1,738,433 research outputs found
Plant basal resistance: genetics, biochemistry, and impacts on plant-biotic interactions
No full textBasal resistance depends largely on a diverse range of defence mechanisms that become active upon attack by pathogens or insects. These mechanisms range from rapid stomatal closure and production of reactive oxygen species, to callose deposition and defence gene induction. It is commonly assumed that the speed and intensity of these inducible defences determines the effectiveness of basal resistance. The present dissertation describes different aspects of basal resistance in Arabidopsis thaliana and Zea mays. Chapter 2 of the dissertation describes natural variation between Arabidopsis accessions in basal defence responsiveness to pathogen-associated molecular patterns (PAMPs) and the defence hormone salicylic acid (SA). Quantitative trait loci (QTL) analysis identified different loci regulating the sensitivity of PAMP-induced callose and SA-induced defence gene expression. One QTL controlling SA responsiveness was found to contribute to basal resistance against Pseudomonas syringae pv. tomato. In Chapter 3, the contribution of benzoxazinoids (BXs) in basal resistance of maize is described, using maize bx1 mutant lines that are impaired in the first dedicated step of BX biosynthesis. Compared to wild-type lines, bx1 lines displayed reduced penetration resistance against aphids and fungus. Furthermore, infestation of wild-type plants by aphids and fungi stimulated the conversion of DIMBOA-glucoside into HDMBOA-glucoside and DIMBOA, which was most pronounced in the apoplast of challenged tissues. Interestingly, these events preceded major tissue damage or symptom development, suggesting that BX-dependent basal resistance does not necessarily depend on tissue damage. Upon further investigation of wild-type and bx1 mutant lines, we observed significantly reduced callose deposition in bx1 plants after PAMP treatment. Furthermore, DIMBOA infiltration of the apoplast mimicked PAMP-induced callose in wild-type plants. Hence, DIMBOA acts as a regulatory signal in the expression of cell wall-based basal resistance of maize. BXs have also been reported to act as allelopathic signals belowground, which are further investigated in Chapter 4. Chromatographic analysis revealed that DIMBOA is the dominant BX species in root exudates of maize. To investigate the impact of BXs on root-colonizing rhizobacteria, transcriptome analysis was performed of DIMBOA-treated Pseudomonas putida KT2440. This global analysis pointed towards increased transcription of bacterial genes that are involved in break-down of aromatic metabolites and chemotaxis. The latter response was confirmed by in vitro assays, which demonstrated chemotaxis of the bacteria towards DIMBOA. Furthermore, root colonisation assays with GFP-expressing P. putida KT2440 revealed that wild-type plants allowed more bacterial colonization than BX-deficient bx1 plants, indicating that BXs can recruit rhizobacteria from the soil. Preliminary results that are presented in Chapter 5 show that root colonization by P. putida KT2440 primes aboveground basal defences against herbivores, thereby further highlighting the central and multifaceted function of DIMBOA in maize basal resistance
Soil mineral-organic matter-microorganism interactions and ecosystem health /
No full textSoil Mineral-Organic Matter-Microorganism Interactions and Ecosystem Health presents up-to-date information on the dynamics, transformations and bioavailability of xenobiotics in soil and their impact on ecosystem health, the ecological significance of interactions of metals and metalloids with soil colloids, enzymes and microbial biomass and the role of minerals-organic matter - soil biota interactions in the restoration of perturbed ecosystems. The title comprises two volumes: Volume A: Dynamics, Mobility and Transformation of Pollutants and Nutrients. Volume B: Ecological Significance of the Interactions mong Clay Minerals, Organic Matter and Soil Biota. This title could serve as a basic reference for students, teachers, and researchers by providing in-depth knowledge of the current state of the art in a particular area of soil science.Papers presented at the 3rd Symposium on "Soil Mineral-Organic Matter Microorganism Interactions and Ecosystem Health", held in Naples and Capri, Italy, May 22 to 26, 2000.Includes bibliographical references and index.[v. 1]. Dynamics, mobility and transformation of pollutants and nutrients -- [v. 2. Ecological significance of the interactions among clay minerals, organic matter and soil biota].Soil Mineral-Organic Matter-Microorganism Interactions and Ecosystem Health presents up-to-date information on the dynamics, transformations and bioavailability of xenobiotics in soil and their impact on ecosystem health, the ecological significance of interactions of metals and metalloids with soil colloids, enzymes and microbial biomass and the role of minerals-organic matter - soil biota interactions in the restoration of perturbed ecosystems. The title comprises two volumes: Volume A: Dynamics, Mobility and Transformation of Pollutants and Nutrients. Volume B: Ecological Significance of the Interactions mong Clay Minerals, Organic Matter and Soil Biota. This title could serve as a basic reference for students, teachers, and researchers by providing in-depth knowledge of the current state of the art in a particular area of soil science.Print version record.Elsevie
The Nascent Polypeptide-Associated Complex Modulates
No full textsed on our results, we define two distinct modes of interaction between SRP and the ribosome--nascent chain complex: salt-resistant interactions between SRP54 and signal sequences, and salt-sensitive interactions between additional components of SRP and the ribosome. We conclude that NAC does not directly influence signal sequence recognition by SRP but, rather, that it negatively modulates interactions that occur between SRP and the ribosome itself. These results are discussed in terms of a model wherein SRP and NAC regulate each others' activity during protein targeting. Background In eucaryotic and procaryotic cells, signal sequences that direct proteins into the secretory pathway contain few structural features that distinguish them from other proteins. In general, clusters of as few as seven consecutive hydrophobic amino acids function as signal sequences. In yeast, about 20 % of random peptide sequences can function as signal sequences (although many function with lo
