Relative Electrical Conductivity Research Articles

Chemical Profile, Antioxidant and Antibacterial Activities, Mechanisms of Action of the Leaf Extract of Aloe arborescens Mill.

Aloe arborescens Mill's extracts have been explored for antibacterial and antioxidant efficacies. However, there is limited information on its chemical composition and mechanism of action. The purpose of this study was to assess the chemical composition, antibacterial and antioxidant activities and mechanism of the whole leaf extract of A. arborescens Mill. The phytochemical profile was analysed with gas chromatography mass spectrometry (GC-MS). The antioxidant and antibacterial activities were screened using 1,1diphenyl2picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and micro-dilution assays, respectively. The effects of the extract on the bacterial respiratory chain dehydrogenase, membrane integrity and permeability were analysed using iodonitrotetrazolium chloride, 260 absorbing materials and relative electrical conductivity assays. GC-MS spectrum revealed 26 compounds with N,N'-trimethyleneurea (10.56%), xanthine (8.57%) and 4-hexyl-1-(7-ethoxycarbonylheptyl)bicyclo[4.4.0]deca-2,5,7-triene (7.10%), being the major components. The extract also exhibited antioxidant activity with median concentration (IC50) values of 0.65 mg/mL on DPPH and 0.052 mg/mL on ABTS. The extract exhibited minimum inhibitory concentration (MIC) values ranging from 0.07 to 1.13 mg/mL. The extract inhibited the bacterial growth by destructing the activity of the respiratory chain dehydrogenase, membrane integrity and permeability. Therefore, the leaf extract has the potential to serve as a source of antibacterial and antioxidant compounds.

Methyl jasmonate treatment alleviates chilling injury and improves antioxidant system of okra pod during cold storage.

Okra pod is sensitive to low temperature, which results in chilling injury under improper low-temperature storage. This study aimed to evaluate the effect of different concentrations of methyl jasmonate (MeJA) treatment on okra pod stored at 4 ± 1°C for 12 days and illuminate the mechanism of MeJA alleviating chilling injury. Compared to the control, MeJA treatments maintained lower relative electric conductivity (REC), chilling injury (CI) degree, and lignin content, as well as higher total soluble solids, total soluble sugar, pectin content, and chlorophyll content. The factor analysis was applied to comprehensively evaluate the effects of MeJA so that 1μmol/L MeJA was screened as the optimum concentration to maintain the okra quality throughout the storage time. In contrast with control, MeJA not only accelerated the generation of antioxidant substances (phenolics and flavonoids) but also increased the superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD) activity, inhibited malondialdehyde (MDA), hydrogen peroxide (H2O2) content accumulation, and the polyphenol oxidase (PPO) activity. This work confirmed that MeJA could effectively alleviate chilling injury and maintain the quality during cold-stored by regulating reactive oxygen species (ROS) metabolism. These results provide theoretical guidance for the application of MeJA in okra storage and preservation.

Modeling of the Transient Electric Field in Multilayer Dielectric Composites Under Impulsive HV Energization

This article presents the theoretical analysis of composite electrical insulation, formed from layered dielectric materials and subjected to impulsive energization. The 1-D planar and cylindrical geometries were considered, consisting of an arbitrary number of layers with arbitrary relative permittivity and electrical conductivity. Analytical solutions have been successfully derived for the time-dependent electric field inside the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${i}$ </tex-math></inline-formula> th layer. To demonstrate the usage of the model under complex multilayer topologies where analytical solutions are nontrivial, the characteristics of a 20-layer-graded composite under microsecond and sub-microsecond impulses were analyzed and validated against a finite-element (FE) solver. Results indicate that the transient electric field response under impulsive energization is strongly dependent on the interplay between the composite relaxation time constants and the characteristic timescales associated with the applied impulse. The model is a further development for the design and coordination of functionally graded materials (FGMs) and composite insulation for high-voltage (HV) system design. This is particularly relevant under fast-rising impulsive conditions as often encountered in many pulsed power applications.

QTL Mapping and a Transcriptome Integrative Analysis Uncover the Candidate Genes That Control the Cold Tolerance of Maize Introgression Lines at the Seedling Stage.

