Secretory tissues in the East African shrubby aloes

Examination of Aloe leaf sections revealed the presence of three types of cells at the phloem pole of the vascular bundles, aloin cells, outer bundle sheath cells and fibres. Three species contain fibres alone and produce a sparse exudate with few components staining purple with Fast Blue B on thin-layer chromatograms. The majority of species have aloin cells of various sizes and in the tetraploid species these produce a copious exudate containing anthraquinone and chromone derivatives. It is suggested that the aloin cells act as storage tissue and that the compounds are synthesized in the surrounding layer of cells of smaller diameter, many of which can be seen to contain globules of unknown constitution. Anatomical observations support the idea that the shrubby tetraploid Aloe species are derived from a form similar to the diploid Aloe morijensis. Two forms of this species have been described, one with fibres only and few exudate components and another with both fibres and aloin cells and an exudate containing compounds of the tetraploid species. A line of diploid plants similar in anatomy and chemistry to the first form is represented by A. fibrosa and A. babatiensis while a line of tetraploids with affinities to the second form is represented by A. nyeriensis, A. cheranganiensis, A. elgonica, A. dawei and A.yavellana.     

Chromosome number and flavonoid synthesis in Briza L. (Gramineae)

Following a recent reidentification of the apigenin C-glycosides in diploid Briza media, the luteolin C-glycosides were reexamined and three acylated derivatives of a luteolin C-glycoside were found. In an attempt to identify the chromosome or group of chromosomes responsible for the change in flavonoid synthesis from 4'-hydroxy- in diploid plants to 3',4'-dihydroxyflavone C-glycosides in autotetraploid plants, leaf flavonoids of artificially produced aneuploids of B. media were examined. Among these plants three different leaf flavonoid profiles were recognized: diploid, tetraploid, and a "modified" tetraploid pattern. All the aneuploids with the normal or "modified" tetraploid pattern were trisomic for one of the small acrocentric chromosomes. Induced polyploids of other Briza species were usually found to have similar flavonoid patterns in the two chromosome races. Flavonoid sulfates were found in three South American species but are absent from all the European species.     

Morphological, anatomical, cytological and biochemical aspects of evolution in East African shrubby species of Aloë L. (Liliaceae)

Twelve previously described shrubby species of Aloé L. from Kenya, Congo, Tanzania and Uganda were investigated using a multidisciplinary. approach. Half of the species were found to be tetraploids (24, 28), and because of the rarity ot tetrapolody in the genus it is suggested that these are very closely related and of common origin. Studies of their gross morphology and leaf surface sculpturing reveal clinical variation patterns. These patterns indicate the diploid species likely to be similar to the ancestor of the tetraploids, and the geographic region where the chromosome doubling probably occurred. Variations in the composition of the leaf exudates largely confirm the conclusions drawn from the cytological and anatomical observations. A taxonomic revision based on the experimental findings changes the status of Rift Valley forms of A. kedongensis to a subspecies of A. nyeriensis and also enlarges the latter to include A. ngobitensis .     

Occurrence of ploidy shift in a strain of the imperfect yeast Candida albicans

A clinical isolate of Candida albicans, a member of the Fungi Imperfecti, was polyploid as shown by the fact that it contained two kinds of nuclei, one of diploid and one of tetraploid DNA content. These determinations were made by fluorescence microscopy-photometry. The nucleus-associated organelles (NAOs), or spindle pole bodies, of yeast cells in this isolate were classified into two groups, one diploid and the other tetraploid, according to their dimensions as determined by serial thin-sectioning electron microscopy. A ploidy shift from diploid to tetraploid was found in individual cells of a culture of this isolate undergoing diphasic growth in minimal salts medium. A process of shift-down or reduction of ploidy from tetraploid to diploid was also observed by electron microscopy during these growth conditions: this appeared to occur in large cells which showed multiple spindle formation during nuclear division, a phenomenon apparently similar to the process of meiosis II during sporogenesis of Saccharomyces cerevisiae, but differing in that it produces diploid daughter nuclei by the vegetative process.     

RELATIONSHIP BETWEEN PLOIDAL LEVEL AND CAM IN FIVE SPECIES OF TALINUM (PORTULACACEAE)

Plants (N = 102) from 23 populations of Talinum, representing five morphologically similar species, were examined in a test of the hypothesis that ploidal level may be correlated with levels of Crassulacean acid metabolism. When grouped by species and ploidal level, two groups of tetraploid plants, T. calcaricum and tetraploid individuals of T. calycinum, had significantly greater malic acid accumulations than any other group, including diploid individuals of T. calycinum. Another tetraploid, T. teretifolium, did not show greater malic acid fluctuations than the diploids, including two putative ancestors (T. mengesii and T. parviflorum). Similarly, malic acid fluctuations in tetraploid individuals of T. parviflorum were not different from diploid individuals of the same species. Nonetheless, when all plants were compared, nocturnal accumulations of malic acid in tetraploid plants were significantly greater than those of diploid plants.     

