Croissance individuelle et dynamique de population de Daphnia Magna en culture dans les eaux usées traitées

Résumé Pour atteindre les buts visés par le recyclage biologique des eaux usées, il faut exploiter une population d'organismes filtreurs dont l'augmentation nette de biomasse est rapide et importante. L'augmentation nette de biomasse sera favorisée par une croissance individuelle, une reproduction et une survie excellentes dans l'eau usée traitée. L'étude de ces paramèters sur des cohortes de Daphnia magna soumises à différentes conditions expérimentales, indique qu'il s'agit d'un organisme prometteur pour le recyclage biologique. Dans nos conditions expérimentales, D. magna montre un bilan azoté positif durant toute sa vie. La production rapide de biomasse est favorisée par une température élevée (15 °C) et une nourriture abondante. L'eau traité montre les signes d'une certaine toxicité envers les juvéniles mais non envers les adultes. Nos données établissent que la production d'oeufs requiert une taille minimale de la femelle de 2,7 mm, information primordiale pour l'exploitation future de la population.

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To realize the objectives of the biological recycling of wastewaters, it is necessary to exploit a population of filtering organisms, the biomass of which shows a rapid and important net increase. The net increase of biomass is favored by excellent individual growth, reproduction and survival in treated wastewaters. The study of these parameters, with cohorts of Daphnia magna submitted to different treatments, indicated that it is a promising organism for biological recycling. Under our experimental conditions, D. magna exhibited a positive nitrogen balance for the whole of its life. The rapid production of biomass was favored by high temperature (15 °C) and abundant food. The treated wastewaters proved to be somewhat toxic to juveniles but not to adults. Our results demonstrated that the egg production requires a female minimal size of 2.7 mm; this information is most important in the future exploitation of the population.

     

The intracellular distribution of adenylate kinase in the leaves of spinach,wheat and barley

Of the total adenylate-kinase activity in 10-d-old barley and wheat leaves, 40–50% is localised in the chloroplasts, while in mature spinach leaves 50–70% of the enzyme is chloroplastic. The extra-chloroplastic adenylate-kinase activity is associated with the mitochondria, very little, if any, is freely soluble in the cytoplasm. The adenylate pool of the cytoplasm could have access to adenylate-kinase activity in the intermitochondrial space because of the free permeation of adenylates across the outer mitochondrial membrane. Thus the adenylate pool of the cytoplasm could be subject to adenylate-kinase equilibrium. The mitochondrial adenylate kinase appeared to the localised exclusively in the intermembrane space.     

Asymmetric maturation of a dimeric transfer RNA precursor

Six of the eight transfer RNAs coded by bacteriophage T4 are synthesized via three dimeric precursor molecules. The sequences of two of these have been determined. Both of these precursors give rise to equimolar amounts of the cognate tRNA molecules in vivo. In contrast, even in wild-type infections, tRNA^Ile is present in ≤ 30% the amount of tRNA^Thr, with which it is processed from a common dimeric precursor.We have now determined the sequence of this dimer. In addition to the nucleotides present in tRNA^Thr and tRNA^Ile, it contains nine precursor-specific residues, located at the 5′ and 3′ termini and at the interstitial junction of the two tRNA sequences. While the three dimers share the majority of structural features in common, pre-tRNA^{Thr + Ile} is the only case in which an encoded tRNA 3′ -C-C-A terminus is present in the interstitial region.The processing of this dimer in various biosynthetic mutants has been analyzed in vivo and in vitro and shown to be anomalous in several respects. These results suggest that the apparent underproduction of tRNA^Ile can be explained by a novel processing pathway that generates a metabolically unstable tRNA^Ile product. Data from DNA sequence analysis of the T4 tRNA gene cluster (Fukada & Abelson, 1980) support the conclusion that the asymmetric maturation of this precursor is a consequence of the unique disposition of the -C-C-A sequence. These results argue that gene expression can be modulated at the level of RNA processing. The biological significance of this phenomenon is discussed in relation to evidence that tRNA^Ile has a unique physiological role.     

Selective lesions of acinar pancreatic cells in rats poisoned with abrin

Rats poisoned with abrin (2.5 micrograms/100 g body weight) died within 36 h with severe necrosis of acinar pancreatic cells. Incorporation in vivo of labelled amino acids into pancreatic protein was greatly impaired 6 h after poisoning. Microsomes isolated from the pancreas of poisoned rats at 6 h had a reduced capacity for protein synthesis in vitro. Incorporation in vivo of orotic acid into pancreatic RNA was decreased 12 h after poisoning.     

Conduite antisociale et longueur du chromosome Y

Summary A new case of free trisomy for the short arm of No. 9 chromosome identified by Giemsa staining and Giemsa-11 technique is reported.     

The characteristics of shuttling RNAs confirmed

Shuttling RNAs are recognized as molecules that migrate against steep concentration gradients from one nucleus (through the cytoplasm) into another nucleus in the same cell. In previous work these molecules were identified through experiments involving the separation of two kinds of nuclei utilizing differences in the nuclei that may have produced misleading results. In the experiments reported here normal, randomly-chosen ameba (A. proteus) nuclei containing [³²P]RNA were implanted into unlabeled normal, randomly-chosen cells and, after suitable incubation, the labeled RNAs present in each kind of nucleus were characterized by gel electrophoresis. The previously obtained results were confirmed: i.e. (a) the recipient cell nuclei acquired the same four small, distinct RNAs, which are recognized as shuttling ones because they migrate from one nucleus to the other; (b) the grafted nuclei possess, in addition to the four shuttling RNAs, three small, distinct RNAs, which are recognized as non-shuttling RNAs. New evidence also is presented to show that the acquisition by a nucleus of labeled RNAs in the above kind of experiment is not a result of new synthesis of RNAs from the labeled turnover products emanating from the transplanted nucleus.