Chilling injury owing to low temperatures severely affects the growth and development of maize (Zea mays.L) seedlings during the early and late spring seasons. The existing maize germplasm is deficient in the resources required to improve maize's ability to tolerate cold injury. Therefore, it is crucial to introduce and identify excellent gene/QTLs that confer cold tolerance to maize for sustainable crop production. Wild relatives of maize, such as Z. perennis and Tripsacum dactyloides, are strongly tolerant to cold and can be used to improve the cold tolerance of maize. In a previous study, a genetic bridge among maize that utilized Z. perennis and T. dactyloides was created and used to obtain a highly cold-tolerant maize introgression line (MIL)-IB030 by backcross breeding. In this study, two candidate genes that control relative electrical conductivity were located on MIL-IB030 by forward genetics combined with a weighted gene co-expression network analysis. The results of the phenotypic, genotypic, gene expression, and functional verification suggest that two candidate genes positively regulate cold tolerance in MIL-IB030 and could be used to improve the cold tolerance of cultivated maize. This study provides a workable route to introduce and mine excellent genes/QTLs to improve the cold tolerance of maize and also lays a theoretical and practical foundation to improve cultivated maize against low-temperature stress.

Effects of Exogenous Melatonin on Chrysanthemum Physiological Characteristics and Photosynthesis under Drought Stress

Melatonin has been confirmed to relieve drought stress in various plant species. However, the mechanism in garden chrysanthemums remains to be elucidated. Here, we examined the putative role of exogenous melatonin application in improving drought-stress tolerance in Chrysanthemum seedlings. Treatment with melatonin (100 µM) significantly mitigated the negative effects of drought stress on the seedling photosynthetic parameters and physiological and biochemical indexes. The increased tolerance conferred by exogenous melatonin was attributable to increased photosynthetic activity, which alleviates drought-induced oxidative damage by reducing malondialdehyde accumulation. In other words, the combined application of MT and PEG was better than their individual applications, as it prevented heat-induced membrane damages by declining the hydrogen peroxide (28%), malondialdehyde contents (38%), and relative electrical conductivity (19%) as compared to PEG. Interestingly, the melatonin application stimulated the activity of major antioxidant enzymes such as superoxide dismutase (21%), catalase (26%) and polyphenol oxidase (35%). In addition, exogenous melatonin promoted photosynthesis. Compared with the PEG drought-stress treatment, the melatonin treatment significantly increased the net photosynthetic rate (39%), stomatal conductance (27%), and transpiration rates (18%), while decreasing the intercellular CO2 concentration (10%). The photochemical quenching coefficient (46%), photosystem II (PSII) maximum photochemical quantum yield (22%), apparent electron transfer rate (37%), and PSII potential photochemical efficiency (18%) showed an upward trend. In summary, exogenous spraying of MT can effectively improve drought tolerance and mitigate the damage caused by drought stress in the “Xuanqiu ninghong” Chrysanthemum.

Comparative analysis of petal epidermal wax composition and loss-water resistance in five cut lily cultivars (Lilium spp)

Plant epidermal wax is the primary barrier to non-stomatal transpiration, and of great significance for plants to resist loss-water stress. In this study, the crystal morphology and chemical composition of the petal epidermal wax of five cut lily cultivars were studied. The waxy crystal morphology of five cultivars was ellipsoidal. Petal epidermal wax was mainly composed of very long-chain fatty acids and their derivatives. The carbon chain lengths of straight-chain alkanes were in the range of C19–C34, with the main ones being C19, C25, and C34. The content of C25 straight-chain alkanes in cultivar ‘Manissa’ was as high as 65.9%. Further research on the water permeability of each material showed that ‘Manissa’ had the highest total wax content and low water permeability, while cultivar ‘Siberia’ had the lowest wax content and the highest water permeability. Determination of relative water content, relative electrical conductivity, and malondialdehyde content indicated that loss-water stress caused the least damage to cultivars ‘Manissa’ and ‘Ruby’, while ‘Siberia’ suffered the most serious injury. These results demonstrated that lily cut flower petals with higher epidermal wax content, had stronger loss-water stress tolerance, and there was a positive correlation between the two. These findings provide new options for genetic breeding to improve the loss-water stress tolerance of cut flowers.

