PGSE diffusion NMR studies on mononuclear and dinuclear cationic platinum salts of (S)-MeO-Biphep and (R)-p-tolyl-BINAP

PGSE diffusion NMR studies on a series of mononuclear and dinuclear cationic platinum salts derived from (S)-MeO-Biphep and (R)-p-tolyl-BINAP are reported. The data show that (a) one can readily distinguish between mononuclear and dinuclear cations (b) the amount of ion pairing can be estimated qualitatively and (c) the charge delocalization rather than the amount of formal charge per metal cation is important for the position of the anion. The solid-state structure of the chloro-bridged salt, [Pt(μ-Cl){(S)-MeO-Biphep}]₂(CF₃SO₃)₂, is reported.     

Unstable B-chromosomes in a European population of Allium schoenoprasutn L. (Liliaceae)

In Allium schoenoprasum , small, dichromatic B-chromosomes occur in 74% of plants at Lac de Tracens, Pare National des Pyrénées. B-chromosomes from Lac de Tracens were compared with the previously well characterized Bs from British populations of A. schoenoprasum at the River Wye, Powys, and were found to differ in terms of both their morphology and the level of mitotic instability. At Lac de Tracens, two morphological types of B-chromosome were observed: a telocentric of about 1.15 μm in length and a metacentric of about 1.35 μm in length; the most frequent B-type in the River Wye populations (B^-1) was not found. B-chromosomes from the River Wye are essentially stable at root tip mitosis, whereas 25 out of 29 plants from Lac de Tracens (86%) showed between-cell variation in B-number, with non-modal numbers in 330 out of 794 cells (41.6%). Most of the variability occurred within individual roots, rather than between roots of single bulbs or of sister bulbs. No meiotic pairing was observed between the different Bs in hybrids from the geographically isolated populations, suggesting a lack of homology. An independent origin of B-chromosomes in the British and French populations is suggested.     

Cytogenetic studies in Papaver L.; the x= 6 and x= 7 diploids

Although hybridization between species in Papaver is difficult, a combination of karyotypic and genomic analysis has allowed the definition of up to six, apparently independent genomes, in the 2n= 12 and 1n= 14 diploids. In the 2n= 14 group there is considerable karyotypic differentiation and karyotypes off. atlanticum and P. hybridum are sufficiently dissimilar from each other and from the rest to allow the recognition of the two genomes as unique although no hybrids with other x= 7 diploids were produced. The genome of P. atlanticum is defined as C₇C₇ and that of P. hybridum H₇H_7.P. alpinum and P. rhaeticum only hybridized successfully with each other and the near perfect bivalent formation in their hybrid, together with the extreme similarity of their karyotypes, suggests that they are very closely related. They are designated J₇J₇. All the other x=7 diploids are karyotypically similar and the analysis of meiosis in their hybrids demonstrates thay they all share the same genome to some extent. There is however some differentiation among them. P. commutatum, P. glaucum, P. macrostemum and P. rhoeas are genomically very similar and all can be regarded as A₇A₇. P.fugax and P. tauricola appear to share an identical genome, partially differentiated from A₇A₇ and are defined as A²₇A²₇ while P. postii, although showing some little homology with A₇A₇ is sufficiently differentiated from it to be regarded as more distant than A²₇A²₇ and is described as A³₇A³₇. Although no hybrids between the two 2n= 12 diploids P. apulum and P.pavoninum were produced their karyotypes are sufficiently different to be individually recognized. The only hybrid produced between the x= 6 and x= 7 groups (P. apulum×P. hybridum) showed no homology between the chromosomes of the two genomes and, although this may not be true for any other x=6/x=7 combinations it is best to recognize the two x= 6 genomes as independent of the x= 7. The genome of P. apulum is thus regarded as I₆I₆ and that of P. pavoninum as P₆P₆.     

A simple PCR-based method for scoring the ph1b deletion in wheat

 The amplified fragment length polymorphism (AFLP) technique was used to isolate DNA sequences present in the euploid wheat Chinese Spring but not in the Chinese Spring ph1b mutant (which has a deletion of the Ph1 gene, a suppressor of homoeologous chromosome pairing). The polymorphic DNA fragments identified by AFLP were then cloned, sequenced, and used to design two primer pairs. These primers were used in a PCR-based assay to specifically amplify products from the Chinese Spring euploid but not from the ph1b mutant. This PCR assay can be carried out from extracted genomic DNA or directly from alkaline-treated wheat leaves, and the reaction products can be scored on a plus-minus basis, making the screening amenable to automation. The reliability of the assay was tested using a F₁-derived doubled-haploid population of 55 lines which segregate for the ph1b deletion. This PCR-screening technique is less time and labour consuming, and more accurate and reliable, than cytologically based conventional methods. Received: 4 September 1997 / Accepted: 19 September 1997     