Aneuploidy and genetic variation in the Arabidopsis thaliana triploid response

Polyploidy, the inheritance of more than two genome copies per cell, has played a major role in the evolution of higher plants. Little is known about the transition from diploidy to polyploidy but in some species, triploids are thought to function as intermediates in this transition. In contrast, in other species triploidy is viewed as a block. We investigated the responses of Arabidopsis thaliana to triploidy. The role of genetic variability was tested by comparing triploids generated from crosses between Col-0, a diploid, and either a natural autotetraploid (Wa-1) or an induced tetraploid of Col-0. In this study, we demonstrate that triploids of A. thaliana are fertile, producing a swarm of different aneuploids. Propagation of the progeny of a triploid for a few generations resulted in diploid and tetraploid cohorts. This demonstrated that, in A. thaliana, triploids can readily form tetraploids and function as bridges between euploid types. Genetic analysis of recombinant inbred lines produced from a triploid identified a locus on chromosome I exhibiting allelic bias in the tetraploid lines but not in the diploid lines. Thus, genetic variation was subject to selection contingent on the final ploidy and possibly acting during the protracted aneuploid phase.     

Centromeric repetitive DNA sequences in the genus Brassica

Representatives of two major repetitive DNA sequence families from the diploid Brassica species B. campestris and B. oleracea were isolated, sequenced and localized to chromosomes by in situ hybridization. Both sequences were located near the centromeres of many chromosome pairs in both diploid species, but major sites of the two probes were all on different chromosome pairs. Such chromosome specificity is unusual for plant paracentromeric repetitive DNA. Reduction of stringency of hybridization gave centromeric hybridization sites on more chromosomes, indicating that there are divergent sequences present on other chromosomes. In tetraploid species derived from the diploids, the number of hybridization sites was different from the sum of the diploid ancestors, and some chromosomes had both sequences, indicating relatively rapid homogenization and copy number evolution since the origin of the tetraploid species.     

Ancestry of American polyploid Hordeum species with the I genome inferred from 5S and 18S-25S rDNA

* BACKGROUND AND AIMS: The genus Hordeum exists at three ploidy levels (2x, 4x and 6x) and presents excellent material for investigating the patterns of polyploid evolution in plants. Here the aim was to clarify the ancestry of American polyploid species with the I genome. * METHODS: Chromosomal locations of 5S and 18S-25S ribosomal RNA genes were determined by fluorescence in situ hybridization (FISH). In both polyploid and diploid species, variation in 18S-25S rDNA repeated sequences was analysed by the RFLP technique. * KEY RESULTS: Six American tetraploid species were divided into two types that differed in the number of rDNA sites and RFLP profiles. Four hexaploid species were similar in number and location of both types of rDNA sites, but the RFLP profiles of 18S-25S rDNA revealed one species, H. arizonicum, with a different ancestry. * CONCLUSIONS: Five American perennial tetraploid species appear to be alloploids having the genomes of an Asian diploid H. roshevitzii and an American diploid species. The North American annual tetraploid H. depressum is probably a segmental alloploid combining the two closely related genomes of American diploid species. A hexaploid species, H. arizonicum, involves a diploid species, H. pusillum, in its ancestry; both species share the annual growth habit and are distributed in North America. Polymorphisms of rDNA sites detected by FISH and RFLP analyses provide useful information to infer the phylogenetic relationships of I-genome Hordeum species because of their highly conserved nature during polyploid evolution.     

Ecological factors influencing tetraploid speciation in snow buttercups (Ranunculus Adoneus): niche differentiation and tetraploid establishment

Chromosome doubling plays an important role in generating new species of flowering plants. However, reproductive incompatibilities between newly formed tetraploid plants and their diploid progenitors are expected to create a significant barrier to the persistence and establishment of neopolyploid populations. Ecological differentiation can reduce this barrier via prezygotic isolation arising from spatial separation. Alternatively, superior viability or fecundity of neotetraploid plants might compensate for the reproductive cost of incompatible pollen from diploid neighbors. The performance of plants of both cytotypes can be assessed in their respective habitats through reciprocal transplants, although such experiments have not been used previously in the study of tetraploid speciation. We used a series of seed and seedling transplant experiments to assess ecological differentiation and competitive ability during early establishment phases for tetraploid and diploid forms of the snow buttercup (Ranunculus adoneus). At two sites, seeds from diploids and tetraploids had similar germination probabilities. Tetraploid snow buttercup seedlings had a significant growth advantage in a controlled environment chamber experiment. However, in the field diploid and tetraploid buttercup seedlings did not differ consistently in survival or growth, nor did the two cytotypes show reciprocal advantages in performance, as expected if ecological differentiation has occurred. At the seed and seedling stages, neither niche differentiation nor tetraploid competitive superiority appears sufficient to explain neotetraploid success in the presence of their diploid progenitors.     

