Showing papers by "University of California, Davis published in 1984"

Preservation of Membranes in Anhydrobiotic Organisms: The Role of Trehalose

Abstract: Trehalose is a nonreducing disaccharide of glucose commonly found at high concentrations in anhydrobiotic organisms. In the presence of trehalose, dry dipalmitoyl phosphatidylcholine (DPPC) had a transition temperature similar to that of the fully hydrated lipid, whereas DPPC dried without trehalose had a transition temperature about 30 degrees Kelvin higher. Results obtained with infrared spectroscopy indicate that trehalose and DPPC interact by hydrogen bonding between the OH groups in the carbohydrate and the polar head groups of DPPC. These and previous results show that this hydrogen bonding alters the spacing of the polar head groups and may thereby decrease van der Waals interactions in the hydrocarbon chains of the DPPC. This interaction between trehalose and DPPC is specific to trehalose. Hence this specificity may be an important factor in the ability of this molecule to stabilize dry membranes in anhydrobiotic organisms.

Sex chromosomes and the evolution of sexual dimorphism.

Abstract: The evolutionary significance of sex chromosomes has generally been associated with their effect on sex determination (see Mittwoch, 1967; Ohno 1967, 1979 for review). Here I will evaluate the idea that sex chromosomes also play an important role in the evolution of sexually dimorphic traits. As a premise I will assume that sexual dimorphism results from natural selection that favors different phenotypic characteristics in the two sexes. For example, in bighorn sheep (Ovis canadensis) horn size and shape are sexually dimorphic. The massive recurved horns of males are presumably an adaptive compromise between the need to blunt head-to-head collisions between fighting males and to act as weapons against predators. The smaller dagger-like horns of females are favored in this' sex since their sole function is defense against predators (Geist, 1971). Many less obvious characteristics are also likely to differ in their selective value between the sexes. In an extensive review of sexual dimorphism in mammals, Glucksmann (1981) suggested that traits such as growth rate, thermoregulation, metabolic rate, biorhythms, sensory modality, and a wide variety of other traits differ between the sexes in their optimal value. Characteristics that are selectively favored in one sex but selected against in the other will be referred to as "sexually-antagonistic" traits. Consider the evolution of a sexually dimorphic trait from a monomorphic state. For example, Geist (1971) used paleontological evidence and taxonomy to argue that the sexually dimorphic horns of bighorn sheep evolved from a sexually monomorphic ancestor. Because an exact record of this evolutionary change is unavailable, I will arbitrarily assume for the purpose of illustration that the size of female horns remained unchanged while the size of male horns increased. The evolution of sexual dimorphism in horn size could have proceeded in at least two ways: 1) The increase in frequency of genes that enhanced horn size in males but not in females, and 2) The increase in frequency of genes that enhanced horn size in both sexes followed by the evolution of modifier genes that restricted the expression of increased horn size to males. The first way will be referred to as the "pleiotropy-mechanism." It requires genetic variability that simultaneously produces the sexually-antagonistic trait (increased horn size) and is sex-limited in its expression. The second way will be referred to as the "modifermechanism." It requires genetic variability for both the sexually-antagonistic trait (increased horn size) and sex-limited expression of this trait. A similar classification was previously proposed by Turner (1978) for the evolution of sexlimited traits in butterflies. Most mutations that have been studied carefully in the laboratory have not been found to be completely sex-limited in their expression. Thus it seems reasonable to assume that most of the genetic variability available for the evolution of sexual dimorphism would be initially expressed in both sexes. This assumption may be unreasonable when considering the enhancement of an established sexually dimorphic trait since developmental canalization (Waddington, 1962) may facilitate sex-limited gene expression. However, during the initial evolution of sexual dimorphism from a monomorphic state, a feasible sequence of events would be the "modifier-mechanism" described above. In the following model I will suggest how the sex chromosomes can facilitate

Soap, cells and statistics – random patterns in two dimensions

Abstract: Random two-dimensional patterns crop up in a wide variety of scientific contexts. What do they have in common? How can they be classified or analysed? These questions are underlined, and partly answered, by a survey of such patterns, paying particular attention to soap cell networks, metallurgical grain structures and the Giant's Causeway.

