The Evolution of Weeds

The number of angiosperm species for which nuclear DNA amount estimates have been made has nearly trebled since the last collected lists of such values were published, and therefore, publication of a more comprehensive list is overdue. This paper lists absolute nuclear DNA amounts for 753 angiosperm species. The data were assembled primarily for reference purposes, and so the species are listed in alphabetical order, as this was felt to be more helpful to cyto- and biochemists whom, it is anticipated, will be among its major users. The paper also reviews aspects of the history, nomenclature, methods, accuracy and problems of nuclear DNA estimation in angiosperms. No attempt is made to reconsider those aspects of nuclear DNA estimation which have been fully revised previously, although the bibliography of such aspects is given. Instead, the paper is intended as a source of basic information regarding the terminology, practice and limitations of nuclear DNA estimation, especially by Feulgen microdensitometry, as currently practiced.

Nuclear DNA Amounts in Angiosperms

Advanced Statistical Methods in Biometric Research.

Three published estimates of the frequency of polyploidy in angiosperms (30 to 35 percent, 47 percent, and 70 to 80 percent) were tested by estimating the genome size of extinct woody angiosperms with the use of fossil guard cell size as a proxy for cellular DNA content. The inferred chromosome numbers of these extinct species suggest that seven to nine is the primitive haploid chromosome number of angiosperms and that most angiosperms (approximately 70 percent) have polyploidy in their history.

http://science.sciencemag.org/content/sci/264/5157/421.full.pdf

Stomatal size in fossil plants: evidence for polyploidy in majority of angiosperms

The role of polyploidy per se in the development of evolutionary novelty remains one of the outstanding questions in flowering plant evolution. Since chromosome doubling usually is associated with hybridization, the effects of doubling are difficult to uncouple from those of hybridity and recombination. Synthetic polyploids in crops typically are inferior to their diploid counterparts under conditions to which the diploids are adapted. This observation has suggested to many that chromosome doubling is a hindrance to progressive evolution. Evidence is presented herein from biochemical, physiological, developmental, and genetical sources which indicates that the nucleotypic effects of chromosome doubling are not necessarily negative. Indeed chromosome doubling may "propel" a population in to a new adaptive sphere, and render it capable of occupying habitats beyond the limits of its diploid progenitor. This postulate is consistent with what we know of the ecological tolerances of diploids and related polyplo...

Polyploidy and Novelty in Flowering Plants

The common onion (Allium cepa) is an excellent plant for the assay of chromosome aberrations after chemical treatment. Other species of allium (A. cepa var. proliferum, A. carinatum, A. fistulosum and A. sativum) have also been used but to a much lesser extent. Protocols have been given for using root tips from either bulbs or seeds of Allium cepa to study the cytological end-points, such as chromosome breaks and exchanges, which follow the testing of chemicals in somatic cells. It is considered that both mitotic and meiotic end-points should be used to a greater extent in assaying the cytogenetic effects of a chemical. From a literature survey, 148 chemicals are tabulated that have been assayed in 164 Allium tests for the clastogenic effect. Of the 164 assays which have been carried out, 75 are reported as giving a positive reaction (i.e., causing chromosome aberrations), 49 positive and with a dose response, 1 positive and temperature-related, 9 borderline positive, and 30 negative; 76% of the chemicals gave a definite positive response. It is proposed that the Allium test be included among those tests routinely used for assessing chromosomal damage induced by chemicals.

Chromosome aberration assays in Allium. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

Higher plants provide valuable genetic assay systems for screening and monitoring environmental pollutants. They are now recognized as excellent indicators of cytogenetic and mutagenic effects of environmental chemicals and are applicable for the detection of environmental mutagens both indoor and outdoor. Comparisons between plant and nonplant genetic assay systems indicate that higher plant genetic assays have a high sensitivity (i.e. few false negatives). Two assays which are considered ideal for in situ monitoring and testing of airborne and aqueous mutagenic agents are the Tradescantia stamen hair assay for mutations and the Tradescantia micronucleus assay for chromosome aberrations. Both assays can be used for in vivo and in vitro testing. Other higher plant genotoxicity assays which have a large number of genetic markers and/or data base and are also highly suitable for testing for genotoxic agents include Arabidopsis thaliana, Allium cepa, Hordeum vulgare, Vicia faba, and Zea mays. Since higher plant systems are now recognized as excellent indicators of the cytotoxic, cytogenetic, and mutagenic effects of environmental chemicals and have unique advantages for in situ monitoring and screening it is recommended that higher plant systems be accepted by regulatory authorities as an alternative first-tier assay system for the detection of possible genetic damage resulting from pollution or the use of environmental chemicals. The results from higher plant genetic assays could make a significant contribution in protecting the public from agents that can cause mutation and cancer. The advantages possessed by higher plant genetic assays, which are inexpensive and easy to handle, make them ideal for use by scientists in developing countries.