Portrayal of interactions between humans and coyotes (Canis latrans): content analysis of Canadian print media (1998-2010)
No full textPrint media is one form of public discourse that provides a means to examine human-coyote interactions. We conducted a content analysis of 453 articles addressing coyote events reported in the Canadian print media between 1998 and 2010. We found 119 articles about human-coyote interactions, of which 32 involved a report of coyote biting (26) or attempting to bite (6) a person. 108 articles were about coyote-dogs and 32 about coyotes-cat interactions. Remaining articles were on topics unrelated to interactions (e.g. culls). Basing our analysis in grounded theory, we identified important descriptive and emotional themes surrounding these events. The most common words describing coyotes were: brazen, wiley, mangy, nuisance, wild and vicious.Interactions were described as attacks in 185 articles, while only 32 “attacks” were identified. Coyotes were portrayed as not natural in cities, as an invasive species, and more recently using language depicting criminal behaviour. Descriptions of coyotes killing or attacking people were inflammatory (e.g. savaged, ripped juts open), whereas descriptions of people killing coyotes were not (e.g. euthanized). Five emotional responses emerged describing humans involved in coyote interactions. Of these, statements of fear were most prevalent and yielded the richest understanding of perceptions about the risk of coyote-human interactions, including:fear for children’s safety (73), fear for disease (44), fear for pet safety (43), and fear for self or others safety(35). Traumatic response was reported in 28 articles, while sadness and grief were described in 17. Two other themes were: 1) animal welfare concerns, 2) frustration due to lack of agency response. Popular media plays a critical role in shaping public understanding and can influence people’s emotional experiences, perceptions and management consequences. We highlight that coyotes are prejudiced (and stereotyped) based on the isolated and sensationalized incidents. Coyotes in particular elicit a wide range of emotional responses in people, and there is often a wide gap between perception and reality of risk when understanding whether it is possible for humans and coyotes to co-exist. Hence, there is a strong need for media literacy about the unintended or intended maligning of coyotes to the general public, as the consequence can be social amplification of risk and the unwarranted persecution of coyotes
The rhizosphere microbiome and plant health
No full textThe diversity of microbes associated with plant roots is enormous, in the order of tens of thousands of species. This complex plant-associated microbial community, also referred to as the second genome of the plant, is crucial for plant health. Recent advances in plant–microbe interactions research revealed that plants are able to shape their rhizosphere microbiome, as evidenced by the fact that different plant species host specific microbial communities when grown on the same soil. In this review, we discuss evidence that upon pathogen or insect attack, plants are able to recruit
protective microorganisms, and enhance microbial activity to suppress pathogens in the rhizosphere. A comprehensive understanding of the mechanisms that govern selection and activity of microbial communities by plant roots will provide new opportunities to increase crop production
Citational Justice and the Politics of Knowledge Production
No full textCitation is how we acknowledge our debt to those who came before; those who helped us find our way when the way was obscured because we deviated from the paths we were told to follow. Sara Ahmed reminds us that just citational practices recognize the knowledge contributions of less dominant, routinely overlooked voices. Pursuing citational justice, then, entails moving away from individualistic views of authorship and toward a shared, reciprocal understanding of how knowledge is produced. Drawing from our experiences working within HCI, we extend an invitation for a just citational practice—one that makes space for the diversity of human experience and recognizes that human-computer interactions must be responsive to cultural and geographic differences. We outline parts of our ongoing conversations as a collective to motivate a careful citation practice across our field, interrogating how we can best honor one another’s ideas and labor without alienation or appropriation.</p
Simulating interactions among multiple characters
No full textIn this thesis, we attack a challenging problem in the field of character animation:
synthesizing interactions among multiple virtual characters in real-time. Although
there are heavy demands in the gaming and animation industries, no systemic
solution has been proposed due to the difficulties to model the complex behaviors
of the characters.
We represent the continuous interactions among characters as a discrete Markov
Decision Process, and design a general objective function to evaluate the immediate
rewards of launching an action. By applying game theory such as tree expansion
and min-max search, the optimal actions that benefit the character the most in
the future are selected. The simulated characters can interact competitively while
achieving the requests from animators cooperatively.
Since the interactions between two characters depend on a lot of criteria, it is
difficult to exhaustively precompute the optimal actions for all variations of these
criteria. We design an off-policy approach that samples and precomputes only
meaningful interactions. With the precomputed policy, the optimal movements
under different situations can be evaluated in real-time.
