Showing papers in "Basic life sciences in 1980"

Polyploidy and distribution.

Abstract: Since Polyploidy has been recognized as a widespread and common phenomenon among eukaryotes, particularly higher plants, biologists have been interested in possible causal connections between Polyploidy and distribution, and have tried to present relevant generalizations and “rules.” A quick historical survey of this topic takes us back to the first relevant studies on angiosperms during the thirties: Hagerup (1) and Tischler (2) demonstrated a frequency increase of polyploids from southern to northern latitudes and interpreted it as the result of greater hardiness of polyploids under extreme ecological conditions. Manton (3), on the basis of her studies on Biscutella in glaciated and unglaciated areas in Europe, was the first to stress the better colonizing potential of polyploids. The further elaboration of this question in the forties and fifties can be exemplified by contributions from A. and D. Love (4,5), Stebbins (6,7), and many others. During the same time studies concerned with Polyploidy and distribution were extended to some animal and other plant groups (cf. contributions in this Conference), foremost to the pteridophytes, again by Manton (8). Her finding of very high chromosome base numbers in many fern plants paved the way to our understanding of paleoPolyploidy, a phenomenon to which publications by Favarger (9) and S. and G. Mangenot (10) have further contributed during the sixties.

Polyploidy in species populations.

Abstract: Polyploidy in populations of well-differentiated plant species is now widely recognized (1,2). Most reports, however, are limited to a few individuals from one or several populations and thereby illustrate only a fraction of the extant genomic diversity in most species. They rarely purport populational dynamics involving Polyploidy as an evolutionary process. Nevertheless, there are recent notable exceptions and these will be utilized freely in this review of Polyploidy within species populations.

Polyploidy in Angiosperms: Monocotyledons

Abstract: Several different estimates of polyploid frequency in angio-sperms have been made, including G.L. Stebbins’ (1,2) figure, first published in 1950, of 30–35%, and suggestions by M.J.D. White in 1942 (3) of at least 40%, and by Grant in 1963 (4) of 47%. These figures represent different ways of calculating Polyploidy and different interpretations of the meaning of the word in the context of plant systematics. Stebbins’ estimate includes as polyploid those species which have gametic chromosome numbers that are multiples of the basic diploid number found in their genus, in other words, intrageneric Polyploidy. White’s figure is based on the simple observation that even haploid numbers exceed odd by about 40% and he thus assumed this 40% to be largely attributable to a polyploid origin. Grant postulated that species with haploid numbers in excess of n=13 would mainly be polyploid and those with n=13 or less, predominantly diploid. Grant’s study also included the only estimate I have encountered of Polyploidy in each of the two subclasses of angiosperms. He calculated a frequency of 43% in Dicotyledonae and a much higher 58% in Monocotyledonae. These figures were based on chromosome data accumulated by 1955 for some 17,138 species.

Origins of polyploids.

Abstract: Polyploidy is a conspicuous feature of chromosomal evolution in higher plants. Stebbins (1) estimates that between 30 and 35 percent of flowering plant species have gametic chromosome numbers in multiples of the basic number characteristic of the genus to which they belong. Polyploidy is common in some groups and rare or absent in others. Levin and Wilson (2) calculate that relative increase in chromosome diversity in woody angiosperms is about 14% that of herbaceous angiosperms. Habit, habitat and the breeding system seem to contribute to origin and success of polyploids.

Polyploidy in Plants: Unsolved Problems and Prospects

Abstract: The papers that have been presented at the present synposium provide in themselves ample evidence that problems connected with Polyploidy are of prime importance for understanding the evolution not only of most plants, but also of many groups of animals. Although chromosome doubling as a tool for plant breeders has become much reduced in importance during recent years, its revival may become practical as more becomes known and understood about the reasons why this process has been of great importance for the origin of species in nature (1).

Evolutionary implications of polyploidy in amphibians and reptiles.

