The Adsorption and Desorption of Pb(2+) and Cd(2+) in Freeze-Thaw Treated Soils.

Adsorption and desorption are important processes that influence the potential toxicity and bioavailability of heavy metals in soils. However, information regarding adsorption and desorption behavior of heavy metals in soils subjected to freeze-thaw cycles is poorly understood. In the current study, the effect of freeze-thaw cycles with different freezing temperature (-15, -25, -35°C) on soil properties was investigated. Then the adsorption and desorption behavior of Pb(2+) and Cd(2+) in freeze-thaw treated soils was studied. The adsorption amounts of Pb(2+) and Cd(2+) in freeze-thaw treated soils were smaller than those in unfrozen soils (p < 0.05), due to the fact that pH, cation exchange capacity, organic matter content, free iron oxide content, and CaCO3 content in freeze-thaw treated soils were smaller than those in unfrozen soils. The adsorption amounts of Pb(2+) and Cd(2+) in soils treated with lower freezing temperatures were higher than those in soils treated with higher freezing temperatures. Desorption percentages of Pb(2+) and Cd(2+) in unfrozen soils were smaller than those in freeze-thaw treated soils (p < 0.05). The desorption percentages of Pb(2+) and Cd(2+) were smaller in soils treated with lower freezing temperatures than those in soils treated with higher freezing temperatures. The results obtained highlight the change of the adsorption and desorption behavior of typical heavy metals in freeze-thaw treated soils located in seasonal frozen soils zone in northeast China.

Enhanced photosynthetic efficiency by nitrogen-doped carbon dots via plastoquinone-involved electron transfer in apple.

Artificially enhancing photosynthesis is critical for improving crop yields and fruit qualities. Nanomaterials have demonstrated great potential to enhance photosynthetic efficiency; however, the mechanisms underlying their effects are poorly understood. This study revealed that the electron transfer pathway participated in nitrogen-doped carbon dots (N-CDs)-induced photosynthetic efficiency enhancement (24.29%), resulting in the improvements of apple fruit qualities (soluble sugar content: 11.43%) in the orchard. We also found that N-CDs alleviated mterf5 mutant-modulated photosystem II (PSII) defects, but not psa3 mutant-modulated photosystem I (PSI) defects, suggesting that the N-CDs-targeting sites were located between PSII and PSI. Measurements of chlorophyll fluorescence parameters suggested that plastoquinone (PQ), the mobile electron carrier in the photosynthesis electron transfer chain (PETC), was the photosynthesis component that N-CDs targeted. In vitro experiments demonstrated that plastoquinone-9 (PQ-9) could accept electrons from light-excited N-CDs to produce the reduced plastoquinone 9 (PQH2-9). These findings suggested that N-CDs, as electron donors, offer a PQ-9-involved complement of PETC to improve photosynthesis and thereby fruit quality. Our study uncovered a mechanism by which nanomaterials enhanced plant photosynthesis and provided some insights that will be useful in the design of efficient nanomaterials for agricultural/horticultural applications.

Oxidative post-translational modification of catalase confers salt stress acclimatization by regulating H2O2 homeostasis in Malus hupehensis.

Reactive oxygen species (ROS) play an essential role as both signaling molecule and damage agent during salt stress. As a signaling molecule, proper accumulation of H2O2 is crucial to trigger stress response and enhance stress tolerance. However, the dynamic regulation mechanism of H2O2 remains unclear. Here, we show that MhCAT2 (catalase 2 in Malus hupehensis) undergoes oxidative modification in an O2•--dependent manner and that oxidation at His225 residue reduces the MhCAT2 activity. Furthermore, the substitution of His225 with Tyr weakens the activity of MhCAT2. The oxidation modification provides a post-translational brake mechanism for the excessive scavenging of H2O2 caused by salt stress-induced catalase (CAT) over-expression. Overall, this finding provides mechanistic insights on stress tolerance augmentation by an O2•--mediated switch that regulates H2O2 homeostasis in Malus hupehensis.

Separated Respiratory Phases for In Vivo Ultrasonic Thermal Strain Imaging.

Thermal strain imaging (TSI) uses echo shifts in ultrasonic B-scan images to estimate changes in temperature which is of great values for thermotherapies. However, for in vivo applications, it is difficult to overcome the artifacts and errors arising from physiological motions. Here, a respiration separated TSI (RS-TSI) method is proposed, which can be considered as carrying out TSI in each of the exhalation and inhalation phases and then combining the results. Normalized cross correlation (NXcorr) coefficient between RF images along the timeline are used to extract the respiratory frequency, after which reference frames are selected to identify the exhalation and inhalation phases, and the two phases are divided quasi-periodically. RF images belonging to both phases are selected by applying NXcorr thresholds, and motion compensation together with a second frame selection helps to obtain two finely matched image sequences. After TSI calculations for each phase, the two processes are merged into one through extrapolation and interphase averaging. Compared to TSI based on dynamic frame selection (DFS), RS-TSI ensures that frames are selected during both the exhalation and inhalation phases while setting the frame selection range according to the respiratory frequency helps to improve motion compensation. The temporal intervals of TSI output are approximately half that employing DFS.

