Photosystem II energy coupling in chloroplasts with H2O2 as electron donor.

NH2OH-treated, non-water-splitting chloroplasts can oxidize H2O2 to O2 through Photosystem II at substantial rates (100--250 muequiv . h-1 . mg-1 chlorophyll with 5 mM H2O2) using 2,5-dimethyl-p-benzoquinone as an electron acceptor in the presence of the plastoquinone antagonist dibromothymoquinone. This H2O2 leads to Photosystem II leads to dimethylquinone reaction supports phosphorylation with a P/e2 ratio of 0.25--0.35 and proton uptake with H+/e values of 0.67 (pH 8)--0.85 (pH 6). These are close to the P/e2 value of 0.3--0.38 and the H+/e values of 0.7--0.93 found in parallel experiments for the H2O leads to Photosystem II leads to dimethylquinone reaction in untreated chloroplasts. Semi-quantitative data are also presented which show that the donor leads to Photosystem II leads to dibromothymoquinone (leads to O2) reaction can support phosphorylation when the donor used is a proton-releasing reductant (benzidine, catechol) but not when it is a non-proton carrier (I-, ferrocyanide).     

Determination of the active portion of the folic acid molecule in cellular slime mold chemotaxis.

From earlier work it is known that folic acid attracts the amoebae of various species of cellular slime molds (11). Here we have tested a wide variety of pteridines, pyrimidines, and pyrazines to determine what part of the folic acid molecule is chemotactically active. It was shown that the activity lies in the pteridine ring itself. Furthermore, the cell-free supernatants of slime mold amoebae contain an enzyme that renders pterin and folic acid chemotactically inactive, which apparently increases the chemotactic sensitivity of the amoebae to those compounds. Despite the fact that slime mold amoebae secrete small amounts of folic acid-related compounds, there is no evidence that folates are acrasins; rather it is postulated that attraction to folates may be a food-seeking device for the amoebae which prey on folate-secreting bacteria in the soil.     

Parasite reliance on its host gut microbiota for nutrition and survival

Studying the microbial symbionts of eukaryotic hosts has revealed a range of interactions that benefit host biology. Most eukaryotes are also infected by parasites that adversely affect host biology for their own benefit. However, it is largely unclear whether the ability of parasites to develop in hosts also depends on host-associated symbionts, e.g., the gut microbiota. Here, we studied the parasitic wasp Leptopilina boulardi (Lb) and its host Drosophila melanogaster. Results showed that Lb successfully develops in conventional hosts (CN) with a gut microbiota but fails to develop in axenic hosts (AX) without a gut microbiota. We determined that developing Lb larvae consume fat body cells that store lipids. We also determined that much larger amounts of lipid accumulate in fat body cells of parasitized CN hosts than parasitized AX hosts. CN hosts parasitized by Lb exhibited large increases in the abundance of the bacterium Acetobacter pomorum in the gut, but did not affect the abundance of Lactobacillus fructivorans which is another common member of the host gut microbiota. However, AX hosts inoculated with A. pomorum and/or L. fructivorans did not rescue development of Lb. In contrast, AX larvae inoculated with A. pomorum plus other identified gut community members including a Bacillus sp. substantially rescued Lb development. Rescue was further associated with increased lipid accumulation in host fat body cells. Insulin-like peptides increased in brain neurosecretory cells of parasitized CN larvae. Lipid accumulation in the fat body of CN hosts was further associated with reduced Bmm lipase activity mediated by insulin/insulin-like growth factor signaling (IIS). Altogether, our results identify a previously unknown role for the gut microbiota in defining host permissiveness for a parasite. Our findings also identify a new paradigm for parasite manipulation of host metabolism that depends on insulin signaling and the gut microbiota.Subject terms: Animal physiology, Microbial ecology     

The two binding sites for DCMU in Photosystem II

Measurements on the fluorescence induction of Triton X-100 extracted Photosystem II (PSII) particles confirmed the existence of the two sites of inhibition in PSII for the herbicide DCMU. The two sites were located on the reducing and oxidizing sides of PSII, respectively. The inhibition on the oxidizing side, unlike that on the reducing side which was of the "none or all" type, was found only to slow down the electron donation at low concentrations of DCMU. The results also suggested that the inhibitions of DCMU at these two sites were mutually exclusive, i.e., the binding on one site prevented the binding on the other site.     

