Analysis of cadmium translocation, partitioning and tolerance in six barley (Hordeum vulgare L.) cultivars as a function of thiol metabolism

Six barley cultivars widely differing for cadmium (Cd) tolerance, partitioning, and translocation were analyzed in relation to their thiol metabolism. Results indicated that Cd tolerance was not clearly related to the total amount of Cd absorbed by plants, resulting instead closely dependent on the capacity of the cultivars to trap the metal into the roots. Such behaviors suggested the existence of root mechanisms preserving shoots from Cd-induced oxidative damages, as indicated by the analysis of thiobarbituric acid-reactive substances \u2014diagnostic indicators of oxidative stress\u2014whose increases in the shoots were negatively related to Cd root retention and tolerance. Cd exposure differentially affected glutathione (GSH) and phytochelatin (PC) levels in the tissues of each barley cultivar. The capacity to produce PCs appeared as a specific characteristic of each barley cultivar, since it did not depend on Cd concentration in the roots and resulted negatively related to the concentration of the metal in the shoots, indicating the existence of a cultivar-specific interference of Cd on GSH biosynthesis, as confirmed by the existence of close positive linear relationships between the effect of Cd on GSH levels and PC accumulation in both roots and shoots. The six barley cultivars also differed for their capacity to load Cd ions into the xylem, which was negatively related to PC content in the roots. Taken as a whole, these data indicated that the different capacity of each cultivar to maintain GSH homeostasis under Cd stress may strongly affect PC accumulation and, thus, Cd tolerance and translocation

Gene Expression Biomarkers for Evaluating Nitrogen Nutritional Status in Rice

Over the last five decades the increase in rice yield has been associated with a dramatic increment in the use of nitrogen (N) fertilizers. Understanding of plant molecular responses to N is critical for our ability to improve the agricultural sustainability of rice cropping systems by developing a comprehensive approach that allows the selection of varieties with enhanced efficiency in their ability to use N and the development of new strategies to better manage N fertilization practices. In order to develop novel tools for real-time assessing of rice N nutritional status, we analyzed the expression profiles of seven putative gene expression markers in the shoots of rice plants grown under different N availability and environmental conditions. Our results suggest that five out of the seven genes analyzed have the potential to be used as agronomic tools to monitor and optimize the N nutritional status of rice

Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics

Powerful nanosecond laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in excess of 0.5 kT. The quasi-static currents are provided from hot electron ejection from the laser-irradiated surface. According to our model, which describes the evolution of the discharge current, the major control parameter is the laser irradiance Ilasλlas2. The space-time evolution of the B-fields is experimentally characterized by high-frequency bandwidth B-dot probes and proton-deflectometry measurements. The magnetic pulses, of ns-scale, are long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport through solid dielectric targets, yielding an unprecedented 5-fold enhancement of the energy-density flux at 60 μm depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes, and to laboratory astrophysics

Search for heavy gauge W ′ bosons in events with an energetic lepton and large missing transverse momentum at √s = 13 TeV

A search is presented for W′ bosons in events with an electron or muon and large missing transverse momentum, using proton–proton collision data at √s=13 TeV collected with the CMS detector in 2015 and corresponding to an integrated luminosity of 2.3 fb−1. No evidence of an excess of events relative to the standard model expectations is observed. For a W′ boson described by the sequential standard model, upper limits at 95% confidence level are set on the product of the production cross section and branching fraction and lower limits are established on the new boson mass. Masses below 4.1 TeV are excluded combining electron and muon decay channels, significantly improving upon the results obtained with the 8 TeV data. Exclusion limits at 95% confidence level on the product of the W′ production cross section and branching fraction are also derived in combination with the 8 TeV data. Finally, exclusion limits are set for the production of generic W′ bosons decaying into this final state using a model-independent approach

Cadmium increases the optimal external concentration for sulfate in Arabidopsis thaliana