1-Methylcyclopropene (1-MCP) treatment differentially mediated expression of vacuolar processing enzyme (VPE) genes and delayed programmed cell death (PCD) during ripening and senescence of apple fruit

• 1-MCP reduced VPE activity and delayed vacuolar-mediated PCD in apple fruit. • MdVPE s had varying expression patterns in response to 1-MCP during ripening. • MdVPE s were differentially expressed after transient over-expression of MdERF2. The main purpose of this research was to evaluate the impacts of 1-methylcyclopropene (1-MCP) treatment on vacuolar processing enzyme ( VPE ) genes and programmed cell death (PCD) during ripening and senescence of apple fruit ( Malus × domestica Borkh.). The ethylene antagonists 1-MCP (1 μL L −1 ) was applied to apples after harvest. Both treated and control fruit were stored at 20 ± 2°C. The data showed that 1-MCP treatment maintained flesh firmness, delayed climacteric peaks of respiration and ethylene, reduced VPE activity, relative electrical conductivity (REC), malondialdehyde (MDA) content and reactive oxygen species (ROS) accumulation during ripening. Transmission electron microscopy (TEM) and DNA ladder assay revealed that 1-MCP delayed vacuolar-mediated PCD in ripening apple fruit. Generally, expression of MdVPEγ1, MdVPEγ2, MdVPEδ4 and MdVPEδ7 was down-regulated by 1-MCP treatment, while expression of MdVPEα4 and MdVPEβ2 was enhanced by it during ripening compared with controls. 1-MCP treatment differentially reduced expression of MdVPEα1, MdVPEα2 and MdVPEα5 at the early ripening stage but promoted their expression at the late ripening stage, while it had the opposite effects on MdVPEβ1, MdVPEβ3 and MdVPEγ4 expression. After transient overexpression of MdERF2, MdVPEs displayed varying expression patterns, among which MdVPEα2 transcripts increased greater than the other genes. Our results indicated that MdVPEs expression and vacuolar-mediated PCD were mediated by ethylene signal during ripening and senescence of apple fruit.

Finite difference time domain method of lightpropagation through inhomogeneous media

Propagation of arbitrarily polarized light through inhomogeneous media is modeled in this paper. The model can include parameters of the media such as relative dielectric constant, relative magnetic constant and electric conductivity. The orientation of the electric field strength of the light source could be defined arbitrarily, and in this paper two polarization modes are considered: transverse electric (TE) mode and transverse magnetic (TM) mode. The electric field vector could change its orientation in dependence on the characteristics of the media. The model developed in this paper is based on the finite difference time domain (FDTD) method and Maxwell’s equations. A two-dimensional formulation of FDTD is applied in this computing. Several cases were considered, and the results obtained in this paper agree with the literature. The model shown in this paper does not require much time for computer processing and can be easily applied for specific cases of media, source, and light.

Reduction of High-Temperature Damage on Paeonia ostii through Intercropping with Carya illinoinensis

Paeonia ostii is an emerging woody oil crop, but the high temperature in summer is extremely unfavorable for its growth and development. Understory intercropping cultivation would provide shaded environments which could effectively reduce the ambient temperature. In order to explore whether understory intercropping cultivation would reduce the effects of high-temperature stress on P. ostii, the changes of leaf physiological indicators and leaf microstructures of sole-cropping and intercropping P. ostii were investigated. P. ostii that intercropping cultivated under Illinois pecans (Carya illinoinensis (Wangenh.) K. Koch) with 4 m × 4 m and 4 m × 8 m rowing spaces were used as samples in this study. The results showed that with continuous high temperature, the high-temperature damage index of P. ostii kept increasing, whereas the leaf relative water content continued to decline. Compared to sole-cropping, the high-temperature damage index, relative electrical conductivity, proline content, antioxidant enzymes superoxide dismutase (SOD), and ascorbate peroxidase (APX) activities of intercropping P. ostii under C. illinoinensis were significantly decreased, whereas the leaf relative water content was higher. Moreover, compared to sole-cropping, intercropping P. ostii under C. illinoinensis increased SPAD and chlorophyll contents, made mesophyll cell ultrastructures more intact, and made the chloroplasts rounder and more filled with starch granules and lipid globules, leading to enhanced photosynthesis (Pn) and transpiration rates (Tr). Notably, the reduction of high-temperature damage on intercropping P. ostii under C. illinoinensis with 4 m × 4 m rowing spaces was more significant than that under C. illinoinensis with 4 m × 8 m rowing spaces. This research provides some reference values for efficient plantation of P. ostii in the middle and lower reaches of the Yangtze River in China.

