Differential physiological responses of portuguese bread wheat (Triticum aestivum L.) genotypes under aluminium stress

Open Access JournalThe major limitation of cereal production in acidic soils is aluminium (Al) phytotoxicity which inhibits root growth. Recent evidence indicates that different genotypes within the same species have evolved different mechanisms to cope with this stress. With these facts in mind, root responses of two highly Al tolerant Portuguese bread wheat genotypes—Barbela 7/72/92 and Viloso mole—were investigated along with check genotype Anahuac (Al sensitive), using different physiological and histochemical assays. All the assays confirmed that Barbela 7/72/92 is much more tolerant to Al phytotoxicity than Viloso Mole. Our results demonstrate that the greater tolerance to Al phytotoxicity in Barbela 7/72/92 than in Viloso Mole relies on numerous factors, including higher levels of organic acid (OAs) efflux, particularly citrate efflux. This might be associated with the lower accumulation of Al in the root tips, restricting the Al-induced lipid peroxidation and the consequent plasma membrane integrity loss, thus allowing better root regrowth under Al stress conditions. Furthermore, the presence of root hairs in Barbela 7/72/92 might also help to circumvent Al toxicity by facilitating a more efficient uptake of water and nutrients, particularly under Al stress on acid soils. In conclusion, our findings confirmed that Portuguese bread wheat genotype Barbela 7/72/92 represents an alternative source of Al tolerance in bread wheat and could potentially be used to improve the wheat productivity in acidic soils

Covariant representations of the relativistic Brueckner T-matrix and the nuclear matter problem

We investigate nuclear matter properties in the relativistic Brueckner approach. The in-medium on-shell T-matrix is represented covariantly by five Lorentz invariant amplitudes from which we deduce directly the nucleon self-energy. We discuss the ambiguities of this approach and the failure of previously used covariant representations in reproducing the nucleon self-energies on the Hartree-Fock level. To enforce correct Hartree-Fock results we develop a subtraction scheme which treats the bare nucleon-nucleon potential exactly in accordance to the different types of meson exchanges. For the remaining ladder kernel, which contains the higher order correlations, we employ then two different covariant representations in order to study the uncertainty inherent in the approach. The nuclear matter bulk properties are only slightly sensitive on the explicit representation used for the kernel. However, we obtain new Coester lines for the various Bonn potentials which are shifted towards the empirical region of saturation. In addition the nuclear equation-of-state turns out to be significantly softer in the new approach.Comment: 39 pages Latex using Elsevier style, 16 PS figure

Scalar and vector decomposition of the nucleon self-energy in the relativistic Brueckner approach

We investigate the momentum dependence of the nucleon self-energy in nuclear matter. We apply the relativistic Brueckner-Hartree-Fock approach and adopt the Bonn A potential. A strong momentum dependence of the scalar and vector self-energy components can be observed when a commonly used pseudo-vector choice for the covariant representation of the T-matrix is applied. This momentum dependence is dominated by the pion exchange. We discuss the problems of this choice and its relations to on-shell ambiguities of the T-matrix representation. Starting from a complete pseudo-vector representation of the T-matrix, which reproduces correctly the pseudo-vector pion-exchange contributions at the Hartree-Fock level, we observe a much weaker momentum dependence of the self-energy. This fixes the range of the inherent uncertainty in the determination of the scalar and vector self-energy components. Comparing to other work, we find that extracting the self-energy components by a fit to the single particle potential leads to even more ambiguous results.Comment: 35 pages RevTex, 7 PS figures, replaced by a revised and extended versio

Rare K and B Decays in the Littlest Higgs Model without T-Parity

We analyze rare K and B decays in the Littlest Higgs (LH) model without T-parity. We find that the final result for the Z^0-penguin contribution contains a divergence that is generated by the one-loop radiative corrections to the currents corresponding to the dynamically broken generators. Including an estimate of these logarithmically enhanced terms, we calculate the branching ratios for the decays K^+ -> pi^+ nu bar nu, K_L -> pi^0 nu bar nu, B_{s,d} -> mu^+ mu^- and B -> X_{s,d} nu bar nu. We find that for the high energy scale f=O(2-3) TeV, as required by the electroweak precision studies, the enhancement of all branching ratios amounts to at most 15% over the SM values. On the technical side we identify a number of errors in the existing Feynman rules in the LH model without T-parity that could have some impact on other analyses present in the literature. Calculating penguin and box diagrams in the unitary gauge, we find divergences in both contributions that are cancelled in the sum except for the divergence mentioned above.Comment: 39 pages, 8 figures, typos corrected, comment on (2.17) and (2.18) added, references added, results unchange

