Acid deposition: Effects of sulphuric acid at pH 3 on chemical and biochemical properties of bracken litter

The effects of increased acid deposition on some biochemical and chemical properties of bracken litter overlying a podzolic soil contained in monolith lysimeters were investigated. Pairs of lysimeters each received 1500 mm yr^?1 of “rain” consisting either of distilled water or pH 3.0 sulphuric acid applied evenly over a 5-yr period. The acid-treatment resulted in a marked acidification of the litter, associated with accelerated leaching of Ca²⁺, Mg²⁺, K⁺ and Mn²⁺. Acid treatment also increased the concentration of extractable Al³⁺ in the litter. The biochemical changes observed in the litter as a consequence of acidification included decreases of 33% in ATP content and 54% in respiration rate. Significant reductions in the mineralization rates of urea, glucose and acetate, and in the activities of 4-nitrophenylphosphatase, $\text{β-N-}\text{acetyl-}\text{d}\text{-glucosaminidase}$, exo-1,4,β-d-xylosidase and peroxidase were also observed in the acid-treated litter. The acid-treated litter also contained slightly less total N, ammonium-N and total P, and slightly more residual hexose carbohydrate than the control litter. The effects observed were consistent with a decrease in microbial activity associated with litter acidification and were reflected in a small (5.5%) but significant (P < 0.05) decrease in litter decomposition. Acid treatment decreased the ATP content of the mineral soil by about 13% in the 3 cm immediately beneath the litter, but below this depth no significant difference was observed.     

Characterization of organic phosphorus in leachate from a grassland soil

The degree of eutrophication in fresh water ecosystems may be influenced by the forms of phosphorus (P) leached from agricultural systems. Physico-chemical fractionation of P in leachate from a grassland soil carried out over a two year period indicated that the majority of the P loss from the Lismore soil occurred in unreactive particulate (55-76%) P forms. ³¹P nuclear magnetic resonance analysis of a selected leachate sample indicated that unreactive P was mainly comprised of monoester and diester forms of organic P. The presence of phosphomonoesterase (20-200 μg p nitrophenol l⁻¹ h⁻¹) and phosphodiesterase (68 μg bis-p nitrophenol l⁻¹ h⁻¹) activity in leachate resulted in hydrolysis of 10-21% of total unreactive P (TUP), indicating that some of the monoesters and diesters can be eventually hydrolyzed into inorganic P forms during P transport. Enzyme hydrolysis showed that 23% of the TUP was present as labile monoester P (LMP), followed by 20% as inositol hexakisphosphate (IHP) and 14% as diesters (phospholipids and nucleic acids). The findings of this study suggest that LMP, IHP and diesters are an important component of organic P leaching from the grassland soil.     

Aerosol and precipitation chemistry relationships at big bend national park

Aerosol chemistry, precipitation and visibility parameters are currently being measured at Big Bend National Park in Texas. This is part of a large-scale air resource evaluation program which the National Park Service is sponsoring in several southwestern national parks and monuments to determine the potential impact of local and distant pollutant sources on the environmental quality within these areas. Analysis of aerosol samples collected at six sites in the Southwest indicates that soil-derived components, organic materials and the acid-base ions of sulfate, nitrate, and ammonium are the major constituents of suspended airborne particulate matter in the remote areas of the arid region. Comparison of particulate matter chemistry and precipitation chemistry data at Big Bend National Park shows consistent features which indicate that the airborne alkaline soil material and NH₃ largely neutralize the atmospheric acidic species of H₂SO₄ and HNO₃. Given the similarity of the particulate matter composition and loading at the other monitoring sites, it is suggested that the trace chemical composition of precipitation will be similar in many remote regions of the Southwest.     

Allelic changes in bread wheat cultivars were associated with long-term wheat trait improvements

Genetic impacts under selective breeding of agricultural crops have been frequently investigated with molecular tools, but inadequate attention has been paid to assess genetic changes under long-term genetic improvement of plant traits. Here we analyzed allelic changes with respect to wheat trait improvement in 78 Canadian hard red spring wheat cultivars released from 1845 to 2004 and screened with 370 mapped SSR markers. The improvements in quality, maturity, yield, disease, stem rust, leaf rust, sawfly resistance, and agronomy were considered. A total of 154 (out of 370) loci with significant allelic changes across 21 chromosomes were detected in the 78 wheat cultivars separated into improved versus non-improved groups for eight traits. The number of significant loci for improving a trait ranged from four for quality to 68 for yield and averaged 35. Many more loci with significant allelic reduction for improving a trait were detected than those with significant allelic increase. Selection for early maturity introduced more alleles, but improving the other traits purged more alleles. Significantly lower numbers of unique alleles were found in the cultivars with improved traits. The distributions of unique allele counts also varied greatly across the 21 chromosomes with respect to trait improvement. Significant SSR variation between two cultivar groups was observed for improvement in seven traits, but not in stem rust. The proportional SSR variation residing between two groups ranged from 0.014 to 0.118. The proportional SSR variations within the improved cultivar groups consistently were much lower than those within the non-improved groups. These findings clearly demonstrate the association between allelic changes and wheat trait improvements and are useful for understanding the genetic modification of the wheat genome by long-term wheat breeding.     

Pertussis toxin S1 mutant with reduced enzyme activity and a conserved protective epitope

Pertussis toxin (PTX) is a major virulence factor in whooping cough and can elicit protective antibodies. Amino acid residues 8 to 15 of PTX subunit S1 are important for the adenosine diphosphate-ribosyltransferase activity associated with the pathobiological effects of PTX. Furthermore, this region contains at least a portion of an epitope that elicits both toxin-neutralizing and protective antibody responses in mice. The gene encoding the S1 subunit was subjected to site-specific mutagenesis in this critical region. A mutant containing a single amino acid substitution (Arg9----Lys) had reduced enzymatic activity (approximately 0.02% of control) while retaining the protective epitope. This analog S1 molecule may provide the basis for a genetically detoxified PTX with potential for use as a component of an acellular vaccine against whooping cough.