Simple Phenotypic Sensor for Visibly Tracking H2O2 Fluctuation to Detect Plant Health Status.

Hydrogen peroxide (H2O2), as a main component of reactive oxygen species (ROS), serves as a key signaling molecule relevant to plant stress response and health status. Many strategies have been developed for detecting or quantifying H2O2 concentration. However, reports on simply, visibly tracking H2O2 fluctuation in vivo are limited. Here, for visibly tracking the plant H2O2 wave, a green fluorescent phenotypic probe was designed by merging a H2O2-sensitive tertiary amine moiety with the core fluorophore tetraphenylethene skeleton. The green fluorescence emission is quenched up to 52% by H2O2 with good sensitivity, selectivity, and reversibility within the plant physiological range of 10-100 µM H2O2. In response to various abiotic stresses, including mechanical damage, high salt, strong light and drought, fluorescence fluctuations, response to H2O2 concentration alterations in vivo was visible to the naked eye under irradiation of commercially available UV light (365 nm) after simple injection of this H2O2 probe solution into seedling leaves. This phenotypic fluorescent H2O2 probe illustrates great potential as early sensors of plant health under stress without the aid of skillful operation and specialized equipment.

New strategy of light quality regulation with leaf-spraying fluorescent coatings for enhancing photosynthesis efficiency.

Fluorescent coatings are a kind of emerging light quality regulation material that can improve plant light utilization efficiency through easy manipulation at a low price. Compared with the scheme of fluorescent nanomaterials alone or those physically dispersed in polymeric materials for photosynthesis enhancement, fluorescent polymeric coatings (FPCs) originating from the covalent copolymerization of nanomaterial monomers can function stably and continuously, circumventing the high-cost manipulation of continuous leaf-spraying or hydroponics of the previous scheme in practical applications. Herein, we developed a kind of FPCs consisting of UV-to-blue light-converting nitrogen-doped carbon dots (N-CDs) as the fluorescent monomer to induce the copolymerization of N-CDs and tannic acid (TA). In the FPCs, N-CDs and TA are covalently cross-linked together. The fluorescent ability of N-CDs and the strong adhesion of TA are integrated organically to the whole to endow FPCs with excellent properties of prolonged fluorescence capacity, rain-erosion resistance and stability. After spraying FPCs on tomato leaves grown under the full spectrum, both the chlorophyll content of the leaves and effective photochemical efficiency were increased significantly, and the growth rate was promoted with 38.3% and 43.2% enhancement in the dry and fresh weight. We also analyzed the human cytotoxicity of the coating and the toxicological experiments showed that the coating did not affect the proliferation of human cells.

Thermal strain imaging in vivo using interpolated IQ-images.

Thermal strain imaging (TSI) is a promising technique for ultrasonic thermometry, especially in the applications of thermal therapies. The accuracy of TSI is dependent on the sampling rate and line density of B-Scan images, and the prevalent IQ-demodulated ultrasound data outputted from low- and middle-end machines are therefore insufficient. Here, the feasibility of using interpolated IQ images for TSI (based on the "infinitesimal echo strain filter" model) is studied through in vivo experiments targeting the perirenal fat of pigs. It is demonstrated that, axial interpolations, especially those using the zero-padding algorithm, can recover the capabilities of the low-sampling-rate complex IQ images in TSI, and make their performances comparable to those of RF/IQ complex images with higher sample rate. Meanwhile, interpolations along the lateral direction can increase the line density of IQ images, reduce TSI errors, and reveal more details in the temperature maps. In the experiments, the variation in the thermometry coefficient (the k-value) is well below 3%. The findings here bring down the requirement of high sampling rate as well as high line density of US images in TSI, making it possible to be applied on common US machines.

Selection of surfactant in remediation of DDT-contaminated soil by comparison of surfactant effectiveness.

With an aim to select the most appropriate surfactant for remediation of DDT-contaminated soil, the performance of nonionic surfactants Tween80, TX-100, and Brij35 and one anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in enhancement of DDT water solubility and desorption of DDT from contaminated soil and their adsorption onto soil and ecotoxicities were investigated in this study. Tween80 had the highest solubilizing and soil-washing ability for DDT among the four experimental surfactants. The adsorption loss of surfactants onto soil followed the order of TX-100 > Tween80 > Brij35 > SDBS. The ecotoxicity of Tween80 to ryegrass (Lolium perenne L.) was lowest. The overall performance considering about the above four aspects suggested that Tween80 should be selected for the remediation of DDT-contaminated soil, because Tween80 had the greatest solubilizing and soil-washing ability for DDT, less adsorption loss onto soil, and the lowest ecotoxicity in this experiment.