Contrasting responses of oligochaete communities to the abatement of eutrophication in Lake Geneva

Tubificid and lumbriculid worms were used to monitor, at depths of 150 m, the recovery of Lake Geneva (Switzerland) from eutrophication. As predicted from the decrease of phosphorus concentrations, relative abundance of oligotrophic species was higher from 1988 to 1993 than in 1983, i.e. before the abatement of eutrophication. However, this trend towards oligotrophication can be reversed, as indicated by a decrease of oligotrophic species, recorded in 1993. But this change corresponded to the effects of an increase of water temperature on the abundance of the mesotrophic species Potamothrix vejdovskyi rather than to a deterioration of the profundal. In addition to this short-term setback, oligochaete communities located at a depth of 150 m responded more slowly and less clearly to the decrease of phosphorus concentrations than those located at a depth of 40 m. However, the zoobenthos indicated more clearly the recovery of Lake Geneva than the phytoplankton.     

Extrusion de chromatine dans le cytoplasme deChara vulgaris L. après irradiation

Zusammenfassung Dic Vermehrung der Chromatinmasse im Cytoplasma der neugebildeten internodialen Zellen derChara vulgaris wird beschrieben und in ihrer Abhängigkeit von induzierten Änderungen im endomitotischen Prozeß besprochen.     

Nance-Horan syndrome: linkage analysis in 4 families refines localization in Xp22.31–p22.13 region

Nance-Horan syndrome (NHS) is an X-linked disease characterized by severe congenital cataract with microcornea, distinctive dental findings, evocative facial features and mental impairment in some cases. Previous linkage studies have placed the NHS gene in a large region from DXS143 (Xp22.31) to DXS451 (Xp22.13). To refine this localization further, we have performed linkage analysis in four families. As the maximum expected Lod score is reached in each family for several markers in the Xp22.31–p22.13 region and linkage to the rest of the X chromosome can be excluded, our study shows that NHS is a genetically homogeneous condition. An overall maximum two-point Lod score of 9.36 (θ = 0.00) is obtained with two closely linked markers taken together, DXS207 and DXS1053 in Xp22.2. Recombinant haplotypes indicate that the NHS gene lies between DXS85 and DXS1226. Multipoint analysis yields a maximum Lod score of 9.45 with the support interval spanning a 15-cM region that includes DXS16 and DXS1229/365. The deletion map of the Xp22.3–Xp21.3 region suggests that the phenotypic variability of NHS is not related to gross rearrangement of sequences of varying size but rather to allelic mutations in a single gene, presumably located proximal to DXS16 and distal to DXS1226. Comparison with the map position of the mouse Xcat mutation supports the location of the NHS gene between the GRPR and PDHA1 genes in Xp22.2. Received: 14 June 1996 / Revised: 10 October 1996     

Molecular characterization of a second copy of holocarboxylase synthetase gene (hcs2) in Arabidopsis thaliana.

Holocarboxylase synthetase (HCS), catalyzing the covalent attachment of biotin, is ubiquitously represented in living organisms. Indeed, the biotinylation is a post-translational modification that allows the transformation of inactive biotin-dependent carboxylases, which are committed in fundamental metabolisms such as fatty acid synthesis, into their active holo form. Among other living organisms, plants present a peculiarly complex situation. In pea, HCS activity has been detected in three subcellular compartments and the systematic sequencing of the Arabidopsis genome revealed the occurrence of two hcs genes (hcs1 and hcs2). Hcs1 gene product had been previously characterized at molecular and biochemical levels. Here, by PCR amplification, we cloned an hcs2 cDNA from Arabidopsis thaliana (Ws ecotype) mRNA. We observed the occurrence of multiple cDNA forms which resulted from the alternative splicing of hcs2 mRNA. Furthermore, we evidenced a nucleotide polymorphism at the hcs2 gene within the Ws ecotype, which affected splicing of hcs2 mRNA. This contrasted sharply with the situation at hcs1 locus. However, this polymorphism had no apparent effect on total HCS activity in planta. Finally, hcs2 mRNAs were found 4-fold less abundant than hcs1 mRNA and the most abundant hcs2 mRNA spliced variant should code for a truncated protein. We discuss the possible role of such a multiplicity of putative HCS proteins in plants and discuss the involvement of each of hcs genes in the correct realization of biotinylation.     

