Searching for resonances in the unbound Be-6 nucleus by using a radioactive Be-7 beam

Knowledge of the He-3(He-3,2p)He-4 reaction is important for understanding stellar burning and solar neutrino production. Previous measurements have found a surprisingly large rise in the cross section at low energies that could be due to a low-energy resonance in the He-3 + He-3 (Be-6) system or electron screening. In the Be-6 nucleus, however, no excited states have been observed above the first 2(+) state at E (x) = 1.67 MeV up to 23 MeV, even though several are expected. The H-2(Be-7,H-3)Be-6 reaction has been studied for the first time to search for resonances in the Be-6 nucleus that may affect our understanding of the He-3(He-3,2p)He-4 reaction. A 100-MeV radioactive Be-7 beam from the Holifield Radioactive Ion Beam Facility (HRIBF) was used to bombard CD2 targets, and tritons were detected by using the silicon detector array (SIDAR). A combination of reaction mechanisms appears to be necessary to explain the observed triton energy spectrum.

Fragmentation of extracellular DNA by long-term exposure to radiation from uranium in aquatic environments

Persistent harmful scenarios associated with disposal of radioactive waste, high-background radiation areas and severe nuclear accidents are of great concern regarding consequences to both human health and the environment. Of particular concern is the extracellular DNA in aquatic environments contaminated by radiological substances. Strand breaks induced by radiation promote decrease in the transformation efficiency for extracellular DNA. The focus of this study is the quantification of DNA damage following long-term exposure (over one year) to low doses of natural uranium (an alpha particle emitter) to simulate natural conditions, since nothing is known about alpha radiation induced damage to extracellular DNA. A high-resolution Atomic Force Microscope was used to evaluate DNA fragments. Double-stranded plasmid pBS as a model for extracellular DNA was exposed to different amounts of natural uranium. It was demonstrated that low concentrations of U in water (50 to 150 ppm) produce appreciable numbers of double strand breaks, scaling with the square of the average doses. The importance of these findings for environment monitoring of radiological pollution is addressed.

Endophytic and rhizospheric enterobacteria isolated from sugar cane have different potentials for producing plant growth-promoting substances

Background and aims Endophytic and rhizospheric environments differ in many respects, leading to the presence of different bacterial communities at each site. However, microorganisms such as enterobacteria can be found both within plants and in the surrounding soil. Bacteria must present differences in the traits that affect such environments in order to successfully colonise them. The present study compared the plant growth-promoting potential of diazotrophic enterobacteria isolated from the rhizosphere and from within surface-disinfected plants. Methods A total of 46 diazotrophic enterobacterial strains (21 rhizospheric and 25 putatively endophytic) belonging to the Klebsiella and Enterobacter genera, which are prevalent in sugar cane plantations, were isolated from the rhizosphere and from surface-disinfected plants. Their ability to synthesise amino acids using combined nitrogen obtained from nitrogen fixation, and their ability to synthesise indole-3-acetic acid (IAA) were determined by high performance liquid chromatography. Endogenous ethylene production by the bacteria was measured using gas chromatography, and biocontrol of phytopathogenic fungi was determined qualitatively using a dual culture technique. Results The putative endophytes released significantly higher amounts of amino acids than the rhizospheric bacteria, whilst the latter produced higher quantities of ethylene and were more actively antagonistic to fungi. Both types of bacteria released similar amounts of IAA. Conclusion Endophytic and rhizospheric bacteria differ in their capacity to release plant growth-promoting substances, which may be a reflection of their adaptations and an indication of their potential impact on their natural environment.

Molluscicidal activity of some marine substances against the snail Biomphalaria glabrata (Mollusca, Planorbidae)

Freshwater snails of the genus Biomphalaria play a major role as intermediate hosts of Schistosoma mansoni, the etiologic agent of schistosomiasis. While Biomphalaria spp. control by molluscicides is one of the main strategies to reduce the snail population in infected areas, there are few effective molluscicides commercially available. Natural products may be considered as potentially useful and safe molluscicides. We have evaluated the molluscicidal activity of 12 extracts from ten marine organisms on adult and embryonic stages of Biomphalaria glabrata. Only extracts of the red algae Liagora farinosa and of the sponge Amphimedon viridis presented molluscicidal activity. Lethal concentration (LC)(50) values obtained were 120 mu g/mL for L. farinosa CH2Cl2 extract (apolar fraction) and 20 mu g/mL for A. viridis extract and halitoxin. The polar alga fraction and halitoxin had no effect on B. glabrata embryos. The algae apolar fraction was active on B. glabrata in all embryonic development stages, with LC50 values for blastulae at 42 mu g/mL, gastrulae at 124 mu g/mL, trochophore at 180 mu g/mL, and veliger at 222 mu g/mL. This is the first report of extracts from marine organisms which presented molluscicidal activity.