Molecular Biology of Osmoregulation

Abstract: The drought of 1983 resulted in some 10 billion dollars in agricultural losses and has focused attention on the vulnerability of our major crops to this devastating form of environmental stress. This article is concerned with the molecular biology of a new class of genes, called osm (osmotic tolerance) genes, that protect bacteria like Escherichia coli against osmotic stress and may work in a similar manner in plants and animals. Osm genes govern the production of a class of molecules, such as betaine and proline, that protect the cell and its constituents against dehydration. These osmoprotectant molecules have been known for many years to accumulate in plants but have only recently been shown to have potent antistress activity for bacteria.

Comparative ecophysiology of C3 and C4 plants

Abstract: . In this review we relate the physiological significance of C4 photosynthesis to plant performance in nature. We begin with an examination of the physiological consequences of the C4 pathway on photosynthesis, then discuss the ecophysiological performance of C4 plants in contrasting environments. We then compare the performance of C3 and C4 plants when they occur together in similar habitats, and finally discuss the distribution of C4 photosynthesis with respect to the physical environment, phylogeny, and life form.

Age related decline in proprioception

Abstract: Joint-position sense of the knee was measured in 29 subjects with normal knee joints ranging in age from 20 to 82 years. Joint-position sense was determined by two common techniques that measure the threshold to detection of motion and the ability to reproduce passive knee positioning. Joint-position sense was found to deteriorate with increasing age as measured by both tests, with a correlation coefficient that was significant at the p less than 0.001 level for each test. The two tests were found to correlate at the p less than 0.025 level, indicating that the same biologic parameter was being measured by both tests. Deterioration of proprioception, or joint-position sense, as measured may be a sensitive indicator of subclinical degenerative joint disease of the knee, as well as a means of quantitating proprioception in suspected neuropathic joints.

Nitrogen transformations and loss in flooded soils and sediments

Abstract: This paper presents a critical review on nitrogen (N) transformations functioning in flooded soils and sediments, and their role in N loss from the system. Nitrogen transformations reviewed include (1) ammonification (organic ? ammonium N) (2) nitrification (ammonium ? nitrate), (3) ammonia volatilization (ammonium N ? NH3), (4) denitrification (nitrate ? gaseous products N2O and N2). Transport processes reviewed were ammonium and nitrate diffusion. Inorganic N in flooded soils and sediments and waters is converted to gaseous forms by two processes, i.e., (1) nitrification‐denitrification; and (2) NH3 volatilization. The former process seems to be more predominantly involved in the ammonium N loss from the sediments, whereas the latter process occurs under specialized conditions, mainly in the overlying waters. The processes involved in converting organic N to gaseous end products include ammonification of organic N to ammonium N, upward diffusion of ammonium N into the aerobic soil layer, oxidation of am...

