Fanconi Anemia Complementary Group A (FANCA) Facilitates the Occurrence and Progression of Liver Hepatocellular Carcinoma.

BACKGROUND: Liver hepatocellular carcinoma (LIHC) is a serious liver disease worldwide, and its pathogenesis is complicated. AIMS: This study investigated the potential role of FANCA in the advancement and prognosis of LIHC. METHODS: Public databases, quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blot (WB) and immunohistochemistry (IHC) were employed to measure FANCA expression between tumor and normal samples. The relationship between FANCA expression and prognosis of LIHC patients were examined. Functional enrichment of FANCA-related genes was performed. Furthermore, univariate and multivariate analyses were conducted to determine the independent prognosis value of FANCA in LIHC. Finally, influence of FANCA knockout on the proliferation, migration, and invasion of HepG2 cell was validated with cloning formation, CCK8, and Transwell assays. RESULTS: Expression analysis presented that FANCA had high expression level in LIHC tissues and cells. Receiver operating characteristic (ROC) curve analysis showed that FANCA was of great diagnosis value in LIHC. Clinicopathological analysis revealed that FANCA was significantly greater expressed in the advanced stage than in the early stage of LIHC. Univariate, multivariate, and Kaplan-Meier survival analysis confirmed that high expression of FANCA was strongly associated with poor survival of LIHC patients. In addition, high level of FANCA in LIHC showed a negative association with immunoinfiltrated B cells, T cells, and stromal scores. Moreover, Knockout of FANCA significantly inhibited HepG2 cell proliferative activity, migration, and invasion ability. CONCLUSIONS: Our data revealed that high level of FANCA was closely associated with LIHC malignant progression, suggesting its potential utility as a diagnostic, predictive indicator, and therapeutic target.

Partially Dissecting Electron Fluxes in Both Photosystems in Spinach Leaf Disks during Photosynthetic Induction.

Photosynthetic induction, a gradual increase in photosynthetic rate on a transition from darkness or low light to high light, has ecological significance, impact on biomass accumulation in fluctuating light and relevance to photoprotection in strong light. However, the experimental quantification of the component electron fluxes in and around both photosystems during induction has been rare. Combining optimized chlorophyll fluorescence, the redox kinetics of P700 [primary electron donor in Photosystem I (PSI)] and membrane inlet mass spectrometry in the absence/presence of inhibitors/mediator, we partially estimated the components of electron fluxes in spinach leaf disks on transition from darkness to 1,000 �mol photons�m-2�s-1 for up to 10 min, obtaining the following findings: (i) the partitioning of energy between both photosystems did not change noticeably; (ii) in Photosystem II (PSII), the combined cyclic electron flow (CEF2) and charge recombination (CR2) to the ground state decreased gradually toward 0 in steady state; (iii) oxygen reduction by electrons from PSII, partly bypassing PSI, was small but measurable; (iv) cyclic electron flow around PSI (CEF1) peaked before becoming somewhat steady; (v) peak magnitudes of some of the electron fluxes, all probably photoprotective, were in the descending order: CEF1 > CEF2 + CR2 > chloroplast O2 uptake; and (vi) the chloroplast NADH dehydrogenase-like complex appeared to aid the antimycin A-sensitive CEF1. The results are important for fine-tuning in silico simulation of in vivo photosynthetic electron transport processes; such simulation is, in turn, necessary to probe partial processes in a complex network of interactions in response to environmental changes.

Dynamical Signature of Symmetry Fractionalization in Frustrated Magnets.

The nontriviality of quantum spin liquids (QSLs) typically manifests in the nonlocal observables that signify their existence; however, this fact actually casts a shadow on detecting QSLs with experimentally accessible probes. Here, we provide a solution by unbiasedly demonstrating a dynamical signature of anyonic excitations and symmetry fractionalization in QSLs. Employing large-scale quantum Monte Carlo simulation and stochastic analytic continuation, we investigate the extended XXZ model on the kagome lattice, and find out that, across the phase transitions from Z_{2} QSLs to different symmetry breaking phases, spin spectral functions can reveal the presence and condensation of emergent anyonic spinon and vison excitations, in particular, the translational symmetry fractionalization of the latter, which can be served as the dynamical signature of the seemingly ephemeral QSLs in spectroscopic techniques such as inelastic neutron or resonance (inelastic) x-ray scatterings.

