An initial test of a method for the estimation of real mean particle size from shadowed samples

During shadowing, a "cap" of metal develops on small particles. This cap increases apparent particle with (measured normal to the shadowing direction) by an extent which cannot be predetermined. The extent of this increase in particle size (here defined as the "cap," X) is estimated in the present method by using opposite (180 degrees sample rotation) bidirectional shadowing. It is argued that the bidirectional cap is the sum of the two unidirectional caps, and therefore that X = 2A - (B + C), where A is the mean bidirectionally shadowed particle size, and B and C are the two mean unidirectionally shadowed particle sizes. As a validation of the method, the mean diameter of air-dried ferritin was estimated and the results appear to confirm the hypothesis (mean diameter by present method, 10.7 +/- 0.2 nm; mean diameter by previous methods, 10.89 nm).     

Suitability of Taxodium distichum for Afforesting the Littoral Zone of the Three Gorges Reservoir

The littoral zone ecosystem of the Three Gorges Reservoir (TGR) has become significantly degraded by annual cycles of prolonged winter flooding and summer drought. For purposes of flood control and sediment management, the water level in the reservoir is lowered by 30 m during the summer monsoon season and raised again to 175 m above sea level each year at the end of the monsoon period. To explore an effective way to promote biodiversity and associated ecosystem services, we examined Taxodium distichum as a species for afforesting the littoral zone. Sapling growth variations were measured after two rounds of winter flooding. Dominant influence factors were determined by redundancy analysis. Herb community similarities between the experimental afforested areas and nearby control areas were assessed to detect the ecosystem influence of the experimental afforestation. 94.5% of saplings planted at elevations above 168 m survived. All measured growth indices (tree height, diameter at breast height, crown width and foliage density) decreased as the flood depth increased. Completely submerged saplings had a mean dieback height of -0.65 m. Greater initial foliage density led to increased tree height and stem diameter. Shannon-Wiener indices were not significantly different between plots in experimental and control areas, but the low similarity of herb communities between experimental and control areas (0.242 on average) suggested that afforestation would enrich plant community structure and improve littoral zone ecosystem stability. Because littoral zone afforestation provides several ecosystem services (habitat, carbon sink, water purification and landscaping), it is a promising revegetation model for the TGR.     

Analysis of male sterile mutations in the mouse using haploid stage expressed cDNA probes

A differential hybridization screening procedure has identified cDNAs which correspond to RNAs which are expressed in mouse testis and at lower levels in liver and spleen. The sensitivity of this procedure is such that approximately 0.5% of 1.4 X 10(4) cDNA clones are revealed as "testis specific". We have focused on ten cDNA clones which have been used to identify RNAs expressed in the haploid phase of spermatogenesis. Using Northern blots to analyse RNA isolated from the testes of mutant mice (Tfm/Y and Sxr/+) blocked at specific stages in spermatogenesis or RNA from sexually immature mice, 8 clones have been identified which correspond to RNAs expressed uniquely or at much higher levels in meiotic or post meiotic cells.     

Characterization of a nif-regulated flavoprotein (FprA) from Rhodobacter capsulatus. Redox properties and molecular interaction with a [2Fe-2S] ferredoxin.

A flavoprotein from Rhodobacter capsulatus was purified as a recombinant (His)6-tag fusion from an Escherichia coli clone over-expressing the fprA structural gene. The FprA protein is a homodimer containing one molecule of FMN per 48-kDa monomer. Reduction of the flavoprotein by dithionite showed biphasic kinetics, starting with a fast step of semiquinone (SQ) formation, and followed by a slow reduction of the SQ. This SQ was in the anionic form as shown by EPR and optical spectroscopies. Spectrophotometric titration gave a midpoint redox potential for the oxidized/SQ couple of Em1 = +20 mV (pH 8.0), whereas the SQ/hydroquinone couple could not be titrated due to the thermodynamic instability of SQ associated with its slow reduction process. The inability to detect the intermediate form, SQ, upon oxidative titration confirmed this instability and led to an estimate of Em2 - Em1 of > 80 mV. The reduction of SQ by dithionite was significantly accelerated when the [2Fe-2S] ferredoxin FdIV was used as redox mediator. The midpoint redox potential of this ferredoxin was determined to be -275 +/- 2 mV at pH 7.5, consistent with FdIV serving as electron donor to FprA in vivo. FdIV and FprA were found to cross-react when incubated together with the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, giving a covalent complex with an Mr of approximately 60 000. Formation of this complex was unaffected by the redox states of the two proteins. Other [2Fe-2S] ferredoxins, including FdV and FdVI from R. capsulatus, were ineffective as electron carriers to FprA, and cross-reacted poorly with the flavoprotein. The possible function of FprA with regard to nitrogen fixation was investigated using an fprA-deleted mutant. Although nitrogenase activity was significantly reduced in the mutant compared with the wild-type strain, nitrogen fixation was apparently unaffected by the fprA deletion even under iron limitation or microaerobic conditions.     

Suberin production by isolated tomato fruit protoplasts

The multilamellar wall secreted by protoplasts isolated from locule tissue of tomato (Lycopersicon esculentum L.) fruit was purified, and an extract was obtained after depolymerization with BF₃-methanol. Analysis of this extract using thin layer chromatography demonstrated the presence of fatty acid methyl esters, fatty alcohols, dicarboxylic acid dimethyl esters, and ω-hydroxy acid methyl esters. These components were quantified using an Iatroscan thin layer chromatography-flame ionization detection system. The different chain lengths in each group were identified and quantified using gas chromatography. The results clearly indicated the presence of suberin.     

Elimination of R plasmids from the photosynthetic bacterium Rhodobacter capsulatus

Rhodobacter capsulatus (formerly Rhodopseudomonas capsulata) could be cured of R plasmids of the P1 incompatibility group, including derivatives used as cloning vectors, by repeated subculturing in a growth medium containing only yeast extract and peptone (YP medium). Loss of R plasmid material from the cells was complete, as shown by agarose gel electrophoresis, and by the absence of hybridization between total DNA and radioactively labelled R plasmid DNA. Prolonged subculturing in YP medium often resulted in the accumulation of auxotrophs, and led to the appearance of strains containing chromosomal insertions of plasmid DNA.