Parnassia palustris: a genetically diverse species in Scandinavia

Patterns of variation at nine enzyme loci were examined in 528 plants representing diploid and tetraploid populations of Parnassia palustris s. l. in Europe to assess genetic variation patterns and migration history. Half of the plants showed a unique multilocus phenotype and 75% of all phenotypes occurred only in Scandinavia. Diploid populations showed similar levels of genetic diversity as other widespread outbreeding species with animal-mediated pollination and F -statistics indicated excessive heterozygosity and low rates of gene flow among them. In spite of dramatic population histories caused by the ice ages, diploid populations have maintained the same genetic diversity in Scandinavia as in central and southern Europe. Northern populations have apparently been established through the gradual advance of genetically variable populations and patterns of variation at individual loci indicate different migration routes, from the south-south-west and the east-north-east, respectively. The data strongly support a repeated autoploid origin of the tetraploid cytotype which has been much more successful than the diploid progenitors in colonizing new land since the last ice age. High genetic diversity in Scandinavia has apparently been obtained by a combination of immigration of plants from different source areas and recurrent formation of autotetraploids from diploid progenitors.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 347−372.     

The phylogenetic relationship of possible progenitors of the cultivated peanut

The cultivated peanut (Arachis hypogaea L.) is an allotetraploid composed of A and B genomes. The phylogenetic relationship among the cultivated peanut, wild diploid, and tetraploid species in the section Arachis was studied based on sequence comparison of stearoyl-ACP desaturase and oleoyl-PC desaturase. The topology of the trees for both fatty acid desaturases displayed two clusters; one cluster with A genome diploid species and the other with B genome diploid species. The two homeologous genes obtained for each of the two fatty acid desaturases from the tetraploid species A. hypogaea and A. monticola were separated into the A and B genome clusters, respectively. The gene phylogenetic trees showed that A. hypogaea is more closely related to the diploid species A. duranensis and A. ipaensis than to the wild tetraploid species A. monticola, suggesting that A. monticola is not a progenitor of the cultivated peanut. In addition, for the stearoyl-ACP desaturase, the A. duranensis sequence was identical with one of the sequences of A. hypogaea and the A. ipaensis sequence was identical with the other. These results support the hypothesis that A. duranensis and A. ipaensis are the most likely diploid progenitors of the cultivated tetraploid A. hypogaea.     

Long-term ploidy stability of shoot primordium cultures and produced plants of melon

The chromosome number of cells in the shoot primordium aggregates and produced plants of melon [Cucumis melo L. 'Prince' (2n=2x=24)] was examined. Shoot primordium aggregates were induced from shoot-tips cultured in liquid medium and shaken at low speed (2 rpm). They were maintained by subculturing small pieces (5mm<) every 4 weeks. Shoot primordium aggregates just after induction contained about 97 diploid and 3 tetraploid cells, which was similar to those maintained in shoot primordium cultures for 6 years. This indicates that the ploidy level was maintained stably. On the other hand, plants produced from the shoot primordium aggregates just after induction were either diploid, tetraploid or mixoploid with both diploid and tetraploid cells. These ploidies were again observed among plants produced from shoot primordium cultures that were 2, 3 or 4 years old. A majority of produced plants were diploid while the total frequency of tetraploids and mixoploids was less than 8 of plants produced from all ages. Therefore, the frequency of somaclonal variation with respect to ploidy among plants produced from shoot primordium aggregates is likely to be stable at a low level over the long term.     

Variation in flavonoid patterns in relation to chromosome changes in Gibasis schiedeana

The distribution of $\text{C-}\text{glycoflavones}$ has been examined in the leaves of plants from five diploid and 12 tetraploid populations of Gibasis schiedeana. Five different chromatographic patterns were found; one occurs only in a single population of diploid plants, two were found in seven populations of tetraploids and the other two in the remaining plants from both diploid and tetraploid populations. Flavonoids were also investigated in three different types of artificially produced triploids. The effects of the changes in ploidy, which are accompanied by Robertsonian fusion and variation in the number of B chromosomes as contributory factors in the observed differences in flavonoid patterns are discussed.     

