Selenium compounds in the fathead minnow (Pimephales promelas)--I. Uptake, distribution, and elimination of orally administered selenate, selenite and l-selenomethionine

Treatment of fathead minnows (Pimephales promelas) with either [75Se]selenate, -selenite or -l-selenomethionine by gavage at 20 ng Se/g resulted in organ uptake and early distribution patterns which differed significantly between compounds. The greatest differences in uptake between compounds was observed in liver tissue which accumulated much less [75Se]selenate than either selenite or l-selenomethionine. The 75Se burdens and relative distribution among the various organs were nearly identical during the elimination phase for [75Se]selenate and -selenite. This suggests that selenium derived from these compounds converge to a common metabolic pool. The whole body T1/2, rate of 75Se uptake and magnitude of 75Se accumulation were generally greater for [75Se]selenomethionine than the inorganic forms. Selenium-75 was present in the bile following the oral administration of each compound. The partitioning of selenate and selenite into the plasma and cellular fraction of blood differs with both the compound and time following exposure.     

Characterization of two class II chitinase genes from peanut and expression studies in transgenic tobacco plants

Two different genes encoding class II chitinases from peanut (Arachis hypogaea L. cv. NC4), A.h.Chi2;1 and A.h.Chi2;2, have been cloned. In peanut cell suspension cultures, mRNA levels of A.h.Chi2;2 increased after ethylene or salicylate treatment and in the presence of conidia from Botrytis cinerea. The second gene, A.h.Chi2;1, was only expressed after treatment with the fungal spores. Transgenic tobacco plants containing the complete peanut A.h.Chi2;1 gene exhibited essentially the same expression pattern in leaves as observed in peanut cell cultures. Expression characteristics of transgenic tobacco carrying a promoter-GUS fusion of A.h.Chi2;1 are described.     

Enzyme activity measurements on isolated organs of Brachionus plicatilis (Rotifera)

A method is described by which the integument of Brachionus plicatilis, together with its intracellular lamina, is quickly dissolved before other parts or tissues of the animal are destroyed. After removing the integument several parts of the body can be separated and fractionated in a more or less intact state by centrifugation in a Percoll gradient. The measurement of enzyme activities has indicated that this procedure might provide a way of localizing enzymes within the rotifer body.     

Rapid identification of Arabidopsis insertion mutants by non-radioactive detection of T-DNA tagged genes

To assist in the analysis of plant gene functions we have generated a new Arabidopsis insertion mutant collection of 90 000 lines that carry the T-DNA of Agrobacterium gene fusion vector pPCV6NFHyg. Segregation analysis indicates that the average frequency of insertion sites is 1.29 per line, predicting about 116 100 independent tagged loci in the collection. The average T-DNA copy number estimated by Southern DNA hybridization is 2.4, as over 50% of the insertion loci contain tandem T-DNA copies. The collection is pooled in two arrays providing 40 PCR templates, each containing DNA from either 4000 or 5000 individual plants. A rapid and sensitive PCR technique using high-quality template DNA accelerates the identification of T-DNA tagged genes without DNA hybridization. The PCR screening is performed by agarose gel electrophoresis followed by isolation and direct sequencing of DNA fragments of amplified T-DNA insert junctions. To estimate the mutation recovery rate, 39 700 lines have been screened for T-DNA tags in 154 genes yielding 87 confirmed mutations in 73 target genes. Screening the whole collection with both T-DNA border primers requires 170 PCR reactions that are expected to detect a mutation in a gene with at least twofold redundancy and an estimated probability of 77%. Using this technique, an M2 family segregating a characterized gene mutation can be identified within 4 weeks.     