Photoinhibition and photoinhibition-like damage to the photosynthetic apparatus in tobacco leaves induced by pseudomonas syringae pv. Tabaci under light and dark conditions.

BACKGROUND: Pseudomonas syringae pv. tabaci (Pst), which is the pathogen responsible for tobacco wildfire disease, has received considerable attention in recent years. The objective of this study was to clarify the responses of photosystem I (PSI) and photosystem II (PSII) to Pst infection in tobacco leaves. RESULTS: The net photosynthetic rate (Pn) and carboxylation efficiency (CE) were inhibited by Pst infection. The normalized relative variable fluorescence at the K step (W k) and the relative variable fluorescence at the J step (V J) increased while the maximal quantum yield of PSII (F v/F m) and the density of Q A-reducing PSII reaction centers per cross section (RC/CSm) decreased, indicating that the reaction centers, and the donor and acceptor sides of PSII were all severely damaged after Pst infection. The PSI activity decreased as the infection progressed. Furthermore, we observed a considerable overall degradation of PsbO, D1, PsaA proteins and an over-accumulation of reactive oxygen species (ROS). CONCLUSIONS: Photoinhibition and photoinhibition-like damage were observed under light and dark conditions, respectively, after Pst infection of tobacco leaves. The damage was greater in the dark. ROS over-accumulation was not the primary cause of the photoinhibition and photoinhibition-like damage. The PsbO, D1 and PsaA proteins appear to be the targets during Pst infection under light and dark conditions.

Exopisiod B and farylhydrazone C, two new alkaloids from the Antarctic-derived fungus Penicillium sp. HDN14-431.

Two new compounds, exopisiod B (1) and farylhydrazone C (2), together with two known compounds (3-4), were isolated from the Antarctic-derived fungus Penicillium sp. HDN14-431. Their structures including absolute configurations were elucidated by spectroscopic methods and TDDFT ECD calculations. The cytotoxicity and antimicrobial activities of all compounds were tested.

The clinicopathologic significance of the loss of BAF250a (ARID1A) expression in endometrial carcinoma.

OBJECTIVE: AT-rich interactive domain 1A (ARID1A) is a tumor suppressor gene that encodes the BAF250a protein. Recent studies have shown the loss of ARID1A expression in several types of tumors. We aimed to investigate the clinical and pathologic role of BAF250a in endometrial carcinoma. METHODS: We examined the expression of BAF250a and its correlation with the expression of p53, estrogen receptor, progesterone receptor, glucocorticoid receptor, hypoxiainduciblefactor-1α, and vascular endothelial growth factor in normal and various malignant endometrial tissues. RESULTS: The expression of BAF250 was significantly down-regulated in endometrial carcinoma when compared with normal endometrial tissues. The loss of BAF250a expression was found in 25% of endometrial carcinoma samples but not in normal endometrial tissues, complex endometrial hyperplasia, and atypical endometrial hyperplasia samples. Subtypes of endometrial carcinoma, especially uterine endometrioid carcinoma and uterine clear cell carcinoma, had higher frequency of loss of BAF250a expression. In addition, the expression of BAF250a was positively correlated with estrogen receptor and negatively correlated with p53 in poorly differentiated endometrial adenocarcinoma. Moreover, the expression of BAF250a was significantly associated with the differentiation status of endometrial carcinoma but not associated with clinical stage, the depth of myometrial invasion, lymph node metastasis, and overall survival of patients with endometrial carcinoma. CONCLUSIONS: Our data showed that loss of BAF250a is frequently found in high-grade endometrioid and clear cell carcinomas but not in other types of endometrial carcinoma. The loss of BAF250a expression does not have prognostic value for endometrial carcinoma.

Intense boundary emission destroys normal radio-frequency plasma sheath.

The plasma sheath is the non-neutral space charge region that isolates bulk plasma from a boundary. Radio-frequency (RF) sheaths are formed when applying RF voltage to electrodes. Generally, applied bias is mainly consumed by a RF sheath, which shields an external field. Here we report evidence that an intense boundary emission destroys a normal RF sheath and establishes a type of RF plasma where external bias is consumed by bulk plasma instead of a sheath. Ions are naturally confined while plasma electrons are unobstructed, generating a strong RF current in the entire plasma, combined with a unique particle and energy balance. The proposed model offers the possibility for ion erosion mitigation of a plasma-facing component. It also inspires techniques for reaction rate control in plasma processing and wave mode conversion.

