Effect of Mn deficiency and legume inoculation on rhizosphere pH in highly alkaline soils

Plant and Soil - Although plant growth is often limited at high pH, little is known about root-induced changes in the rhizospheres of plants growing in alkaline soils. The effect of Mn deficiency...     

Electron Transfer Dynamics in Rhodobacter sphaeroides Reaction Center Mutants with a Modified Ligand for the Monomer Bacteriochlorophyll on the Active Side

The histidine ligand of the monomer bacteriochlorophyll molecule on the active side (B_A) of the photosynthetic reaction center from Rhodobacter sphaeroides was mutated to a number of other amino acids. Histidine (H) at the position L153 was replaced with aspartic acid (D), glutamic acid (E), glutamine (Q), glycine (G), leucine (L), phenylalanine (F), serine (S), valine (V) and tyrosine (Y). These mutations were created to investigate how the alteration of the ligand residue affects the properties of the B_A molecule and changes the dynamics of the primary charge separation in reaction centers. In all of the mutants, the changes in the ligand result in a blue-shift of the B_A absorption spectrum, in both visible and near-infrared spectral regions, with the size of the shift varying between mutants. The primary electron transfer time constants in these mutant reaction centers range from 4.5 to 18 ps, being substantially slower than the wild-type value of 3 ps. The decrease in the electron transfer rate is interpreted as being due to an increase in the free energy of the initial charge-separated state P⁺B_A^–.This revised version was published online in October 2005 with corrections to the Cover Date.     

Trends in Dissolved Organic Carbon in UK Rivers and Lakes

Several studies have highlighted an increase in DOC concentration in streams and lakes of UK upland catchments though the causal mechanisms controlling the increase have yet to be fully explained. This study, compiles a comprehensive data set of DOC concentration records for UK catchments to evaluate trends and test whether observed increases are ubiquitous over time and space. The study analysed monthly DOC time series from 198 sites, including 29 lakes, 8 water supply reservoirs and 161 rivers. The records vary in length from 8 to 42 years going back as far as 1961. Of the 198 sites, 153 (77%) show an upward trend in DOC concentration significant at the 95% level, the remaining 45 (23%) show no significant trend and no sites show a significant decrease in DOC concentration. The average annual increase in DOC concentration was 0.17 mg C/l/year. The dataset shows: (i) a spatial consistent upward trend in the DOC concentration independent of regional effects of rainfall, acid and nitrogen deposition, and local effects of land-use change; (ii) a temporally consistent increase in DOC concentration for period back as far as the 1960s; (iii) the increase in DOC concentration means an estimated DOC flux from the UK as 0.86 Mt C for the year 2002 and is increasing at 0.02 Mt C/year. Possible reasons for the increasing DOC concentration are discussed.     

Ecophysiological response to severe drought in Pinus halepensis Mill. trees of two provenances

As a result of predicted regional climatic changes the need to select for the more drought-tolerant genotypes (ecotypes) among Mediterranean conifers has become clear. Aleppo pine (Pinus halepensisMill.) seems to be one of the most drought-tolerant pine species. Nevertheless, the existence of geographical trends in their genetic differentiation indicates potentially large differences in drought-tolerance among provenances. This assumption was verified by the finding of large variation among provenances in their internal water relations. Hence, the aim of this study was to compare the ecophysiological behaviour of several Aleppo pine provenances under contrasting climatic conditions. Growth parameters (height and diameter) and survival rate were measured in two provenance trials, one planted under sub-desertic conditions at the northern edge of the Negev desert, and the second under thermo-Mediterranean climatic conditions in the central coastal plains, Israel. Ecophysiological parameters such as: predawn needle water potential, sap flow in the xylem (i.e. transpiration), photosynthesis and water-use efficiency were measured in trees of selected provenances. The results suggest that it is not possible to predict provenance performance under harsh conditions from their performance under more favourable ones. Therefore, selection must be carried out under the exact conditions in which the trees from the resultant selection will be planted. The present study clearly emphasises the need for broad selection programs of P. halepensis.     

Separation-of-Function Mutations in Saccharomyces cerevisiae MSH2 That Confer Mismatch Repair Defects but Do Not Affect Nonhomologous-Tail Removal during Recombination

Yeast Msh2p forms complexes with Msh3p and Msh6p to repair DNA mispairs that arise during DNA replication. In addition to their role in mismatch repair (MMR), the MSH2 and MSH3 gene products are required to remove 3' nonhomologous DNA tails during genetic recombination. The mismatch repair genes MSH6, MLH1, and PMS1, whose products interact with Msh2p, are not required in this process. We have identified mutations in MSH2 that do not disrupt genetic recombination but confer a strong defect in mismatch repair. Twenty-four msh2 mutations that conferred a dominant negative phenotype for mismatch repair were isolated. A subset of these mutations mapped to residues in Msh2p that were analogous to mutations identified in human nonpolyposis colorectal cancer msh2 kindreds. Approximately half of the these MMR-defective mutations retained wild-type or nearly wild-type activity for the removal of nonhomologous DNA tails during genetic recombination. The identification of mutations in MSH2 that disrupt mismatch repair without affecting recombination provides a first step in dissecting the Msh-effector protein complexes that are thought to play different roles during DNA repair and genetic recombination.     