Interspecific hybridization and the analysis of meiotic chromosome pairing inDahlia (Asteraceae — Heliantheae) species with x = 16

The successful production of a large number of artificial hybrids betweenDahlia species based on x = 16 has allowed a detailed study of their genomic relationships. Chromosome behaviour in these artificial hybrids was extremely similar to that observed in parental species suggesting that there is a considerable degree of homology between the genomes of theseDahlia species. Using GISH it can be demonstrated that in these hybrids bivalent formation involved pairing only between parental genomes. The ability of GISH to differentiate between parental genomes in artificial hybrids was variable, indicating that molecular divergence of highly repeated sequences has accompanied the evolution of these species. However, the extent of chromosome pairing and chiasma formation in the hybrids does not reflect the differences that can be detected by GISH. Seyeral of the new hybrid combinations have resulted in horticulturally interesting plants.     

Cytogenetics of the trigeneric hybrid, (Hordeum vulgare ×Triticum aestivum) ×Secale cereale

Summary Chromosome pairing was studied in hybrids of (Hordeum vulgare ×Triticum aestivum) ×Secale cereale. Chiasma frequency per cell varied from 1.94 to 3.16 between the different hybrids. This variation was attributed to genetic variability in rye parents which affected homoeologous pairing. The pairing of rye chromosomes as revealed by Giemsa C-banding was a combination of nonhomologous association between rye chromosomes and associations with chromosomes of wheat and barley. Contribution No. 634 Ottawa Research Station     

A biosystematic study of theOryza meyeriana complex (Poaceae)

To determine the taxonomic status and to clarify the biosystematic relationships of wild rice species, i.e.,Oryza granulata andO. meyeriana in theO. meyeriana complex (Poaceae), a series of intraspecific and interspecific hybridization experiments, genomic analyses through meiotic pairing, and morphological studies were conducted. Hybridization results demonstrate comparatively high crossability with about 34–39% of seed set, and very limited reproductive isolation betweenO. granulata andO. meyeriana. Chromosome pairing in the parental species and their F₁ hybrids indicate very high genomic affinity between the two taxa. Morphological analyses of the parental accessions and their intra- and interspecific hybrids show a large variation among the samples included, but no appreciable grouping was observed. The traditionally used character, i.e., spikelet length, does not contribute significantly to the grouping of the samples included. Based on the facts that the two taxa have negligible reproductive barriers and share almost identical genomes, the authors believe thatO. granulata andO. meyeriana do not warrant separate taxonomic status, and recommend that they be combined asOryza granulata.     

Perturbation of Surface Tension of Water by Polyhydric Additives: Effect on Glucose Oxidase Stability

An experimental investigation is reported on the influence of some polyhydric additives (ethanediol, 1,2-propanediol and glycerol) on the thermal behaviour of Aspergillus niger glucose oxidase. Spectroscopic measurements performed to follow protein unfolding showed that all the cosolvents destabilize the enzyme and caused an increase in the standard enthalpy and entropy of transition. Furthermore the melting temperature was found to be intimately related to the surface tension of the medium. The obtained results were interpreted as the consequence of preferential protein-cosolvent interactions determined by the perturbation of the surface tension of water.     

Better Cryo-EM Specimen Preparation: How to Deal with the Air–Water Interface?

Cryogenic electron microscopy (cryo-EM) is now one of the most powerful and widely used methods to determine high-resolution structures of macromolecules. A major bottleneck of cryo-EM is to prepare high-quality vitrified specimen, which still faces many practical challenges. During the conventional vitrification process, macromolecules tend to adsorb at the air–water interface (AWI), which is known unfriendly to biological samples. In this review, we outline the nature of AWI and the problems caused by it, such as unpredictable or uneven particle distribution, protein denaturation, dissociation of complex and preferential orientation. We review and discuss the approaches and underlying mechanisms to deal with AWI: 1) Additives, exemplified by detergents, forming a protective layer at AWI and thus preserving the native folds of target macromolecules. 2) Fast vitrification devices based on the idea to freeze in-solution macromolecules before their touching of AWI. 3) Thin layer of continuous supporting films to adsorb macromolecules, and when functionalized with affinity ligands, to specifically anchor the target particles away from the AWI. Among these supporting films, graphene, together with its derivatives, with negligible background noise and mechanical robustness, has emerged as a new generation of support. These strategies have been proven successful in various cases and enable us a better handling of the problems caused by the AWI in cryo-EM specimen preparation.     

Structural basis for different membrane-binding properties of E. coli anaerobic and human mitochondrial β-oxidation trifunctional enzymes

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