Short-term UV-B exposure induces metabolic and anatomical changes in peel of harvested lemons contributing in fruit protection against green mold.

UV-B radiation (UVBR) is a small fraction of the solar spectrum from 280 to 315nm. UVBR produces photomorphogenic acclimation responses in plants, modulating their cellular structure and physiology. Here, changes in the peel of harvested lemons after short time exposure to UVBR were analyzed and its potential effects against fungal infection were studied. In the flavedo, UVBR treatment induced variations in the respiratory profiles and increased the phenolic compound contents. Final products of the flavonoid pathway (flavones, flavonols and anthocyanins) increased more markedly than their precursors (flavanones and dihydroflavonols). The increased accumulation of soluble phenolics in the flavedo of treated lemons is associated with the high antioxidant activity found in the flavedo of these samples. Supporting the biochemical determinations, anatomical observations showed abundant intravacuolar deposits of phenolic compounds and an increase in the cell wall thickness in UVBR-treated samples. Metabolic and anatomical modifications associated to UVBR improved natural defenses against Penicillium digitatum, the causal agent of green mold disease. Our results suggest that mature postharvest lemons exposed to the artificial radiation showed phenotypic plasticity, allowing an acclimation response to UVBR which confers fruit resistance to pathogens. Thus, combination of UVBR with other treatments could represent an important improvement to control postharvest diseases on citrus.

Effects of magnetic field gradients on the aggregation dynamics of colloidal magnetic nanoparticles.

We have used low-field (1)H nuclear-magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) to investigate the aggregation dynamics of magnetic particles in ionic ferrofluids (IFFs) in the presence of magnetic field gradients. At the beginning of the experiments, the measured NMR spectra were broad and asymmetric, exhibiting two features attributed to different dynamical environments of water protons, depending on the local strength of the field gradients. Hence, the spatial redistribution of the magnetic particles in the ferrofluid caused by the presence of an external magnetic field in a time scale of minutes can be monitored in real time, following the changes in the features of the NMR spectra during a period of about an hour. As previously reported [Heinrich et al., Phys. Rev. Lett., 2011, 106, 208301], in the homogeneous magnetic field of a NMR spectrometer, the aggregation of the particles of the IFF proceeds in two stages. The first stage corresponds to the gradual aggregation of monomers prior to and during the formation of chain-like structures. The second stage proceeds after the chains have reached a critical average length, favoring lateral association of the strings into hexagonal zipped-chain superstructures or bundles. In this work, we focus on the influence of a strongly inhomogeneous magnetic field on the aforementioned aggregation dynamics. The main observation is that, as the sample is immersed in a certain magnetic field gradient and kept there for a time τinh, magnetophoresis rapidly converts the ferrofluid into an aggregation state which finds its correspondence to a state on the evolution curve of the pristine sample in a homogeneous field. From the degree of aggregation reached at the time τinh, the IFF sample just evolves thereafter in the homogeneous field of the NMR spectrometer in exactly the same way as the pristine sample. The final equilibrium state always consists of a colloidal suspension of zipped-chain bundles with the chain axes aligned along the magnetic field direction.

Use of Phosphite Salts in Laboratory and Semicommercial Tests to Control Citrus Postharvest Decay.

Potassium phosphite (KP) concentrations that inhibited the germination of 50% of Penicillium digitatum conidia were 229, 334, 360, 469, 498, or 580 mg/liter at pH 3, 4, 5, 6, 7, or 8, respectively. Increasing phosphate content in media reduced phosphite toxicity. To control green or blue mold, fruit were inoculated with P. digitatum or P. italicum, then immersed 24 h later in KP, calcium phosphite (CaP), sodium carbonate, sodium bicarbonate, or potassium sorbate for 1 min at 20 g/liter for each at 25 or 50°C. Mold incidence was lowest after potassium sorbate, CaP, or KP treatments at 50°C. CaP was often more effective than KP but left a white residue on fruit. KP was significantly more effective when fruit were stored at 10 or 15°C after treatment compared with 20°C. Acceptable levels of control were achieved only when KP was used in heated solutions or with fungicides. KP was compatible with imazalil (IMZ) and other fungicides and improved their effectiveness. KP increased thiabendazole or IMZ residues slightly. Phosphite residues did not change during storage for 3 weeks, except they declined when KP was applied with IMZ. KP caused no visible injuries or alteration in the rate of color change of citrus fruit in air or ethylene at 5 µl/liter.