Abstract: In plants, Polyploidy is recognized to be a wide-spread phenomenon and of considerable practical and evolutionary importance, whereas polyploid animal species have been relegated for the most part, to insignificance in terms of their existence or evolutionary importance. Evolutionary and genetic authorities have adhered mostly to Mullers’s 1925 (1) contention that sexual imbalance in polyploids would not permit bisexual polyploids to exist as natural entities in animals as they do in plants, which are capable of vegetative reproduction. Asexual polyploids are also condemned, in animals, by the commonly held, and mathematically “proven” (2) viewpoint that this method of reproduction reduces genetic recombination and is tantamount to phylogenetic suicide (3–5). It is evident, however, that an increasing number of polyploid amphibians and reptiles are being encountered in natural populations living in North America, South America, Europe, Asia, and Africa. To ignore their existence or to pass judgement on their evolutionary significance without adequate study is incomprehensible. In spite of the theoretical dogma surrounding animal polyploids, there is a growing bank of data which suggests that naturally occurring animal polyploids may play an interesting and significant role in population genetics and speciation.

Role of Polyploidy in the Evolution of Fishes

Abstract: Polyploidy is not generally believed to have played a major role in the evolution of animals. This view has been fostered principally by G. L. Stebbins and M. J. D. White, both of whom as early as the 1940’s advocated that Polyploidy at best has played a secondary role in evolution; neither of them has substantially altered this view in recent years (1,2). Some of the arguments against the importance of Polyploidy are: (a) that the large amount of gene duplication in polyploids dilutes the effects of new mutations so significant adaptive changes are unlikely, (b) that Polyploidy in animals is restricted mainly to asexual forms which are evolutionary dead ends, and (c) the number of polyploid animals relative to diploids is small.

Maximizing Heterozygosity in Autopolyploids

Abstract: Polyploidy appears dependent on heterozygosity! The largest group of polyploids, the allopolyploids (disomic polyploids), have fixed heterozygosity in the two or more divergent genomes they possess (e.g., wheat, oats, cotton, tobacco, etc.). Hexaploid wheat, for example, although self-pollinated and basically homozygous at loci in each of its three genomes, has internal hybridity among loci with similar function in its three genomes. Disomic polyploids thus are able to capitalize on the merits of both the self- and cross-fertilizing systems (1).

Visual guidance in Drosophila.

Abstract: One of the last enquiries inspired by Theodosius Dobzhansky is entitled, “How far do flies fly?”.1 The paper refers to several field studies where a labelled strain of Drosophila was released and its dispersal measured by recapture of labelled flies on subsequent days. If the dispersal is simply due to random movements of the flies, then it should be analogous to the dispersal of small particles performing Brownian movements. Expected, in this case, is a normal distribution of the flies such that the increase of their mean distance from the release point is proportional to the square root of the time elapsed since the release. The expected time dependence of the dispersal seems to hold, more or less, for colonies of D. pseudoobscura, and the diffusion model may be considered as a reasonable first approximation of the locomotor behavior. However, the expected profile of the distribution has not been verified. Conspicuously more flies were recaptured both near the release point and at the outer periphery of the field. This discrepancy was explained by the tendency of Drosophila either to remain in a favorable habitat, or to cover great distances in search of such a habitat. The observation suggests that the control of locomotion can be adapted by the fly to different situations and requirements. The locomotor behavior of D. melanogaster has been extensively studied in laboratory experiments. Most of the results obtained so far refer to optomotor responses which enable the fly to maintain a given course and altitude over extended periods of time.

Polyploidy in Angiosperms: Dicotyledons

Abstract: As summarized by Goldblatt (1) in the previous article, “Polyploidy in angiosperms: monocotyledons,” recent estimates of polyploid frequency among angiosperms vary from 30–35% to 47%. The highest value is based on the postulation that haploid numbers in excess of n=13 would be mainly polyploid and those with n=13 or less would be predominantly diploid (2). On this basis 43% of dicotyledons and 58% of monocotyledons from a sample of 17,138 species were considered polyploid. Goldblatt (1) believes, however, that limiting Polyploidy to haploid numbers over n=13 is too conservative and that at least species with numbers of n=ll and above have Polyploidy in their evolutionary history, and perhaps also many of those with n=10 and n=9 may be aneuploid derivatives of ancestors with higher numbers. He suggests that at least 70% and most likely above 80% of monocotyledons are in some sense polyploid.

