The quantity of OA and activity of cellulase and polygalacturonase are involved in variation of virulence in Sclerotium rolfsii

In order to understand the pathogenic mechanisms of Sclerotium rolfsii on peanut and to analyze the variation of virulence in S.rolfsii strains,the highly virulent strain(ZY2)and weakly virulent strain(GP3-1)were investigated under both in vivo and in vitro conditions.The results indicated that S.rolfsii directly infected peanut by producing infection cushions.ZY2 formed infection cushions earlier than GP3-1,and ZY2 produced a greater number of infection cushions compare to GP3-1.Both strains could utilize cellulose,xylose,or polygalacturonic acid in the Czapek medium.The activities of cellulase(CL)and polygalacturonase(PG)in the inoculated peanut stems increased significantly at 9 h after inoculation.The activities of CL and PG produced by ZY2 in the inoculated stems were significantly higher than that produced by GP3-1.Both strains could produce oxalic acid(OA),and the content of OA produced by ZY2 in the inoculated stems was higher than that produced by GP3-1.In summary,it suggested that S.rolfsii destroyed peanut cells through physical and biochemical factors by secreting a large amount of OA,CL and PG during the formation of infection cushions.The difference in OA content,activity of CL and PG produced by highly and weakly virulent strains played important roles in variation of virulence.

Pathogenicity of Cell Wall Degrading Enzymes Produced by Botryodiplodia theobromae Pat. against Mangoes

[ Objective ] This study aimed to confirm the roles of cell wall degrading enzymes （CWDEs） produced by Botryodiplodia theobromae Pat. in the infec- tion of mango fruits. [ Method] Change of activities of five types of CWDEs produced by B. theobromae Pat. were studied under both in vitro culture and inocula- tion conditions, along with the pathogenicity and the ability of producing CWDEs of four post-harvest fangal pathogens（B, theobromae Pat. , Colletotrichum gloeos- porioides Penz. , Phomopsis mangiferae Ahmad and Dothiorella dominicana Pet. et Cif. ） which cause stem-end rot of mangoes. [ Result] B. theobromae Pat. was a- ble to produce polygalacturonase（PG）, pectinmethylgalacturonase（PMG）, polygalacturonic acid trans-eliminase （PGTE）, pectin methyltrans-eliminase （PMTE） and cellulase （ Cx. ） under both in vitro culture and inoculation conditions, of which activities of PG, Cx and PMG were significantly higher in than that in either PGTE or PMTE. Among three primary CWDEs, the peak of activities of PG and Cx appeared earlier and that of PMG occured later. The pathogenicity of B. theo- bromae Pat. was significantly higher than that of any other three pathogens; it is the same with the abilities of producing pectinase. [ Conclusion] This paper pro- vides theoretical bases for further exploring the mechanism of host-pathogen interaction and decreasing the post-harvest loss of mango fruits.

Mycoparasitism of Nematode-Trapping Fungus Monacrosporium ellipsosporumand Its Biochemical Basis

Monacrosporium ellipsosporum, a nematode-trapping fungus, was isolated by baiting with sclerotiaof Sclerotinia sclerotiorum in soil from a tobacco field in Yuxi, Yunnan Province. Colonizationfrequency of the sclerotia by the fungus was 18% in natural soil. Reinoculation tests byplacing surface-sterilized sclerotia on fungal cultures for two weeks and then surface-sterilized again led to 32% sclerotia be infected. Dual culture tests in PDA plates did notgive rise to a suppression zone between the colonies of M. ellipsosporum and its counterpartfungi S. sclerotiorum and Rhizoctonia solani, suggesting there was little or no nutritionalcompetition and absent of antifungal compounds. However, M. ellipsosporum could grow overabsent of S. sclerotiorum and R. solani, and significantly inhibited their growth on agarplates. Scanning electron and light microscopic observations showed that hyphae of M. ellipsosporumgrew along and appressed on hypha of S. sclerotiorum and coiled around hyphae of R. solani.Assays of cell wall-degrading enzymes showed that M. ellipsosporum grew well in chitin agarmedia, with clear transparent hydrolysis zones. Activities of total chitinase, exo-chitinase,β-1, 3-glucanase and protease were 140.2±11.9, 82.9±4.1, 111.2±7.6 and 76.1±4.3 U respect-ively, after incubation for 4 days at 30 ℃ in liquid media containing ground sclerotia of S.sclerotiorum as sole nutrient source. These enzymes might be important in the mycoparasiticactivity of M. ellipsosporum.

A Banana PHD-Type Transcription Factor MaPHD1 Represses a Cell Wall-Degradation Gene MaXTH6 during Fruit Ripening

Plant homeobox domain(PHD)-type transcription factors(TFs) are involved in a variety of biological processes. However, its involvement in commercially important fruit ripening process remains largely unclear. In the present work, the characterization of a PHD-type TF termed MaPHD1 from banana fruit is reported. Multiple alignments of the deduced amino acid sequence revealed that Ma PHD1 showed a high homology with Arabidopsis thaliana Alfin1-like proteins belonging to plant-specific sub-family of PHD finger proteins. MaPHD1 was found localized in the nucleus and exhibited trans-repression ability. It was down-regulated by ethylene and ripening. Electrophoretic Mobility Shift Assay(EMSA) and transient expression analysis demonstrated that Ma PHD1 directly bound to the G-rich motifs in the promoter of Ma XTH6, which is associated with cell wall degradation, and subsequently repressed its expression. These findings suggest that MaPHD1 may be negatively associated with banana fruit ripening, at least in part, by the direct suppression of Ma XTH6. Taken together, these findings provide new insights into the transcriptional regulatory networks of banana fruit ripening.