The use of spun columns in the purification of double-stranded cDNA appropriate for tailing

A reliable estimation of the efficiency of adding homopolymeric tails to double-stranded cDNA molecules by terminal deoxynucleotidyl transferase is extremely important in the construction of cDNA libraries. Appreciable differences in transformation efficiency result when the homopolymer tails to be annealed are of inadequate length. We report here that the use of a Sephadex G-50 spun column to remove oligo(dT)12-18 frequently coprecipitating in ethanol with the cDNA results in a more dependable estimation of tail lengths.     

Preparation and characterization of radioactive castanospermine

A procedure for the preparation of tritiated castanospermine is described. The tritiated alkaloid was shown to be chromatographically identical to the native material and exhibited the same inhibitory properties. Radiolabeled castanospermine tightly bound to purified intestinal sucrase. Following gel chromatography, each mole of enzyme was shown to have bound 1 mol of the radioactive alkaloid. Cultured MDCK cells were also shown to take up the labeled castanospermine. This compound should be a useful tool in the investigation of enzymes that are responsible for the processing of glycoprotein oligosaccharides.     

Fungal-Fungal Associations Affect the Assembly of Endophyte Communities in Maize (Zea mays)

Many factors can affect the assembly of communities, ranging from species pools to habitat effects to interspecific interactions. In microbial communities, the predominant focus has been on the well-touted ability of microbes to disperse and the environment acting as a selective filter to determine which species are present. In this study, we investigated the role of biotic interactions (e.g., competition, facilitation) in fungal endophyte community assembly by examining endophyte species co-occurrences within communities using null models. We used recombinant inbred lines (genotypes) of maize (Zea mays) to examine community assembly at multiple habitat levels, at the individual plant and host genotype levels. Both culture-dependent and culture-independent approaches were used to assess endophyte communities. Communities were analyzed using the complete fungal operational taxonomic unit (OTU) dataset or only the dominant (most abundant) OTUs in order to ascertain whether species co-occurrences were different for dominant members compared to when all members were included. In the culture-dependent approach, we found that for both datasets, OTUs co-occurred on maize genotypes more frequently than expected under the null model of random species co-occurrences. In the culture-independent approach, we found that OTUs negatively co-occurred at the individual plant level but were not significantly different from random at the genotype level for either the dominant or complete datasets. Our results showed that interspecific interactions can affect endophyte community assembly, but the effects can be complex and depend on host habitat level. To our knowledge, this is the first study to examine endophyte community assembly in the same host species at multiple habitat levels. Understanding the processes and mechanisms that shape microbial communities will provide important insights into microbial community structure and the maintenance of microbial biodiversity.     

The stimulatory effect of ROCK inhibitor on bovine corneal endothelial cells

Reagents which can promote the proliferation, adhesion and migration of cultured corneal endothelial cells (CECs) will be helpful for the treatment of reduced visual acuity due to CECs deficiency. The objectives of this study were to investigate the potential use of an inhibitor of Rho-associated protein kinase (ROCK), Y-27632, to cultured bovine corneal endothelial cells (B-CECs) and evaluated its effects on the proliferation, adhesion and migration of B-CECs. The proliferation of cultured B-CECs was moderately enhanced by 10 μM Y-27632. Y-27632 induced fibroblast-like morphological changes in the cultured B-CECs and normal cell morphology could recover after Y-27632 removal. In addition, Y-27632 was found to significantly enhance the adhesion and migration of B-CECs. Furthermore, the hanging drop aggregation assay showed that Y-27632 promoted B-CECs to form cellular networks and sheets, which proliferated along the liquid–air interface and migrated to the surface of the lid of dish. Our study demonstrated that Y-27632 is a potentially powerful reagent which can enhance the proliferation of cultured B-CECs. Y-27632 will be useful in CEC injection therapy and topical application for CEC deficiency.     

银合欢基因文库的构建和种子贮藏蛋白基因的分离

本文以λEMBL_3为载体,构建了银合欢(Leucaena leucocephala)的基因文库,所得重组子为3.5×10~6pfu。以大豆种子贮藏蛋白α′亚基基因为探针,从基因文库中分离得到了4个阳性克隆,并初步绘制了其中3个重组子的物理图谱。结果表明在这3个重组子的基因内部有一致的酶切位点。亚克隆的部分核苷酸序列与 GenBank 中的基因序列比较,表明与大豆种子贮藏蛋白α′亚基基因高度同源。