The main sulfur (S) source for plants is the sulfate ion (SO42-), which is taken up by roots through specific plasma membrane high-affinity SO42- transporters. Once inside the plant, SO42- is allocated to different sinks where it is first assimilated into cysteine (Cys), a key intermediate from which most of S-containing compounds are synthetized. Considering the central role of Cys, it appears evident that both SO42- uptake and assimilation have to be finely modulated to meet the metabolic demand for S arising from Cys consuming activities, which largely contribute to define the total S requirement of plants. Such a demand may consistently vary under the different environmental conditions that plants may experience during their growth. Abiotic stresses may increase the metabolic demand for some Cys derived compounds, causing an increase in the activity of the SO4 2- assimilatory pathway. An example of this has been largely described in plants exposed to cadmium (Cd) in which the activation of glutathione- (GSH) consuming adaptive responses may increase the demand for both SO42- and S metabolites. Indeed, GSH is the key intermediate for the synthesis of phytochelatins (PCs), a class of Cys-rich metal-binding peptides involved in Cd detoxification. The large amount of PCs produced by plants represents an additional sink for S, which generates a typical demand-driven transcriptional regulation of genes involved in SO42- uptake, SO42- assimilation and GSH biosynthesis. To better understand the relationship existing between Cd accumulation and S metabolism, we analyzed the growth of Arabidopsis thaliana under a wide range of SO42- external concentrations (from 1 to 150 \u3bcM), in the presence or absence of 0.1 \u3bcM Cd2+. Plant growth was dependent on SO42- external concentration in both the experimental conditions. The growth isotherms were saturating curves properly described by the following single exponential rise to maximum function: = !"# 19 (1 12 !! !"! !! ) Such a function allowed us to estimate the theoretical critical concentration for SO42-, defined as the external concentration of the anion, which produces 95% of the maximum fresh weight. Data analysis indicated that the presence of Cd significantly changed the demand for S to maximize shoot growth, since the critical value for SO42- external concentration was higher in Cd treated (40 \u3bcM) than in control plants (29 \u3bcM). Moreover, the negative effect exerted by Cd on shoot growth decreased as SO42- concentration in the external medium increased. No effects of Cd on shoot growth were observed for SO42- external concentrations higher than the critical one. Differently, the detrimental effect exerted by Cd on root growth was independent of SO42- external concentration. Finally, Cd exposure negatively affected thiol metabolism, since shoot GSH concentration was lower in Cd-treated than in control plants, in all the experimental conditions. However, the effect of Cd on GSH levels decreased as SO42- external concentration increased, up to reach the critical value. Thus, at least our experimental conditions, the minimum shoot GSH concentration that have to be maintained to contrast Cd toxicity is around 375 nmol g-1 FW

Effetti dell’esposizione a cadmio sulla concentrazione critica di solfato in piante di Arabidopsis