To simulate the interactions for a large number of characters with minimal
computational overhead, we propose a method to precompute short durations of
interactions between two characters as connectable patches. The patches are concatenated
spatially to generate interactions with multiple characters, and temporally
to generate longer interactions. Based on the optional instructions given by
the animators, our system automatically applies concatenations to create a huge
scene of interacting crowd.
We demonstrate our system by creating scenes with high quality interactions. On one hand, our algorithm can automatically generate artistic scenes of interactions
such as the fighting scenes in movies that involve hundreds of characters. On
the other hand, it can create controllable, intelligent characters that interact with
the opponents for real-time applications such as 3D computer games
Dynamics of Network Formation Processes in the Co-Author Model
No full textThis article studies the dynamics in the formation processes of a mutual consent network in game theory setting: the Co-Author Model. In this article, a limited observation is applied and analytical results are derived. Then, 2 parameters are varied: the number of individuals in the network and the initial probability of the links in the network in its initial state. A simulation result shows a finding that is consistent with an analytical result for a state of equilibrium while it also shows different possible equilibria.Dynamics, Network, Game Theory, Model,Simulation, Equilibrium, Complexity
Helical mode interactions and spectral energy transfer in magnetohydrodynamic turbulence
No full textSpectral transfer processes in magnetohydrodynamic (MHD) turbulence are investigated by decomposition of the velocity and magnetic fields in Fourier space into helical modes. In 1992, Waleffe (Phys. Fluids A, 4:350 (1992)) used this decomposition to calculate triad interactions for isotropic hydrodynamic turbulence and determined whether a given triad contributed to forward or reverse energy transfer depending on the helicities of the interacting modes. The problem becomes more difficult in MHD due to the need to treat a coupled system of partial differential equations and the energy transfers between the magnetic and velocity fields. This requires the development of techniques that extend Waleffe's work, which are subsequently used to calculate the direction of energy transfer processes originating from triad interactions derived from the MHD equations. In order to illustrate the possible transfer processes that arise from helical mode interactions, we focus on simplified cases and putting special emphasis on interactions resulting in reverse spectral energy transfer. This approach also proves to be helpful in determining the nature of certain energy transfer processes, where transfer of energy between different fields and between the same field can be distinguished. Reverse transfer of magnetic energy was found if the helicities of two modes corresponding to the smaller wavenumbers are the same, while for reverse transfer of kinetic energy Waleffe's result is recovered. Reverse transfer of kinetic to magnetic energy is facilitated if the interacting magnetic field modes are of opposite helicity, and no reverse transfer of magnetic to kinetic energy was found. More generally, the direction of energy transfer not only depends on helicity but also on the ratio of magnetic to kinetic energy. For the magnetically dominated case reverse transfer occurs of all helicities are the same, the kinetically dominated case two modes need to have the same helicity while the third mode is of opposite helicity to allow reverse transfer
Orbital interactions
No full textIt is widely accepted that the sharing of electrons constitutes a bond. Conversely,
molecular interactions that do not involve electron transfer, such as van der Waals
forces and electrostatics are defined as “non-bonding” or “non-covalent” interactions.
More recently computational and experimental observations have shown situations
where the division between “bonding” and “non-bonding” interactions is blurred. One
such class of interactions are known as σ-hole interactions.
Chapter 1 provides a literature review of investigations into the nature of σ-hole
interactions, highlighting the individual contributing factors.
Chapter 2 provides a detailed analysis into the nature of chalcogen-bonding
interactions. Synthetic molecular balances are employed for experimental
measurements of conformational free energies in different solvents, facilitating a
detailed examination of the energetics and associated solvent and substituent effects
on chalcogen-bonding interactions. The chalcogen-bonding interactions examined
were found to have surprisingly little solvent dependence. The independence of the
conformational free energies on solvent polarity, polarisability and H-bond
characteristics showed that electrostatic, solvophobic or dispersion forces were not
dominant factors in accounting for the experimentally observed trends. A molecular
orbital analysis provided a quantitative relationship between the experimental free
energies and the molecular orbital energies, which was consistent with chalcogen-bonding
interactions being dominated by an n→σ* orbital delocalisation.
Chapters 3 and 4 both use the molecular orbital modelling approach established in
Chapter 2 to investigate the potential partial covalency in H-bonding and
carbonyl···carbonyl interactions. H-bonding is generally considered to be an
electrostatically dominated interaction. However, computational results have
suggested a partial covalent character in H-bonding. The molecular orbital analysis
revealed an n→σ* electron delocalisation in all H-bonding systems evaluated.
However, no quantitative correlation could be found with experimental free energies.
Similarly, the nature of carbonyl···carbonyl interactions has been subject to debate,
with electrostatic or an n→π* electron delocalisation having been proposed as the
dominant factors. The molecular orbital analysis employed here showed that n→π*
delocalisation was exceptionally geometry dependent. Studies of literature systems
reveal that n→π* delocalisation contributes to overall stability of a range of systems,
with a quantitative link between molecular orbital energy and conformational free
energies
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