Allozyme diversity within and divergence among species ofTolpis(Asteraceae-Lactuceae) in the Canary Islands: systematic, evolutionary, and biogeographical implications

Plants endemic to oceanic islands represent some of the most unusual and rare taxa in the world. Enzyme electrophoresis was used to assess genetic diversity within and divergence among all endemic species of a small genus of plants on the Canary Islands. Our results show that the genus Tolpis is similar to many other island groups in having generally low allozyme divergence among species, with the highest divergence found among four groups of endemics. The two rare and highly localized species T. glabrescens and T. crassiuscula are each divergent from all other species in the Canaries. Tolpis coronopifolia is also divergent at allozyme loci; this is the only endemic species that is a self-compatible annual (or weak biennial). A large, morphologically variable species complex consisting of T. laciniata and T. lagopoda together with several named and unnamed morphological variants shows low allozyme divergence among its elements. The evolution of polyploidy from diploid ancestors in situ in oceanic archipelagos is uncommon, but the tetraploid T. glabrescens is an exception. Allozyme data do not implicate any extant diploid Tolpis species as parents of the polyploid. It is possible that T. glabrescens originated early in the evolution of Tolpis in the Canary Islands and that its parents are now extinct. The nonendemic T. barbata shows no greater divergence from the Canary Island endemics than some endemics exhibit among themselves. Both changes in allele frequencies and unique alleles are responsible for genetic divergence among species of Tolpis.     

Isozyme Variation and Ploidy Levels within the Apomictic Ranunculus auricomus Complex: Evidence for a Sexual Progenitor Species in Southeastern Austria

Abstract: Allozyme variation of 11 enzymes in each of three populations of the diploid species Ranunculus notabilis and the tetraploid R. variabilis of the predominantly apomictic R. auricomus complex has been studied by horizontal starch gel electrophoresis. Genetic interpretation of electrophoretic patterns is supported by chromosome counts and densitometric ploidy level determination. R. notabilis is confirmed as diploid (2 n = 16), and R. variabilis as tetraploid (2 n = 32). Two triploids and one tetraploid individual were sorted out as putative hybrids. Genetic variability measures based on both allelic frequencies and genotype frequencies were calculated for 13 polymorphic loci. Allelic and genotypic variation in R. notabilis is similar to other sexual plants, and the species is shown to be an outbreeder and not a dihaploid apomict. Corresponding values in R. variabilis confirm a previously assumed clonal population structure. A higher frequency of observed heterozygotes in R. variabilis indicates its hybridogenous origin and the lack of meiosis. Putative hybrids showed combinations of morphological phenotype and electrophoretic patterns of both species. Genetic identity is high among species (0.905), but still lower than within species ( R. notabilis : 0.965, R. variabilis : 0.940); corresponding distance values allow a clear separation of the two species in a dendrogram. Genetic identity and distance values between R. notabilis and R. variabilis resemble those of other progenitor-derivative species pairs. The results favour the hypothesis that R. notabilis is an ancient sexual species of the R. auricomus complex and also one progenitor of the presumably allopolyploid R. variabilis.     

Hybridization in the genera Vulpia and Festuca (Poaceae): the characteristics of artificial hybrids

The chromosome numbers and morphological characteristics, including life–form, vegetative and floral measurements and pollen fertility, of 70 artificial interspecific Vulpia hybrid plants and 49 artificial intergeneric Festuca rubra agg. x Vulpia hybrid plants are presented, together with comparable data from 60 artificial Festuca rubra agg. x Vulpia fasciculata plants produced by R. Cotton. The inheritance of various characters is summarized. It is concluded that most characters of the tetraploid Vulpia fasciculata are dominant over those of diploid species of Vulpia , but that most characters of the hexaploid Festuca rubra agg. are dominant over those of diploid and tetraploid species of Vulpia. In diploid x diploid Vulpia crosses the pubescent ovary tip is dominant to the glabrous state, but the inheritance of lemma pubescence is more complicated. The keeled lemmas of V. fasciculata and V. pyramidata are dominant to the rounded ones of other Vulpia species, but recessive to the rounded ones of F rubra agg. Bearing in mind such generalizations as these, the parentage of wild hybrids should be capable of correct interpretation. The significance of the results in our understanding of the origin of V. fasciculata is discussed.     

