Meiotic chiasmata were analysed in metaphase I pollen mother cells (PMCs) of wild-type Arabidopsis thaliana and in two meiotic mutants. Fluorescence in situ hybridisation (FISH) with 45S rDNA and 5S rDNA as probes was used to identify the five chromosome pairs. A wild-type chiasma frequency of 9.24 per cell was found, consistent with estimated genetic recombination values. Individual bivalent chiasma frequencies varied according to chromosome size; chromosome 1 had the highest mean chiasma frequency (2.14) while the short acrocentric chromosomes had the lowest frequencies (1.54 and 1.56). FISH analysis was extended to two meiotic mutants (asy1 and dsy1) having low residual bivalent and chiasma frequencies. Mutant dsy1 gave no indication of chromosome preference for residual bivalent formation; instead it showed a general reduction in bivalent and chiasma frequencies. In asy1, the longest chromosome (1) had the lowest bivalent frequency and chiasma frequency while the short acrocentric chromosome 2 had the highest frequencies. This chromosome pair may be preferentially involved in synapsis and chiasma formation because of their association with the nucleolus. However, other factors may be operating since the other acrocentric chromosome (4), with similar size and structure to chromosome 2, did not share these chiasma properties.

We present the first detailed cytological study of male meiosis in Daphnia (Crustacea: Branchiopoda: Cladocera)—an aquatic microcrustacean with a cyclical parthenogenetic life cycle. Using immunostaining of the testes in Daphnia magna for baseline knowledge, we characterized the different stages of meiotic division and spermiogenesis in relation to the distribution of proteins involved in synapsis, early recombination events and sister chromatid cohesion. We also studied post-translational histone modifications in male spermatocytes, in relation to the dynamic chromatin progression of meiosis. Finally, we applied a DNA fragmentation test to measure sperm quality of D. magna, with respect to levels of inbreeding. As a proxy for fertility, this technique may be used to assess the reproductive health of a sentinel species of aquatic ecosystems. Daphnia proves to be a model species for comparative studies of meiosis that is poised to improve our understanding of the cytological basis of sexual and asexual reproduction.Electronic supplementary materialThe online version of this article (doi:10.1007/s00412-015-0558-1) contains supplementary material, which is available to authorized users.

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Induction of High-Temperature Superconductivity in Pulsed Laser Ablated La2CuO4 Thin Films by Room Temperature Chemical Oxidation. -Stoichiometric, c-axis oriented La2CuO4 films of ≈3700Å tickness are deposited on single crystalline SrTiO3 substrates by pulsed laser ablation from a sintered oxide target. Controlled room temp. oxidation wih aquous NaOH/Br2 solution is then utilized to introduce excess holes in the valence band of La2CuO4. This induces superconductivity with Tc (onset) values of 30-33 K in the otherwise antiferromagnetic semiconductor. -(LEES, S. T.; EDWARDS, P. P.; GAMESON, I.; JONES, M. O.; SLASKI, M.; RIAL, C.; AMADOR, U.; MORAN, E.; Adv. Mater. (Weinheim, Ger.) 9 (1997) 10, 823-826; Sch. Chem., Univ. Birmingham, Edgbaston, Birmingham B15 2TT, UK; EN)