Isozyme gene duplication in diploid and tetraploid potatoes

Summary Isozyme techniques allow the study of gene redundancy in different ploidy levels of potato (Solanum tuberosum). In tetraploid potatoes all isozyme loci are duplicated. No sign of structural or regulatory divergence was found, as is expected due to their tetrasomic inheritance patterns. In addition to this genetic redundancy, produced by a relatively recent polyploidization event, some additional redundancy was found for at least three enzymes even in diploid groups and species. These older duplicate genes show structural and regulatory divergence, indicating they appeared by a separate polyploidization event far in the past. Their common origin is still recognizable by both their expression in the same subcellular compartment and by the dimerizing ability of the isozymes they encode. To account for the present chromosome number x = 12 of the Solanaceae family, the most frequently found among the species, a hypothetical polyploidization event is proposed.     

Phylogenetic relationships and gene flow between sympatric diploid and tetraploid plants ofDactylis glomerata (Gramineae)

Phylogenetic relationships between sympatric, morphologically indistinguishable diploid and tetraploid plants ofDactylis glomerata L. (Gramineae) in Galicia (Spain) were assessed using allozyme markers for 6 distinct systems. The study exploited recent introduction in Galicia and subsequent hybridization of an alien 4xDactylis subspecies possessing distinct allozymes from those of all the native plants. Opportunities for gene exchanges between the ploidies were estimated from in situ observations of flowering, examination of progenies in 2x/4x natural and experimental crosses, and enzyme analyses. Results show a high genetic similarity between the Galician diploids and tetraploids, which possess peculiar alleles in common. Although the ploidy levels usually have distinct flowering periods, interploidal crosses do occasionally occur. Gene flow is likely much more important from the diploid to the tetraploid level. A good genetic intermixing occurs between the Galician and the alien tetraploid entities which have simultaneous flowering. Autopolyploidization of the diploids followed by various rates of hybridization is proposed as one very probable origin of natural tetraploids inDactylis.     

Competitive relationships between two water plant species: Najas marina L. and Myriophyllum spicatum L.

The interrelationships between two submerged macrophytes, Najas marina and Myriophyllum spicatum, were investigated. Double-reciprocal analysis was used to distinguish between the possible types of negative relationships. Results have demonstrated that interspecific inhibition was more severe than the intraspecific one. The intensity of inhibition was negatively correlated with the density of the examined species. The mutual inhibitory effect and the pattern of the obtained results suggest that competitive relationships exist between Najas marina and Myriophyllum spicatum.     

The role of fish in distribution and germination of seeds of the submerged macrophytes Najas marina L. and Ruppia maritima L.

Summary The effects of three species of fish (tilapia, grass carp and common carp) on the seeds of Najas marina L. and of Ruppia maritima L. were investigated. Practically all the seeds that were injested by the common carp were digested. The two other fish were less affective: they digested seeds with soft seed-coats but excreted a good portion of the hard ones. Germination of the excreted seeds was improved. Seeds have been retained in the digestion tracts of the fish for up to 65 h. It is thus suggested that tilapias and grass-carps play a role in the distribution and the improvement of reproduction of Najas and Ruppia.     

Inter-relationships between Najas marina L. and three other species of aquatic macrophytes

The ability of Najas marina L. to thrive in the presence of the submerged hydrophytes (Myriophyllum spicatum L. and Potamogeton lucens L.) and of an emerged hygrophyte (Scirpus litoralis Schard.) was investigated in Tel Aviv, Israel. Najas plants were unaffected by the presence of Potamogeton lucens and Scirpus litoralis, but were significantly suppressed by Myriophyllum. Bilateral negative relationships exist between Najas and Myriophyllum and these seem to be of an allelophatic nature, depending more on the nature of the accompanying species rather than on their mass.     