Dynamics of the field-induced formation of hexagonal zipped-chain superstructures in magnetic colloids.

Combining nuclear magnetic resonance and molecular dynamics simulations, we unravel the long-time dynamics of a paradigmatic colloid with strong dipole-dipole interactions. In a homogeneous magnetic field, ionic ferrofluids exhibit a stepwise association process from ensembles of monomers over stringlike chains to bundles of hexagonal zipped-chain patches. We demonstrate that attractive van der Waals interactions due to charge-density fluctuations in the magnetic particles play the key role for the dynamical stabilization of the hexagonal superstructures against thermal dissociation. Our results give insight into the dynamics of self-organization in systems dominated by dipolar interactions.

Fast measurements of average flow velocity by Low-Field ¹H NMR.

In this paper, we describe a method for measuring the average flow velocity of a sample by means of Nuclear Magnetic Resonance. This method is based on the Carr-Purcell-Meiboom-Gill (CPMG) sequence and does not require the application of any additional static or pulsed magnetic field gradients to the background magnetic field. The technique is based on analyzing the early-time behavior of the echo amplitudes of the CPMG sequence. Measurements of average flow velocity of water are presented. The experimental results show a linear relationship between the slope/y-intercept ratio of a linear fit of the first echoes in the CPMG sequence, and the average flow velocity of the flowing fluid. The proposed method can be implemented in low-cost Low-Field NMR spectrometers allowing a continuous monitoring of the average velocity of a fluid in almost real-time, even if the flow velocity changes rapidly.

Cellular damage induced by a sequential oxidative treatment on Penicillium digitatum.

AIM: To investigate the cellular damage on Penicillium digitatum produced by a sequential oxidative treatment (SOT), previously standardized in our laboratory, to prevent the conidia growth. Lethal SOT consists of 2-min preincubation with 10 ppm NaClO followed by 2-min incubation with 6 mmol l(-1) CuSO(4) and 100 mmol l(-1) H(2)O(2) at 25°C. METHODS AND RESULTS: After the application of lethal SOT or sublethal SOT (decreasing only the H(2)O(2) concentration), we analysed several conidia features such as germination, oxygen consumption, ultrastructure and integrity of the cellular wall and membrane. Also, we measured the production of reactive oxygen species (ROS) and the content of thiobarbituric acid-reactive species (TBARS). With the increase of H(2)O(2) concentration in the SOT, germination and oxygen consumption of conidia became inhibited, while the membrane permeability, ROS production and TBARS content of conidia increased. Several studies revealed ultrastructural disorganization in P. digitatum conidia after lethal SOT, showing severe cellular damage without apparent damage to the cell wall. In addition, mycelium of P. digitatum was more sensitive than conidia to the oxidative treatment, because growth ceased and permeability of the membranes increased after exposure of the mycelium to a SOT with only 50 mmol l(-1) H(2)O(2) compared to a SOT of 100 mmol l(-1) for these effects to occur on conidia. CONCLUSION: Our insights into cellular changes produced by the lethal SOT are consistent with the mode of action of the oxidant compounds, by producing both alteration of membrane integrity and intracellular damage. SIGNIFICANCE AND IMPACT OF THE STUDY: Our results allow the understanding of SOT effects on P. digitatum, which will be useful to develop a reliable treatment to control postharvest diseases in view of its future application in packing houses.

Noise-resilient multi-frequency surface sensor for nuclear quadrupole resonance.

A planar nuclear quadrupole resonance (NQR) sensor has been developed. The sensor is resilient to environmental noise and is capable of simultaneous independent multi-frequency operation. The device was constructed as an open multimodal birdcage structure, in which the higher modes, generally not used in magnetic resonance, are utilized for NQR detection. These modes have smooth distributions of the amplitudes of the corresponding radiofrequency magnetic fields everywhere along the sensor's surface. The phases of the fields, on the other hand, are cyclically shifted across the sensor's surface. Noise signals coming from distant sources, therefore, induce equal-magnitude cyclically phase-shifted currents in different parts of the sensor. When such cyclically phase-shifted currents arrive at the mode connection point, they destructively interfere with each other and are cancelled out. NQR signals of polycrystalline or disordered substances, however, are efficiently detected by these modes because they are insensitive to the phases of the excitation/detection. No blind spots exist along the sensor's surface. The sensor can be used for simultaneous detection of one or more substances in locations with environmental noise.

