Allozyme diversity and introgression in the Galapagos Islands endemic Gossypium darwinii and its relationship to continental G. barbadense

Gossypium darwiniiWatt is a tetraploid cotton endemic to the Galapagos Islands. Opinion has been divided as to whether or not it deserves recognition at the specific rank, with some considering it a variety of its presumed progenitor, the widely distributed South American species G. barbadense L. A previous hypothesis states that much of the perceived intergradation between the two taxa arose as a consequence of introgression from G. barbadense following its introduction to the archipelago during the past several hundred years. We performed allozyme analysis on 58 accessions of G. darwinii from six islands, using 17 enzymes collectively encoded by 59 loci. Levels of variation were high for an island endemic, with a mean number of alleles per locus of 1.34 and an average panmictic heterozygosity of 0.062. Principal component analysis revealed clustering of accessions according to their island of origin, and a spatial pattern of island-clusters that approximates geographical relationships among islands. Genetic relationships of G. darwinii with G. barbadense and G. hirsutum L. were studied using previously generated allozyme data. Significant introgression of G. hirsutum alleles was detected; however morphological considerations support the hypothesis that much of G. darwinii's diversity stems from interspecific gene flow from G. barbadense, Evidence is presented suggesting that the occurrence of G. hirsutum alleles in G. darwinii derives not from direct hybridization, but from a mediated transfer through introduced, G. hirsutum-introgressed; G. barbadense. Gossypium darwinii and G. barbadense are nearly fixed for different alleles at four loci and each contains a large number of unique alleles. Notwithstanding the high interspecific Nei's genetic identity (0.949), the allozyme data support geographical and morphological evidence in suggesting that a specific rank for G. darwinii is warranted.     

Distribution of charged residues stabilizes individual helices in myoglobins

The effect of the distribution of charged residues on stability of alpha helices in isolated peptides and in globular proteins exemplified by myoglobins from 62 different species is discussed. A highly simplified set of rules is used to account for the interaction of charged groups with the dipole of an alpha helix. Only the position and sign of a charge with respect to the center of the helix and its ability to participate in intrahelical salt bridges determine its effect. These rules lead to a linear correlation between the helicity in variant C-peptide helices from RNAse and the extent to which the charge distribution opposes the helix dipole. Of the sample of 496 helices in the myoglobins studied, 456 exhibit arrangements of charges which oppose the effective dipole moment of the helix according to this calculation. A number of variants occur which leave the backbone moment of helices A-D unchanged, or even add to it. However no such variants exist in the sequences of helices E-H. We suggest that the E, F, G and H helices in myoglobins which show the strongest reversal of the helix dipole participate in the structures of early intermediates in folding of the chain. Stable helix structures should be more likely to occur in these isolated sequences also, and introduction of charge alterations in helices E to H should affect the initial refolding rate of mutant myoglobins.     

Primary Infection of Barley by Erysiphe graminis f. sp. hordei in Relation to Leaf-Age Dependent Resistance and the Roles of the Epidermis and Mesophyll in this Resistance

Abstract The infection frequency of both compatible and incompatible races of Erysiphe graminis f. sp. hordei decreased gradually with increasing leaf age on undetached primary barley leaves. The length of secondary hyphae of the compatible race was approximately the same regardless of age, but secondary hyphae were slightly longer on younger seedlings than on older seedlings in the case of the incompatible race. Both the infection frequency and length of secondary hyphae of the two races weredistinctly different. On composite sections produced by exchanging the epidermal layers of young and relatively mature primary leaves, the infection frequency of the compatible race was higher on the epidermis of young leaves than on the epidermis of older, leaves, regardless of which mesophyll was under the epidermis. The epidermis appears to play a major role in age-dependent resistance, while the mesophyll may act disparately by providing a factor promotive to mildew infection in addition to supporting the resistance function of the epidermis.     

Cell position and light influence C4 versus C3 patterns of photosynthetic gene expression in maize.