Variation of microsatellites BM224 and Bcal7 in populations of green toads (Bufo viridis complex) with various nuclear DNA content and ploidy

We studied variation of microsatellites BM224 and Bcal7 in three species of the Bufo viridis diploid-polyploid complex. We found that locus Bcal7 in all examined samples was monomorphic. Three alleles of microsatellite BM224 were found. Among tetraploid toads, the western species B. oblongus had only one allele variant, whereas the eastern species B. pewzowi had two other alleles. Similar distribution of alleles was observed in triploid specimens, collected in the area borders of tetraploid and diploid species. Among samples of diploid toad B. viridis, we found all three allele variants of microsatellite BM224. Their distribution was geographically determined. A comparison of allele distribution with genome size variation in diploid toads showed very similar patterns.     

Albumin evolution in polyploid species of the genusXenopus

Electrophoresis of serum from 21 Xenopus species and subspecies reveals variable numbers of albumin bands. The diploid X. tropicalis has one albumin, while the tetraploid species (laevis, borealis, muelleri, clivii, fraseri, epitropicalis) have two. The octoploid species (amieti, boumbaensis, wittei, vestitus, andrei) have two to three bands, and the dodecaploid X. ruwenzoriensis has three. The molecular weight of the Xenopus albumins varies from 68 kd (in the tropicalis group) to 74 kd. The subspecies of X. laevis possess two albumins of different molecular weights (70 and 74 kd), whereas most species have only 70-kd albumins. Peptide maps have been obtained from albumin electromorphs by limited proteolysis in sodium dodecyl sulfate (SDS) gels, using S. aureus V8 protease. The peptide patterns produced by electromorphs from the same tetraploid Xenopus species generally differ from each other, suggesting that the two albumin genes contain a substantial amount of structural differences. In addition, the peptide maps are diagnostic for most tetraploid species and for some subspecies of X. laevis as well. Proteolysis of albumins from most octoploid and dodecaploid species results in patterns which are very similar to the ones produced by the electromorphs from X. fraseri. The albumins of X. vestitus differ from those of the other octoploid species. X. andrei possesses two fraseri-type and one vestitus-type albumin, which indicates that it probably originated by allopolyploidy.     

Cytogeography of Solidago gigantea (Asteraceae) and its invasive ploidy level

Aim Newly formed polyploids experience problems of establishment and spread similar to those faced by newly introduced alien species. To understand the significance of polyploidy in biological invasions, we mapped the distribution of ploidy levels in Solidago gigantea Aiton in its native range in North America, and in Europe and East Asia where it is invasive. Location North America, Europe and East Asia. Methods Flow cytometry was used to measure ploidy levels in a total of 834 plants from 149 locations. Together with data from contributors and a literature review, ploidy‐level data were assembled for 336 locations. Cytogeographical maps from North America and Europe were prepared, incorporating new and previously published ploidy‐level data. Results In the native range, diploid, tetraploid and hexaploid plants were found, and also one triploid and one pentaploid plant (2n = 3x and 2n = 5x, respectively, each being new reports for this species). There was a high degree of geographical separation among the ploidy levels, and populations with mixed ploidy were rare. However, four zones were identified where plants of different ploidy could come into contact. In Europe and East Asia, only tetraploid plants were found. Main conclusions The geographical pattern in North America suggests that the ploidy levels are ecologically differentiated, although further investigations are needed to identify the nature of these differences. Alien populations appear to be exclusively tetraploid, but it is not clear whether this is because tetraploids were selectively introduced or because diploids were unsuccessful. In any case, comparisons between native and introduced populations need to account for ploidy level.     

Genetic differentiation and spatiotemporal history of diploidy and tetraploidy of Clintonia udensis

Polyploidy is an important factor shaping the geographic range of a species. Clintonia udensis (Clintonia) is a primary perennial herb widely distributed in China with two karyotypic characteristics—diploid and tetraploid and thereby used to understand the ploidy and distribution. This study unraveled the patterns of genetic variation and spatiotemporal history among the cytotypes of C. udensis using simple sequence repeat or microsatellites. The results showed that the diploids and tetraploids showed the medium level of genetic differentiation; tetraploid was slightly lower than diploid in genetic diversity; recurrent polyploidization seems to have opened new possibilities for the local genotype; the spatiotemporal history of C. udensis allows tracing the interplay of polyploidy evolution; isolated and different ecological surroundings could act as evolutionary capacitors, preserve distinct karyological, and genetic diversity. The approaches of integrating genetic differentiation and spatiotemporal history of diploidy and tetraploidy of Clintonia udens would possibly provide a powerful way to understand the ploidy and plant distribution and undertaken in similar studies in other plant species simultaneously contained the diploid and tetraploid.