Molecular evolution over the mutational landscape

Abstract: A common observation in phylogenetic comparisons of the amino acid sequences of a particular protein is that the rate of evolution of the protein is nearly constant over extended periods of time. This constancy was first noticed by Zuckerkandl and Pauling (1965) and prompted them to call the amino acid substitution process a "molecular evolutionary clock." Since 1965 a great deal of additional data has supported the basic idea of the molecular clock although detailed studies have shown the clock to be a rather erratic one. The detailed studies have been of two different sorts: broadly based statistical studies of a number of proteins over relatively few species (e.g., Langley and Fitch, 1974), or very detailed looks at a particular protein over a large number of species (e.g., Baba et al., 1981). In general, these studies support the crucial observation made by Ohta and Kimura (1971) that the variance in the evolutionary rate is higher than would be expected if the substitution process were a Poisson process. A major goal of theoretical population genetics must be to account for this elevated variance. There are formidable statistical problems associated with the estimation of the variance in the rate of substitutions of amino acids. The problem is compounted by the fact that the variance is only interesting when compared to the mean as in the ratio K = Var(N,)/E(N1), where N, is the number of substitutions in a period of time, t. Obtaining accurate estimates of ratios is difficult in the best of statistical settings. For protein evolution data where the number of substitutions on each leg must themselves be inferred by a procedure such as Fitch and Margoliash's (1967) maximum parsimony procedure, the sampling variance of the final estimate must be relatively high (and itself almost impossible to estimate). Nonetheless, a number of studies have all pointed to a value of K of around 2 to 3. Ohta and Kimura (1971) were the first to estimate K and did so using the available data on hemoglobins and cytochrome c. They reported a value in the range 1.5 to 2.5. The studies by Langley and Fitch (1974) improved on this in the sense of using more data although their procedure was not expressly designed to estimate K. They concluded K was around 2.5. Later, Gillespie and Langley (1979) re-examined the statistical procedure used in the earlier studies and through a very crude argument also claimed that K was around 2.5. In studies that examine only a single protein over a large number of species the aim has been not so much to estimate K as to look more directly for periods of relatively fast or slow evolution in the protein. These studies, such as those by Goodman et al. (1982) generally present fairly convincing evidence of variations in the rates of evolution although Kimura (1981) has called into question the ability of these studies to uncover variation in the rates of evolution. These observations are critical for an understanding of the forces responsible for amino acid substitutions. One of the most appealing theories for the evolution of proteins is the neutral allele theory first proposed by Kimura (1968a, 1968b) and King and Jukes (1969). This theory predicts that the rate of substitutions will be constant although it does not imply that K will equal one as has been commonly assumed. Rather it was shown by Gillespie and Langley (1979) that K will always be greater than one under the neutral allele theory and will actually increase with

Tripartite structure of the Brassica campestris mitochondrial genome

Abstract: Physical mapping studies indicate a novel sequence arrangement, consisting of three circular chromosomes, for the mitochondrial genome of Brassica campestris (Chinese cabbage, turnip). A master chromosome, 218 kilobases (kb) long, contains the entire sequence complexity of the mitochondrial genome, including two copies of an ∼2-kb element present as direct repeats separated by 135 and 83kb. The two smaller circles are 135 and 83kb in size, contain one copy each of the 2-kb repeat element, and are postulated to interconvert with the master chromosome via a co-integration-resolution pathway mediated by reciprocal recombination within the 2-kb repeat.

Heat and Mass Transfer in Porous Media

Abstract: In this article we use the method of volume averaging to derive the governing equations for heat and mass transport in a rigid porous medium. These equations involve spatial derivations of the temperature and concentration and suitable representations of these deviations are required in order to obtain a closure. In our approach, the closure is based on the governing differential equations for the spatial deviations and it allows for the direct determination of the transport coefficients that appear in the volume-averaged equations. These calculated coefficients are compared with experimental measurements for the following cases: diffusion and reaction in porous media, heat conduction in two-phase systems, dispersion of a non-adsorbing solute and thermal dispersion in a packed bed. For conductive and diffusive transport, excellent agreement between theory and experiment is found using the spatially periodic model of a porous medium. The comparison between theory and experiment for convective processes indicates that the details of the structure of a real porous medium are important and not adequately described by the spatially periodic models used in this study.

Mixing of siliciclastic and carbonate sediments in shallow shelf environments

Abstract: The inhibiting effect that siliciclastic material has on carbonate-secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form. However, many modern and ancient shelf deposits contain a spectrum of sediments that are of “mixed” composition. The processes responsible for this mixing can be grouped into four categories: (1) punctuated mixing, where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another; (2) facies mixing, where sediments are mixed along the diffuse boundaries between contrasting facies; (3) in situ mixing, where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates; and (4) source mixing, where admixtures are formed by the uplift and erosion of nearby carbonate source terranes. The allochemical constituents of mixed sediments are both coralgal and foram-mollusc in composition. The foram-mollusc assemblage is the most common because of the effects of increased turbidity, unstable substrates, and the clogging of filter-feeding mechanisms associated with a siliciclastic influx.

