Simple method to reduce interference from excess magnesium in cadmium immunoassays

In order to develop a rapid inexpensive test for cadmium in rice, we identified an antibody specific for cadmium-EDTA complexes; this antibody binds to cadmium-EDTA with a Kd of approximately 10(-8) M. Although the antibody's cross reactivity to magnesium was minimal (Kd approximately 10(-5) M), the high toxicity of cadmium coupled with the high natural occurrence of magnesium in rice resulted in a situation where magnesium interfered with cadmium determination and resulted in falsely elevated estimates of cadmium. Fortunately, the formation constant of EDTA for cadmium is approximately 5 x 10(7) times higher (at pH 7) than the formation constant of EDTA for magnesium, and we were able to eliminate the magnesium interference by judicious selection of the EDTA concentration used in the assay. The resulting equilibria are complex, but we show that a relatively simple two-step model in which cadmium and magnesium compete for EDTA followed by cadmium-EDTA and magnesium-EDTA competing for antibody provided a good fit to the measured data. These analyses enabled appropriate selection of the optimum EDTA concentration for an immunoassay with improved selectivity.     

Ultrasonic shear wave velocities of MgSiO3 perovskite at 8 GPa and 800 K and lower mantle composition

Ultrasonic interferometric measurements of the shear elastic properties of MgSiO3 perovskite were conducted on three polycrystalline specimens at conditions up to pressures of 8 gigapascals and temperatures of 800 kelvin. The acoustic measurements produced the pressure (P) and temperature (T) derivatives of the shear modulus (G), namely ( partial differentialG/ partial differentialP)T = 1.8 +/- 0.4 and ( partial differentialG/ partial differentialT)P = -2.9 +/- 0.3 x 10(-2) gigapascals per kelvin. Combining these derivatives with the derivatives that were measured for the bulk modulus and thermal expansion of MgSiO3 perovskite provided data that suggest lower mantle compositions between pyrolite and C1 carbonaceous chondrite and a lower mantle potential temperature of 1500 +/- 200 kelvin.     

Mantle seismic structure beneath the MELT region of the east pacific rise from P and S wave tomography

Relative travel time delays of teleseismic P and S waves, recorded during the Mantle Electromagnetic and Tomography (MELT) Experiment, have been inverted tomographically for upper-mantle structure beneath the southern East Pacific Rise. A broad zone of low seismic velocities extends beneath the rise to depths of about 200 kilometers and is centered to the west of the spreading center. The magnitudes of the P and S wave anomalies require the presence of retained mantle melt; the melt fraction near the rise exceeds the fraction 300 kilometers off axis by as little as 1%. Seismic anisotropy, induced by mantle flow, is evident in the P wave delays at near-vertical incidence and is consistent with a half-width of mantle upwelling of about 100 km.     

The Cornucopia of Small RNAs in Plant Genomes

Regulatory small RNAs (approximately 20 to 24 nt in length) are produced through pathways that involve several key evolutionarily conserved protein families; the variants of these proteins found in plants are encoded by multigene families and are known as Dicer-like, Argonaute, and RNA-dependent RNA polymerase proteins. Small RNAs include the well-known classes of microRNAs (miRNAs, ~21 nt) and the small-interfering RNAs (siRNAs, ~24 nt). Both of these types of molecules are found across a broad set of eukaryotic species, although the siRNAs are a much larger and more diverse class in plants due to the abundance of heterochromatic siRNAs. Well-studied species such as Arabidopsis have provided a foundation for understanding in rice and other species how small RNAs function as key regulators of gene expression. In this paper, we review the current understanding of plant small RNA pathways, including the biogenesis and function of miRNAs, siRNAs, trans-acting siRNAs, and heterochromatic siRNAs. We also examine the evolutionary relationship among plant species of both their miRNAs and the key enzymatic components of the small RNA pathways. Many of the most recent advances in describing small RNAs have resulted from advances in sequencing technologies used for identifying and measuring small RNAs, and these technologies are discussed. Combined with the plethora of genetic tools available to researchers, we expect that the continued elucidation of the identity and functions of plant small RNAs will be both exciting and rewarding.     

Quantitative real-time PCR assays for detection and quantification of all seven Eimeria species that infect the chicken

The development and validation of real-time quantitative PCR (qPCR) assays specific to all seven Eimeria species that cause coccidiosis in the chicken is described. The presented work utilizes previously published assays for Eimeria maxima, E. necatrix and E. tenella and adds assays for E. acervulina, E. brunetti, E. mitis and E. praecox. These assays target unique single copy sequences derived from sequence characterized amplified region (SCAR) markers. All seven qPCR markers were sequenced from multiple strains and confirmed to be non-polymorphic and identical to the original SCAR sequence. Sequences conserved within each species were chosen with the aim of developing genuinely universal markers, providing global coverage. An exact match for the primers and TaqMan(?) probe during PCR cycling enables precise relative quantification of multiple species in a mixture regardless of the strains present. All markers utilized in these qPCR assays are absolutely species-specific and support reproducible quantification across a wide linear range, unaffected by the presence of non-target species or other contaminating DNA. The sensitivity of these assays indicates that DNA equivalent to a single sporulated oocyst can be consistently detected. These assays will be a valuable tool from both industry and research perspectives. Comparison of our panel of qPCR assays with results derived by microscopy, the traditional Gold Standard, using poultry farm field samples support their efficacy.     

Alleles at a quantitative trait locus for stem solidness in wheat affect temporal patterns of pith expression and level of resistance to the wheat stem sawfly

The stem solidness trait in wheat has been the most effective mechanism for management of the wheat stem sawfly (WSS) for six decades. However, recent results have shown that in certain genotypes, the degree of stem solidness is not a useful indicator of WSS resistance. A morphological characterization of solidness expression indicated that in the genotype ‘Conan’, very solid pith undergoes rapid retraction during stem maturation, resulting in significantly less solidness at maturity. In other solid‐stemmed genotypes, including the standard WSS‐resistant cultivar ‘Choteau’, dense pith in the stem remains nearly unchanged throughout plant development. In cage trials, ‘Conan’ plants were less preferred for oviposition by the WSS when paired with ‘Choteau’ plants. Field bioassays using near‐isogenic lines differing for alleles at Qss.msub‐3BL showed that the Conan allele provides higher levels of early stem solidness and rapid pith retraction during stem maturation. These results suggest that the traditional approach for increasing WSS resistance by selecting for increasing stem solidness needs to be modified to consider temporal variations in pith expression associated with alleles at Qss.msub‐3BL.     

Can soil plant analysis development values predict chlorophyll and total Fe in hybrid poplar?

Iron chlorosis caused by an elevated soil pH remains an important selection criteria in evaluating hybrid Populus trials in northwest New Mexico. Compared to expensive extraction methods or visual ranking scales, the soil plant analysis development (SPAD) chlorophyll meter is a handheld tool that objectively indicates leaf color. SPAD calibration curves pertaining to Fe status in Populus leaves were developed for two clones: NM-6 (Populus nigra × Populus maximowiczii) and OP-367 (Populus deltoides × Populus nigra). Hybrids were grown in the greenhouse in a sandy loam soil of pH > 8 and the same soil amended with composted biosolids enriched with 420 mg kg⁻¹ Fe. SPAD measurements related to foliar Fe as follows: r ² = 0.72 for NM-6 and r ² = 0.58 for OP-367. SPAD measurements correlated with total chlorophyll as follows: r ² = 0.66 for NM-6 and r ² = 0.85 for OP-367. Based on the total chlorophyll content (supported with foliar element data), Fe sufficiency threshold values from SPAD measurements were estimated in these two clones.