Ploidy reduction and genome segregation in cultured carrot cell lines. I. Prophase chromosome reduction

Cytological analysis of different carrot cell lines in culture has shown various cytogenetic anomalies generating new levels of ploidy and novel chromosome numbers. Polyploidy may be considered a reservoir of variability that can be released in the form of distinct new segregants of different ploidy. Mechanisms alternative to mitosis (reductional grouping, prophase chromosome reduction) operate from a polyploid state (possibly reached by means of endopolyploidy, endomitosis, nuclear fusion, or restitution nuclei) to generate new levels of ploidy and novel chromosome numbers necessary for selection to operate in vitro. The segregational phenomena require chromosome recognition in haploid set complements and abnormal behaviour of mitoses; the resulting chromosome variability suggests that chromosomes are arranged, in the resting nuclei, in an orderly and predictable manner.The knowledge of the molecular events governing these mechanisms, and how to control them, would be of great help for future applications of plant cell culture.     

The use of DNA markers to estimate the extent and nature of genetic variability in Solatium tuberosum cultivars

High levels of DNA polymorphism were detected in 27 Solanum tuberosum cultivars examined. Combinations of at least two c-DNA clones have been identified which in conjunction with EcoRI allow important UK potato cultivars to be characterised by their molecular profiles. The widely grown North American cultivar Russett Burbank was also successfully fingerprinted. Estimates of genetic diversity based on restriction fragment length polymorphism (RFLP) data indicate the important role that wild potato species and exotic germplasm have played in the development of the cultivars studied. A graphical method for simultaneously highlighting similarities and differences between genotypes for individual hybridising fragments is presented. This approach is particularly useful in identifying and recording fragments which are unique to certain genotypes. Two potato cultivars: Fiona and Morag produce unique RFLP profiles when digested with EcoRI and EcoRV and probed with a flax ribosomal DNA sequence. Both Fiona and Morag possess incomplete or partial (quantitative) type resistance to G. pallida which was transferred from S. vernei. The preferential transmission of the r-DN A fragments from S. vernei may indicate that this locus is associated with genetic factors controlling resistance to G. pallida.     

Information-theoretical entropy as a measure of sequence variability.

We propose the use of the information-theoretical entrophy, S = -sigman pi log2 pi, as a measure of variability at a given position in a set of aligned sequences. pi stands for the fraction of times the i-th type appears at a position. For protein sequences, the sum has up to 20 terms, for nucleotide sequences, up to 4 terms, and for codon sequences, up to 61 terms. We compare S and Vs, a related measure, in detail with Vk, the traditional measure of immunoglobulin sequence variability, both in the abstract and as applied to the immunoglobulins. We conclude that S has desirable mathematical properties that Vk lacks and has intuitive and statistical meanings that accord well with the notion of variability. We find that Vk and the S-based measures are highly correlated for the immunoglobulins. We show by analysis of sequence data and by means of a mathematical model that this correlation is due to a strong tendency for the frequency of occurrence of amino acid types at a given position to be log-linear. It is not known whether the immunoglobulins are typical or atypical of protein families in this regard, nor is the origin of the observed rank-frequency distribution obvious, although we discuss several possible etiologies.     

Whole-lake experimentation as a tool to assess ecosystem health,response to stress and recovery: the Experimental Lakes Area experience

The rationale and methods for and value of whole-lake experimentation are described using the Experimental Lakes Area (ELA), northwestern Ontario, as the example. The ELA consists of 46 lakes (< 100 ha in surface area), their watersheds, and several streams protected for research purposes in near-pristine boreal forest on the Precambrian Shield near Kenora, Ontario. Over more than 20 y, whole-lake experimentation has provided unique information on the effects on lakes of nutrient additions, acidification, Cd addition, and biomanipulation. Experiments are planned to study the effects of PCB addition and flooding. Recovery, mitigation, and remediation have been explored in some experiments. As well, the fate of radioactive metals in a lake and the effects of acidification on a poor fen and an upland watershed are studied. Comparison between the experimental systems and unmanipulated reference systems has proven to be essential. These reference systems also have a role in defining (absolute) aquatic ecosystem health for small, pristine Precambrian Shield lakes. The ELA experimental data base is available, as well, for calibrating indices of relative aquatic ecosystem health, i.e., environmental degradation, using the dose-responses of lakes to eutrophication, acidification, Cd addition, and other stressors.     

Different substitution tendencies of leaf flavones in theVeronica hederifolia group (Scrophulariaceae)

Flavonoid patterns of several provenances ofVeronica triloba, V. sublobata, andV. hederifolia s. str. have been investigated. 7-0-glucuronides of apigenin and luteolin as well as of 6-substituted (6-hydroxyluteolin and hispidulin) and 3′-methylated (chrysoeriol) derivatives represent characteristic accumulation tendencies in theV. hederifolia group. The three species show slightly different flavonoid profiles.V. hederifolia exhibits a cumulative pattern of all compounds occurring either inV. triloba orV. sublobata, thus supporting the hypothesis of an allopolyploid origin ofV. hederifolia.     

