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

NPR1-dependent salicylic acid signalling controls sodium entry into the roots while preventing potassium loss through depolarization-activated outward-rectifying potassium and ROS-activated non-selective cation channels during salt and oxidative stresse

Salicylic acid improves salinity tolerance in Arabidopsis by restoring membrane potential and preventing salt-induced K(+) loss via a GORK channel

Despite numerous reports implicating salicylic acid (SA) in plant salinity responses, the specific ionic mechanisms of SA-mediated adaptation to salt stress remain elusive. To address this issue, a non-invasive microelectrode ion flux estimation technique was used to study kinetics of NaCl-induced net ion fluxes in Arabidopsis thaliana in response to various SA concentrations and incubation times. NaCl-induced K+ efflux and H+ influx from the mature root zone were both significantly decreased in roots pretreated with 10–500 μM SA, with strongest effect being observed in the 10–50 μM SA range. Considering temporal dynamics (0–8-h SA pretreatment), the 1-h pretreatment was most effective in enhancing K+ retention in the cytosol. The pharmacological, membrane potential, and shoot K+ and Na+ accumulation data were all consistent with the model in which the SA pretreatment enhanced activity of H+-ATPase, decreased NaCl-induced membrane depolarization, and minimized NaCl-induced K+ leakage from the cell within the first hour of salt stress. In long-term treatments, SA increased shoot K+ and decreased shoot Na+ accumulation. The short-term NaCl-induced K+ efflux was smallest in the gork1-1 mutant, followed by the rbohD mutant, and was highest in the wild type. Most significantly, the SA pretreatment decreased the NaCl-induced K+ efflux from rbohD and the wild type to the level of gork1-1, whereas no effect was observed in gork1-1. These data provide the first direct evidence that the SA pretreatment ameliorates salinity stress by counteracting NaCl-induced membrane depolarization and by decreasing K+ efflux via GORK channels.Maheswari Jayakannan, Jayakumar Bose, Olga Babourina, Zed Rengel, and Sergey Shabal

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

Aluminium-induced ion transport in Arabidopsis: the relationship between Al tolerance and root ion flux

Aluminium (Al) rhizotoxicity coincides with low pH; however, it is unclear whether plant tolerance to these two factors is controlled by the same mechanism. To address this question, the Al-resistant alr104 mutant, two Al-sensitive mutants (als3 and als5), and wild-type Arabidopsis thaliana were compared in long-term exposure (solution culture) and in short-term exposure experiments (H+ and K+ fluxes, rhizosphere pH, and plasma membrane potential, Em). Based on biomass accumulation, als5 and alr104 showed tolerance to low pH, whereas alr104 was tolerant to the combined low-pH/Al treatment. The sensitivity of the als5 and als3 mutants to the Al stress was similar. The Al-induced decrease in H+ influx at the distal elongation zone (DEZ) and Al-induced H+ efflux at the mature zone (MZ) were higher in the Al-sensitive mutants (als3 and als5) than in the wild type and the alr104 mutant. Under combined low-pH/Al treatment, alr104 and the wild type had depolarized plasma membranes for the entire 30 min measurement period, whereas in the Al-sensitive mutants (als3 and als5), initial depolarization to around –60 mV became hyperpolarization at –110 mV after 20 min. At the DEZ, the Em changes corresponded to the changes in K+ flux: K+ efflux was higher in alr104 and the wild type than in the als3 and als5 mutants. In conclusion, Al tolerance in the alr104 mutant correlated with Em depolarization, higher K+ efflux, and higher H+ influx, which led to a more alkaline rhizosphere under the combined low-pH/Al stress. Low-pH tolerance (als5) was linked to higher H+ uptake under low-pH stress, which was abolished by Al exposure

Quantum noise in a nano mechanical Duffing resonator

We determine the small signal gain and noise response of an amplifier based on the nonlinear response of a quantum nanomechanical resonator. The resonator is biased in the nonlinear regime by a strong harmonic bias force and we determine the response to a small additional driving signal detuned with respect to the bias force.Comment: submitted to the Focus Issue on 'Mechanical Systems at the Quantum Limit', edited by Markus Aspelmeyer and Keith Schwa

Parametric amplification with weak-link nonlinearity in superconducting microresonators

Nonlinear kinetic inductance in a high Q superconducting coplanar waveguide microresonator can cause a bifurcation of the resonance curve. Near the critical pumping power and frequency for bifurcation, large parametric gain is observed for signals in the frequency band near resonance. We show experimental results on signal and intermodulation gain which are well described by a theory of the parametric amplification based on a Kerr nonlinearity. Phase dependent gain, or signal squeezing, is verified with a homodyne detection scheme.Comment: Submitted to Physica Scripta, topical issue: Nobel Symposium on Quantum Bits, 2009. 10 pages, 5 figures. Version 2 contains a few new sentences about the current-phase relation of weak link

Competition between uptake of ammonium and potassium in barley and Arabidopsis roots: molecular mechanisms and physiological consequences

Plants can use ammonium (NH4+) as the sole nitrogen source, but at high NH4+ concentrations in the root medium, particularly in combination with a low availability of K+, plants suffer from NH4+ toxicity. To understand the role of K+ transporters and non-selective cation channels in K+/NH4+ interactions better, growth, NH4+ and K+ accumulation and the specific fluxes of NH4+, K+, and H+ were examined in roots of barley (Hordeum vulgare L.) and Arabidopsis seedlings. Net fluxes of K+ and NH4+ were negatively correlated, as were their tissue concentrations, suggesting that there is direct competition during uptake. Pharmacological treatments with the K+ transport inhibitors tetraethyl ammonium (TEA+) and gadolinium (Gd3+) reduced NH4+ influx, and the addition of TEA+ alleviated the NH4+-induced depression of root growth in germinating Arabidopsis plants. Screening of a barley root cDNA library in a yeast mutant lacking all NH4+ and K+ uptake proteins through the deletion of MEP1–3 and TRK1 and TRK2 resulted in the cloning of the barley K+ transporter HvHKT2;1. Further analysis in yeast suggested that HvHKT2;1, AtAKT1, and AtHAK5 transported NH4+, and that K+ supplied at increasing concentrations competed with this NH4+ transport. On the other hand, uptake of K+ by AtHAK5, and to a lesser extent via HvHKT2;1 and AtAKT1, was inhibited by increasing concentrations of NH4+. Together, the results of this study show that plant K+ transporters and channels are able to transport NH4+. Unregulated NH4+ uptake via these transporters may contribute to NH4+ toxicity at low K+ levels, and may explain the alleviation of NH4+ toxicity by K+