Polyploidy in pteridophytes.

Abstract: Chromosome studies of pteridophytes had their major impetus in the work of Irene Manton (1) who was the first to show the far-reaching significance of Polyploidy in these plants. Her work was followed not only by numerous investigations by her own students at the University of Leeds but by researchers in many parts of the world, including especially India, Japan, New Zealand, Costa Rica, United States, Canada, Germany, Italy, and Hungary. Two major works have appeared in the past couple of years, namely the very thorough analysis of “Evolutionary Patterns and Processes in Ferns” by J.D. Lovis (2) and “A Cytotaxonomical Atlas of the Pteridophyta” by A Love, D. Love, and R.E.G. Pichi-Sermolli (3,4).

Physiology of Polyploids

Abstract: A number of facts suggest that the multiplication of the genome has played an important role in the evolution of all major phylogenetic groups (1–4). Multiplication might be achieved either by an increase of the DNA/chromosome ratio (cryptic Polyploidy) or by the doubling of the entire chromosome complement (conventional Polyploidy), the latter being widespread in higher plants. Polyploidy has been found in at least 30% of the genera of flowering plants. Moreover, it has been suggested that most genera of flowering plants with a basic gametic chromosome number of 12 or more are the product of an ancient Polyploidy (4).

Responses of Plants to Saline Environments

Abstract: Plants can only grow and reproduce when their cells are bathed by water and permeated by it. Algae and the most active organs of higher plants, the leaves, and the roots, are 85–95 percent water by weight. Desiccation or freezing do not necessarily spell death of all plant cells but slow down to imperceptible rates the metabolic processes of growth and development. Water, then, is of the essence in the functioning of plants.

Mutants of Brain Structure and Function: What is the Significance of the Mushroom Bodies for Behavior?

Abstract: For approaching the enormous complexity of the insect brain one may choose first to study the sensory and motor periphery in the hope to finally work one’s way up to the central processing stages of the brain or, alternatively, one may parachute in the midst of the jungle, experimentally altering the brain and try to understand the concomitant changes in behavior. While with the first approach in recent years an impressive volume of basic knowledge about neural integration of sensory data and about the generation of motor patterns has been provided, only few of these studies have really been concerned with central brain functions. Of the parachutists, on the other hand, only few signs of survival have reached the outside world (e.g., Wadepuhl and Huber, 1979).

Some Applications and Misapplications of Induced Polyploidy to Plant Breeding

Abstract: Plant breeders are eternal optimists, always searching for and expecting significant breakthroughs in plateaus of yield, quality, or adaptation. These breakthroughs have been achieved in some crops, notably maize (Zea mays) and grain sorghum (Sorghum bicolor) (1); but they have been elusive in others, particularly forage crops, in which conventional breeding methods have usually produced disappointing results (2,3). With the 1937 discovery of the “colchicine technique” for inducing Polyploidy, breeders seized upon this then-unconventional technique as a means of penetrating yield barriers. Since 1937, breeders, using polyploid methods on many crops, have gone through repeated cycles of high expectations followed by low realizations. The foremost lesson to be learned from the breeders’ 40-year experience (“struggle” may be a better word) with induced Polyploidy is that it is not a panacea for plant improvement. Nevertheless, as a forage breeder-cyto-geneticist, I still look on the intelligent manipulation of Polyploidy as one of the most, if not the most, promising means of improving yields of certain crop plants, particularly the perennial forages.

Polyploidy in Insect Evolution

Abstract: The number of existing insect species is estimated to be of the order of between two and a half and three million. More than a third of this number has already been described. In comparison with this diversity, the list of known polyploid insect forms is exceedingly small, less than one hundred.

Energy Cost of Ion Transport

Abstract: For a plant to survive in a saline environment it is necessary to have specific control of internal ion concentrations.