Die Variabilität vegetativer und generativer Flechtenstrukturen und ihre Bedeutung für die Systematik

Die Entstehung von Stützleisten in den Thalli von Cladonia chlorophaea und Cetraria islandica, sowie die Entwicklung sekundärer Soredien im Inneren der Podetien von Cladonia chlorophaea werden beschrieben. Gemeinsam mit anderen Entwicklungsvorgängen von Flechten zeigen die Beobachtungen eine sehr geringe Determination der Flechtengewebe. Die Struktur wird weitgehend durch die Funktion bestimmt, während gleichzeitig bestimmte ontogenetische Abläufe unveränderbar sind. Die Bedeutung dieser Erscheinungen für die Systematik wird diskutiert.     

Morphological studies of Asian rice and its related wild species and the recognition of a new Australian taxon

In order to clarify the taxonomy and the interrelationships among Asiatic cultivated rice, Oryza sativa , and its related wild species ( O. rufipogon, O. nivara and O . barthii ), 41 morphological characters were examined. Numerical taxonomic methods were used to analyse the data and to illustrate species relationships.
Distinctive differences among the materials studied suggest the retention of O. rufipogoon, O. nivara and O . sativa as three distinct species. The origin of O. sativa from O. nivara through domestication is discussed. An annual wild taxon from Australia, which had been classified as a form of O. nivara , is shown to be distinct from typical O. nivnra and is raised to specific rank. This species has been named O. meridionalis Ng.     

Criteria for the identification of potential colonizers*

Man's interference with the environment encourages colonization by species that are often undesirable, hence a technique by which potential colonizers can be identified is urgently required. It can be developed when general prerequisites for successful colonization are identified. These prerequisites can then serve as criteria to distinguish potential colonizers from non-colonizers. The proposed relevant prerequisites are associated with two problems encountered by all colonists: small founding populations and a difference in the environmental conditions between the source area and the target, making the target rather unpredictable. Both these features increase the risk of random extinction, which can be overcome by possessing a potential for rapid population growth (high r) and for rapid adaptation to environmental conditions (high genetic variability). The parameters associated with meeting these prerequisites can serve for the identification of potential colonizers and for ranking species as to their colonization ability. The proposed technique may best be tested by comparing the intrinsic growth rate and the electrophoretic variability of species that have recently colonized with closely related species that have not done so under similar circumstances. The colonization of the eastern Mediterranean by Red Sea species immigrating via the Suez Canal created an appropriate system for such a test.     

Genetic variation in Cameroon: Thermostability variants of hemoglobin and of glucose-6-phosphate dehydrogenase

The technique of heat denaturation was used in addition to electrophoresis for the detection of thermostability variants of hemoglobin and glucose-6-phosphate dehydrogenase in an attempt to measure the amount of genetic variability present in villages in the United Republic of Cameroon, Equatorial Africa. A minimum of three to a maximum of 13 thermostability variants were estimated for HbA and HbS, and a minimum of two to a maximum of ten thermostability variants were estimated for GdA, GdB, and GdA —. It is suggested that hemoglobin and glucose-6-phosphate dehydrogenase thermostability variants are genetically determined and that the sites of these variants are at the hemoglobin and glucose-6-phosphate dehydrogenase structural loci. The evidence for the existence of these hidden variants and their importance in the neutralist v. selectionist controversy are discussed.This work was supported in part by National Institutes of Health Grant HL 16005. S. C. B. was an International Telephone and Telegraph International Fellow to Cameroon, was supported by Training Grant NIH-GM 07197, and is currently an Insurance Medical Scientist Scholar. This work is in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Genetics by S. C. B.     

Enzyme polymorphism in a population of Calomys musculinus (Rodentia,Cricetidae)

NAD-linked lactate, malate, glycerophosphate, alcohol and nonspecific dehydrogenases, aspartate aminotransferases, and soluble esterases from extracts of tissues of individuals from a wild population of Calomys musculinus (Rodentia, Cricetidae) have been analyzed by means of starch gel electrophoresis and specific staining. Allelic frequencies and heterozygosity have been determined. Mendelian inheritance of some of the variants detected was confirmed by breeding experiments. Ten out of fifteen (66.6%) of the genetic loci investigated presented polymorphism. Mean heterozygosity per locus was very high (H=0.2014, se 0.046).This work has been supported, in part, by grants from the Secretaria de Ciencia y Tecnología de la Nación (National Program for Endemic Diseases) and from the Fundación Emilio Ocampo. C. N. G. is a Fellow and A. B. a Career Investigator of the Consejo Nacional de Investigaciones Científicas y Técnicas of Argentina.