The genes encoding E-selectin (SELE) and lymphotactin (SCYC1) lie on separate chicken chromosomes although they are closely linked in human and mouse

Three differentially expressed selectin genes (SELE, SELP, and SELL), important in the initial stages of leukocyte extravasation, have been reported in mammals. All three genes map close to the chemokine SCYC1 (small inducible cytokine subfamily C, member 1) in a large conserved chromosomal segment that extends from RXRG (retinoic acid receptor, gamma) to TNNT2 (troponin T2) on Chromosome (Chr) 1 in both human and mouse. In the mouse, we demonstrate that Sele is flanked by Prrx1 (paired-related homeobox gene 1) and Scyc1 and define the order of, and distances between, loci as centromere-Prrx1-(0.7+/-0.7 cM)-Sele-(1.2+/-0.9 cM)-Scyc1-telomere. In the chicken, we isolated BAC clones containing PRRX1, SELE, and SCYC1 and positioned them by fluorescent in situ hybridization. SELE and PRRX1 mapped to the short arm of chicken Chr 8 and SCYC1 mapped to the region equivalent to 1q11-1q13 on the long arm of chicken Chr 1. The location of SELE on chicken Chr 8 was independently established by linkage analysis of COM0185, an (AT)16 microsatellite locus identified in a BAC clone that contained SELE. COM0185 was linked to several loci that mapped to one end of chicken Chr 8, with the order of loci, and genetic distances (in cM) between them defined as MSU0435, MSU0325-(7.8+/-3.7)-COM0185-(5.8+/-3.2)-ROS0338-(9.6+/-4.0)-ABR0322-(3.8+/-2.6)-GLUL. We have therefore positioned an evolutionary breakpoint in mammals and chickens between SELE and SCYC1. Furthermore, comparative mapping analysis of the RXRG-TNNT2 chromosomal segment that is conserved on human and mouse Chr 1 indicates that it is divided into four segments in the chicken, each of which maps to a different chromosome.     

Integrated stream and wetland restoration: A watershed approach to improved water quality on the landscape

Water quality in Upper Sandy Creek, a headwater stream for the Cape Fear River in the North Carolina Piedmont, is impaired due to high N and P concentrations, sediment load, and coliform bacteria. The creek and floodplain ecosystem had become dysfunctional due to the effects of altered storm water delivery following urban watershed development where the impervious surface reached nearly 30% in some sub-watersheds. At Duke University, an 8-ha Stream and Wetland Assessment Management Park (SWAMP) was created in the lower portion of the watershed to assess the cumulative effect of restoring multiple portions of stream and former adjacent wetlands, with specific goals of quantifying water quality improvements. To accomplish these goals, a three-phase stream/riparian floodplain restoration (600 m), storm water reservoir/wetland complex (1.6 ha) along with a surface flow treatment wetland (0.5 ha) was ecologically designed to increase the stream wetland connection, and restore groundwater wetland hydrology. The multi-phased restoration of Sandy Creek and adjacent wetlands resulted in functioning riparian hydrology, which reduced downstream water pulses, nutrients, coliform bacteria, sediment, and stream erosion. Storm water event nutrient budgets indicated a substantial attenuation of N and P within the SWAMP project. Most notably, (NO₂⁻ + NO₃⁻)-N loads were reduced by 64% and P loads were reduced by 28%. Sediment retention in the stormwater reservoir and riparian wetlands showed accretion rates of 1.8 cm year⁻¹ and 1.1 cm year⁻¹, respectively. Sediment retention totaled nearly 500 MT year⁻¹.     

Single molecule detection of DNA looping by NgoMIV restriction endonuclease

Single molecule fluorescence resonance energy transfer (FRET) and fluorescence correlation spectroscopy were used to investigate DNA looping by NgoMIV restriction endonuclease. Using a linear double-stranded DNA (dsDNA) molecule labeled with a fluorescence donor molecule, Cy3, and fluorescence acceptor molecule, Cy5, and by varying the concentration of NgoMIV endonuclease from 0 to 3 x 10(-6) M, it was possible to detect and determine diffusion properties of looped DNA/protein complexes. FRET efficiency distributions revealed a subpopulation of complexes with an energy transfer efficiency of 30%, which appeared upon addition of enzyme in the picomolar to nanomolar concentration range (using 10(-11) M dsDNA). The concentration dependence, fluorescence burst size analysis, and fluorescence correlation analysis were all consistent with this subpopulation arising from a sequence specific interaction between an individual enzyme and a DNA molecule. A 30% FRET efficiency corresponds to a distance of approximately 65 A, which correlates well with the distance between the ends of the dsDNA molecule when bound to NgoMIV according to the crystal structure of this complex. Formation of the looped complexes was also evident in measurements of the diffusion times of freely diffusing DNA molecules with and without NgoMIV. At very high protein concentrations compared to the DNA concentration, FRET and fluorescence correlation spectroscopy results revealed the formation of larger DNA/protein complexes.