Olfactory Behavior of Drosophila Melanogaster

Abstract: The olfactory system of Drosophila is readily amenable to genetic dissection. The response to smell involves interaction between a chemical stimulant and the receptor surface, transduction, neural excitation, transmission across synapses and integration by the central nervous system finally leading to motor activity. By an appropriate choice of mutants, attention can be focussed on any one of this series of complex processes. In this paper I will describe the properties of olfactory mutations on the X-chromosome and compare the behavior of mutants with normal flies.

Genetic and Physiological Factors Affecting Repair and Mutagenesis in Yeast

Abstract: Current views of DNA repair and mutagenesis in the yeast Saccharomyces cerevisiae are discussed in the light of recent data and with emphasis on the isolation and characterization of genetically well-defined mutations that affect DNA metabolism in general (including replication and recombination). Various “pathways” of repair are described, particularly in relation to their involvement in mutagenic mechanisms. In addition to genetic control, certain physiological factors such as “cell age,” DNA replication, and the regulatory state of the mating-type locus are shown to also play a role in repair and mutagenesis.

The role of organic solutes in osmoregulation in halophytic higher plants.

Abstract: Excessive salt accumulations prevent or limit the growth of crops on at least 50 million hectares of agricultural land, particularly in areas where arid or semi-arid conditions exist (Carter, 1975). If these lands are to be used to increase plant productivity it is pertinent to examine the characteristics of plants which have evolved under the influence of natural selection in saline environments, in order to recognize characters that are likely to increase the fitness of plants in such habitats. Halophytes growing in coastal and estuarine ecosystems are of particular interest, because of readily available supplies of saline water and nutrients (with the possible exception of nitrogen). Coastal environments are nutrient sinks, and the tidal input of large quantities of water and mineral ions, represents an energy subsidy to these ecosystems (Odum, 1974). In arid regions, in contrast, the combined effects of drought and salinity present a formidable obstable to the breeder attempting to introduce varieties which will give an adequate yield.

Breeding salt-tolerant crop plants.

Abstract: To date there has been a moderate amount of work done on the development of salt tolerant crop plants. Fuchs (1955) speculated that breeding for salt tolerance should be quite similar to breeding for drought tolerance. In the 1960’s, Dewey (1962) developed a program for breeding salt tolerant crested wheatgrass, Epstein and Jefferies (1964) wrote on the genetic control of ion absorption and salt tolerance, Hunt (1965) demonstrated heritability of salt tolerance in intermediate wheatgrass, Ramage (personal communication) began his studies of developing salt tolerant barley in Arizona, and there were others, but not many. By now, there are programs under way for the improvement of the salt tolerance of several crops including alfalfa, barley, corn, grapes, and even walnuts. In the United States Department of Agriculture/Current Research Information System (USDA/CRIS) data base, there are about 30 active projects and 17 recently completed ones that include the topic of improving the salt tolerance of crops in some form of breeding program.

Osmoregulation in yeast.

Abstract: For the purposes of this article, osmoregulation will be defined as the maintenance of approximately constant cell volume and turgor pressure in the face of changing water potential. Microorganisms must accomodate the entire range of environmental water potential whereas the range is narrowed for the cells of healthy higher plants and animals by regulatory systems associated with their more complex anatomy and physiology. For this reason, cellular responses to extreme environmental conditions are best seen in microorganisms and, indeed, microorganisms are the only inhabitants of certain types of extreme environments such as hypersaline lakes.

Polyploidy in Gymnosperms

Abstract: A discussion in gymnosperms as a group is somewhat meaningless so far as discerning trends or ascertaining general principles It is now generally recognized (1, 2) that g3niinosperms as a class probably never existed, and that gymnospermy should be regarded as a way of life rather than suggesting that the plants possessing naked seeds are somehow closely related So before surveying the occurrence of Polyploidy in gymnosperms, it might be appropriate to indicate the kinds and degree of relationships of plants that are loosely included in the group

Isolation and Characterization of Repair-Deficient Mutants of Drosophila melanogaster

Abstract: Mutagen-sensitive mutants of Drosophila melanogaster are being utilized to determine the number and function of genes which control various aspects of DNA metabolism including replication, repair and recombination and to define the relationship of each of these functions to mutation production.

