Essential oil of Ayapana triplinervis from Reunion Island: A good natural source of thymohydroquinone dimethyl ether

Three specimens of Ayapana triplinervis (Vahl) R.M. King & H. Rob from Reunion Island (Indian Ocean) collected at two distant locations (North of the island; samples 1 and 2, South of the island; sample 3), in different growth phases (flowering; samples 1 and 3, vegetative; sample 2) were investigated for their leaf essential oil composition. This study reports the chemical character of this species on the island and investigates the relationship between essential oil composition, developmental stage and geographic location. Analysis by GC–FID and GC–MS enabled us to identify and quantify a total of 39 constituents accounting for 97.1–98.0% of the oils. The three essential oil samples, all obtained by hydrodistillation, showed a high percentage of the aromatic compound thymohydroquinone dimethyl ether (89.9–92.8%). All other minor components remained more or less unchanged both qualitatively and quantitatively with respect to the stage of growth. On the contrary, variations were observed with geographic distribution. The geographical variation of the chemical composition of the volatile oil of A. triplinervis from several sites in the world is also briefly discussed.     

Isolation and Pathogenicity of Rhizosphere Fungi of Cocoyam in Relation to Cocoyam Root Rot Disease

Cocoyam is the second most important staple crop of Cameroon and root rot is a destructive disease of this plant. Pythium myriotylum (Pm), Fusarium solani (Fs), and Rhizoctonia solani (Rs) were isolated from the rhizosphere of root rot affected cocoyams and from the soil of a cocoyam experimental field plot temporarily devoid of same in Mamu, Cameroon. Pm was isolated from the above soil by the cocoyam leaf disc baits. Fs and Rs were also isolated from the same soils by the water dilution method and from the roots of diseased cocoyams but were always associated with mycelial growth of Pm. Pathogenicity of Pm and in combinations with Fs or Rs or Fs + Rs all developed cocoyam root rot disease (CRRD) symptoms on 3– and 7–month old cocoyam plantlets 2–7 days after inoculation. Symptoms included rotted roots and wilting with general chlorosis of inoculated plantlets. No symptoms of CRRD were noted on cocoyam plantlets inoculated with Fs, Rs, Fs + Rs, and distilled water. Results indicated that CRRD is not caused by several pathogens but only by Pm. Pm isolates from the soils and roots of diseased cocoyams and those maintained in the ROTREP laboratory have significantly bigger diameter of mycelial colony growth in 24 h–period at 31 °C on lima bean sucrose agar, V–8 juice sucrose agar, and potato sucrose agar than on potato dextrose agar and 2 % water agar. The cocoyam plantlets were raised axenically from tissue culture of explants in the laboratory.     

The recycling of a secretory granule membrane protein

We have used N-hydroxysuccinimido-d-biotin as a reagent for labeling proteins exposed at the surface of cultured bovine adrenal chromaffin cells during Ba2+-stimulated secretion. A specific secretory granule membrane constituent, dopamine-beta-hydroxylase (DBH), has been investigated using immunoprecipitation followed by electrophoresis. Within 30 min of stimulation, exposed DBH had been cleared from the cell surface. Nevertheless, quantitation of labeled DBH using [125I] streptavidin suggested that it remained undegraded over a period of 24 h, a time during which secretory granule stores of catecholamines were being replenished. Subcellular fractionation of the cultured cells suggested that, after 3 or 4 h, the biotinylated DBH, which was still membrane-bound, was located in particulate material that also contained cytochrome b561, another major secretory granule membrane component.     

Presence of a small plasmid in clinical isolates of Streptococcus pneumoniae

Twenty-four of 63 enteric Gram-negative organisms (38.1%) which were isolated from 35 apparently healthy Nigerian students were found to have low trimethoprim resistance (MIC less than 1000 mg/l). These isolates were also found to be resistant to several other antibiotics and trimethoprim resistance was found to be transferable from 15 (62.5%) of the trimethoprim resistant organisms into E. coli EC 1005. It is likely that the high percentage of trimethoprim resistance encountered in this study is related to the high rate of resistance transfer which was observed.     

Replisome pausing in mutagenesis

E. coli cells containing a temperature-sensitivednaE mutation, in the α-subunit of holoenzyme DNA polymerase III, do not survive at the restrictive temperature. Such cells may survive in the presence of thepcbA1 mutation, an allele of thegyrB gene. Such survival is dependent on an active DNA polymerase I. Evidence indicates that DNA polymerase I interacts directly in the replisome (REP·A). Despite normal survival for cells using thepcbA replication pathway after some type of DNA damage, we have noted a failure of damage-induced mutagenesis. Here we present evidence supporting a model of replisome pausing in cells dependent upon thepcbA replication pathway. The model argues that the (REP·A) complex pauses longer at the site of the lesion, allowing excision repair to occur completely. In the normal replication pathway (REP·E) bypass of the lesion occurs, fixing the mutation.