Growth and establishment of mangrove (Avicennia marina) on the coastlines of Kuwait

Mangrove (Avicennia marina) communities constitute an importantcomponent of the renewable natural vegetation resources of the coastalzones of the Arabian Gulf south of Kuwait. Attempts to introduce themangrove into the intertidal zones of the coastline of Kuwait are underwaybecause of the expected favorable environmental impact of this plant, andbecause of its moderating influence on the local climate and enhancementof the aesthetic and recreational value of the coastlines and fisheryresources. Propagules were collected from natural stands of mangrove inBahrain and the United Arab Emirates. Silvicultural practices were followedto produce healthy plants after growing of propagules in the greenhouse.Observations indicated that there is a positive correlation betweenpropagule weight and the length of the seedling stem. Outplanting wasdone in two sites in the intertidal zone around the Sulabikhat Bay, Kuwait.Data on plant survival showed that the most suitable level for successfulestablishment of mangrove was around or below the 3-meter contour tidalline. After 7 years of growth, plants reached a mean height of 250 cm,which is close to the height of their parent trees in Bahrain. The U.A.E.stock plants reached 288 cm after 5 years of growth in Kuwait. Plantsflowered and produced viable seeds. The biological feasibility ofestablishing mangrove plantations in the intertidal flats of Kuwait's coastlineswas documented from the field observation of the experimental plantations.Studies to document the environmental impact of the introduction areunderway.     

Sexual tetraploid and apomictic pentaploid populations ofHieracium pilosella (Compositae)

Five species are recognized inHieracium subgen.Pilosella sect.Pilosellina Fries. Four are diploid (2x, 2n = 18), one (H. pilosella L.) is highly variable morphologically and cytologically (from 2x to 10x), in its mode of reproduction (self-incompatibility, agamospermy, amphimixis, apo-amphimixis) and in its hybridization pattern. A part of this huge agamic complex was analysed by comparing sexual 4x and apomictic 5x plants (crossing and germination experiments, measurements of vegetative reproduction by stolons etc.). In the experimental garden apomictic 5x produced more stolons than the sexual 4x plants and the total length of the stolons per rosette was greater. However, in nature, the competitive potential of the sexual plants seems to be higher, presumably as a result of the higher mortality of ramets in 5x. Sexual 4x plants often grow in dense and grazed grass vegetation, whereas 5x apomicts often occur in dunes with patchy vegetation. Apomicts produce more capitula per rosette, and sexual rosettes form only about 60% of the number of viable achenes as compared to apomictic ones. Therefore, apomicts appear to be characterized by a greater colonizing ability than sexual plants. Apomictic plants produce equal numbers of viable achenes under conditions of both open pollination and isolation. Sexual plants do not form any viable achenes after isolation and produce a somewhat lower percentage of achenes after open pollination than do apomictics. 5xreproduce exclusively apomictically. Apo-amphimixis was never observed in pentaploids and only very rarely in tetraploids. Addition hybrids are very rare. The cross sexual 4x × apomictic 5x failed in 70% of the attempts, but the recombination of genomes carrying genes for apomixis is possible and results in apomictic 4x and sexual 5x, both with a reduced number of viable achenes. In nature sexual and apomictic plants may occur in close proximity. In such cases the germination rate of the achenes of 4x and 5x is lower; this may indicate that apomictic plants fertilize sexual plants in nature (unidirectional gene-flow). 5x plants form euploid gametes carrying two or three genomes. The results of the crossing experiments can be explained in terms ofNogler's theory of monogenic inheritance of apospory.Variation and evolution inHieracium subg.Pilosella sect.Pilosellina I.     

Hordein polymorphism in diploid and tetraploid Mediterranean populations of the Hordeum murinum L. complex

Polymorphism analyses of the hordeins, main storage proteins in barley, were conducted on 35 natural populations of Hordeum murinum s.l. from North Africa; this specific complex includes three subspecies with two ploidy levels: H. murinum subsp. glaucum (2n=2x=14), H. murinum subsp. leporinum and subsp. murinum (2n=4x=28). Twenty of these populations belong to the diploid subsp. glaucum, 14 other tetraploid populations belong to the subsp. leporinum. In addition, six populations of the tetraploid murinum were sampled in France: two along the Mediterranean coast and four in Brittany. The polymorphism observed in the electrophoretic patterns highlights strong correlations between bioclimatic features and di- and tetraploid taxa distribution. Moreover, the variation was not randomly distributed within the different ploidy levels, and is correlated with environmental factors. The ecological differentiation of the two main taxa, H. murinum subsp. leporinum and subsp. glaucum is clearly highlighted.     