A combined genetic and mosaic approach to the study of oogenesis in Drosophila.

Abstract: An embryologist usually becomes interested in oogenesis with the realization that many of the decisions made by the cells in the early embryos reflect a distribution of determinants present in some form already in the egg prior to fertilization. This allows us to reduce the question of why different regions of the blastoderm have different embryonic fates into two subquestions: (1) How do the different regions of the egg cytoplasm become different from each other? (2) How are these initial cytoplasmic differences interpreted by the individual blastoderm cells in choosing their particular fates?

Selection of salt-tolerant plants using tissue culture.

Abstract: Plants in nature have evolved a number of adaptive mechanisms to cope with the presence of salt in their environment. The most significant of these mechanisms entails actual tolerance by the plant of high levels of salt within the tissue. This “true tolerance” has been found to provide the greatest tolerance of salt, and is characteristic of most plants inhabiting extremely saline environments. These plants accumulate large amounts of ions from the soil, and maintain growth despite internal concentrations considerably higher than levels that are lethal to plants which utilize other strategies for coping with salinity (Levitt, 1972).

Cytogenetics of polyploids.

Abstract: Following Winge’s classic paper on Polyploidy (1), there have been a large number of publications dealing with various aspects of the subject. However, this symposium is probably the first to bring together at one place and at one time so many different viewpoints and disciplines dealing with this subject.

An Assessment of Quaternary Ammonium and Related Compounds as Osmotic Effectors in Crop Plants

Abstract: In this paper I shall attempt to assess whether or not the accumulation of certain amino acids and their N-methylated derivatives, particularly glycinebetaine, is a specific adaption related to enhanced salt tolerance in, at least, some halophytic species. As a result I shall neglect other extremely important aspects of salt tolerance and toxicity but these have been considered elsewhere (Wyn Jones, 1980; Wyn Jones et al, 1979).

Osmoregulation in the Halophilic Algae Dunaliella and Asteromonas

Abstract: The genus Dunaliella of the order Volvocales includes a variety of ill-defined species of unicellular green microscopic algae (Butcher, 1959). Members of the genus Dunaliella are generally ovoid in shape, 4-15μm wide and 10-25μm long. The cells are motile, due to the presence of two equal long flagellae in each cell, and contain one large cup-shaped chloroplast which occupies about half of the cell volume. The chloroplast contains a large pyrenoid surrounded by polysaccharide granules, the storage product.

Relationship of DNA Lesions and their Repair to Chromosomal Aberration Production

Abstract: Though the roles of some specific DNA lesions in the production of chromosomal aberrations is clearly established, those of others remain unclear. While the study of aberration production in human genetic DNA repair deficiency diseases has been extremely rewarding already, eukaryotic repair systems are obviously complex, and one is tempted to feel that such studies may have raised as many questions as they have provided answers. For example, the “standard” sort of xeroderma pigmentosum is chromosomally sensitive to ultraviolet light and to those chemical agents inducing ultraviolet-type DNA repair. But both it and the variant form have been reported to also be sensitive to the crosslinking agent mitomycin C in one study [18], implying a common step or steps in the repair of pyrimidine cyclobutane dimers and DNA crosslinks. However, just to complicate matters, another study of chromosomal aberration production in xeroderma pigmentosum cells had found them no more sensitive to mitomycin C than normal cells [50]. Similarly, Fanconi’s anemia cells, which are chromosomally sensitive to crosslinking agents, and appear to be defective in the “unhooking” of linked polynucleotide strands [15, 16, 49, 51], are reported to be chromosomally sensitive to ethyl methanesulfonate as well [29], and to be sensitive to ionizing radiation [7, 19, ]0], again implying overlapping repair systems. It seems certain that further study of chromosomal aberration production in repair deficient cells by agents inducing various DNA lesions will reveal even greater complexity in eukaryotic DNA repair systems and their role in chromosomal aberration production. Nevertheless, there seems hope, at least, that such studies may also ultimately lead to a complete understanding of the molecular mechanisms involved.