ANAPHASE PROMOTING COMPLEX/CYCLOSOME-mediated cyclin B1 degradation is critical for cell cycle synchronization in syncytial endosperms

Although it is known that in most angiosperms mitosis in early endosperm development is syncytial and synchronized, it is unclear how the synchronization is regulated. We showed previously that APC11, also named ZYGI, in Arabidopsis activates zygote division by interaction and degradation of cyclin B1. Here, we report that the mutation in APC11/ZYG1 led to unsynchronized mitosis and over-accumulation of cyclin B1-GUS in the endosperm. Mutations in two other APC subunits showed similar defects. Transgenic expression of stable cyclin B1 in the endosperm also caused unsynchronized mitosis. Further, downregulation of APC11 generated multi-nucleate somatic cells with unsynchronized mitotic division. Together, our results suggest that APC/C-mediated cyclin B1 degradation is critical for cell cycle synchronization.

Evaluating electron induced degradation of triple-junction solar cell by numerical simulation

In this paper,the degradation related parameters of GaInP/GaAs/Ge triple-junction solar cell induced by electron irradiation are carried out by numerical simulation.The degradation results of short-circuit current,open-circuit voltage,maximum power have been investigated,and the degradation mechanism is analyzed.Combining the degradation results,the degradation of normalized parameters versus displacement damage dose is obtained.The results show that the degradation increases with the increase of the electron fluence and electron irradiation energy.The degradation normalized related parameters versus displacement damage dose can be characterized by a special curve that is not affected by the type of irradiated particles.By calculating the annual displacement damage dose and the on-orbit operation time of special space orbit,the degradation of normalized parameters can be obtained with the fitting curve in the simulation.The study will provide an approach to estimate the radiation damage of triple-junction solar cell induced by space particle irradiation.

Study of degradation of fuel cell stack based on the collected high-dimensional data and clustering algorithms calculations

Accurate perception of the performance degradation of fuel cell is very important to detect its health state.However,inconsistent operating conditions of fuel cell vehicles in the test result in errors in the data.In order to obtain a more credible degradation rate,this study proposes a novel method to classify the experimental data collected under different working conditions into similar operating conditions by using dimensionality reduction and clustering algorithms.Firstly,the experimental data collected from fuel cell vehicles belong to high-dimensional data.Then projecting high-dimensional data into three-dimensional feature vector space via principal component analysis(PCA).The dimension-reduced three-dimensional feature vectors are input into the clustering algorithm,such as K-means and density-based noise application spatial clustering(DBSCAN).According to the clustering results,the fuel cell voltage data with similar operating conditions can be classified.Finally,the selected voltage data can be used to precisely represent the true performance degradation of an on-board fuel cell stack.The results show that the voltage using the K-means algorithm declines the fastest,followed by the DBSCAN algorithm, finally the original data, which indicates that the performance of the fuel cell actually declines faste. Early intervention can prolong its life to the greatest extent.

Method for improving illumination instability of organic-inorganic halide perovskite solar cells

Organohalogen perovskites are attracting con- siderable attention for use in solar cells. However, the stability of these devices will determine whether they can be made commercially viable. Device encapsulation or the use of a hydrophobic hole-transporting material can pre- vent the permeation of water into the perovskite layer and enhance the humidity stability of the cells under dark conditions. With regard to the light stability of solar cells, recent studies have yielded contradictory results. This work investigated the degradation mechanism of perovskite solar cells under illumination. Further, a simple method was proposed for improving their illumination stability. Amino acids were inserted between the compact TiO2 layer and the perovskite layer to effectively prevent the decomposition of the perovskite layer owing to the superoxide anions and hydroxyl radicals generated under illumination from the H2O and O2 adsorbed onto the TiO2 layer.

Recalcitrant cell wall of Ulva lactuca seaweed is degraded by a single ulvan lyase from family 25 of polysaccharide lyases

Green macroalgae,e.g.,Ulva lactuca,are valuable bioactive sources of nutrients;but algae recalcitrant cell walls,composed of a complex cross-linked matrix of polysaccharides,can compromise their utilization as feedstuffs for monogastric animals.This study aimed to evaluate the ability of pre-selected Carbohydrate-Active enZymes(CAZymes)and sulfatases to degrade U.lactuca cell walls and release nutritive compounds.A databank of 199 recombinant CAZymes and sulfatases was tested in vitro for their action towards U.lactuca cell wall polysaccharides.The enzymes were incubated with the macroalga,either alone or in combination,to release reducing sugars and decrease fluorescence intensity of Calcofluor White stained cell walls.The individual action of a polysaccharide lyase family 25(PL25),an ulvan lyase,was shown to be the most efficient in cell wall disruption.The ulvan lyase treatment,in triplicate measures,promoted the release of 4.54 g/L(P<0.001)reducing sugars,a mono-and oligosaccharides release of 11.4 and 11.2 mmol/100 g of dried alga(P<0.01),respectively,and a decrease of 41.7%(P<0.001)in cell wall fluorescence,in comparison to control.The ability of ulvan lyase treatment to promote the release of nutritional compounds from alga biomass was also evaluated.A release of some monounsaturated fatty acids was observed,particularly the health beneficial 18:1c9(P<0.001).However,no significant release of total fatty acids(P>0.05),proteins(P?0.861)or pigments(P>0.05)was found.These results highlight the capacity of a single recombinant ulvan lyase(PL25 family)to incompletely disrupt U.lactuca cell walls.This enzyme could enhance the bioaccessibility of U.lactuca bioactive products with promising utilization in the feed industry.