Population genetics of Cordia alliodora (Boraginaceae), a neotropical tree. 1. Genetic variation in natural populations

We provide an estimate of genetic differentiation within and among 11 populations of Cordia alliodora, an economically important timber tree Cordia alliodora is a widespread species that is distributed throughout Central and South America. Our survey of isozyme variation was conducted on material gathered for international provenance trials over approximately 1,000 km in Central America. Results from provenance trials indicate that there are significant differences between Atlantic and Pacific coast provenances for quantitative characters. Genetic data support some of these findings. Populations of C. alliodora show significant differences in allele frequency at various loci. Significant differences in multilocus allele frequencies occur at 13 of the 55 possible combinations. Eight of these 13 populations are situated on opposite coasts. This physical separation corresponds well with the results of provenance trials that indicate differentiation among the Atlantic and Pacific populations in quantitative morphological traits. We also found a significant negative correlation between levels of heterozygosity and the amount of rainfall, indicating that populations from the drier zone are genetically more heterogenous than populations from the wet zone. Our study indicates that in situ and ex situ conservation should accord high priority to the dry zone populations; furthermore, conservation of this widespread species would require preservation of multiple populations.     

Population genetics of Cordia alliodora (Boraginaceae), a neotropical tree. 2. Mating system

A multilocus mixed mating model was used to evaluate the mating system of a natural population of Cordia alliodora (Boraginaceae), a neotropical tree. The population was highly outcrossed (t_m = 0.966 ± 0.027), in agreement with results from controlled crosses. Departures from the mixed mating model were evident, suggesting some nonrandom, correlated mating. Pollen pool heterogeneity and variation in estimates of individual outcrossing rates indicated that the population may be genetically substructured. Individual outcrossing rates obtained for the samples taken from within different parts of the same tree indicated reduced levels of outcrossing due to limited sampling of the pollen pool. The incompatibility mechanism in C. alliodora, combined with variation in flowering and stand density, appears to lead to both temporal and spatial substructuring of the population.     

Postcranial paleoneurology of the Diapsida

The relationships between the size of the spinal cord and the size of the neural canal, and between gross spinal cord anatomy and locomotor style, were documented in a wide range of living diapsids. Observed relationships were used to make predictions about spinal cord anatomy and about limb use and position in related fossil taxa. In particular, the data suggest that the brachial plexus, and therefore the cervical/dorsal vertebral transition, of the theropod dinosaurs studied was located considerably posterior to its presently accepted location, and that the forelimbs of the giant carnosaurs Tyrannosaurus rex and Carnotaurus sastrei were of biologically insignificant use. Neural canal measurements support previous interpretations of locomotor style in extinct crocodilians, and can be used to predict limb placement in plesiosaurs.     

Tomato alcohol dehydrogenase: Purification and substrate specificity

Alcohol dehydrogenase of tomato (Lycopersicon esculentum) has been purified to homogeneity, using affinity chromatography on Cibacron F3GA-agarose. The enzyme is a dimer, M_r 90,000–100,000. The coenzyme is NAD⁺; no NADP⁺-dependent activity was detected even in crude extracts. Among saturated substrates, ethanol and acetaldehyde show the lowest apparent K_m values (2.67 and 0.174 mm, respectively) and highest V values, supporting a primary role in acetaldehyde metabolism, with action also on “flavor aldehydes”; 2-unsaturated alcohols show still lower K_m values, probably due to a more favorable K_eq. This enzyme and other plant alcohol dehydrogenases form a definite class, intermediate in specificity between liver and yeast alcohol dehydrogenases: they differ from the former in being essentially inactive on secondary and aromatic substrates, from the latter in showing only a mild decrease in V with increasing chain length of alkyl substrates, and from both in showing the lowest K_m as well as highest V on ethanol and acetaldehyde. The tomato enzyme differs from other reported plant enzymes in showing substantial activity on geraniol. Kinetic studies are in agreement with an ordered sequential mechanism. The enzyme is inhibited slowly by iodoacetamide, and reversibly by acetamide and zinc-chelating compounds.     

