Karyotype, meiotic behavior and pollen features of Senna occidentalis

Meiotic behavior, pollen morphology, interphasic nucleus pattern and karyotype description for Senna occidentalis (Caesalpinioideae — Fabaceae) are presented. The species had non-reticulate interphasic nucleus and homogeneous chromosome condensing with minute distal late-condensing portions in prometaphase. In mitotic metaphase, chromosome number was 2n = 28 (9 m + 5 sm), with secondary constriction in one chromosome pair. Detection of four nucleoli indicated existence of two chromosome pairs bearing Nucleolar Organizer Region (NOR). Meiotic behavior was regular, with high meiotic index (95%). Pollen grains, classified as polar/spheroidal, presented 90% viability.

Laser isolation of plant sex chromosomes: studies on the DNA composition of the X and Y sex chromosomes of Silene latifolia

X and Y sex chromosomes from the dioecious plant Silene latifolia (white campion) were isolated from mitotic metaphase chromosome preparations on polyester membranes. Autosomes were ablated using an argon ion laser microbeam and isolated sex chromosomes were then recovered on excised fragments of polyester membrane. Sex chromosome associated DNA sequences were amplified using the degenerate oligonucleotide primed polymerase chain reaction (DOP–PCR) and pools of DOP–PCR products were used to investigate the genomic organization of the S. latifolia sex chromosomes. The chromosomal locations of cloned sex chromosome repeat sequences were analysed by fluorescence in situ hybridization and data complementary to laser ablation studies were obtained by genomic in situ hybridization. In combination, these studies demonstrate that the X and Y sex chromosomes of S. latifolia are of very similar DNA composition and also that they share a significant repetitive DNA content with the autosomes. The evolution of sex chromosomes in Silene is discussed and compared with that in another dioecious species, Rumex acetosa.Key words: FISH, GISH, laser-microdissection, sex chromosome, Silene latifolia.

Bulinus on Aldabra and the subfamily Bulininae in the Indian Ocean area

The molluscan family Planorbidae is widely distributed throughout the temperate and tropical regions of the world. The subfamily Bulininae includes two genera only, Bulinus which is confined to the Ethiopian zoogeographical region, the Mediterranean area, the Middle East and some islands in the Western Indian Ocean, and Indoplanorbis which is common throughout India and Southeast Asia and also occurs on Socotra. These snails have been the subject of particularly intense study because of their importance as intermediate hosts for blood-flukes of the genus Schistosoma parasitic in man and domestic animals. The presence of a species of Bulinus on Aldabra is interesting because of the relative rarity of freshwater molluscs on atolls and also because it has served as a focus for drawing together the results of recent investigations into the distribution, relationships and intermediate host capacity of bulinids in the Indian Ocean area. This area has presented a number of problems in the interpretation of patterns of schistosomiasis transmission and most of these problems stem from misunderstandings about the taxonomy of the host snails and their parasites. Many of the misunderstandings have arisen from the paucity and unreliable nature of morphological criteria for taxonomic studies in basommatophoran snails and these have now been supplemented by cytogenetic, biochemical and immunological information. The methods used include paper chromatography of bodysurface mucus (Wright 1964), electrophoresis of egg proteins on cellulose acetate (Wright & Ross 1965, 1966), starch-gel electrophoresis of digestive-gland enzymes (Wright, File & Ross 1966; Wright & File 1968), Ouchterlony plate gel diffusion and agar-gel immuno-electrophoresis of egg proteins using antisera prepared in rabbits, and colcimid blocking of mitotic metaphase chromosome figures in developing embryos.