Stimulation of mucosal uptake of selenium from selenite by some thiols at various sites of rat intestine

The influence of several thiols (conc. 1 mmol/L) on mucosal uptake of⁷⁵Se from⁷⁵Se-labeled selenite (conc. 10 μmol/L) across the brush border of rat jejunum and cecum was investigated in vitro using a short-term uptake technique.l-Cysteine (l-Cys) stimulated⁷⁵Se uptake in the mid- and distal jejunum and cecum, but not in the proximal jejunum. The effect was maximal in the distal jejunum.d-Cys was less effective in the jejunum and similarly effective in the cecum.l-Leucine (l-Leu) andl-glutamic acid significantly reduced the stimulatory effect ofl-Cys on Se uptake in the distal jejunum, whereas the respective effect ofd-Cys was not diminished byl-Leu. Cysteamine stimulated mucosal⁷⁵Se uptake at all intestinal sites tested, whereas the effect of mercaptopyruvate was restricted to the distal jejunum. Thioglycolate also enhanced⁷⁵Se uptake in the distal jejunum. The stimulatory effects ofl-Cys, mercaptopyruvate, and thiologlycolate were Na⁺-dependent, whereas the effect of cysteamine also occurred in the absence of Na⁺. Mercaptosuccinate,d-penicillamine, ergothioneine, and thiosulfate did not enhance mucosa⁷⁵Se uptake. It is concluded from these findings that the reaction of some thiols with selenite results in Se compounds that are rapidly absorbed by the intestinal epithelium through various Na⁺-dependent and Na⁺-independent, mechanisms. The high bioavailability of Se from selenite found by others might thus be the result of the presence of thiols in the gastrointestinal tract.     

Sequence analysis of WIS-2-1A,a retrotransposon-like element from wheat

WIS-2-1A, a 8624 bp insertion in the Glu-1A-2 locus of chromosome 1A of wheat, consists of two 1755 bp long terminal repeats enclosing a 5114 bp internal region. No long open reading frames could be found, but inspection of the predicted amino acid sequence showed regions with homology to retrotransposon structures, including a methionine tRNA initiator binding site, a nucleotide binding domain, a protease, an integrase and a polymerase. DNA replication errors have resulted in frame-shifts in the protein coding region, suggesting that retrotransposition of WIS-2-1A, if it occurs, must be mediated by trans-acting factors.     

Construction and characterisation of a yeast artificial chromosome library containing three haploid maize genome equivalents

We have constructed a yeast artificial chromosome (YAC) library using high-molecular-weight DNA prepared from agarose-embedded leaf protoplasts of the maize inbred line UE95. This library contains 79 000 clones with an average insert size of 145 kb and should therefore represent approximately three haploid genome equivalents. The library is organised as an ordered array in duplicate microtitre plates. Forty-one pools of DNA from 1920 individual clones have been prepared for rapid screening of the library by the polymerase chain reaction (PCR). Using this approach, together with conventional colony hybridisation, we have been able to identify between one and eight positive clones for every probe used.     

Characterization of cymbidium mosaic virus coat protein gene and its expression in transgenic tobacco plants

Cymbidium mosaic virus (CyMV) is the most prevalent virus infecting orchids. Here, we report the isolation of partial cDNA clones encoding the genomic RNA of CyMV. Like most of the polyadenylated monopartite positive-strand RNA viruses, the open reading frame (ORF) coding for the viral coat protein (CP) is located at the 3 end. The ORF predicts a polypeptide chain of 220 amino acids with a molecular weight of 23 600. Sequence comparison of this ORF to the CP sequences of potato virus X(PVX) and white clover mosaic virus (WCIMV) revealed a strong amino acid homology in the mid-portion of the CP, but the overall homology was low. The CyMV CP gene was placed downstream of a cauliflower mosaic virus 35S promoter and the chimaeric gene was transferred into Nicotiana benthamiana. Transgenic plants expressing the CyMV CP were protected against CyMV infection.     

Thidiazuron stimulates shoot organogenesis and somatic embryogenesis in white ash (Fraxinus americana L.)

Immature and mature nonstratified seeds of white ash (Fraxinus americana L.) were dissected transversely and 2/3 of each seed was placed onto agar-solidified Murashige and Skoog medium. Adventitious buds, shoots, and somatic embryos formed on callus, cotyledons, and hypocotyls of the resulting seedlings. Shoot organogenesis was induced on explants cultured on medium with 10 M thidiazuron but not on explants on media with benzyladenine (BA) or isopentenyladenine. Not all seed sources were equally capable of shoot organogenesis and embryogenesis. Atypical of adventitious regeneration of other woody plants, mature seed explants of white ash were more organogenic with shoots that elongated better than explants from immature seeds. Somatic embryogenesis was observed in cultures where mature seeds were first cultured for 4 weeks on a medium containing 10 M adenine 2,4-dichlorophenoxyacetic acid in combination with 0.1 and 1.0 M thidiazuron, followed by transfer to a medium containing 0.05 M 6-benzyladenine and 0.5 M naphthaleneacetic acid. Adventitious shoots and epicotyls from both seedlings and germinated somatic embryos were rooted under intermittent mist and acclimatized to the greenhouse.Abbreviations BA 6-benzyladenine - 2,4-d 2,4-dichlorophenoxyacetic acid - IBA indolebutyric acid - 2iP isopentenyladenine - NAA naphthaleneacetic acid - TDZ thidiazuron-N-phenyl-N-1,2,3-thiadiazol-5-ylurea - WPM woody plant medium