Genetic tests of the roles of the embryonic ureases of soybean

We assayed the in vivo activity of the ureases of soybean (Glycine max) embryos by genetically eliminating the abundant embryo-specific urease, the ubiquitous urease, or a background urease. Mutant embryos accumulated urea (250-fold over progenitor) only when lacking all three ureases and only when developed on plants lacking the ubiquitous urease. Thus, embryo urea is generated in maternal tissue where its accumulation is not mitigated by the background urease. However, the background urease can hydrolyze virtually all urea delivered to the developing embryo. Radicles of 2-day-old germinants accumulated urea in the presence or absence of the embryo-specific urease (2 micromoles per gram dry weight radicle). However, mutants lacking the ubiquitous urease exhibited increased accumulation of urea (to 4-5 micromoles urea per gram dry weight radicle). Thus, the ubiquitous and not the embryo-specific urease hydrolyzes urea generated during germination. In the absence of both of these ureases, the background urease activity (4% of ubiquitous urease) may hydrolyze most of the urea generated. A pleiotropic mutant lacking all urease accumulated 34 micromoles urea per gram dry weight radicle (increasing 2.5-fold at 3 days after germination). Urea (20 millimolar) was toxic to in vitro-cultured cotyledons which contained active embryo-specific urease. Cotyledons lacking the embryo-specific urease accumulated more protein when grown with urea than with no nitrogen source. Among cotyledons lacking the embryo-specific urease, fresh weight increases were virtually unchanged whether grown on urea or on no nitrogen and whether in the presence or absence of the ubiquitous urease. However, elimination of the ubiquitous urease reduced protein deposition on urea-N, and elimination of both the ubiquitous and background ureases further reduced urea-derived protein. The evidence is consistent with the lack of a role in urea hydrolysis for the embryo-specific urease in developing embryos or germinating seeds. Because the embryo-specific urease is deleterious to cotyledons cultured in vitro on urea-N, its role may be to hydrolyze urea in wounded or infected embryos, creating a hostile environment for pest or pathogen. While the ubiquitous urease is operative in leaves and in seedlings, all or most of its function can be assumed by the background urease in embryos and in seedlings.     

One-dimensional model of the acid hydrolysis of cellulosic substrates in a solid-liquid cyclone reactor

The use of rotating flow in an annulus is investigated as a means of enhancing the yield of glucose and xylose in the acid hydrolysis of cellulosic slurries. A one-dimensional model of such a cyclone reactor is developed for flow cases, co-current and counter-current flow. For the case of 250°C, 1% w/w acid, the one-dimensional model indicates an increase in the maximum glucose yield from 48.1% in a plug flow reactor to 69.3% in a co-current cyclone reactor, and up to 81.0% in a countercurrent cyclone reactor. The corresponding xylose yields are 91.6% for co-current operation and 97.7% for countercurrent operation. In the co-current case the maximum glucose and xylose yields do not occur at the same location in the reactor; however, in the countercurrent case they do. Although product yields are dramatically improved over those obtained in a plug flow reactor, the product concentrations are lower than would typically be obtained in a plug flow reactor.List of Symbols A cm² cross sectional area perpendicular to radial flow - A _c cm² cross sectional area of slurry inlet - A _c cm² cross sectional area of steam inlet - A _w cm² cross sectional area of water inlet - C _c concentration of cellulose as potential glucose (grams of potential glucose/cm³ of total stream) - C _c ^* grams cellulose/cm³ of solids concentration of cellulose as potential glucose - C _ginitial ^* grams glulose/cm³ of solids concentration of cellulose entering reactor - C _g grams glucose/cm³ of total stream concentration of glucose - C _g ^* grams glucose/cm³ of liquid stream concentration of glucose - C _cinitial ^* grams cellulose/cm³ of liquid concentration of glucose entering reactor - C _xn concentration of xylan as potential xylose (grams of potential xylose/cm³ of total stream) - C _xs grams xyclose/cm³ of total stream concentration of nylose - d _f dilution factor - dr cm radial increment - g cm/s² gravitational acceleration - g ^* centrifugal acceleration proportionality constant - h cm height of cyclone reactor - j cm/s flux - K constant in general equation for vortex flow, Eq. (4.9) - k ₁ 1/s kinetic rate constant of cellulose hydrolysis - k _a 1/s kinetic rate constant of xylan hydrolysis - k ₂ 1/s kinetic rate constant of glucose decomposition - k _2a 1/s kinetic rate constant of xylose decomposition - m vortex exponent - M _steam g/s mass rate of steam addition at outer radius - M _water g/s mass rate of cold water addition at outer radius - n cm³/s empirically determined settling parameter - Q cm³/s net volumetric flow in outward radial direction - Q _tot cm³/s total volumetric flow through reactor - q _c cm³/s volumetric flow of slurry feed - q _s cm³/s volumetric flow of stream feed - q _water cm³/s volumetric flow of cold water feed - r cm radial position - r _c 1/s rate of cellulose hydrolysis - r _g 1/s rate of glucose decomposition - r _i cm inner radius - r _o cm outer radius - r _xn 1/s rate of xylan hydrolysis - r _xs 1/s rate of xylose decomposition - s _mom cm g/s² inlet steam momentum - T _bulk s bulk residence time in reactor - T °C reactor temperature - v _c cm³/g specific volume of slurry feed - v _s cm³/g specific volume of steam - v _w cm³/g specific volume of water - V _f cm/s velocity of liquid as a function of radius - V _i cm/s inlet velocity - V _s cm/s velocity of solids as a function of radius - V _steam cm/s inlet steam velocity to cyclone - V cm/s terminal settling velocity - V _q cm/s tangential velocity - w _mom cm g/s² water inlet momentum - Y grams product out/grams reactant in yield of product - solids volumetric fraction - _f solids volumetric fraction in slurry feed - _i initial solids volumetric fraction of slurry - Pi     

High nucleotide substitution error frequencies in clonal pools of vesicular stomatitis virus.