The NPR1-dependent salicylic acid signalling pathway is pivotal for enhanced salt and oxidative stress tolerance in Arabidopsis

The role of endogenous salicylic acid (SA) signalling cascades in plant responses to salt and oxidative stresses is unclear. Arabidopsis SA signalling mutants, namely npr1-5 (non-expresser of pathogenesis related gene1), which lacks NPR1-dependent SA signalling, and nudt7 (nudix hydrolase7), which has both constitutively expressed NPR1-dependent and NPR1-independent SA signalling pathways, were compared with the wild type (Col-0) during salt or oxidative stresses. Growth and viability staining showed that, compared with wild type, the npr1-5 mutant was sensitive to either salt or oxidative stress, whereas the nudt7 mutant was tolerant. Acute salt stress caused the strongest membrane potential depolarization, highest sodium and proton influx, and potassium loss from npr1-5 roots in comparison with the wild type and nudt7 mutant. Though salt stress-induced hydrogen peroxide production was lowest in the npr1-5 mutant, the reactive oxygen species (ROS) stress (induced by 1mM of hydroxyl-radical-generating copper-ascorbate mix, or either 1 or 10mM hydrogen peroxide) caused a higher potassium loss from the roots of the npr1-5 mutant than the wild type and nudt7 mutant. Long-term salt exposure resulted in the highest sodium and the lowest potassium concentration in the shoots of npr1-5 mutant in comparison with the wild type and nudt7 mutant. The above results demonstrate that NPR1-dependent SA signalling is pivotal to (i) controlling Na(+) entry into the root tissue and its subsequent long-distance transport into the shoot, and (ii) preventing a potassium loss through depolarization-activated outward-rectifying potassium and ROS-activated non-selective cation channels. In conclusion, NPR1-dependent SA signalling is central to the salt and oxidative stress tolerance in Arabidopsis.Maheswari Jayakannan, Jayakumar Bose, Olga Babourina, Sergey Shabala, Amandine Massart, Charlotte Poschenrieder and Zed Renge

The Relativistic Dirac-Brueckner Approach to Asymmetric Nuclear Matter

The properties of asymmetric nuclear matter have been investigated in a relativistic Dirac-Brueckner-Hartree-Fock framework using the Bonn A potential. The components of the self-energies are extracted by projecting on Lorentz invariant amplitudes. Furthermore, the optimal representation scheme for the $T$ matrix, the subtracted $T$ matrix representation, is applied and the results are compared to those of other representation schemes. Of course, in the limit of symmetric nuclear matter our results agree with those found in literature. The binding energy $E_b$ fulfills the quadratic dependence on the asymmetry parameter and the symmetry energy is 34 MeV at saturation density. Furthermore, a neutron-proton effective mass splitting of $m_n^* < m_p^*$ is found. In addition, results are given for the mean-field effective coupling constants.Comment: 28 pages, 7 figures, to appear in Nucl. Phys. A, added additional reference

In-medium relativistic kinetic theory and nucleon-meson systems

Within the $\sigma-\omega$ model of coupled nucleon-meson systems, a generalized relativistic Lenard--Balescu--equation is presented resulting from a relativistic random phase approximation (RRPA). This provides a systematic derivation of relativistic transport equations in the frame of nonequilibrium Green's function technique including medium effects as well as flucuation effects. It contains all possible processes due to one meson exchange and special attention is kept to the off--shell character of the particles. As a new feature of many particle effects, processes are possible which can be interpreted as particle creation and annihilation due to in-medium one meson exchange. In-medium cross sections are obtained from the generalized derivation of collision integrals, which possess complete crossing symmetries.Comment: See nucl-th/9310032 for revised version which the authors incompetently resubmitted rather than correctly replacing thi