Identification of microRNA158 from Anthurium andraeanum and Its Function in Cold Stress Tolerance

Anthurium andraeanum is a tropical flower with high ornamental and economic value. Cold stress is one of the major abiotic stresses affecting the quality and value of A. andraeanum; thus, improving the cold tolerance of this species is an important breeding objective. MicroRNAs (miRNAs) have a critical role in plant abiotic stress responses, but their specific molecular regulatory mechanisms are largely unknown, including those related to the cold stress response in A. andraeanum. Here, we identified and cloned the precursor of miR158 from A. andraeanum (Aa-miR158). Both Aa-miR158 and its target gene (c48247) had higher expression levels in strong leaves than in other tissues or organs. Further study revealed that the transcript level of Aa-miR158 was increased by cold stress. Heterologous overexpression of Aa-miR158 improved cold stress tolerance in Arabidopsis, which was associated with decreases in the malondialdehyde (MDA) concentration and relative electrical conductivity (REC) as well as increases in peroxidase (POD) and catalase (CAT) activity. Moreover, overexpressing Aa-miR158 significantly increased the expression of endogenous genes related to cold stress tolerance and reactive oxygen species (ROS) levels in transgenic Arabidopsis under cold stress. Overall, our results demonstrate that Aa-miR158 is significantly involved in the cold stress response and provide a new strategy for cold tolerance breeding of A. andraeanum.

In-situ monitoring of powder bed fusion of metals using eddy current testing

Powder bed fusion of metals (PBF-LB/M) is the most commonly used additive manufacturing process for the layerwise production of metal parts. Although the technology has developed rapidly in recent years, manufactured parts still lack consistent quality primarily owing to process-inherent variability, and the lack of effective sensing technologies enabling the ability to control the process during part production. Thus, there are high costs caused by rigorous post-process part inspection steps required to provide compliant part certificates. In contrast to typically deployed in-situ sensing technologies, eddy current testing (ECT) is a standardized nondestructive testing (NDT) technique able to provide compliant part certificates during post-process inspection according to existing standards. This study investigates the potential of ECT as an in-situ process monitoring technology for PBF-LB/M. Parts made from AlSi10Mg were manufactured on a PBF-LB/M machine using different process parameters yielding different relative densities ranging from 99%– 99.7%. During the build cycle, the parts were measured layer-by-layer with an ECT system mounted on the machine recoater. Signal analysis methods were developed which effectively separate and calibrate the electrical conductivity component (relative electrical conductivity) and the distance component (lift-off) of the ECT signals. The relative electrical conductivity was then compared to X-ray micro-computed tomography ( μ CT) measurement data demonstrating that layer-to-layer differences in relative density of about 0.1% can be successfully detected via ECT. In addition, the lift-off was used to monitor the thickness of the consolidated layers and the layer-to-layer part height. The results show that ECT is an effective technology for in-situ monitoring of the relative part density paving the way for deploying ECT for in-situ NDT of PBF-LB/M-manufactured parts.

The effects of complex agent and sintering temperature on conductive copper complex paste

In this research study, the formulation of precursor-type Cu pastes was done by mixing copper (II) acetate and 2-amino-2-methyl-1-propanol (AMP). Accordingly, the influence of the complex agent amount on the Cu pastes stability was examined at diverse mole ratio ratios. The Cu paste's optimal formulation was then obtained with the copper acetate to AMP ratio of 0.5. The Cu paste with a CuA/AMP ratio at 0.5 was then coated onto glass substrates; they were then sintered under an N2 environment at various temperatures including 140, 180 and 220 °C. Characterization of the copper complex paste was done by Fourier transform infrared (FTIR) spectroscopy, UV–vis spectroscopy as well as Thermal analysis. Pattern's characterization was also done through X-ray diffractometry (XRD), field emission scanning electron microscope (FE-SEM) as well as four-point probe method for the purpose of confirming the related crystal structure, microstructure and electrical conductivity, respectively. It is demonstrated how the sintering temperature could affect the Cu film. The printed patterns on the glass substrate which was cured at the temperature of 180 °C displayed metalized cooper with low resistivity (30 μΩ cm) and dense copper films.