UV-cured nanocomposite coating for surface charging mitigation and breakdown strength enhancement: exploring the combination of surface topographical structure and perfluorooctyl chain.

A facile method using a nanocomposite coating is proposed to suppress surface charge accumulation and enhance the surface breakdown strength of polymeric insulating materials like epoxy resin, by covering a thin 1,1,2,2-tetrahydroperfluorodecyltrimethoxysilane modified alumina (Al2O3) flake/UV curable resin nanocomposite coating. Due to the peculiar characteristics of perfluorooctyl chains at the microscale and the intricate topographical structure of morphology at the mesoscale, the coating exhibits enhanced water/oil repellence, surface charge accumulation resistance, and flashover withstanding capability. It is found that increasing the content of modified Al2O3 is conducive to decreasing the surface free energy of the specimens, rendering them superhydrophobic. Experimental tests in air show that the presence of nanoparticles generates numerous carrier traps at the surface layer, contributing to a much faster charge decay rate. Furthermore, impulse flashover voltage tests under vacuum show a >100% improvement of surface electrical strength. Further experimental results reveal that lower secondary electron emission yield remarkably alleviates the surface charging phenomenon, thus relieving electric field distortion caused by hetero-charges. We envision that such a multifunctional strategy for surface discharge mitigation is efficient, adaptable and easy to scale up, and thereby exhibits great prospects for applications in electronics and electrical power systems.

[Efficacy Analysis of Unrelated Cord Blood Transplantation in the Treatment of Juvenile Myelomonocytic Leukemia].

OBJECTIVE: To explore the clinical efficacy and safety of unrelated umbilical cord blood transplantation (UCBT) in the treatment of Juvenile myelomonocytic leukemia (JMML). METHODS: The clinical data of 5 children with JMML who were treated with unrelated UCBT from October 2011 to July 2019 were retrospectively analyzed. The age of onset for the five children (male) ranged from 0.4 to 5.0 years old, with a median age of 1.5 years old. All the patients received myeloablative conditioning regimen without ATG to whom cyclosporine A (CsA) with short-term mycophenolate mofetil (MMF) was given for GVHD prophylaxis. RESULTS: Four children acquired engraftment. One patient received secondary haploidentical hematopoietic stem cell transplantation because of the failure in the first unrelated UCBT. Grade Ⅲ to Ⅳ aGVHD occurred in 2 cases and was controlled, and none of the patients developed cGVHD. Three cases achieved long-time disease free survival，and no patient relapsed. CONCLUSION: UCBT is an effective treatment for children with JMML.

[Research progress on the effects of atmospheric nitrogen dioxide on plant growth and metabo-lism]. / 大气NO2å½±å“æ¤ç‰©ç”Ÿé•¿ä¸Žä»£è°¢çš„ç ”ç©¶è¿›å±•.

Nitrogen dioxide (NO2) is one type of the atmospheric nitrogen oxides, which is the main component of atmospheric aerosol particles. Reducing the concentration of atmospheric NO2 can decrease the haze in the air. Atmospheric NO2 deposits on plant leaves by both dry and wet deposition. After leaf absorption, atmospheric NO2 was reduced by two metabolism ways: one was the nitrogen metabolism by reductase mainly in cytoplasm and chloroplast, and the other was the pathway of NO2 decomposition reaction in the apoplast and cytoplasm. Plant absorption of NO2 disturbs plant normal growth and physiological metabolism, including vegetative growth and reproductive growth, nitrate reductase (NaR) activity, nitrite reductase (NiR) activity, nitrogen uptake, photosynthetic and other physiological metabolic processes. Here, we reviewed the research progress on the effects of atmospheric NO2 on plant growth and metabolism, and proposed the future research direction of physiological and molecular mechanism of atmospheric NO2 absorption by plants.

[Efficacy Analysis of Unrelated Cord Blood Transplantation for High-Risk Refractory AML1-ETO Positive Myeloid Leukemia].