Nucleotide substitution error frequencies were determined for several specific guanine base positions in the genomes of cloned vesicular stomatitis virus populations. Predetermined sites were examined in coding regions for the N, M, and L proteins and at a site in the genome 5'-end regulatory region. Misincorporation frequencies were estimated to be on the order of 10(-3) to 10(-4) at all positions analyzed. Isolates taken from virus populations after disruption of equilibrium conditions displayed replicase fidelity similar to that of cloned wild-type vesicular stomatitis virus. These mutation frequencies apply to all virus genomes present, including viruses rendered nonviable by lethal mutations. At one selected site in the N gene, two of three G----N base substitutions generated lethal nonsense mutations, yet their frequency was also very high. Biological implications for rapid virus evolution are discussed.     

Identification of gene products programmed by restriction endonuclease DNA fragments using an E. coli in vitro system.

DNA restriction enzyme fragments have been used to programme the synthesis of polypeptides in an in vitro system without apparent loss in fidelity compared with supercoiled templates. The system is extremely sensitive, less than 1 microgram of DNA can be used to direct the synthesis of 35S-labelled polypeptides of sufficiently high specific activity such that products can be identified by SDS-PAGE after a few hours autoradiography. The ability to analyse fragments can be used to readily assign specific proteins to small regions of the coding template, to identify cloned gene products distinct from those of the vector, and to identify cloned genes expressed from their own promoters. The in vitro system can be used successfully with bacterial DNA from other species and efficient extracts can be prepared from any E. coli K-12 strain, which should greatly facilitate the purification of factors controlling the expression of specific genes by complementation assay.     

Does the major histocompatibility complex serve as a specific receptor for Semliki Forest virus?

Murine F9 and PCC4 teratoma cells do not express H-2 major transplantation antigens according to virus-specific T-lymphocyte cytotoxic or serological assays. However, such cells can be infected with and readily replicate many types of viruses (coxsackie B 3, mouse hepatitis, Sindbis, Semliki Forest [SFV], lymphocytic choriomeningitis, Pichinde, vesicular stomatitis, herpes simplex type 1) to the same extent as do murine F12 teratoma cells and mouse embryo fibroblasts, all of which express the H-2 determinants. In contrast, F9 and PCC4 cells are not productively infected with murine cytomegalovirus, whereas F12 and mouse embryo fibroblast cells are. In addition to replicating in H-2-negative murine teratoma cells, SFV replicates in H-2-negative murine lymphoblastoid cells. The ability of SFV to infect cells without H-2 antigens and then to effect viral antigenic expression in the cells' cytoplasm and on their surface with similar kinetics and in equivalent amounts as cells with H-2 antigens indicates that the H-2 receptor is not needed for SFV infection. Daudi cells, which lack HLA antigens, block the replication of SFV. This occurs at some point after receptor binding, as demonstrated by diminished viral mRNA. In addition, a possible membrane defect precludes viral exit in Daudi cells transfected with SFV infectious RNA. These results indicate that a cell's possession of H-2 antigens is not a requirement for SFV infection and that major histocompatibility complex antigens are not specific receptors for this virus.     

Proposal for a uniform nomenclature for defective interfering viruses of vesicular stomatitis virus.

Defective interfering particles of vesicular stomatitis virus have been named according to their parental derivation and to their genomic length and physical properties. This suggested uniform nomenclature can be adapted for other virus systems.     

The effects of manganese doping on UVA absorption and free radical generation of micronised titanium dioxide and its consequences for the photostability of UVA absorbing organic sunscreen components.

The effect of manganese doping on the free radical generation rate, free radical scavenging and UVA absorption properties of micronised sunscreen grade titania has been studied with respect to enhancement of the UVA photostability of test sunscreen formulations containing the organic UVA absorber Parsol 1789. Manganese doping has been shown to increase the UVA:UVB absorption ratio of titania, reduce free radical generation rates by over 90%, and provide free radical scavenging behaviour. Adding manganese-doped titania to a test formulation incorporating Parsol 1789 shows that manganese doping increases UVA attenuation stability by up to 3 times the amount achieved by comparable commercial undoped titania materials. HPLC data shows this to be related to an improved stabilisation of the organic sunscreen components. Manganese doped titania shows improved efficacy over undoped titania in sunscreen formulations containing organic UV absorbers.     

PERSPECTIVE: CHASE-AWAY SEXUAL SELECTION: ANTAGONISTIC SEDUCTION VERSUS RESISTANCE

A model of sexual selection that leads to the evolution of exaggerated male display characters that is based on antagonistic coevolution between the sexes is described. The model is motivated by three lines of research: intersexual conflict with respect to mating, sensory exploitation, and the evolution of female resistance, as opposed to preference, for male display traits. The model generates unique predictions that permit its operation to be distinguished from other established models of sexual selection. One striking prediction is that females will frequently win the coevolutionary arms race with males, leaving them encumbered with costly ornaments that have little value except that their absence understimulates females. Examples from the literature suggest that the model may have broad application in nature. The chase-away model is a special case of the more general phenomenon of Interlocus Contest Evolution (ICE).