FISH-aimed karyotype analysis in Aconitum subgen : aconitum reveals excessive rDNA sites in tetraploid taxa

The location of 5S and 35S rDNA sequences in chromosomes of four Aconitum subsp. Aconitum species was analyzed after fluorescence in situ hybridization (FISH). Both in diploids (2n = 2x = 16; Aconitum variegatum, A. degenii) and tetraploids (2n = 4× = 32; A. firmum, A. plicatum), rDNA repeats were localized exclusively on the shorter arms of chromosomes, in subterminal or pericentromeric sites. All analyzed species showed similar basal genome size (Cx = 5.31-5.71 pg). The most striking features of tetraploid karyotypes were the conservation of diploid rDNA loci and emergence of many additional 5S rDNA clusters. Chromosomal distribution of excessive ribosomal sites suggests their role in the secondary diploidization of tetraploid karyotypes

Karyotype structure and chromosome fragility in the grass Phleum echinatum Host

Phleum echinatum Host (2n = 2x = 10) is an annual Mediterranean species which differs from other representatives of the genus Phleum by reduced chromosome number, asymmetric karyotype and unusually high amount of DNA in the genome. Chromosomes of this plant were studied using conventional acetic-orcein staining and fluorescence in situ hybridization (FISH). FISH showed the major 35S ribosomal DNA (rDNA) site at the secondary constriction of satellite chromosome (3) and the minor 35S rDNA site near 5S rDNA cluster in the monobrachial chromosome 5. Telomeric repeats were detected at all chromosome ends within secondary constriction in satellited chromosome 3 and at the centromeric regions of chromosomes 1 and 2. Intrachromosomally located telomeric repeats are probably traces of chromosomal rearrangements that have shaped P.echinatum genome; they were prone to breakage which was manifested in chromosome fragmentation. The most distinct telomeric signals, suggesting massive amplification of interstitial telomeric sequences (ITRs), were observed at the nucleolar organizer region (NOR) of the third chromosome pair. Double FISH confirmed co-localization of telomeric and 35S rDNA repeats in this locus characterized by the biggest fragility in the karyotype. Fragile sites of P.echinatum, composed of amplified telomeric repeats, may bear a resemblance to metazoan rare fragile sites enriched in microsatellite repeats

Polyploidy, alien species and invasiveness in Polish angiosperms

Chromosome numbers, mainly for Polish flora, were examined in order to investigate whether such features as chromosome numbers and polyploid frequencies are correlated with a plant’s origin (native vs. alien) and invasiveness. Polyploid frequencies were estimated using three methods: the 11 and 14 thresholds and the 3.5 x value. Comparisons of the 2n values were done on different levels: in all angiosperms and in dicots and monocots separately. Invasive and non-invasive plants were compared in the entire dataset and in alien species only. Significant differences in both chromosome numbers and polyploid frequencies between alien and native species were observed. In most cases, native plants had more chromosomes and were more abundant in polyploids than in alien species. Also, monocots had higher polyploid frequencies than dicots. Comparisons of invasive and non-invasive plants done for all of the data and only for alien species showed that invasive species generally had more chromosomes and polyploids were more frequent in them than in the latter group; however, these differences were not always statistically significant. Possible explanations for these observations are discussed

Physiological aspects of sex differences and Haldane’s rule in Rumex hastatulus

Haldane’s rule (HR, impairment of fertility and/or viability of interracial hybrids) seems to be one of few generalizations in evolutionary biology. The validity of HR has been confirmed in animals, and more recently in some dioecious plants (Silene and Rumex). Dioecious Rumex hastatulus has two races differing in the sex chromosome system: Texas (T) and North Carolina (NC), and T × NC males showed both reduced pollen fertility and rarity—two classical symptoms of Haldane’s rule (HR). The reduced fertility of these plants has a simple mechanistic explanation, but the reason for their rarity was not elucidated. Here, we measured selected physiological parameters related to the antioxidant defense system in parental races and reciprocal hybrids of R. hastatulus. We showed that the X-autosome configurations, as well as asymmetries associated with Y chromosomes and cytoplasm, could modulate this system in hybrids. The levels and quantitative patterns of the measured parameters distinguish the T × NC hybrid from the other analyzed forms. Our observations suggest that the rarity of T × NC males is caused postzygotically and most likely related to the higher level of oxidative stress induced by the chromosomal incompatibilities. It is the first report on the physiological aspects of HR in plants

Chromosome numbers and stomatal cell length in Taraxacum sect. Palustria from Poland

Chromosome numbers are given for the following species of Taraxacum sect. Palustria from Poland: T. paucilobum Hudziok (2n = 24, 25), T. belorussicum Val. N. Tikhom. (2n = 24), T. subdolum Kirschner & Štěpánek (2n = 24), T. udum Jordan (2n = 24), T. trilobifolium Hudziok (2n = 24), T. bavaricum Soest (2n = 24), T. portentosum Kirschner & Štěpánek (2n = 32), T. vindobonense Soest (2n = 32), and T. brandenburgicum Hudziok (2n = 32). The chromosome numbers of T. belorussicum and T. portentosum are published for the first time, and for T. subdolum, T. bavaricum and T. brandenburgicum for the first time from Poland. The analyzed group of taxa is heterogenous in respect of stomatal size, and after pooling of data the tetraploids show bigger stomata than the triploids

Male adventitious roots of Rumex thyrsiflorus Fingerh. as a source of genetically stable micropropagated plantlets

Rumex thyrsiflorus Fingerh. is one of the few dioecious plant species that have sex chromosomes. The chromosome constitution of females is 2n = 12A + XX and 2n = 12A + XY1Y2 of males. It is a medicinally important plant species and has also been the object of studies on the structure and function of sex chromosomes and sex ratio. An efficient plant regeneration protocol was developed from karyologically stable male roots that had been derived from a long-term liquid culture. The root segments were grown on MS medium supplemented with the following plant growth regulators: 2.4-D, NAA, kinetin, BAP and TDZ. The highest frequency (81.73 %) of adventitious shoot formation (16.27 shoots/explant) was obtained on MS + 0.5 mg/l TDZ. Regenerated shoots were successfully rooted on ½ MS + 2 % sucrose + 0.5 mg/l IBA and acclimated to in vivo conditions. Histological analysis revealed indirect (via callus) adventitious shoot formation. The cells of the morphogenetic callus were surrounded by a fibrillar structure that was similar to the extracellular matrix. Molecular analysis based on genetic sex markers confirmed that all of the root explants were male. The genetic stability of the regenerated plantlets was confirmed using random amplified polymorphic DNA analysis. This is the first report concerning the micropropagation protocol for R. thyrsiflorus Fingerh. from male roots derived from a long-term liquid culture, which offers a unique opportunity to obtain true-to-type plants of the same sex