ALGAE CONTAINING CHLOROPHYLLS a + c ARE PARAPHYLETIC: MOLECULAR EVOLUTIONARY ANALYSIS OF THE CHROMOPHYTA

Sequence comparisons of small subunit ribosomal RNA coding regions from 12 chlorophylls a + c-containing algae were used to infer phylogenetic relationships within the Chromophyta. Three chromophyte lines of descent, delineated by the Bacillariophyceae, the Phaeophyceae/Xanthophyceae, and the Chrysophyceae/Eustigmatophyceae/Synurophyceae are members of a complex evolutionary assemblage, which also includes representatives of the Oomycota (“lower” fungi). Maximum parsimony and distance matrix methods demonstrate a common evolutionary history for these lineages but their relative branching order could not be determined. Other algal species with chlorophylls a + c, including dinoflagellates and prymnesiophytes, are not members of this complex assemblage. Dinoflagellates are specifically related to apicomplexans and ciliates, and the prymnesiophyte, Emiliania huxleyi, represents an independent photosynthetic lineage that separated from other eukaryotes during the nearly simultaneous divergence of plants, animals, fungi, and a number of other protist lineages. The small subunit rRNA phylogenies of chromophytes/oomycetes were compared to those derived from comparisons of ultrastructural characters. Only tubular, tripartite mastigonemes (flagellar hairs) characterized all studied taxa of chromophytes/oomycetes as a monophyletic assemblage.     

Occurrence of a copia-like transposable element in one of the introns of the potato starch phosphorylase gene

Summary A 37.5 kb region encompassing a set of the naphthalene degrading genes on the Pseudomonas plasmid NAH7 was found to be transposable only in the presence of the transposase encoded by the Tn1721 subgroup of the class II transposons. This newly identified mobile element, designated Tn4655, contained short (38 bp) terminal inverted repeats which shared extensive sequence homology with those of members of the Tn1721 subgroup. Tn4655 transposed by a two-step process involving formation of the cointegrate followed by its subsequent resolution. In contrast to the defect in the trans-acting factor for the first step, a functional system for the latter step was encoded within a 2.4 kb region in Tn4655. Analysis of deletion and insertion mutants demonstrated that the 2.4 kb region contained the cis-acting (res) site and the gene for a trans-acting factor (resolvase); complementation analysis indicated that Tn4655 resolvase function was not interchangeable with those of other well-studied class 11 transposons, including the Tn1721 subgroup. Tn4655 had no DNA sequences that were hybridizable with the transposase or resolvase genes of the Tn1721 subgroup.Abbreviations Ap ampicillin - Cb carbenicillin - Cm chloramphenicol - Km kanamycin - Sm streptomycin - Tc tetracycline - Tp trimethoprim     

Polysome formation and incorporation of new ribosomes into polysomes during germination of the embryonic axis of maize

Isolated axes of Zea mays L. cvs CiV₂ and CUZCO were imbibed for different periods of time, and free polysomes were extracted and analysed by centrifugation in a sucrose gradient. The amount of rRNA per axis was determined at different moments of germination. Polysome reassembly was practically completed by 8 h and 54% of the preformed ribosomes were found in the polysome fraction. An increase in the proportion of large polysomes was also observed during this period of germination. During the following period, the polysome content and the distribution of the various classes of polysomes remained unchanged.
The time of appearance of newly synthesized ribosomes into the polysomes was investigated using axes germinated in the presence of [³H]-uridine. Centrifugal analysis of EDTA-dissociated polysomes and gel electrophoretic analysis of polysomal RNA showed that new ribosomes appeared into polysomes a few hours after completion of the initial polysome assembly. When released into the cytoplasm, the new ribosomes were preferentially incorporated into polysomes rather than stored as free ribosomes.     

Photosynthetic Electron Transport in Plastids in Detached Cucumber Cotyledons Treated with 6-Benzylaminopurine and Potassium

Etiolated cotyledons of cucumber (Cucumis sativus L.) were excisedand incubated for 16 days on agar in the absence or in the presenceof 6-benzylaminopurine (BA) (3 µM) or KCl (10 mM) undercontinuous light. Treatment with BA or KCl increased growthand greening of cotyledons, KCl being particularly active duringthe last few days of the incubation. The rate of photosynthetic electron transport reached a maximumafter 3 days, as did the chlorophyll content, and then it declinedby approximately 95%. An uncoupling from phosphorylation wasobserved in older cotyledons. BA and KCl increased the rateof electron flow per cotyledon, and KCl delayed the onset ofthe decline in this rate. PS I and PS II activities per chlorophyllunit were lower in BA-treated cotyledons, but KCl-treated cotyledonsbehaved like the controls. Fluorescence analysis indicated that the level of active chlorophyllsinvolved in the transfer of energy in PS II decreased between3 and 7 days under all conditions tested. In BA-treated cotyledons,the proportion of active chlorophylls was consistently lowerthan that in the control. Thus, it appears that, in the absenceof exogenous K⁺, cytokinin has only a low antisenescence effecton photosynthetic activity, and that K⁺ may enhance the photosyntheticelectron flow between plastoquinone and plastocyanin via thecytochrome b₆-f complex. (Received August 2, 1989; Accepted January 23, 1990)