A Molecular Marker-Based Linkage Map of Phaseolus Vulgaris L

A seed and flower color marker (P), nine seed protein, nine isozyme and 224 restriction fragment length polymorphism marker loci were used to construct a linkage map of the common bean, Phaseolus vulgaris L. (n = 11). The mapping population consisted of a backcross progeny between the Mesoamerican breeding line 'XR-235-1-1' and the Andean cultivar 'Calima'; the former was used as the recurrent parent. A bean PstI genomic library enriched for single copy sequences (95%) was the source of DNA probes. Sixty percent of the probes tested detected polymorphisms between the parental genotypes with at least one of the four restriction enzymes used here (DraI, EcoRI, EcoRV and HindIII). The computer software Mapmaker was used to determine the linkage relationships and linear order of segregating markers. These markers assorted into 11 linkage groups covering 960 cM of the bean genome. Partial linkage data were used to estimate the total length of the genome at 1200 cM. This estimate and that for the physical size of the genome yield an average ratio of 530 kb/cM. The relatively small size of the genome makes this crop species a good candidate for the isolation of genes via chromosome walking techniques.     

The lysis of Gram-negative Alcaligenes eutrophus by enzymes from Cytophaga

Summary The use of Cytophaga lysing enzymes was investigated for the liberation of poly--hydroxybutyrate (PHB) granules from the Gram-negative bacterium Alcaligenes eutrophus. Complete cell lysis was approached within a 60 minute period. Contrary to previous findings for the lysis of Gram-negative bacteria, prior removal of the outer membrane was not essential for enzymic lysis. The destabilisation of the outer membrane by the removal of divalent cations resulted in no significant improvement in the disruption process.     

Energy transfer in complexes of E. coli single-stranded DNA-binding protein with single-stranded poly-(2-thiouridylic acid)

The complexes of point-mutated Escherichia coli single-stranded DNA-binding protein (Eco SSB) with poly-(2-thiouridylic acid) (poly S2U) have been studied by optical detection of magnetic resonance spectroscopy (ODMR). Previous work has determined that two of four tryptophan (Trp) residues in Eco SSB undergo stacking interactions with nucleic acid bases. Selective photoexcitation of S2U bases was performed and subsequent triplet----triplet energy transfer from S2U to nearby Trp residues in the protein took place. The zero-field splitting (ZFS) parameters and sublevel kinetics were determined for each Trp residue sensitized by S2U. The sublevel lifetimes of the two sensitized residues are similar to those of normal Trp. The ZFS parameters, on the other hand, show a dramatic reduction relative to those of the uncomplexed protein, implying a more polarizable environment for the sensitized Trp residues and/or charge transfer interactions with the S2U bases.     

Carbon Flow in Mercury Biomethylation by Desulfovibrio desulfuricans

Radiocarbon incorporation from pyruvate and serine into monomethylmercury by Desulfovibrio desulfuricans was consistent with the proposal that the methyl group originates from C-3 of serine. Immunodiagnostic assays measured 4 to 35 μg of tetrahydrofolate and 58 to 161 ng of cobalamin or a closely related cobalt porphyrin per g of cell protein in D. desulfuricans. The light-reversible inhibition of mercury methylation by propyl iodide in D. desulfuricans indicates methyl transfer by a cobalt porphyrin.     

Collagenase Production by Nematode-Trapping Fungi

A number of species of nematode-trapping fungi, which capture and digest nematodes having keratin and collagen in their cuticles, were tested for the ability to produce extracellular collagenase and keratinase. Collagenase, which is active on ichthyocol, earthworm collagen, and procollagen from chicken embryo fibroblasts, was found in the growth medium of all tested species; keratinase was not found. The enzyme from Arthrobotrys amerospora was concentrated by precipitation with (NH₄)₂SO₄ and further purified by adsorption on collagen at 0°C. The collagenase was active over a pH range of 2.5 to 10.0. It was not inactivated by dialysis against ethylenediaminetetraacetic acid for 48 h or by the sulfhydryl group inhibitors N-ethylmaleimide and p-chloromercuribenzoate. The production of collagenase may aid the fungus to penetrate the cuticle of its prey.     

Subunit structure and kinetic properties of L-beta-hydroxy acid dehydrogenase of Drosophila.

L-beta-hydroxyacid dehydrogeanse (L-gulonate:NAD+ 3-oxidoreductase, EC 1.1.1.45) of Drosophila is made up of two non-identical subunits with molecular weights of 40 000 and 23 500. Michaelis constants calculated at saturating concentrations of the other substrate were 0.13 mM for NAD+, 0.85 mM for L-gulonate, 14.8 mM for L-beta-hydroxybutyrate; dissociation constants (Kia) were 2.8 mM for L-gulonate, 22 mM for L-beta-hydroxybutyrate. The maximum velocity with L-gulonate as substrate was ten-fold greater than with beta-hydroxybutyrate. As product inhibitors, both NADH and acetoacetate are competitive vs. both substrates, suggesting a rapid equilibrium random mechanism.