Formation of cyanide from carbon 1 of 1-aminocyclopropane-1-carboxylic acid during its conversion to ethylene.

Abstract: It has been shown that 1-aminocyclopropane-1-carboxylic acid (ACC) is the immediate precursor of ethylene, which is derived from C-2 and C-3 of ACC. When [1-14C]ACC was administered to etiolated mungbean (Vigna radiata) hypocotyls, ≈16% of the ACC was converted to ethylene and about 10% of the radioactivity was converted to [14C]asparagine in 7 hr. In etiolated epicotyls of common vetch (Vicia sativa), after 7 hr about 14% of the ACC was converted to ethylene and 16% of the radioactivity was converted to β-cyanoalanine plus γ-glutamyl-β-cyanoalanine. Itis known that in most plants cyanide is metabolized to asparagine via the intermediate β-cyanoalanine, whereas in a fewplants such as V. sativa, β-cyanoalanine is converted to the conjugate γ-glutamyl-β-cyanoalanine. We confirmed that [14C]cyanide was metabolized into [14C]asparagine in mungbean and into [14C]cyanoalanine plus its conjugate in V. sativa. Moreover, after feeding plant tissue with [1-14C]ACC, [14C]asparagine isolated from mungbean and β-[14C]cyanoalanine from V. sativa were labeled in the C-4 position, as would be expected if these two compounds were derived from [14C]cyanide. When the conversion of ACC to ethylene in V. sativa tissue was inhibited by high temperature (41°C), the conversion of [1-14C]ACC to β-[14C]cyanoalanine and γ-glutamyl-β-[14C]cyanoalanine was similarly inhibited. When [carboxyl-14C]ACC was administered to mungbean and V. sativa, 14CO2 was recovered in an amount equivalent to the amount of ethylene produced. These data indicate that in the conversion of ACC to ethylene the carboxyl group yields CO2, and C-1 is released as HCN.

Simian AIDS: isolation of a type D retrovirus and transmission of the disease

Abstract: A type D retrovirus related to but distinct from Mason-Pfizer monkey virus was isolated in vitro from the blood of two rhesus monkeys (Macaca mulatta) with simian acquired immunodeficiency syndrome (SAIDS). Three juvenile rhesus monkeys that were injected intravenously with tissue culture fluids containing this virus developed SAIDS after 2 to 4 weeks.

Isotope composition of sulphate in acid mine drainage as measure of bacterial oxidation

Abstract: The formation of acid waters by oxidation of pyrite-bearing ore deposits, mine tailing piles, and coal measures is a complex biogeochemical process and is a serious environmental problem. We have studied the oxygen and sulphur isotope geochemistry of sulphides, sulphur, sulphate and water in the field and in experiments to identify sources of oxygen and reaction mechanisms of sulphate formation. Here we report that the oxygen isotope composition of sulphate in acid mine drainage shows a large variation due to differing proportions of atmospheric- and water-derived oxygen from both chemical and bacterially-mediated oxidation. 18O-enrichment of sulphate results from pyrite oxidation facilitated by Thiobacillus ferrooxidans in aerated environments. Oxygen isotope analysis may therefore be useful in monitoring the effectiveness of abatement programmes designed to inhibit bacterial oxidation. Sulphur isotopes show no significant fractionation between pyrite and sulphate, indicating the quantitative insignificance of intermediate oxidation states of sulphur under acid conditions.

