Boeckella diamantina n.sp. (Calanoida,Centropagidae), from a high Andean lake in Mendoza,Argentina

A new species of Boeckella from limnetic samples of Laguna del Diamante, a high lake in the Andes (34°10 S) is described and illustrated. The species is defined by the characters of the male fifth leg: the right two segmented endopod bears four peculiar, short, claw-like spines, the left endopod is a simple finger-like projection. This species is related to B. gibbosa, also a species from the Andes and B. vallentini from Malvinas (Falkland Islands) and other subantarctic islands. It is distinguished from them by diagnostic features of the fifth legs of the male and abdominal structure and fifth legs of the female. Some current views on the features used in the taxonomy of the genus Boeckella are discussed.     

On the evolution of protamines in bony Fish: Alternatives to the “Retroviral horizontal transmission” hypothesis

Fish protamines are highly specialized molecules which are responsible for chromatin condensation during the last stages of spermatogenesis (spermiogenesis). However, not all fish contain protamines in their sperm nuclei; rather, there seems to be a random distribution of protamines within this group. The origin of this sporadic presence of protamines in the sperm and its significance have not yet been precisely determined. In this paper we have conducted an exhaustive survey of the literature available on the different types of nuclear protein composition of the sperm of teleost fish in order to try to correlate these data with what is presently known about the taxonomy of this group. The results of this analysis have allowed us to make the following observations. The divergence between protamines and histones has occurred several times during the evolution of the bony fish. However, the relative frequency of this divergence is almost negligible during the differentiation of genera and species (intrafamily variation) and is very small during the differentiation of families (interfamily variation). Nevertheless, the divergence is very noticeable among the different orders. It is therefore possible to conclude from all this that the sporadic distribution of protamines in bony fish is not a random event as initially believed. Furthermore, such a heterogeneous distribution of protamines cannot be easily accounted for by a mechanism of horizontal retroviral transmission through repeated and independent acquisition of a prot amine gene as has been recently proposed (Jankowski, Stater, Dixon (1986) J Mol Evol 23:1–10). Rather, it could possibly be explained by a repeated and independent loss of the expression of the protamine gene (or loss of the gene itself) which mainly occurred during the diversification of the orders of this group.Correspondence to: J. Ausio     

New species and a new combination in Myrtaceae from northeastern South America

Three new species of Myrtaceae (Calyptranthes bracteata, Eugenia gonglycocarpa, andMyrcia rupta) from northeastern South America are described and illustrated, and a new combination (Eugenia tetramera) is proposed. The closed-calyx and the completely or partially fused cotyledons ofMyrcia rupta, unusual features for the genus, are discussed and compared with related species inMyrcia andMarlierea.     

Keepers of maize in Chiapas,Mexico

This study concerns the knowledge and selection of biological diversity of maize (Zea mays) within its center of domestication in Mesoamerica. Maize farmers in central Chiapas of Southern México keep local varieties (landraces) belonging to six races and four race mixtures. Fifteen local varieties are recognized. In spite of widespread adoption of a modern, high yielding variety, maize farmers continue to select local varieties for specific soils and because of agronomic and use criteria. Farmers maintain maize varieties primarily through seed selection. Spatial and temporal separation do not seem sufficient to maintain varieties. The management of improved varieties can lead from a uniform population to a heterogeneous one as hybridization with local maize populations occurs.     

Compositional heterogeneity of the Escherichia coli genome: A role for VSP repair?

E. coli genes that contain a high frequency of the tetranucleotide CTAG are also rich in the tetramers CTTG, CCTA, CCAA, TTGG, TAGG, and CAAG (group-I tetramers). Conversely, E. coli genes lacking CTAG are rich in the tetranucleotides CCTG, CCAG, CTGG, and CAGG (group-II tetramers). These two gene samples differ also in codon usage, amino acid composition, frequency of Dcm sites, and contrast vocabularies. Group-I tetramers have in common that they are depleted by very-short-patch repair (VSP), while group-II tetramers are favored by VSP activity. The VSP system repairs G:T mismatches to G:C, thereby increasing the overall G+C content of the genome; for this reason the CTAG-rich sample has a lower G+C content than the CTAG-poor sample. This compositional heterogeneity can be tentatively explained by a low level of VSP activity on the CTAG-rich sample. A negative correlation is found between the frequency of group-I tetramers and the level of gene expression, as measured by the Codon Adaptation Index (CAI). A possible link between the rate of VSP activity and the level of gene expression is considered.Correspondence to: A. Marine     

Expression of the BnmNAP subfamily of napin genes coincides with the induction of Brassica microspore embryogenesis