Il solfato (SO42-) presente nelle soluzioni dei suoli e assorbito attraverso le radici rappresenta la principale fonte di zolfo utilizzata dalle piante. In seguito all\u2019assorbimento, lo ione SO42- \ue8 allocato verso gli organi sink dove \ue8 in parte assimilato a formare cisteina (Cys), l\u2019intermedio chiave per la sintesi di tutte le molecole organiche contenenti zolfo ridotto. In virt\uf9 del ruolo svolto dalla Cys nel metabolismo, appare evidente che le piante debbano possedere meccanismi di regolazione fine che controllano l\u2019assorbimento e l\u2019assimilazione del SO42- e che siano in grado di incontrare la domanda metabolica di Cys necessaria a soddisfare le loro necessit\ue0 di zolfo (S) ridotto. Tale domanda \ue8 soggetta a notevoli fluttuazioni - in funzione delle condizioni ambientali - e contribuisce in modo significativo a determinare i fabbisogni complessivi di S delle piante. Nelle piante esposte a cadmio (Cd), l\u2019aumento di attivit\ue0 metaboliche che consumano glutatione ridotto (GSH) pu\uf2 ripercuotersi sulla domanda di SO42- e di Cys. Il GSH, infatti, non solo \ue8 coinvolto nel mitigare condizioni di stress ossidativo indotte dall\u2019accumulo di Cd, ma rappresenta anche il substrato per la sintesi di fitochelatine, peptidi ricchi in Cys che, partecipando ai processi di detossificazione del Cd, divengono rapidamente la principale classe di tioli non proteici presenti nelle cellule delle piante. Allo scopo di chiarire le relazioni fra accumulo di Cd, metabolismo tiolico e necessit\ue0 nutrizionali di SO42-, sono state analizzate le curve di crescita di piante di Arabidopsis thaliana allevate in un ampio intervallo di disponibilit\ue0 di SO42- (1-150 \u3bcM), in presenza e in assenza di CdCl2 0.1 \u3bcM. I risultati ottenuti indicavano che la crescita del germoglio era, in ambedue le condizioni, dipendente dalla concentrazione di SO42- nel mezzo di allevamento. Le curve di crescita potevano essere propriamente descritte da una funzione esponenziale tendente ad un massimo, del tipo: FW = FWmax (1\u2013 e-bx) dove x indica la concentrazione di SO42- nel mezzo di crescita ed FW il peso fresco del germoglio. Tale funzione consentiva di calcolare la concentrazione critica di SO42-, definita come la concentrazione dell\u2019anione nel mezzo di allevamento che restituiva il 95% della crescita massima raggiungibile dal germoglio (FWmax). L\u2019analisi dei dati indicava che la presenza di Cd nel mezzo aumentava significativamente la concentrazione di SO42- necessaria a massimizzare la crescita del germoglio: il valore critico della concentrazione di SO42- muoveva infatti da 29 \u3bcM, nelle piante controllo, a 40 \u3bcM, nelle piante esposte a Cd. Inoltre, l\u2019effetto negativo esercitato dal Cd sulla crescita del germoglio diminuiva all\u2019aumentare della concentrazione di SO42- nel mezzo, fino a raggiungere il valore di concentrazione critica, al disopra del quale il metallo cessava di produrre effetti inibitori sulla crescita. Contrariamente a quanto osservato per il germoglio, l\u2019effetto del Cd sulla crescita delle radici era indipendente dalla concentrazione di SO42- nel mezzo. L\u2019esposizione a Cd riduceva inoltre i livelli di GSH misurabili nel germoglio, che risultavano in tutte le condizioni analizzate inferiori rispetto a quelli del controllo. Tuttavia, anche in questo caso, l\u2019effetto dell\u2019esposizione a Cd sui livelli di GSH diminuiva all\u2019aumentare della concentrazione di SO42- nel mezzo, fino al raggiungimento del valore critico. L\u2019andamento consentiva di evincere che la concentrazione minima di GSH necessaria a contrastare la tossicit\ue0 del Cd nei germogli era pari a 375 nmol g-1 FW

Sentinel plants to improve sulfur use efficiency: living instruments for nondestructive analysis

Developing specific bioassays based on the use of \u201csentinel plants\u201d to quickly determine nutrient bioavailability and/or crop nutritional status may represent a reliable and efficient strategy to obtain valuable, timely and low-cost information about changes in nutrient availabilities and nutritional requirements in a crop system. Two Arabidopsis pilot bioindicators - carrying the GUS reporter gene under the control of two portions of theintergenic region between At1g12030 and At1g12040 - have been characterized for their potential ability to provide information about the sulfur nutritional status of the plant and/or the sulfate concentration in the growing medium. For this purpose, the two lines were grown in agar plates under a continuous sulfate gradient ranging from 0 to 150 \ub5M in order to describe the growth of both roots and shoots as a function of sulfate external concentration and to determine the critical concentration of sulfate (i.e. the minimum concentration of sulfate necessary to achieve maximum biomass) in the growing medium. The main results indicate that both the pilot lines are able to correctly indicate the critical concentration of sulfate in the external medium also in the presence of interfering metal ions (such as cadmium) able to increase the plant metabolic demand for sulfur. Moreover, the two intergenic regions are suggested as bi-directional promoters able to control the expression of two flanking genes under sulfur limitation