Multiple origins of self-fertilization in tristylous Eichhornia paniculata (Pontederiaceae): Inferences from style morph and isozyme variation

Populations of Eichhornia paniculata (Pontederiaceae) exhibit a wide range of mating systems, from predominant outcrossing to high levels of self-fertilization. The origin of self-fertilization in this tristylous species is associated with the loss of style-length morphs from populations and the spread of self-pollinating, floral variants. We examined geographic variation in style morph and allozyme frequencies to determine whether the loss of style morphs and transition to selfing could have multiple origins in E. paniculata. Surveys of floral variation in 167 populations from six states in northeastern Brazil revealed that at least one style morph was absent from 29.3%. Non-trimorphic populations occurred in all states and ranged in frequency from 9% in Ceará to 68% in Alagoas. Selfing variants occurred in 8.5% and 55% of trimorphic and non-trimorphic populations, respectively, and were distributed among five of six states with primary concentrations in Alagoas and Pernambuco. A comparison of electrophoretic variation at 24 isozyme loci in 28 trimorphic, 13 dimorphic and 3 monomorphic populations indicated that non-trimorphic populations contained 84% of the allelic variation present in trimorphic populations and were markedly differentiated from one another. Analyses of genetic distance and the distribution of rare alleles indicated that non-trimorphic populations were often more similar to neighbouring trimorphic populations than to one another. Populations with selfing variants occurred at low frequency in three genetically distinct parts of the range. These results, in combination with genetic and morphological evidence suggest that style morphs are lost repeatedly from populations of E. paniculata and that selfing variants may have originated on at least three separate occasions in northeastern Brazil.     

COMPARISON OF PLANT DNA CONTENTS DETERMINED BY FEULGEN MICROSPECTROPHOTOMETRY AND LASER FLOW CYTOMETRY

An improved procedure is reported for determining DNA amounts of plant nuclei. Nuclei stained with propidium iodide, isolated from chopped plant leaves, were passed through an Ortho Cytofluorograph with a Lexel model 95 argon laser (514 nm) and the fluorescence measured, integrated, and recorded using an Ortho 2140 Data Acquisition computer. All nuclear samples were mixed with nuclei of Sultan barley (2C DNA content = 11.12 pg [picogram]) as an internal standard. DNA contents of ten plant species, ranging from 2C = 1.7 pg to 36.1 pg measured by flow cytometry, correlated strongly (r = 0.99, slope = + 1.00) with DNA contents determined from Feulgen-stained nuclei of the same species using microspectrophotometry. The flow cytometric procedures were sufficiently sensitive to detect differences in DNA content between inbred lines of corn and their F1 hybrids. Our results obtained with improved procedures, specifically using propidium iodide as a fluorochrome and plant nuclei instead of chicken erythrocytes as an internal standard, demonstrate that laser flow cytometry can be a precise, rapid, and reliable method for determining nuclear DNA content of plants.     

Mutations of aspartate 103 in the Hm2 receptor and alterations in receptor binding properties of muscarinic agonists

Aspartate 103 (D103) in the third transmembrane domain of the Hm2 receptor was mutated to glutamate (D103E), asparagine (D103N), or alanine (D103A). As measured by [3H]-NMS, no significant binding was observed in D103A, while a 2-fold decrease in ligand affinity was seen in D103E and a 32-fold decrease in affinity was found in the D103N mutant. Examination of reference agonists showed greater loss of affinity in D103N than in D103E with the rank order of change being: L-607,207>carbachol>arecoline>pilocarpine>oxotremorine>McN-A-343. Of the novel 1-azabicyclo[2.2.1]-heptan-3-one oxime agonists examined, arylacetylene oximes showed little alteration in binding in either the D103E or D103N mutants, while the geometric isomers of several bicyclic aryl-ene-yne oximes showed significant changes in affinity, especially in the D103N mutant. Thus, overall size of the agonist and/or spatial orientation of the molecule within the binding pocket contribute to changes measured in binding.     

Estrogen Enhances Performance of Female Rats during Acquisition of a Radial Arm Maze

Estrogen can influence the expression of behaviors not associated directly with reproduction, including learning and memory. However, the effects of estrogen on learning and memory in mammals are complex, dependent on a variety of factors. The radial arm maze is a traditional experimental task that takes advantage of the natural foraging strategy of rats and provides an appropriate measure for studying the effects of estrogen on working memory in this species. In the experiments reported here, ovariectomized rats were implanted subcutaneously with 5-mm Silastic capsules containing 25% estradiol diluted with cholesterol. Control females received 5-mm Silastic capsules containing 100% cholesterol. Results of three separate experiments demonstrated that estradiol administered by Silastic implants for 30 days prior to eight-arm radial maze training, during the 24 days of maze training, or both significantly improved working memory performance compared to females treated with cholesterol alone, as indicated by improved arm choice accuracy over trials. The positive effect of estradiol exposure prior to training suggests that estrogen may induce neuronal changes that persist beyond the period of exposure with functional consequences for behavior.     

Elemental signatures of human diets from the Georgia Bight

Multielement analysis was performed on bone samples extracted from the femora of 39 adults from three mortuary sites (Johns Mound, Santa Catalina de Guale, and Santa Catalina de Guale de Santa Meria) and time periods (late preagricultural, early contact, and late contact) in the Georgia Bight. This study was used to investigate whether elemental analysis would support or contradict other lines of data regarding diets and dietary change previously generated for the region. The data are in agreement with an earlier interpretation, based on stable isotopes, that dietary maize increases through time but fails to support the idea that marine resources decreased in importance. Rather, it appears that the wild plant food component of the diets decreases as maize increases in importance; throughout the sequence, marine resources comprise a significant portion of the diets. © 1995 Wiley-Liss, Inc.     

Velvetleaf,Abutilon theophrasti (malvaceae), history and economic impact in the United States

Velvetleaf,Abutilon theophrasti, a native of China, was originally introduced into the New World before 1750 as a potential fiber crop for the American colonies. Initial introductions may have come from England because of similar interests in the development of fiber crops. Commercial fiber production from velvetleaf was attempted by U.S. farmers for more than a century. The latest known attempts were made in the latter part of the 19th century in Illinois and New York. Velvetleaf never competed well with hemp, at least partly due to a lack of proper machinery for fiber processing. These early experimental plantings were apparently the source of velvetleaf as a weed in row crops. One velvetleaf plant is capable of producing as many as 8,000 seeds, and viability may extend beyond 50 yr. The plant is well adapted to our upper Midwest where maize (Zea mays) and soybeans (Glycine max) are the major row crops. The reservoir of velvetleaf seed in the soil is increasing. The current annual economic loss due to velvetleaf in maize and soybeans is estimated to be approximately $343 million per year.