Increase in membrane permeability of electrolytes and betacyanin in beet root disc by fenitrothion

Effect of fenitrothion (phosphorothioic acid, 0,0-dimethyl 0-4-nitro-m-tolyl ester), an organophosphorous insecticide, on membrane permeability employing the leakage of betacyanin and electrolytes as the criteria were studied in beet root(Beta vulgaris) discs. The leakage of both betacyanin and electrolytes increased with increasing concentrations (10–150 ppm) of fenitrothion in the incubation medium. At 0.33 mM the increase in electrolyte leakage was approximately linear for the first 6h, while the increase in betacyanin leakage started with a lag of about 2 h. Long term incubation (24 h) showed a biphasic nature (in the semilog plot) for the increase in betacyanin leakage, while the increase in electrolyte leakage appeared more complex. In the control sample, the Arrhenius plots (25–50°C) of leakage showed a break at 40°C. In treated samples no break was observed, but the slope decreased (for both electrolyte and betacyanin leakage) as compared to the respective slopes in the control in the temperature region greater than 40°C. The results are discussed in terms of the possible effect of the insecticide on the active transport in plant membranes     

Hybridity,polyploidy and change in breeding system in a Ruellia hybrid

Summary Ruellia tweediana and R. tuberosa are large flowered chasmogamous diploids (n=17) with normal meiosis and fertility. F ₁ hybrids, successful in only one direction (R. tweediana x R. tuberosa), are vegetatively vigorous and possess 17 often heteromorphic bivalents with high degree of segregational irregularities. It is exclusively cleistogamous and completely pollen and seed sterile. Like F ₁, the artificial amphidiploid (n=34) is also cleistogamous but shows preferential chromosome pairing with complete restoration of fertility. The parental chromosomes are sufficiently differentiated and cleistogamy is either genie or due to gene-cytoplasm interaction but sterility is entirely chromosomal. All floral parts excepting calyx are highly deformed. Such a deformity is associated with sterility in the F ₁ but with fertility in the amphidiploid. This is perhaps the first case of origin by hybridization of a true breeding and fully fertile cleistogamous taxon from two chasmogamous species. It also shows the extent and nature of change in breeding system brought about by hybridization and/or polyploidy.The chromosome numbers in the six, out of 16, obligate cleistogamous taxa (Table 4) show that they are high polyploids. Perhaps their origin has been in the same manner as in the present case.

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Zusammenfassung Ruellia tweediana und R. tuberosa sind großblütige, chasmogame Diploide (n=17) mit normaler Meiosis und Fertilität. Die F ₁-Hybriden, die nur in einer Richtung gelingen (R. tweediana x R. tuberosa), sind vegetativ kräftig und besitzen häufig 17 heteromorphe Bivalente mit einem hohen Anteil an Spaltungsunregelmäßigkeiten. Die Hybride ist ausschließlich kleistogam und vollkommen pollen- und samensteril. Wie die F ₁ ist auch die künstlich hergestellte Amphidiploide (n=34) kleistogam und zeigt eine präferentielle Chromosomenpaarung mit völliger Wiederherstellung der Fertilität. Die elterlichen Chromosomen sind genügend differenziert. Die Kleistogamie ist entweder genisch bedingt oder auf eine Gen-Cytoplasma-Interaktion zurückzuführen, die Sterilität ist ausschließlich durch die Chromosomen verursacht. Alle Teile der Blüte mit Ausnahme der Calyx sind stark deformiert. Bei der F ₁ ist diese Deformation mit Sterilität verbunden, die amphidiploide Form ist jedoch fertil. Das ist vielleicht der erste Fall eines aus der Kreuzung zweier chasmogamer Spezies hervorgegangenen reinerbigen und voll fertilen kleistogamen Taxons. Es läßt sich auch der Umfang und die Art der durch Hybridisierung und durch Polyploidie verursachten Änderung des Zuchtsystems erkennen. Die Chromosomenzahl bei 6 von 16 obligaten kleistogamen Taxa (Tab. 4) zeigt, daß sie hochpolyploid sind. Vielleicht sind sie auf eine gleiche Weise wie im vorliegenden Falle entstanden.

     

Adherence of multiple serovars of Chlamydia trachomatis to a common receptor on HeLa and McCoy cells is mediated by thermolabile protein(s)

Several aspects of the adherence of purified elementary bodies (EB) of Chlamydia trachomatis to HeLa and to McCoy cells were examined using different techniques, including an ELISA. Serovar-specific, biotinylated monoclonal antibodies were used to detect cell-bound chlamydiae. In addition, purified chlamydiae were biotinylated and their adherence properties were studied. The assays were done at 4 degrees C to exclude the energy-dependent internalization of the cell-bound EB and host-cell membrane recycling that occur at 37 degrees C. Saturation kinetics were routinely observed at 4 degrees C, and the rate of adherence remained linear for approximately 60 min. Lineweaver-Burk analysis of the kinetics data showed that adherence of any one serovar was competitively inhibited by other serovars of C. trachomatis. This competition for the same receptor on the two alternative hosts, HeLa and McCoy, was also seen when the adherence assays were done at 37 degrees C in the presence of sodium azide, an energy poison that inhibits endocytosis of cell-bound chlamydiae. Chlamydiae exposed to 56 degrees C for 5 min, or treated with low doses of trypsin, failed to exhibit competitive inhibition, having suffered considerable loss of the ability to adhere to host-cells. These data suggest that heat- and trypsin-labile chlamydial moieties participate in the adherence reaction, and that oculo-genital serovars of C. trachomatis, including that of lymphogranuloma venereum, attach to the same receptor on the host-cell membrane.     

Structural insights into thermostable direct hemolysin of Vibrio parahaemolyticus using single-particle cryo-EM

Thermostable direct hemolysin (TDH) is a ~19 kDa, hemolytic pore-forming toxin from the gram-negative marine bacterium Vibrio parahaemolyticus, one of the causative agents of seafood-borne acute gastroenteritis and septicemia. Previous studies have established that TDH exists as a tetrameric assembly in physiological state; however, there is limited knowledge regarding the molecular arrangement of its disordered N-terminal region (NTR)—the absence of which has been shown to compromise TDH's hemolytic and cytotoxic abilities. In our current study, we have employed single-particle cryo-electron microscopy to resolve the solution-state structures of wild-type TDH and a TDH construct with deletion of the NTR (NTD), in order to investigate structural aspects of NTR on the overall tetrameric architecture. We observed that both TDH and NTD electron density maps, resolved at global resolutions of 4.5 and 4.2 Å, respectively, showed good correlation in their respective oligomeric architecture. Additionally, we were able to locate extra densities near the pore opening of TDH which might correspond to the disordered NTR. Surprisingly, under cryogenic conditions, we were also able to observe novel supramolecular assemblies of TDH tetramers, which we were able to resolve to 4.3 Å. We further investigated the tetrameric and inter-tetrameric interaction interfaces to elaborate upon the key residues involved in both TDH tetramers and TDH super assemblies. Our current structural study will aid in understanding the mechanistic aspects of this pore-forming toxin and the role of its disordered NTR in membrane interaction.