California irrigation management information system

Abstract: Knowing when and how much to irrigate is an important factor in a grower 's overall farm management . The California Irrigation Management Informat ion System (CIMIS) is a system, in the developmental stages, that will be capable of providing evapotranspirat ion information on a timely basis to all regions of the state. This information can then be used in microcomputers , p rogrammable calculators, etc., to help California growers determine their irrigation schedule. Upon completion of CIMIS research by the University of California, it is anticipated that the State Department of Water Resources (funding agency for CIMIS) will implement CIMIS on a statewide basis. Water losses from an irrigated field can be separated into three distinct categories: 1. Evapotranspirat ion 2. Deep percolation 3. Runoff Deep percolation and runoff can be estimated and accounted for by considering irrigation efficiency, which also accounts for distribution uniformity. If an estimate of irrigation efficiency is known, then accumulated evapotranspirat ion can be used to determine when and how much to irrigate. This method of irrigation scheduling is called the \"Water Budget\" or \" C h e c k b o o k \" approach. Researchers on the CIMIS project are mainly concerned with obtaining weather information to calculate accurate real-time (current) estimates of evapotranspirat ion and with disseminating that information to growers rapidly enough to be of value in their irrigation management. Consequently a network of automated, electronic weather stations has been installed around the state to allow for daily transfer of weather data to a central data acquisition computer once each day. Figure 1 shows a schematic diagram of the network design for the research phase of CIMIS. Data are transferred via telephone from the weather stations to a data acquisition computer and then to a central computer where a reference value of evapotranspirat ion is calculated and the data are stored in a data base for later analysis. During the research phase of CIMIS, reference evapotranspirat ion is disseminated to field researchers in County Extension offices and to grower cooperators via a network of user terminals.

Physiological Responses to Salinity in Selected Lines of Wheat

Abstract: Two selections of bread wheat, Triticum aestivum L., differing in their relative salt resistance, were grown in salinized solution culture, and relative growth rates, osmotic adjustment, ion accumulation, and photosynthesis were monitored to study the responses of the plants to salinity. Differences in water relations were minimal and were only apparent for 3 days following salinization. The lines differed substantially in their relative growth rates and photosynthetic responses for several weeks following salinization, despite full osmotic adjustment. Concentrations of major cations and Cl − in the plant organs were remarkably similar in both lines, indicative of minimal differences in gross ion absorption and translocation. The authors interpret these results to suggest that the major difference between these two lines of wheat was their response to specific ion effects, at the level of the organ, tissue, cell, and subcellular entities. Superior compartmentation of toxic ions by the more salt-tolerant line, presumably in the vacuole, might have enabled it to maintain its cytoplasmic metabolic apparatus in a stabler and more nearly normal state than the sensitive line was able to do; a measure of true cytoplasmic toleration of salt may also be a factor.

Disruptive selection on habitat preference and the evolution of reproductive isolation: a simulation study.

Abstract: There has been a wide diversity of theoretical work on the genetic mechanisms that promote speciation under sympatric (non-allopatric) conditions (see Thoday and Gibson, 1970; Bush, 1975; Endler, 1977; White, 1978; Futuyma and Mayer, 1980; Templeton, 1981 for review). The conclusion from this work is that sympatric speciation is genetically possible but it is not clear whether or not it has played a major role in the generation of species under natural conditions. Assessing the evolutionary importance of sympatric speciation awaits the identification of those environmental circumstances that are most likely to promote the process. Here I suggest that environmental conditions which produce disruptive selection on habitat preference represent a special case in which sympatric speciation is particularly likely to occur. By habitat preference I mean any tendency of an organism to become non-randomly associated with a particular spatial and/ or temporal part of an environment.

Anatomical and physiological substrates of event-related potentials. Two case studies.

Abstract: Because an excellent tutorial introduction to the anatomical and physiological substrates of event-related potentials (ERPs) is available (Goff et al.. 1978), our objective in this chapter is not a general tutorial review. Rather, we intend to consider in detail the anatomical and physiological substrates of two classes or families of ERPs that have been the subject of intense investigation in recent years: (a) the auditory “ N I P ~ complex” and (b) P300 and related “endogenous” potentials. Our hope is that such a “case study” approach to ERP substrates will not only provide the reader with a thorough review of recent research findings, but will also provide a critical analysis of both the theoretical and empirical foundations of inferences about the neural substrates of ERPs. Our consideration of each family of potentials will consist of (a) a brief descriptive introduction, including the identifying characteristics of the potentials under consideration and the experimental conditions under which they can be obtained; (b) a detailed consideration of the different types of evidence that have been used to formulate and