Resistance evaluation of Canna indica, Cyperus papyrus, Iris sibirica, and Typha latifolia to phytotoxic characteristics of diluted tequila vinasses in wetland microcosms

Tequila vinasse has a high contaminating capacity due to its physicochemical characteristics. Efficient and low-cost alternative treatments are required to reduce and control the environmental impacts caused by raw vinasse discharges, mainly from micro and small factories. One option is wetland technologies in which vegetation plays an important role in the proper functioning of the system; thus, the species to be used must be properly selected based on their resistance and tolerance to the toxic effects of vinasse. Therefore, this study aims to evaluate the resistance of four macrophyte species to tequila vinasse in wetland microcosms that is, Canna indica, Cyperus papyrus, Iris sibirica, and Typha latifolia which were exposed to 5, 7, 10, 12, and 15% of vinasse diluted with domestic wastewater. The control parameters (relative content, evapotranspiration, pH, electrical conductivity, and apparent color) showed that the plants in general developed stress symptoms. However, statistical analysis revealed a significant difference (p < 0.05) between plant species and vinasse treatments, further evidencing that I. sibirica is the species with the greatest potential to be used as emergent vegetation in treatment wetlands for the purification of tequila vinasse.

Enhancement of cucumber resistance under salt stress by 2, 4-epibrassinolide lactones.

This study investigated the effects of exogenous 2, 4-epibrassinolide lactone (EBR) on the growth, photosynthetic pigments, antioxidant defense system, ion homeostasis, MAPK cascade and key genes of SOS signaling pathway of cucumber seedlings under salt stress using cucumber "Xinchun 4" as the test material. The experiment was set up with four treatments: foliar spraying of distilled water (CK), 50 mmol.L-1 NaCl (NaCl), 50 mmol.L-1 NaCl+foliar spray of 0.02 μmol.L-1 EBR (EBR+NaCl), and 50 mmol.L-1 NaCl+foliar spray of 24 μmol.L-1 Brassinazole (BRZ) (BRZ+NaCl). The results showed that EBR+NaCl treatment significantly increased plant height, above-ground fresh weight, total root length, total root surface area, average rhizome and photosynthetic pigment content compared to NaCl treatment. Meanwhile, compared with NaCl treatment, EBR+NaCl treatment significantly increased superoxide dismutase, catalase and ascorbate peroxidase (SOD, CAT and APX) activities, significantly promoted the accumulation of osmoregulatory substances (soluble sugars and proline), and thus effectively reduced malondialdehyde (MDA) content and relative electrical conductivity of cucumber leaves. Exogenous spraying of EBR also significantly reduced Na+/K+ under NaCl stress, effectively alleviating the toxic effects of Na+ ions. In addition, exogenous EBR induced the up-regulated expression of CsMAPK3, CsMAPK4, CsMAPK6 and CsMAPK9 genes in the MAPK cascade signaling pathway and CsSOS1, CsSOS2 and CsSOS3 genes in the SOS signaling pathway to enhance salt tolerance in cucumber under NaCl stress. Therefore, exogenous spraying EBR may effectively reduce the damage of salt stress on cucumber seedlings by improving antioxidant capacity, maintaining ion homeostasis and activating salt-tolerant related signaling pathways, which might promote the growth of cucumber seedlings and the establishment of root system morphology. This study provides a reference for EBR to improve the salt tolerance of cucumber.

Overexpression of Pyrus sinkiangensis HAT5 enhances drought and salt tolerance, and low-temperature sensitivity in transgenic tomato.