QTL mapping in outbred tetraploid (and diploid) diallel populations

Over the last decade, multiparental populations have become a mainstay of genetics research in diploid species. Our goal was to extend this paradigm to autotetraploids by developing software for quantitative trait locus (QTL) mapping in connected F1 populations derived from a set of shared parents. For QTL discovery, phenotypes are regressed on the dosage of parental haplotypes to estimate additive effects. Statistical properties of the model were explored by simulating half-diallel diploid and tetraploid populations with different population sizes and numbers of parents. Across scenarios, the number of progeny per parental haplotype (pph) largely determined the statistical power for QTL detection and accuracy of the estimated haplotype effects. Multiallelic QTL with heritability 0.2 were detected with 90% probability at 25 pph and genome-wide significance level 0.05, and the additive haplotype effects were estimated with over 90% accuracy. Following QTL discovery, the software enables a comparison of models with multiple QTL and nonadditive effects. To illustrate, we analyzed potato tuber shape in a half-diallel population with three tetraploid parents. A well-known QTL on chromosome 10 was detected, for which the inclusion of digenic dominance lowered the Deviance Information Criterion (DIC) by 17 points compared to the additive model. The final model also contained a minor QTL on chromosome 1, but higher-order dominance and epistatic effects were excluded based on the DIC. In terms of practical impacts, the software is already being used to select offspring based on the effect and dosage of particular haplotypes in breeding programs.     

Deleya marina as a model organism for studies of bacterial colonization and biofilm formation

Deleya marina was used as a model organism to identify cellular components essential to surface colonization, an important early step in biofouling. Model components include the test bacteriumD. marina, its phenotypic variants, and a rapid microplate adhesion assay. Studies ofD. marina exopolymer and motility properties are discussed in the context of colonization processes and model development. A testable hypothesis is presented which was formulated to explain events in surface colonization byD. marina.     

Mechanisms of sulphide tolerance in the peanut worm,Sipunculus nudus (Sipunculidae) and in the lugworm,Arenicola marina (Polychaeta)

Summary The peanut worm Sipunculus nudus and the lugworm Arenicola marina are inhabitants of intertidal flats. Both species may be exposed to H₂S within their habitat. Sulphide concentrations in the vicinity of A. marina burrows are as high as 340 mol · 1^-1, whereas the pore water in sipuncle areas contains much lower sulphide levels of 13 mol · 1^-1 at most. During in vivo sulphide incubations, H₂S increases within the coelomic fluid of both species. In S. nudus the concentration of total sulphide after 8 h is about 40% of that of the incubation medium containing 200 and 1000 mol · 1^-1, respectively, which is partly due to the acidification of the coelomic fluid by 0.2 pH units during anaerobiosis. After 8 h, the sulphide concentration in A. marina was only 15% of that in the incubation medium containing 1000 mol · 1^-1. When oxygen is available, both species oxidize sulphide to thiosulphate, but in A. marina this capability is more pronounced than in S. nudus. If sulphide is not completely oxidized internally both intertidal worms switch to an anaerobic metabolism as indicated by the accumulation of opines and succinate.Abbreviations ATP adenosine triphosphate - HEPES N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid - HPLC high-performance liquid chromatography - wwt wet weight     

Giemsa C-banded karyotypes of diploid and tetraploidHordeum bulbosum (Poaceae)

The similar-looking basic genomes ofHordeum bulbosum (2x and 4x) have five rather similar metacentric, one submetacentric, and one satellited choromosome. C-banding patterns are characterized by one or two centromeric, or juxtacentromeric, small to larger bands in most chromosomes, by bands at the nucleolar organizers, by small or very small telomeric bands, and by the nearly complete lack of intercalary bands. Banding pattern polymorphism is widespread. Banding patterns supported by chromosome morphology enable identification of homologues, and discrimination between non-homologues inH. bulbosum (2x). The C-banded karyotype ofH. bulbosum (4x) supports an autopolyploid origin, but it was possible to identify only homologues of submetacentrics and SAT-chromosomes.     