ELECTRON MICROSCOPE STUDY OF MITOCHONDRIAL 60S AND CYTOPLASMIC 80S RIBOSOMES FROM LOCUSTA MIGRATORIA

Purified mitochondrial ribosomes (60S) have been isolated from locust flight muscle. Purification could be achieved after lysis of mitochondria in 0.055 M MgCl₂. Mitochondrial 60S and cytoplasmic 80S ribosomes were investigated by electron microscopy in tissue sections, in sections of pellets of isolated ribosomes, and by negative staining of ribosomal suspensions. In negatively stained preparations, mitochondrial ribosomes show dimensions of ~270 x 210 x 215 Å; cytoplasmic ribosomes measure ~295 x 245 x 255 Å. From these values a volume ratio of mitochondrial to cytoplasmic ribosomes of 1: 1.5 was estimated. Despite their different sedimentation constants, mitochondrial ribosomes after negative staining show a morphology similar to that of cytoplasmic ribosomes. Both types of particles show bipartite profiles which are interpreted as "frontal views" and "lateral views." In contrast to measurements on negatively stained particles, the diameter of mitochondrial ribosomes in tissue sections is ~130 Å, while the diameter of cytoplasmic ribosomes is ~ 180–200 Å. These data suggest a volume ratio of mitochondrial to cytoplasmic ribosomes of 1:3. Subunits of mitochondrial ribosomes (40S and 25S) were obtained by incubation under dissociating conditions before fixation in glutaraldehyde. After negative staining, mitochondrial large (40S) subunits show rounded profiles with a shallow groove on a flattened side of the profile. Mitochondrial small subunits (25S) display elongated, triangular profiles.     

SEM of internal structures of Brachionus plicatilis (Rotifera)

Examination by scanning electron microscopy of sectioned rotifers provides views on their internal structures which complement the results of other techniques. Thus, additional information has been obtained for example, on the digestive tract, on nerve connections and on the morphology of the mastax. Our observations confirm that nearly all organs are connected in some way to the integument, suggesting that integument structures may be responsible for the holding together of the whole rotifer body.     

A gentle method for the preparation of hard parts (trophi) of the mastax of rotifers and scanning electron microscopy of the trophi ofBrachionus plicatilis (Rotifera)

Summary Trophi of the rotiferBrachionus plicatilis were prepared by dissolving rotifer tissues and lorica with sodium dodecyl sulfate (SDS) and dithiothreitol (DTT) and were examined by scanning electron microscopy in order to obtain information on the functional morphology of these structures. The trophi are not composed of distinct parts but form a continuous structure of rigid pieces and connecting membranous regions. The membranous components allow movements of the rigid parts against each other and/or restrict the extent of such movements. The main hinge for the movement of the trophi is the membranous connection between the two rami; movements of rami and unci occur together since these parts are tightly connected by two narrow membranes in the subuncus region. The subunci seem to constitute masticating devices which act against grooved ridges of the rami and might make it feasible to disintegrate nutrient particles to as small as 1 m. Crushing of coarser nutrients might be performed by the opposite surfaces of the two rami.Abbreviations br bulla rami - c crest along the ventral surface of the manubrium - cd distal part of the manubrium (cauda) - cv proximal part of the manubrium (clava) - d1 entrance from the bowl-shaped recess at the dorsal side of the manubrium into one of the (three) cavities within the proximal part of the manubrium - d2 second dorsal entrance into one of the (three) cavities within the proximal part of the manubrium - eu edge at the distal end of the uncus which fits into a notch at the proximal end of the manubrium - gr small, oblong grooves at the distal surface of the reinforced projecting ridges of the rami - f fulcrum - h hinge between the two rami - l ligaments extending from the central membranes to the dorsal surfaces of the unci - m central membranous structures - ma manubrium - p partition between the cavities within the ramus - ps large, proximal surfaces of the rami - r ramus - rd reinforced ridge on the anterio/dorsal part of the ramus - rv ventral, triangular surface of the ramus - su subuncus - sur root-like structures connecting the subuncus with the uncus plate - t teeth-like proximal endings of the uncus ridges - u uncus - um membranous connection between uncus and manubrium - ur membranous connection between uncus and ramus in the subuncus region - uvr ridges on the ventral side of the uncus - ve ventral entrance into one of the (three) cavities within the proximal part of manubrium     

Selenium compounds in the fathead minnow (Pimephales promelas)--II. Quantitative approach to gastrointestinal absorption, routes of elimination and influence of dietary pretreatment

Following administration by gavage [75Se]selenate and [75Se]selenite were absorbed from the gastrointestinal tract of fathead minnows (Pimephales promelas) at 94 and 80% efficiency, respectively. Approximately 12% of the [75Se]selenate administered by i.p. injection was eliminated via the urine, and across the gill within 2 hr. The urine was the primary route of elimination followed by the gill. The bile contained significantly lower amounts of 75Se than that eliminated either across the gill or in the urine. The mucus is capable of binding significant amounts of 75Se. Dietary pretreatment with selenite reduced the retention of a subsequent [75Se]selenite dose administered by gavage.