OBJECTIVE: To analyze the clinical outcomes of engraftment, graft-versus-host disease (GVHD) and survival in the patients with AML1-ETO positive acute myeloid leukemia (AML) treated with unrelated umbilical cord blood transplantation (UCBT). METHODS: Forty-Five patients with high-risk refractory AML1-ETO positive AML were treated with a single UCBT in a single center from July 2010 to April 2018. All the patients underwent a myeloablative preconditioning regimen，and cyclosporine A (CSA) combined with mycophenolate mofetil (MMF) was used to prevent GVHD. RESULTS: The median value of total nucleated cells (TNC) in cord blood was 5.21 (1.96-12.68)×107/kg recipient body weight, and that of CD34+ cells was 5.61 (0.56-15.4)×105/kg recipient weight. The implantation rate of neutrophil at 42 d and that of platelet at 120 d were 95.6% and 86.7%, respectively. The median time of absolute neutrophil count (ANC)＞0.5×109/L and platelet 20×109/L were 16 (12-18) d and 37 (17-140) d after transplantation, respectively. The cumulative incidence of Ⅰ -Ⅳ grade acute GVHD (aGVHD) at 100 d after transplantation was 48.9% (95% CI 33.5%-62.6%), Ⅱ-Ⅳ grade aGVHD occurred in 12 cases (33.3%) (95% CI 20%-47.2%) , and Ⅲ-Ⅳ grade a GVHD in 8 cases (20%) (95% CI 9.8% -32.8%). In 5 cases of 40 patients survived over 100 days, the chronic GVHD (cGVHD) occurred after transplantation, among which 4 were localized, and 1 was extensive. 3 patients relapsed, and the 2-year cumulative relapse rate was 9.5% (95% CI 2.4%-22.8%). The median follow-up time was 23.5 (0.9-89.67) months, 10 patients died, 2-year disease-free survival rate (DFS) was 72.7%, and overall survival rate (OS) was 75.5%. Multivariate analysis showed that Ⅲ-Ⅳ. acute GVHD (aGVHD) affected overall survival. CONCLUSION: UCBT is an effective rescue treatment for patients with high-risk refractory AML1-ETO positive AML.

Changes in soil physicochemical properties and soil bacterial community in mulberry (Morus alba L.)/alfalfa (Medicago sativa L.) intercropping system.

A better understanding of tree-based intercropping effects on soil physicochemical properties and bacterial community has a potential contribution to improvement of agroforestry productivity and sustainability. In this study, we investigated the effects of mulberry/alfalfa intercropping on soil physicochemical properties and soil bacterial community by MiSeq sequencing of bacterial 16S rRNA gene. The results showed a significant increase in the contents of available nitrogen, available phosphate, available potassium, and total carbon in the rhizosphere soil of the intercropped alfalfa. Sequencing results showed that intercropping improved bacterial richness and diversity of mulberry and alfalfa based on richness estimates and diversity indices. The relative abundances of Proteobacteria, Actinobacteria, and Firmicutes were significantly higher in intercropping mulberry than in monoculture mulberry; and the abundances of Proteobacteria, Bacteroidetes, and Gemmatimonadetes in the intercropping alfalfa were markedly higher than that in monoculture alfalfa. Bacterial taxa with soil nutrients cycling were enriched in the intercropping system. There were higher relative abundances of Bacillus (0.32%), Pseudomonas (0.14%), and Microbacterium (0.07%) in intercropping mulberry soil, and Bradyrhizobium (1.0%), Sphingomonas (0.56%), Pseudomonas (0.18%), Microbacterium (0.15%), Rhizobium (0.09%), Neorhizobium (0.08%), Rhodococcus (0.06%), and Burkholderia (0.04%) in intercropping alfalfa soil. Variance partition analysis showed that planting pattern contributed 26.7% of the total variation of bacterial community, and soil environmental factors explained approximately 56.5% of the total variation. This result indicated that the soil environmental factors were more important than the planting pattern in shaping the bacterial community in the field soil. Overall, mulberry/alfalfa intercropping changed soil bacterial community, which was related to changes in soil total carbon, available phosphate, and available potassium.

Optimising the linear electron transport rate measured by chlorophyll a fluorescence to empirically match the gross rate of oxygen evolution in white light: towards improved estimation of the cyclic electron flux around photosystem I in leaves.