The homeodomain-leucine zipper protein HAT belongs to the homeodomain leucine zipper subfamily (HD-Zip) and is important for regulating plant growth and development and stress tolerance. To investigate the role of HAT5 in tolerance to drought, salt, and low temperature stress, we selected a HAT gene from Pyrus sinkiangensis Yü (Pyrus sinkiangensis T.T. Yu). The sequences were analyzed using ioinformatics, and the overexpressed tomato lines were obtained using molecular biology techniques. The phenotypes, physiological, and biochemical indexes of the wild-type and transgenic tomato lines were observed under different stress conditions. We found that the gene had the highest homology with PbrHAT5. Under drought and NaCl stress, osmotic regulatory substances (especially proline) were significantly accumulated, and antioxidant enzyme activities were enhanced. The malondialdehyde level and relative electrical conductivity of transgenic tomatoes under low temperature (freezing) stress were significantly higher than those of wild-type tomatoes. The reactive oxygen species scavenging system was unbalanced. This study found that PsHAT5 improved the tolerance of tomatoes to drought and salt stress by regulating proline metabolism and oxidative stress ability, reducing the production of reactive oxygen species, and maintaining normal cell metabolism. In conclusion, the PsHAT5 transcription factor has great potential in crop resistance breeding, which lays a theoretical foundation for future excavation of effective resistance genes of the HD-Zip family and experimental field studies.

Metabolomic and regular analysis reveal phytotoxic mechanisms of sterigmatocystin in Amaranthus retroflexus L.

Sterigmatocystin (STE) is a common hepatotoxic and nephrotoxic contaminant in cereals, however, its phytotoxicity and mechanisms are poorly understood. Here, the phytotoxic mechanisms of STE were investigated via the metabolomics of Amaranthus retroflexus L. A total of 140 and 113 differential metabolites were detected in the leaves and stems, respectively, among which amino acids, lipids, and phenolic compounds were significantly perturbed. Valine, leucine, isoleucine, and lysine biosynthesis were affected by STE. These metabolic responses revealed that STE might be toxic to plants by altering the plasma membrane and inducing oxidative damage, which was verified by measuring the relative electrical conductivity and quantification of reactive oxygen species. The elevated amino acids, as well as the decreased of D-sedoheptuiose-7-phosphate indicated increased proteolysis and carbohydrate metabolism restriction. Furthermore, the IAA level also decreased. This study provides a better understanding of the impacts of STE on the public health, environment and food security.

Luffa rootstock enhances salt tolerance and improves yield and quality of grafted cucumber plants by reducing sodium transport to the shoot

Soil salinity severely limits crop yield and quality. Grafting onto tolerant rootstocks is known as an effective means to alleviate salt stress. The present study was planned to find out the potential roles, mechanisms and applications of luffa rootstock to improve salt tolerance of grafted cucumber plants. Here, we screened a highly salt-tolerant luffa rootstock by evaluating the growth, photosynthetic performance, antioxidant defense and the accumulation of Na+ and K+ under salt stress. Reciprocal grafting between cucumber and luffa showed that luffa rootstock significantly improved the salt tolerance of cucumber plants, as evidenced by higher fresh weight, photochemical efficiency (Fv/Fm), and lower relative electrical conductivity (REC), which was closely associated with the decreased accumulation of Na+ and increased the accumulation of K+ in shoots of luffa grafted cucumber seedlings, leading to a lower Na+:K+ ratio in shoot when compared with self-grafted cucumber. Furthermore, grafting with intermediate stock of luffa also sufficiently alleviated cucumber salt stress by reducing Na+ accumulation in shoot and the whole plant but increasing Na+ accumulation in interstock and root under salt stress, fully proving the salt tolerance depending on the capacity of luffa interstock to limit the transport of Na+ from the root to the shoot. More importantly, luffa rootstock improved the growth, yield and quality of grafted cucumber plants grown in pots in solar greenhouse as revealed by increased net photosynthetic rate, plant height, leaf number, yield, Vitamin C and soluble sugar but decreased titratable acid under both salinity and normal conditions. Together, these results, for the first time, clearly demonstrated that luffa,a new highly salt-tolerant rootstock, enhances salt tolerance and improves yield and quality of grafted cucumber plants by reducing sodium transport to the shoot.