Genetic variation in sympatric populations of diploid and polyploid brine shrimp (Artemia parthenogenetica)

We examined genetic variation in sympatric diploid and polyploid brine shrimp Artemia parthenogenetica from each of three populations (China, Italy and Spain). Italian and Spanish tetraploids are closely related (I=0.964). Diploids and tetraploids within each of the two European populations are also closely related (mean I=0.905). Most alleles found in diploids also exist in sympatric polyploids. In contrast, the asexual Artemia (2N, 4N and 5N) in our study share few alleles with their close sexual relative, A. tunisiana (mean I=0.002). These results, as well as the work of other authors, strongly suggest that at least the tetraploid Artemia in our study have an autopolyploid origin.Clonal diversity of polyploid Artemia can be very high at least in some population. Both diploids and polyploids had low clonal diversities in the populations dominated by polyploids and high clonal diversities in the population dominated by diploids.The most common genotypes of sympatric diploid and polyploid Artemia frequently differed. Some alleles occurred only in diploids, while others were restricted to polyploids. These results suggest that polyploidy in Artemia has led to genetic divergence from diploid progenitors, and that ploidy-level variation must also be considered in developing an understanding of spatial and temporal allozyme polymorphism in asexual populations.     

Nuclear DNA markers of the Australian tetraploid Microseris scapigera and its North American diploid relatives

The allotetraploid lactucean Microseris scapigera of Australia and New Zealand has presumably arisen in western North America by hybridization between an annual and a perennial diploid species followed by polyploidization and long-distance dispersal. A phylogenetic tree of various North American diploids, based on RFLPs in the nuclear DNA, confirmed the division of the genus into a clade containing the diploid annuals and a clade containing the diploid perennials. Four RFLP markers were shared among all accessions of M. scapigera and all the diploid accessions. Twelve markers found in the outgroup (Uropappus lindleyi) were absent in all Microseris. A cladogram of plants from six populations of M. scapigera based on eight RFLP markers shows a progressive specialization of three clades of two populations each. Two populations without any markers differentiating them from the North American diploids form the basic clade. These consist of plants with an apparently derived morphology that are self-compatible (or agamospermic) and thereby differ from most M. scapigera. Few markers in M. scapigera could be attributed to one or the other parental genome. As yet, we have found only one ITS 1 sequence of the nuclear ribosomal cistrons in M. scapigera. This sequence has features of both parental sequences.     

Species relationships and genetic variation in the diploid wheats (Triticum,Aegilops) as revealed by starch gel electrophoresis

Twenty enzyme loci were examined in the diploid species ofTriticum andAegilops for allelic variation by starch gel electrophoresis. SectionSitopsis, including the five species,Ae. speltoides, Ae. lingissima, Ae. sharonensis, Ae. bicornis andAe. searsii form a close subgroup withAe. speltoides slightly removed from the others.T. monococcum s. lat., was found to be closest to the species of theSitopsis group.Ae. comosa, Ae. umbellulata andAe. uniaristata form a second subgroup withAe. caudata most closely related to these species.Ae. squarrosa appears almost equally related to all of the species, showing no special affinity for any one species group. Nineteen out of twenty loci examined were polymorphic with a mean of 6.7 alleles per locus. Species could be, for most loci, characterized by the presence of predominant alleles. A conspicious genetic characteristic ofTriticum-Aegilops is the sharing of these predominant alleles between species. Within species variation is characterized by a diffuse distribution of secondary alleles.     