The cyclic electron flux (CEF) around photosystem I (PSI) was discovered in isolated chloroplasts more than six decades ago, but its quantification has been hampered by the absence of net formation of a product or net consumption of a substrate. We estimated in vivo CEF in leaves as the difference (ΔFlux) between the total electron flux through PSI (ETR1) measured by a near infrared signal, and the linear electron flux through both photosystems by optimised measurement of chlorophyll a fluorescence (LEFfl). Chlorophyll fluorescence was excited by modulated green light from a light-emitting diode at an optimal average irradiance, and the fluorescence was detected at wavelengths >710nm. In this way, LEFfl matched the gross rate of oxygen evolution multiplied by 4 (LEFO2) in broad-spectrum white actinic irradiance up to half (spinach, poplar and rice) or one third (cotton) of full sunlight irradiance. This technique of estimating CEF can be applied to leaves attached to a plant.

[Comparison of Decitabine Rigimen and Traditional Chemotherapy Regimen in Treatment of Patients with Intermediate or High-Risk Myelodysplastic Syndrome].

OBJECTIVE: To compare the clinical efficacy and relevant adverse reactions of homebred decitabine regimen and traditional chemotherapy regimen in treatment of patients with intermediate or high-risk myelodysplastic syndrome (MDS). METHODS: Forty-eight patients suffered from newly diagnosed intermediate or high-risk MDS from December 2011 to December 2016 were analyzed retrospectively. Among them 29 patients were treated by traditional chemotherapy regimen, and 19 patients were treated by decitabine regimen [15 mg/(m2·d), ivgtt, d1-5]. The clinical efficacy and relevant adverse reactions in two groups were compared. RESULTS: The overall response rate (ORR) of decitabine group was 78.9% (15/19), after 2 cycles of treatment, among them 5 achieved complete remission(CR), 5 achieved partial remission(PR), and 5 achieved hematologic improvement (HI); the ORR of traditional chemotherapy group was 65.9% (16/29), including 6 CR, 5 PR, 8 HI, the ORR and remission rate (PR+CR) in decitabine treatment group were not statistically significantly different from the that in traditional chemotherapy group (x2=0.458,P>0.05; x2=0.499, P>0.05). After 4 cycles of treatment, the ORR in decitabine group was 84.2% (16/19), including 5 CR, 9 PR and 2 HI. The ORR in traditional chemotherapy group was 68.9% (20/29), including 6 CR, 5 PR and 9 HI. The ORR of decitabine group was not statistically significantly different from the that in traditional chemotherapy (x2=0.726,P>0.05), but the remission rate was statistically significantly different(x2=4.534,P<0.05). The overall survival and progression-free survival in the decitabine group were different statistically significantly different from the traditional chemotherapy (P<0.05; P<0.01). The incidences of III-IV grades adverse reactions of hemoglobin, platelet and neutrophile in the patients treated with decitabine and traditional chemotherapy group were 52.6% and 79.3% (P>0.05), 57.9% and 86.2%(P>0.05), 84.2% and 96.6%(P>0.05), respectively. The infection rates were 26.3% and 79.3%(P<0.05), respectively. CONCLUSION: The homebred decitabine can effectively treat intermediate-or high-risk MDS, also can be well tolerated. So, it is worth to be clinically popularized.

Rootstock Alleviates Salt Stress in Grafted Mulberry Seedlings: Physiological and PSII Function Responses.

This study investigated the effect of NaCl stress on Na+ and K+ absorption and transport by roots, nitrogen and phosphorus content in leaves, PSII photochemical activity and reactive oxygen species (ROS) in leaves of mulberry own-root seedlings and grafted seedlings. To determine the response, own-root seedlings of a high yielding mulberry cultivar, Tieba mulberry (Morus alba L.), and the grafted seedlings, obtained by using Qinglong mulberry with high salt tolerance as rootstock and Tieba mulberry as scion, were used. The Na+ content in roots and leaves of grafted seedlings was significantly lower than that in own-root seedlings under salt stress; while K+ content in roots and leaves of grafted seedlings was significantly higher than that in own-root seedlings. The root activity in grafted seedlings was significantly higher than that in own-root seedlings, as well as the content of nitrogen, phosphorous and water. PSII photochemical activity in leaves of grafted seedlings was less significantly affected by salt stress compared to own-root seedlings. The electron transport at the acceptor side of PSII from Q A to Q B was less affected by salt stress, which resulted in a significantly lower ROS content in leaves of grafted seedlings than that of own-root seedlings. Therefore, grafting high-yielding and good-quality Tieba mulberry with salt tolerant Qinglong mulberry as rootstock showed a relatively high salt tolerance. This may be because (1) the root system of rootstock presented high Na+ resistance and has selective absorption capacity for Na+ and K+ (2) the root system of rootstock prevented excess Na+ from being transported to aerial parts in order to reduce adverse effects of Na+ (3) the root system of rootstock had enhanced root activity under salt stress, which accelerated water and nutrient absorption (4) the leaves of grafted seedlings had higher PSII photochemical activity and electron transport rate compared with those of own-root seedlings under salt stress, which effectively reduced ROS burst mediated by photosynthesis and reduced oxidative damage.