Brassica napus cv. Topas microspores can be diverted from pollen development toward haploid embryo formation in culture by subjecting them to a heat stress treatment. We show that this switch in developmental pathways is accompanied by the induction of high levels of napin seed storage protein gene expression. Changes in the plant growth or microspore culture conditions were not by themselves sufficient to induce napin gene expression. Specific members of the napin multigene family were cloned from a cDNA library prepared from microspores that had been induced to undergo embryogenesis. The majority of napin clones represented three members (BnmNAP2, BnmNAP3 and BnmNAP4) that, along with a previously isolated napin genomic clone (BngNAP1), constitute the highly conserved BnmNAP subfamily of napin genes. Both RNA gel blot analysis, using a subfamily-specific probe, and histochemical analysis of transgenic plants expressing a BngNAP1 promoter--glucuronidase gene fusion demonstrated that the BnmNAP subfamily is expressed in embryogenic microspores as well as during subsequent stages of microsporic embryo development.     

A descriptive study of some Antarctic notaspidean opisthobranchs (Gastropoda), with description of a new genus and species

During the expedition “ANTARTIDA 9101”, organized by the Spanish Oceanographic Institute to the South Orkney Islands, four specimens of notaspidean gastropods were collected. Three of them have been identified as Bathyberthella antarctica Willan and Bertsch, 1987. However, one specimen, although externally similar to B. antarctica, had an internal anatomy exhibiting features that have enabled us to consider it to be a new genus and species. This new taxon is characterized by the presence of jaws without mandibular elements, and a vaginal gland that partially surrounds the distal region of the vaginal duct. In this paper the new genus and species is described. Additional anatomical data of the specimens of B. antarctica collected during the expedition are also included.     

Supercritical carbon dioxide extraction of hydrocarbons from the microalgaBotryococcus braunii

Samples of the microalgaBotryococcus braunii were submitted to supercritical fluid extraction with carbon dioxide at 40 °C and pressures of 12.5, 20.0 and 30.0 MPa. The extraction yield and the fraction of the hydrocarbons in the extracts both increased with pressure and at 30 MPa these compounds were obtained rapidly. This behaviour is associated with the localization of the hydrocarbons outside the cell wall. In the extracts, which are fluid, golden and limpid, chlorophyll and phospholipids were not detected.Author for correspondence     

Expression of mutations and protein release by yeast conditional autolytic mutants in batch and continuous cultures

Thermosensitive mutant strains of Saccharomyces cerevisiae that fail to generate an osmotically stable cell wall when grown at a non-permissive temperature release their cell contents upon expression of the mutation. Therefore, they may represent an alternative for the production of homologous or heterologous protein preparations. In order to analyse the expression of two of these mutations, lyt2 and slt2, we grew the corresponding strains under precisely defined conditions in batch and continuous fermentors. A switch in the temperature of batch cultures from 24° C to 37° C determined lysis of the cells with a significant release of intracellular enzymes. These include alkaline phosphatase and periplasmic proteins such as glucan-degrading enzymes, the pattern of cell lysis and protein release being maintained for about 6 h. One-stage continuous cultures of a lyt2 mutant were maintained for long periods at 37° C; a fraction of the population lysed and released the indicated proteins, but eventually a revertant of the lytic phenotype was selected. To avoid this, a two-stage continuous culture system was developed by connecting two fermentors in series, the effluent from the first one at 24°C being fed to the second one adjusted to 37° C. A steady state of cell lysis and protein liberation was reached in the second-stage fermentor without any evidence of selection of revertants. This system can be very useful for developing conditions for the use of yeast strains to produce protein preparations. Correspondence to: C. Nombela     

Life-history studies of heterophyid trematodes in the Neotropical Region: Ascocotyle (Phagicola) diminuta (Stunkard & Haviland, 1924) and A. (P.) angrense Travassos, 1916

The life-cycle of Ascocotyle (Phagicola) diminuta (Stunkard & Haviland, 1924) was reproduced experimentally, starting from cercariae from naturally infected Littoridina castellanosae and L. parchappei (Hydrobiidae) collected from artificial ponds in the Zoological Garden in Buenos Aires and from Los Ranchos stream, Buenos Aires Province, respectively. Metacercariae were found encysted in the gills of experimentally exposed Cnesterodon decemmaculatus (Poecilidae) and of other naturally infected freshwater fishes. Adults were obtained experimentally in chicks and mice and from a naturally infected egret, Egretta thula. A. (P.) angrense Travassos, 1916 was found parasitising the egret Ixobrychus involucris; it is considered a valid species and the morphological differences between it and A. (P.) diminuta were established. The “Phagicola-form” of the cercaria in the present life-cycle is also known in the genus Pygidiopsis.