The Effects of Pathogen Infection on Nitrogen Remobilization in Arabidopsis thaliana

The natural enemies of plants are ubiquitous and can reduce plant fitness. Plants have evolved two defense strategies to ameliorate the fitness cost associated with natural enemy attack. The first strategy, resistance, reduces the frequency and/or severity of natural enemy damage. The second strategy, tolerance, attenuates the fitness cost of natural enemy damage. Very little is known about the traits through which tolerance is manifested, particularly with respect to plant-pathogen systems (pathosystems). Diseased and naturally senescing leaves are often similar in their visible symptoms and molecular activities, suggesting that they may involve similar processes. One process that may be shared by the two phenomena is the efficient remobilization of nitrogen, a limiting nutrient that is heavily remobilized during natural leaf senescence. Nitrogen metabolism during foliar infections is largely unexplored, although plants are known to remobilize nitrogen from diseased leaves. Efficient remobilization of nitrogen from diseased leaves may ameliorate the fitness cost of infection, thereby manifesting tolerance to infection. Using the model pathosystem Arabidopsis thaliana – Pseudomonas syringae we asked the following questions: 1) Does infection by P. syringae pathovar tomato strain DC3000 (Pst DC3000) affect the amount of nitrogen remobilized from leaves? 2) Is there a relationship between the amount of nitrogen remobilized from infected leaves and plant tolerance to infection? To our knowledge, our study is the first to explore the effect of infection on leaf nitrogen remobilization in the context of tolerance. Results show that infected A. thaliana leaves remobilized nitrogen, however infection substantially reduced the amount of nitrogen remobilized. Plant fitness was inversely correlated with the amount of nitrogen retained by infected, senesced leaves, suggesting that the infection-caused impairment of nitrogen remobilization imposed a fitness cost. We detected little genetic variation in the effect of infection on the amount of nitrogen remobilized from infected leaves among 10 A. thaliana accessions. Similarly, we detected little genetic variation in A. thaliana symptom severity and tolerance to infection by Pst DC3000. The latter results contradict recent studies of this pathosystem, indicating that estimates of the broad-sense heritability of resistance and tolerance in this system are highly conditional. The challenge involved with understanding tolerance in an evolutionary context is discussed. We explored the effects of infection on additional A. thaliana traits and found that infected A. thaliana plants produce shorter main stems. The inverse correlation between the nitrogen content of senesced, infected leaves and fitness supports efficient nitrogen remobilization as a promising candidate tolerance trait

Semiclassical dynamics and time correlations in two-component plasmas

The semiclassical dynamics of a charged particle moving in a two-component plasma is considered using a corrected Kelbg pseudopotential. We employ the classical Nevanlinna-type theory of frequency moments to determine the velocity and force autocorrelation functions. The constructed expressions preserve the exact short and long-time behavior of the autocorrelators. The short-time behavior is characterized by two parameters which are expressable through the plasma static correlation functions. The long-time behavior is determined by the self-diffusion coefficient. The theoretical predictions are compared with the results of semiclassical molecular dynamics simulation.Comment: 12 pages, 3 figure

Effects of ion and electron correlations on neutrino scattering in the infall phase of a supernova

Many authors have used one-component plasma simulations in discussing the role of ion-ion correlations in reducing neutrino opacities during the collapse phase of a supernova. In a multicomponent plasma in which constituent ions have even a small range of N/Z ratios neutrino opacities are much larger, in some regions of parameters, than for the case of a one component plasma.Comment: 5 pages. Final version. To be published in Phys. Lett.

Quantum Theory of Irreversibility

A generalization of the Gibbs-von Neumann relative entropy is proposed based on the quantum BBGKY [Bogolyubov-Born-Green-Kirkwood-Yvon] hierarchy as the nonequilibrium entropy for an N-body system. By using a generalization of the Liouville-von Neumann equation describing the evolution of a density super- operator, it is demonstrated that the entropy production for an isolated system is non-negative, which provides an arrow of time. Moreover, following the procedure of non-equilibrium thermodynamics a master matrix is introduced for which a mi- croscopic expression is obtained. Then, the quantum Boltzmann equation is derived in terms of a transition superoperator related to that master matrix

Nonlinear response of electrons to a positive ion

Electric field dynamics at a positive ion imbedded in an electron gas is considered using a semiclassical description. The dependence of the field autocorrelation function on charge number is studied for strong ion-electron coupling via MD simulation. The qualitative features for larger charge numbers are a decreasing correlation time followed by an increasing anticorrelation. Stopping power and related transport coefficients determined by the time integral of this correlation function result from the competing effects of increasing initial correlations and decreasing dynamical correlations. An interpretation of the MD results is obtained from an effective single particle model showing good agreement with the simulation results.Comment: To be published in the proceedings of the International Workshop on Strongly Coupled Coulomb Systems, Journal of Physics

Thermal emission from low-field neutron stars

We present a new grid of LTE model atmospheres for weakly magnetic (B<=10e10G) neutron stars, using opacity and equation of state data from the OPAL project and employing a fully frequency- and angle-dependent radiation transfer. We discuss the differences from earlier models, including a comparison with a detailed NLTE calculation. We suggest heating of the outer layers of the neutron star atmosphere as an explanation for the featureless X-ray spectra of RX J1856.5-3754 and RX J0720.4-3125 recently observed with Chandra and XMM.Comment: 8 pages A&A(5)-Latex, 6 Figures, A&A in press. The model spectra presented here are available as XSPEC tables at http://www.astro.soton.ac.uk/~btg/outgoing/nsspec

Microfield Fluctuations and Spectral Line Shapes in Strongly Coupled Two-Component Plasmas

The spectral line shapes for hydrogen-like heavy ion emitters embedded in strongly correlated two-component electron-ion plasmas are investigated with numerical simulations. For that purpose the microfield fluctuations are calculated by molecular dynamics simulations where short range quantum effects are taken into account by using a regularized Coulomb potential for the electron-ion interaction. The microfield fluctuations are used as input in a numerical solution of the time-dependent Schroedinger equation for the radiating electron. In distinction to the standard impact and quasistatic approximations the method presented here allows to account for the correlations between plasma ions and electrons. The shapes of the Ly-alpha line in Al are investigated in the intermediate regime. The calculations are in good agreement with experiments on the Ly-alpha line in laser generated plasmas.Comment: 5 figure

Analytic approximations for the broadening of the spectral lines of hydrogen-like ions

Broadband approximate expressions for calculating the broadening of the spectral lines of hydrogenlike ions in a multicomponent plasma are derived taking into account both the influence of the interaction between plasma particles on the distribution function of the plasma microfield and the effect of the microfield dynamics on the broadening of the central component of the spectral line. With the approximate expressions proposed, the calculation of the shape of a given spectral line of a certain ion in a plasma with a given ion composition requires only a few seconds of computer time. The approximate expressions provide a good computational accuracy not only for the central component of the spectral line but also for the spectral line wings