Induction characteristics and response of photosynthetic quantum conversion to changes in irradiance in mulberry plants.

A study was conducted, using rapid time course of chlorophyll (Chl) fluorescence parameters, and light-response curves of Chl fluorescence parameters, to determine the induction requirements and response of photosystem II (PSII) photochemistry and non-photochemical reactions after changes in irradiance in greenhouse mulberry plants. The induction of PSII photochemistry rapidly approached to steady state after leaves were treated from darkness to low irradiance (LI). When irradiance of leaves changed from darkness to high irradiance (HI), a biphasic induction was observed. A slight photoinhibition occurred in the leaves exposed to sunlight coming to the greenhouse, whereas a chronic photoinhibition occurred in the leaves fully exposed to sunlight outside the greenhouse. The chronic photoinhibition was demonstrated by sustained reduction of maximal quantum yield of PSII photochemistry (Fv/Fm). Moreover, the leaves of mulberry plants in greenhouse were sensitive to abrupt changes in irradiance and the sensitivity of leaves suffered in a short-term (1h) high light treatment was reduced, based on the changes in photosynthetic quantum conversion. These results demonstrated an inducible response of photosynthetic quantum conversion to changes in irradiance in mulberry.

Multistep Heterogeneous Nucleation in Binary Mixtures of Charged Colloidal Spheres.

Nucleation plays a decisive role in determining the crystal structure and size distribution; however, understanding of the fundamentals of nucleation is quite limited. In particular, it is unclear whether a nucleus forms spontaneously from solution via a single- or multiple-step process. Here we show how a binary mixture of charged colloidal spheres nucleates heterogeneously on a flat substrate by means of Bragg microscopy, laser diffraction, and laser microscopy. In contrast with the conventional one-step and two-step nucleation mechanisms, a novel pathway of multistep heterogeneous nucleation under certain experimental conditions is highlighted by four steps: initial homogeneous fluid → prenucleation clusters → preordered prenucleation clusters → intermediate ordered phase → final crystal. It is expected that the obtained results would be helpful in rationalizing the rich phase behavior exhibited by the binary mixture systems and in developing better and broadly applicable nucleation models as well as in designing defect-free single-crystal alloys.

[Adaptive mechanism of photosynthetic apparatus of plants to light environment: State transition.] / æ¤ç‰©å ‰åˆæœºæž„å¯¹å ‰çŽ¯å¢ƒçš„é€‚åº”æœºåˆ¶: 状态转换.

Under natural conditions, light plants receive usually changes. Thus, the plants have formed corresponding adaptation mechanism in the evolutionary process, which could maintain the energy balance between two light reactions in the process of light changing. Through the movement of leaves and chloroplasts, as well as the accumulation of light-absorbing pigments, plants could regulate light absorption. Also, plants have a mechanism for greatly regulating the distribution of energy absorbed by light-harvesting complex. Especially at low light intensities, plants could mediate reversible phosphorylation of light-harvesting complex2 (LHC2) by regulating kinase and phosphatase in relation to the redox state of the electron transfer chain, which could thereby regulate the allocation of excitation energy between photosystem I (PSI) and photosystem 2(PS2). The state transitions are the quite significant mechanism of plants for adapting to the change of light environment. In this paper, the research progresses of state transitions during the change of light environment were summarized, especially the significance and functions of reversible phosphorylation and movement of LHC2 between PS I and PS2 were discussed. Finally, the future research direction on state transitions of plants was briefly proposed.

Light Suppresses Bacterial Population through the Accumulation of Hydrogen Peroxide in Tobacco Leaves Infected with Pseudomonas syringae pv. tabaci.