ERK1/2 regulates two sequential steps promoting monocyte survival to peroxynitrite.

Previous studies from our laboratory indicate that cytosolic phospholipase A(2) (cPLA(2))-released arachidonic acid promotes monocyte/macrophage survival in the presence of peroxynitrite. In particular, the lipid messenger is metabolised by 5-lipoxygenase (5-LO) to 5-hydroxyeicosatetraenoic acid and causes the mitochondrial translocation of protein kinase Calpha (PKCalpha), an event associated with the cytosolic accumulation of Bad and Bax. Here we show that phosphorylation reactions driven by extracellular regulated kinase 1/2 (ERK1/2) critically regulate the activation/nuclear translocation of 5-LO. Inhibition of ERK1/2 was invariably associated with the cytosolic localisation of PKCalpha, the mitochondrial accumulation of Bad and Bax and with a rapid mitochondrial permeability transition-dependent necrosis. All these events were prevented by nanomolar concentrations of 5-hydroxyeicosatetraenoic acid. Hence, in addition to the previously characterised effects on cPLA(2), ERK1/2 critically regulates 5-LO activity in the absence of additional downstream targets in the survival signalling preventing peroxynitrite toxicity.

Three-dimensional high-inductance birdcage coil for NQR applications.

A birdcage coil capable of operating simultaneously and independently in three orthogonal dimensions has been developed. A co-rotational end-ring mode producing an RF field in the longitudinal direction was utilized in addition to the two common transverse orthogonal modes. Two conductor turns were used for each of the coil's windows, increasing its inductance by a factor of four, thereby, making the coil suitable for low-frequency applications. Two or three-frequency detection can be easily carried out with this device. Orthogonality of the coil's channels allows arbitrarily close frequency positioning of each resonant mode, potentially useful in wide-line NQR studies, in which simultaneous excitation/detection of signals from three adjacent regions of a single wide line can be performed. The coil's performance was evaluated using a three-dimensional scheme, in which a circularly polarized experiment was combined with a linearly polarized measurement at another frequency, resulting in SNR improvement by 55%.

RF probe recovery time reduction with a novel active ringing suppression circuit.

A simple Q-damper device for active probe recovery time reduction is introduced along with a straightforward technique for the circuit's component value optimization. The device is inductively coupled to a probe through a coupling transformer positioned away from the main coil, which makes the design independent of the coil type being used. The Q-damper is a tuned circuit, which is resonant at the same frequency as the probe and can be actively interrupted. When the circuit is interrupted, it is detuned and, thereby, is uncoupled from the probe, which operates normally. Turning the device on leads to re-coupling of the circuits and causes splitting of the probe's resonance line, which can be observed through its drive port. A resistance of an appropriate value is introduced into the Q-damper circuit, resulting in smoothing of the resonance splitting into one broad line, representing the coupled system's low-Q state, in which the energy stored in the main coil is efficiently dissipated. The circuit's component values are optimized by monitoring the shape of this low-Q state. Probe recovery time reduction by, approximately, an order of magnitude has been obtained with this device. Application of the device during an NQR experiment led to an increase in the signal-to-noise ratio by a factor of 4.9.

Utilization of pure nuclear quadrupole resonance spectroscopy for the study of pharmaceutical crystal forms.

Solid-state physical characterization of a pharmaceutical substance is necessary for successful development and approval of the final product. Different physical analytical techniques are available to do so: X-ray diffraction (XRD), IR, Raman, DSC, TG and NMR. Moreover, all of them detect the presence of excipients perturbing the analysis of the pure substance in low doses. In order to study polymorphism and pseudo polymorphism of drug, this paper introduces possible applications of pure nuclear quadrupole resonance, as a non-destructive technique in qualitative and quantitative approaches. Chlorpropamide and diclofenac sodium were used as examples. Unlike the mentioned techniques, the nuclear quadrupole resonance (NQR) signal of pharmaceutical compounds is not perturbed by the presence of solid excipient or other substances unless they possess resonance frequencies in the same frequency range of the compound studied.