A Heat Shock Transcription Factor TrHSFB2a of White Clover Negatively Regulates Drought, Heat and Salt Stress Tolerance in Transgenic Arabidopsis

Heat shock transcription factors (HSF) are divided into classes A, B and C. Class A transcription factors are generally recognized as transcriptional activators, while functional characterization of class B and C heat shock transcription factors have not been fully developed in most plant species. We isolated and characterized a novel HSF transcription factor gene, TrHSFB2a (a class B HSF) gene, from the drought stress-sensitive forage crop species, white clover (Trifolium repens). TrHSFB2a was highly homologous to MtHSFB2b, CarHSFB2a, AtHSFB2b and AtHSFB2a. The expression of TrHSFB2a was strongly induced by drought (PEG6000 15% w/v), high temperature (35 °C) and salt stresses (200 mM L-1 NaCl) in white clover, while subcellular localization analysis showed that it is a nuclear protein. Overexpression of the white clover gene TrHSFB2a in Arabidopsis significantly reduced fresh and dry weight, relative water contents (RWC), maximum photosynthesis efficiency (Fv/Fm) and performance index on the absorption basis (PIABS), while it promoted leaf senescence, relative electrical conductivity (REC) and the contents of malondialdehyde (MDA) compared to a wild type under drought, heat and salt stress conditions of Arabidopsis plants. The silencing of its native homolog (AtHSFB2a) by RNA interference in Arabidopsis thaliana showed opposite trends by significantly increasing fresh and dry weights, RWC, maximum photosynthesis efficiency (Fv/Fm) and performance index on the absorption basis (PIABS) and reducing REC and MDA contents under drought, heat and salt stress conditions compared to wild type Arabidopsis plants. These phenotypic and physiological indicators suggested that the TrHSFB2a of white clover functions as a negative regulator of heat, salt and drought tolerance. The bioinformatics analysis showed that TrHSFB2a contained the core B3 repression domain (BRD) that has been reported as a repressor activator domain in other plant species that might repress the activation of the heat shock-inducible genes required in the stress tolerance process in plants. The present study explores one of the potential causes of drought and heat sensitivity in white clover that can be overcome to some extent by silencing the TrHSFB2a gene in white clover.

Effect of Exogenous Calcium on the Heat Tolerance in Rosa hybrida ‘Carolla’

This study was designed to investigate the effects of exogenous calcium on the tolerance of Rosa hybrida ‘Carolla’ to high-temperature and the physiological mechanisms underlying this response. Leaves of ‘Carolla’ grown under stress were treated by spraying four different concentrations of calcium chloride (CaCl2; 50, 100, 150, or 200 μM). The photosynthetic responses, antioxidant enzyme activities, and osmotic substance contents were measured under high-temperature stress at the flowering stage. Temperature-stressed ‘Carolla’ with CaCl2 treatment showed significantly increased chlorophyll (Chl) content, net photosynthetic rate (An), transpiration rate (E), stomatal conductance (gs), water use efficiency (WUE), superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) activities together with proline (Pro), soluble sugar (SS), and soluble protein (SP) concentrations, while malonaldehyde (MDA) content and relative electrical conductivity (REC) were significantly reduced. The damages caused by high-temperature stress were alleviated by applying CaCl2. Among the CaCl2 treatments, 100 μM CaCl2 best minimized the damage caused by high-temperature to ‘Carolla’. This study showed that exogenous calcium could improve the tolerance of Rosa hybrida ‘Carolla’ to high-temperature stress by regulating photosynthesis, the antioxidant system, and osmotic substances.

Exploration of Phase Dissolution during Solution Treatment for a New Al-3.86Cu-0.89Li-0.38Mg-0.28Ag Alloy

The dissolution of the second phase during solution treatment was of great importance for achieving preferential properties via aging treatment for Aluminum-Lithium (Al-Li) alloys. The microstructure characteristics of an extruded Al-Li alloy and its second phase dissolution during solution treatment were studied, while related electrical conductivity and tensile properties after ageing were tested for verification. The results indicated that as the alloy solution was treated from 500°C to 520°C with a soaking time of 1.5h, the Cu-rich phase dissolved into the matrix continuously. The statistics of remained phase area fraction ascertained no obvious decrement from 510°C to 520°C and only Fe-containing phase with large size was detected. Meanwhile, tensile properties under the same aging regime declared a higher strength was obtained at 510°C. As the solution time varied from 0.5h to 5h at 510°C, the Cu-rich phase was detected in a soaking time of 0.5h while disappeared after 1.5h and only the Fe-containing phase was observed. Correspondingly, electrical conductivity exhibited a moderate growth while tensile strength obviously increased from 0.5h to 1.5h and then maintained a platform, which revealed a preferential solution regime of 510°C/1.5h. This gives a reference for the second phase dissolution during solution treatments and furtherly obtaining preferential solution regimes.