C4 plants such as maize partition photosynthetic activities in two morphologically distinct cell types, bundle sheath (BS) and mesophyll (M), which lie as concentric layers around veins. We show that both light and cell position relative to veins influence C4 photosynthetic gene expression. A pattern of gene expression characteristic of C3 plants [ribulose bisphosphate carboxylase (RuBPCase) and light-harvesting chlorophyll a/b binding protein in all photosynthetic cells] is observed in leaf-like organs such as husk leaves, which are sparsely vascularized. This pattern of gene expression reflects direct fixation of CO2 in the C3 photosynthetic pathway, as determined by O2 inhibition assays. Light induces a switch from C3-type to C4-type gene expression patterns in all leaves, primarily in cells that are close to a vein. We propose that light causes repression of RuBPCase expression in M cells, by a mechanism associated with the vascular system, and that this is an essential step in the induction of C4 photosynthesis.     

Ritual production of environmental history among the Arawakan Wakuénai of Venezuela

This essay examines ritual and ceremonial activities among the Arawakspeaking Wakuénai of the Venezuelan Amazon as processes of constructing power relations in changing historical and ecological conditions. Ritual evocations of the vertical dimension of power relations between mythic ancestors and human descendants adapt local populations to conditions of relatively severe stress, such as epidemics and scarcity of fish in long wet seasons. Other rituals evoke the horizontal dimension of power relations between affinally-related groups as a way of expanding the local descent group in conditions of lowered stress. These two ways of exercising ritual power link human populations to specific natural habitats and provide flexibility needed to adjust to demographic and other historical changes. Through ritual performances, the Wakuénai transform the natural environment into a cultural landscape of socialized objects and, conversely, remember the history of political relations among peoples through spirit-naming of natural species, objects, places, and geographic landmarks.     

Trichloroethylene metabolism by microorganisms that degrade aromatic compounds

Trichloroethylene (TCE) was metabolized by the natural microflora of three different environmental water samples when stimulated by the addition of either toluene or phenol. Two different strains of Pseudomonas putida that degrade toluene by a pathway containing a toluene dioxygenase also metabolized TCE. A mutant of one of these strains lacking an active toluene dioxygenase could not degrade TCE, but spontaneous revertants for toluene degradation also regained TCE-degradative ability. The results implicate toluene dioxygenase in TCE metabolism.     

SR Function in malignant hyperthermia

Malignant hyperthermia (MH) is a genetic disease in man and other animal species that predisposes to a catastrophic hypermetabolic syndrome that is triggered by certain anesthetic agents. A working hypothesis is that a defect in regulation of muscle cell calcium is the primary mechanism that initiates the MH syndrome. This paper reviews the evidence for a defect in muscle cell calcium as regulated by the sarcoplasmic reticulum membrane system. Skeletal muscle biopsied from MH man, pigs and dogs has abnormal in vitro contracture response to halothane and caffeine and these responses can be altered by lowering calcium content of the bathing solution and/or the muscle. Measurements of MH muscle cell Ca2+ by Ca2+-specific microelectrodes in vivo and fura-2 in vitro have demonstrated abnormal Ca2+ levels in resting and in caffeine-stimulated states. The SR membrane system is the primary calcium regulating organelle in skeletal muscle and a likely site for the defect in MH muscle. Two Ca2+ regulating functions of the SR have been explored in SR isolated from MH muscle. An abnormality of the 100K Ca2+-ATPase protein that functions to transport Ca2+ from myoplasm to inside the SR does not appear to be responsible for MH. The most probable defective site in the SR appears to be Ca2+ release channels and a Ca2+-induced Ca2+ release pathway has been shown to be abnormal in SR from MH human and pig muscle.     

Oxidation of γ-Hydroxybutyrate to Succinic Semialdehyde by a Mitochondrial Pyridine Nucleotide-Independent Enzyme

An antibody that inhibits over 95% of the cytosolic NADP+-dependent gamma-hydroxybutyrate (GHB) dehydrogenase activity of either rat brain or kidney was found to inhibit only approximately 50% of the conversion of [1-14C]GHB to 14CO2 by rat kidney homogenate. A similar result was obtained with sodium valproate, a potent inhibitor of GHB dehydrogenase. The mitochondrial fraction from rat brain and kidney was found to catalyze the conversion of [1-14C]GHB to 14CO2. The dialyzed mitochondrial fraction also catalyzed the oxidation of GHB to succinic semialdehyde (SSA) in a reaction that did not require added NAD+ or NADP+ and which was not inhibited by sodium valproate. The enzyme from the mitochondrial fraction which converts GHB to SSA appears to be distinct from the NADP+-dependent cytosolic oxidoreductase which catalyzes this reaction.