: Rohit Prasankumar

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Materials Science and Technology

Ion beam analysis textbook published

Yongqiang Wang (Materials Science in Radiation and Dynamics Extremes, MST-8) in collaboration with former Los Alamos National Laboratory researcher Michael Nastasi (now at the University of Nebraska – Lincoln) and the late Jim Mayer authored a new ion beam analysis textbook. Ion Beam Analysis: Fundamentals and Applications focuses on the fundamentals and applications of ion beam methods of materials characterization. The authors explain the basic characteristics of ion beams as applied to the analysis of materials as well as ion beam analysis of art and archaeological objects. Primarily geared to upper-level undergraduate and graduate students, the book is 450 pages with 15 chapters, and features homework problems after each chapter.

Ion Beam Analysis: Fundamentals and Applications explains how ions interact with solids and describes what information can be gained. The authors begin by covering the fundamentals of ion beam analysis, including kinematics, ion stopping, Rutherford backscattering, channeling, elastic recoil detection, particle induced x-ray emission, and nuclear reaction analysis. Then the book examines applications for a broad range of potential uses in thin film reactions, ion implantation, nuclear energy, biology, and art/archaeology. The authors discuss classical collision theory, detail the fundamentals of five specific ion beam analysis techniques, and illustrate specific applications, including biomedicine and thin film analysis.

Wang leads the Ion Beam Materials Laboratory, a LANL resource devoted to materials research through the use of energetic ion beams. He serves as the acting team leader for MST-8’s Experimental Radiation Sciences team. Wang has authored or coauthored more than 200 peer-reviewed publications including 3 book chapters, 2 U.S. patents, and the Handbook of Modern Ion Beam Materials Analysis-Second Edition (MRS Publisher, 2009). He is a member of the International Committee for Ion Beam Analysis, and he co-chaired the 2014 International Conference on the Application of Accelerators in Research and Industry.

The Materials Science and Engineering Division of the DOE Office of Basic Energy Sciences and the Center for Integrated Nanotechnologies (CINT), a DOE nanoscience user facility jointly operated by Los Alamos and Sandia National Laboratories, provided funding. The research supports the Laboratory’s Materials for the Future and Nuclear and Particle Futures science pillars. Technical contact: Yongqiang Wang

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Physics

Experiments on the head-on merging of supersonic plasma jets

Colliding plasmas are found in plasma systems over a vast range of scales, from the mm-scale hohlraum plasmas of inertial confinement fusion (ICF) experiments to supernova remnants in astrophysics. Colliding plasmas can be in a regime that is neither purely collisional (i.e., the particle mean-free-path is small and the plasma can be treated as a fluid) nor purely collisionless (i.e., the mean-free-path is large and classical collisions between particles can be neglected). This complicates modeling of merging-plasma behavior. The nature of many merging plasmas makes measurements difficult. Through detailed characterization of two laboratory supersonic plasma jets undergoing head-on merging, Plasma Physics (P-24) researchers have demonstrated the transition from collisionless interpenetration to collisional stagnation between two merging jets. The team attributes the transition to an increasing mean-ionization state.

Experiments performed on the Plasma Liner Experiment (PLX) facility at Los Alamos National Laboratory used a fast-framing camera to give an overview of the structure and dynamics [Figure 3(a)] of the merging plasma jets and multi-chord laser interferometry [Figure 3(b)]. Together with visible spectroscopy and spectral simulations, the results provided the experimentally inferred plasma density, temperature, and mean-ionization state.

The two supersonic plasma jets initially interpenetrate [Figure 3(b), left panel], consistent with inferred inter-jet ion-ion collision lengths that are long. As the jets interpenetrate, the mean ionization state increases [Figure 3(b), center panel], possibly due to ion-impact ionization between the counter-streaming ions of each jet. The ion-ion collision length has a strong dependence on mean ionization and so drops rapidly as the mean ionization increases, leading to collisional stagnation of the jets as inter-jet collisions become frequent [Figure 3(b), right panel].

The effect of mean-ionization state on collisionality could be especially important in plasmas of mid- to high-atomic-mass species, and failing to take ionization state into account could mislead interpretation of shock structure. Specifically, shocks may be misidentified as purely collisionless. These measurements are valuable for benchmarking widely used plasma collisionality models in the presence of complex equations of state.

Former P-24 postdoctoral researcher Auna Moser (now at General Atomics) presented the research as an invited talk at the 56th Annual Meeting of the American Physical Society Division of Plasma Physics (October 27-31, 2014 in New Orleans, LA). Other researchers include principal investigator Scott Hsu, John Dunn, and Colin Adams (P-24). The Laboratory Directed Research and Development (LDRD) program funded the research. The Office of Fusion Energy Sciences of the DOE Office of Science sponsored the construction of the PLX facility. The research supports the Laboratory’s Energy Security and Nuclear Deterrence mission areas and the Nuclear and Particle Futures science pillar. Technical contact: Scott Hsu

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