Search Results - (Author, Cooperation:D. J. Crawford)

2011-03-12

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

Adenosine Triphosphate/metabolism ; Fluorescent Dyes ; Introns ; Kinetics ; Microscopy, Fluorescence ; Protein Binding ; RNA Precursors/*metabolism ; *RNA Splicing ; RNA, Fungal/*metabolism ; Ribonucleoprotein, U1 Small Nuclear/metabolism ; Ribonucleoprotein, U2 Small Nuclear/metabolism ; Ribonucleoprotein, U4-U6 Small Nuclear/metabolism ; Ribonucleoprotein, U5 Small Nuclear/metabolism ; Ribonucleoproteins, Small Nuclear/*metabolism ; Saccharomyces cerevisiae/genetics/*metabolism/ultrastructure ; Saccharomyces cerevisiae Proteins/*metabolism ; Spliceosomes/*metabolism

1615-6110

Angiosperms ; Compositae ; Eupatorium ; Chromosomal distance ; chromosomal identity ; karyotype analysis ; statistics phenetics

Springer Online Journal Archives 1860-2000

Biology

Abstract Somatic metaphase karyotypes were analyzed for 22 diploid species ofEupatorium. The karyotypic comparisons were made using two indices: minimal chromosomal distance (MCD), measuring overall dissimilarities, and chromosomal identity (CI), measuring number of morphologically identical chromosomes between species. The resulting phenograms from these indices are largely compatible. The 22 species cluster into four groups in the phenogram using MCD, and the grouping corresponds well with morphology or geographic distribution into the three N. American groupsEutrochium, Uncasia, Traganthes, and the E. Asian group. These results suggest that karyotypes in perennialEupatorium have been considerably conservative and changed not through large chromosomal mutations but through small chromosomal mutations gradually fixed.

Electronic Resource

1615-6110

Angiosperms ; Campanulaceae ; Wahlenbergia ; Breeding system ; pollination ; pollen collecting hairs ; autogamy ; self-compatibility ; nectar ; island biology ; Juan Fernández Islands

Springer Online Journal Archives 1860-2000

Biology

Abstract The reproductive biology ofW. berteroi, W. fernandeziana, and a putative hybrid betweenW. fernandeziana andW. grahamiae, endemic to Robinson Crusoe Island (Juan Fernández archipelago, Chile) was studied. Flowers are hermaphroditic, protandrous, offer nectar, and exhibit secondary pollen presentation involving pollen collecting hairs on the style. These features imply allogamy and biotic pollination. However, male and female phases overlap and no effective pollinators were observed. Experimental data indicate these taxa are self-compatible and facultatively autogamous, a conclusion also suggested by the pollen/ovule ratios. Selfing is accomplished when the stigmatic lobes reflex and touch the style, except forW. berteroi where they do not reflex completely. Autogamy is accomplished in the latter when pollen grains deposited on the inner surface of the corolla throat by the “pollen brush” are gathered by stigmatic lobes when shaken by wind. The degree of autogamy, and perhaps self-compatibility, seems to be inconstant, as implied by the variable natural seed set (overall range 21–188 seeds per fruit). A mixed mating system — primarily outcrossing/entomophilous, but also autogamous — must have been present in the continental ancestors of these taxa. Autogamy promoting self-fertilization is important now — on an island with scarce pollinators — and in the past — when the first founders arrived.

Electronic Resource

1615-6110

Lemnaceae ; Lemna ; Spirodela ; Wolffiella ; Wolffia ; Flavonoids ; morphology ; phylogenetic analysis

Springer Online Journal Archives 1860-2000

Biology

Abstract Diminutive plants of the duckweed family have been difficult to study systematically because of reduction and character state losses that have accompanied their adaptation to aquatic habitats. Phylogenetic analysis of flavonoid and anatomical-morphological data indicate that evolution in the family has proceeded in a linear manner from complex ancestors to reduced species of subfam.Wolffioideae. The high probability of convergence for character reduction and loss, however, renders this conclusion tentative. Cladograms from combined data require only a slight increase in length to resolve all four genera as monophyletic. These studies indicate the need for more suitable data to evaluate hypotheses of duckweed relationships.

Electronic Resource

1573-5109

Argyranthemum ; Chrysanthemum ; germplasm ; Heteranthemis ; island conservation ; island endemics ; Ismelia ; Macaronesia ; ornamental crops ; plant genetic resources

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Abstract Germplasm from one or more populations of each taxon of the Macaronesian endemic genus Argyranthemum Sch. Bip. (Asteraceae: Anthemideae) was collected in the Canary Islands, Madeira, the Selvagens Islands and the Desertas Islands. A total of 253 germplasm samples was collected and they are conserved ex situ at the seed bank of Centro de Investigación y Tecnología Agraria de Canarias (Tenerife, Canary Islands, Spain). Duplicates are held at the germplasm bank of Escuela Técnica Superior de Ingenieros Agrónomos (Madrid, Spain). A preliminary account of the ecogeography of the genus based on field observation is provided. In situ conservation strategies are discussed, particularly with regard to the occurrence of hybridization within Argyranthemum.

Electronic Resource

0021-8995

Chemistry ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Physics

A stress relaxation technique was used to study the kinetics of the photo-oxidation of plasticized poly(vinyl chloride) film. The effects of ultraviolet irradiation were characterized by the slope of a difference line between the stress relaxation curve of an irradiated test sample and that of a nonirradiated control. An activation energy of 12 kcal/-mole was obtained for the rate-controlling reaction, which was postulated to be hydrogen abstraction from the substrate by peroxy radicals. The rate of relaxation was dependent on the radiation energy, being greater at lower energies. It was also independent of oxygen pressure at “high” pressures and dependent at “low” pressure. The nature of the plasticizer and the presence of stabilizer and ultraviolet absorbers all affected the relaxation behavior.

8 Ill.

Electronic Resource