The present status of higher plant bioassays for the detection of environmental mutagens.

Higher plants are recognized as excellent indicators of cytogenetic and mutagenic effects of environmental chemicals and are applicable for the detection of environmental mutagens both indoor and outdoor. They are highly reliable bioassays with a high sensitivity for monitoring and testing for genotoxins. A brief review of major steps in the development of higher plant genotoxic assays is given.

Higher plant assays for the detection of chromosomal aberrations and gene mutations-a brief historical background on their use for screening and monitoring environmental chemicals.

Tests have shown plant bioassays to be excellent for mutagenicity studies. Most studies with plant bioassays, however, have been carried out either in the laboratory, or if, in situ, as monitors of atmospheric contaminants. The primary purpose of this study was to assess the utility of in situ plant mutagenicity bioassays in monitoring water contaminants. The assay systems tested were the Tradescantia stamen hair and micronucleus assays for the detection of gene mutations and chromosomal aberrations respectively, and the Vicia faba bioassay system which detects chromosomal aberrations in root tips. The assays were used to test the effluent from a pulp and paper mill located on the north shore of Lake Superior. Assays were performed in a creek containing raw effluent and in the bay of Lake Superior into which the creek emptied. All in situ treatments were carried out for 24 h. The effluent from the creek was heavy with pulp and debris which coated the plant cuttings and the Vicia faba seedlings and may have restricted the uptake from the effluent. In the creek, at test sites 11.5 km from the source, the effluent was toxic to the Vicia faba roots as evidenced by a reduction in the mitotic index. The data for the Tradescantia stamen hair assay in the creek were equivocal. The cuttings from the creek test sites and the air and water control sites appeared to have undergone a physiological delay. Within a day or two after the return to the laboratory, that is 6-8 days after testing, flowering almost ceased and did not fully resume until about day 35. This reduction in flowering was particularly severe with the cuttings from the effluent and air control sites, making it very difficult to interpret the results. In contrast, the Tradescantia micronucleus and Vicia faba chromosomal aberration data were unequivocal; each produced positive responses at both test sites relative to the air and water controls. The results obtained for the bay sites with all 3 assays were in agreement. In that section of the bay visibly contaminated by the creek effluent, increases in stamen hair mutants, micronuclei, and chromosome aberrations were measured. In general, there was a considerable reduction in the number of mutant events observed for the water samples brought back from the test sites and tested in the laboratory.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of Tradescantia and Vicia faba bioassays for the in situ detection of mutagens in an aquatic environment

Cytological observations on meitotic cells of barley plants (Hordeum vulgare) grown after seed treatment (1000 ppm, 12 hours), or seedling spraying (500 ppm), with one of 15 pesticides (Herbicides: Alanap-3, Atrazine, Banvel-D, Cytrol, Embutox E, Hyvar X, Lorox, Monuron, Simazine; Insecticides: Endrin, Phosphamidon, Sevin; Insect chemosterilants: ENT-50612, Botran) indicated that all of the pesticides were capable of inducing chromosome aberrations and, in certain cases, abnormal cellular behavior, such as cytoplasmic furrowing. The chromosomal aberrations observed included stickiness, extreme clumping or coales-cence (“chromatin bodies”), chromosome bridges and fragments and micronuclei. In addition, asynchronous nuclear and cellular divisions were observed. Chromosome aberrations in meiotic cells of C1 generation plants ranged from 0.26 to 66.50% and in the C2 generation from 0 to 11.34%. Chromosome aberrations in meiotic cells of plants after spraying the seedlings ranged from 0 to 8.70%. Certain pesticide treatments produced chromosome aberrations in the C1 or the C2 generation which exceeded the X-ray (5, 500 R) and ethylmethanesulfonate (EMS, 1000 ppm, 12 hours) treatments used for comparative purposes.

William F. Grant

Papers

Chromosome aberration assays in Allium. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

The present status of higher plant bioassays for the detection of environmental mutagens.

Higher plant assays for the detection of chromosomal aberrations and gene mutations-a brief historical background on their use for screening and monitoring environmental chemicals.

The use of Tradescantia and Vicia faba bioassays for the in situ detection of mutagens in an aquatic environment

Chromosomal Aberrations Induced by Pesticides in Meiotic Cells of Barley