Ribosomal DNA variation within and among individuals ofLisianthius (Gentianaceae) populations

Restriction endonuclease fragment analysis of nuclear ribosomal DNA (rDNA) was completed on 25 individuals each from seven populations of theLisianthius skinneri (Gentianaceae) species complex in Panama. Seven restriction enzymes were used to determine the amount and type of rDNA variation within and among individuals of the populations. No restriction site variation was seen within populations or individuals although site differences were seen among populations. Spacer length variation within and among individuals of populations was mapped to the internal transcribed spacer (ITS) region between the 18S and 5.8S rRNA genes, a region inLisianthius rDNA that previously was shown to exhibit length differences among populations. This is the first reported case of such variation within and among individuals of populations for the ITS region. Presence or absence of ITS spacer length variation is not correlated with levels of isozymic heterozygosity within populations. No detectable length variation within individuals or populations was seen in the larger intergenic spacer (IGS). Although populations varied with respect to IGS length, all individuals of a given population had a single and equivalent IGS length.     

Electrophoretic identification of polyploidCamellia japonica (Theaceae) cultivars and evidence for their sexual origin

Electrophoretic examination of allozymes from 189Camellia japonica cultivars revealed some banding patterns not explainable by codominant diploid genetics. At several loci encoding dimeric enzymes, 5 and 6 banded patterns were observed in 7 cultivars. These patterns are interpreted as resulting from triploidy or aneuploidy, where three variant alleles code for products which are electrophoretically distinguishable and associate to form three homodimers and three heterodimers. The presence of allozyme multiplicity in these clones suggests a sexual rather than a somatic mode of triploid origin.     

Meiotic prophase in diploid and tetraploid strains ofAllomyces macrogynus

Summary Three-dimensional serial section reconstructions of meiotic prophase nuclei ofAllomyces macrogynus (Chytridiomycetes, Blastocladiales) have been carried out. Serial section reconstructions of pachytene nuclei have revealed that the fungus when grown at 23 °C is an autotetraploid and is a diploid when grown at 35 °C for at least 6 months or on a substrate containing para-fluorophenylalanine for 1–2 weeks.Studies of the duplication and migration of the centrioles during the first stages of prophase revealed the existence of four centrioles in the 23 °C strain after centriole duplication and two centrioles in the 35 °C strain after duplication. It is observed that a bivalent attaches to the nuclear envelope at a site where a centriole is situated. It is proposed that the presence of the four centrioles in the 23 °C strain is due to the fact that each bivalent is represented twice in the strain.     

Additional chromosome numbers inPelargonium (Geraniaceae)

Mitotic chromosome counts were made from field collected and subsequently cultivated plants of 61Pelargonium species from 14 sections. The 33 new results are presented. 47 of the species have a basic number of x = 11, nine spp. of x = 9 and five spp. of x = 8. 17 spp. are polyploid. In two sections species with different basic numbers occur, which is of interest for the subgeneric classification. The size of the chromosomes varies between the investigated species. Most but not all species with x = 11 have short, those with x = 8, 9 large, and only exceptionally short chromosomes. Within sections chromosome size is not always uniform. The relationship between the different basic chromosome numbers is discussed.     

Genetic diversity in diploid vs. tetraploid Rorippa amphibia (Brassicaceae)

The frequency of polyploidy increases with latitude in the Northern Hemisphere, especially in deglaciated, recently colonized areas. The cause or causes of this pattern are largely unknown, but a greater genetic diversity of individual polyploid plants due to a doubled genome and/or a hybrid origin is seen as a likely factor underlying selective advantages related to life in extreme climates and/or colonization ability. A history of colonization in itself, as well as a recent origin, and possibly a limited number of polyploidization events would all predict less genetic diversity in polyploids than in diploids. The null hypothesis of higher gene diversity in polyploids has to date hardly been quantified and is here tested in self-incompatible Rorippa amphibia (Brassicaceae). The species occurs in diploid and tetraploid forms and displays clear geographical polyploidy in Europe. On the basis of eight microsatellite loci it can be concluded that the level of gene diversity is higher in tetraploids than in diploids, to an extent that is expected under neutral evolution when taking into account the larger effective population size in the doubled cytotype. There is thus no evidence for reduced genetic diversity in the tetraploids. The evidence presented here may mean that the tetraploids' origin is not recent, has not been affected by bottlenecks and/or that tetraploids were formed multiple times while an effect of introgression may also play a role.