Pseudomonas syringae pv. tabaci (Pst) is a hemibiotrophic bacterial pathogen responsible for tobacco wildfire disease. Although considerable research has been conducted on the tobacco plant's tolerance to Pst, the role of light in the responses of the photosystems to Pst infection is poorly understood. This study aimed to elucidate the underlying mechanisms of the reduced photosystem damage in tobacco leaves due to Pst infection under light conditions. Compared to dark conditions, Pst infection under light conditions resulted in less chlorophyll degradation and a smaller decline in photosynthetic function. Although the maximal quantum yield of photosystem II (PSII) and the activity of the photosystem I (PSI) complex decreased as Pst infection progressed, damage to PSI and PSII after infection was reduced under light conditions compared to dark conditions. Pst was 17-fold more abundant in tobacco leaves under dark compared to light conditions at 3 days post inoculation (dpi). Additionally, H2O2 accumulated to a high level in tobacco leaves after Pst infection under light conditions; although to a lesser extent, H2O2 accumulation was also significant under dark conditions. Pretreatment with H2O2 alleviated chlorotic lesions and decreased Pst abundance in tobacco leaves at 3 dpi under dark conditions. MV pretreatment had the same effects under light conditions, whereas 3-(3,4-dichlorophenyl)-1,1-dimethylurea pretreatment aggravated chlorotic lesions and increased the Pst population. These results indicate that chlorotic symptoms and the size of the bacterial population are each negatively correlated with H2O2 accumulation. In other words, light appears to suppress the Pst population in tobacco leaves through the accumulation of H2O2 during infection.

[Effects of Pseudomonas syringae pv. tabaci infection on tobacco photosynthetic apparatus under light or dark conditions.] / å ‰ç §æˆ–é»‘æš—æ¡ä»¶ä¸‹é‡Žç«ç— èŒä¾µæŸ“å¯¹çƒŸè‰å ‰åˆæœºæž„çš„å½±å“.

Pseudomonas syringae pv. tabaci (Pst) is a hemi-biotrophic bacterial pathogen that causes the formation of brown spots named wildfire disease. Pst has received considerable attention in recent years. However, most of the studies focused on the tolerance and defense mechanisms of the host and non-host plants against Pst infection and a toxin originally described as being from Pst named tabtoxin, little information is available on the photosynthetic performance of tobacco leaves after Pst infection. Exploring the effects of Pst on the photosystem Ⅱ (PSⅡ) will not only help in clarifying tobacco-Pst interaction mechanisms, but also deepen the understanding of bacterial pathogen disease from a physiological perspective. By analyzing chlorophyll a fluorescence transient, performing western blot of thylakoid membrane and measuring the content of reactive oxygen species (ROS) and total chlorophyll, the effects of Pst on PS2 in tobacco were studied under light (200 µmol·m-2·s-1) or dark conditions. The results showed that chlorophyll content significantly decreased and significant chlorosis of the infiltrated zone was observed compared to the untreated ones, and tobacco leaves exhibited a visible and overt wildfire symptom at 3 days post Pst infection (dpi) under light and dark conditions. The H2O2 content increased at 3 dpi compared to untreated ones in tobacco leaves under light and dark conditions, and was much higher under light than dark condition. Besides, markedly increase of the normalized relative variable fluorescence at the K step (WK) and the relative variable fluorescence at the J step (VJ), significant decrease of maximal quantum yield of PS2 (Fv/Fm) and density of QA- reducing PS2 reaction centers per cross section (RC/CSm) were observed in tobacco leaves after Pst infection at 3 dpi under light and dark conditions. Moreover, inhibition of the K and J steps was more pronounced in the dark, as indicated by the greater increase of WK and VJ under darkness compared with the light conditions during Pst inoculation. Dramatic (net) degradation of D1 protein and PsaO, the core protein of PS2 reaction center and oxygen evolving complex (OEC) respectively, at 3 dpi after Pst infection was observed in tobacco leaves under both light or dark conditions, and the decline was more exacerbated under dark than light condition. The results indicated that the electron transport from QA to QB of photosynthesis electron transport chain was severely blocked, OEC was damaged on both the donor and acceptor sides, and the reaction center of PS2 was severely damaged by Pst infection in tobacco lea-ves under either light or dark condition. Photoinhibition and photoinhibition-like damage of PSⅡ was observed after Pst infection, and the damage to PS2 under dark condition was much more severe than under light condition in tobacco leaves.