The acceleration of flowering by a long period of low temperature, vernalization, is an adaptation that ensures plants overwinter before flowering. Vernalization induces a developmental state that is mitotically stable, suggesting that it may have an epigenetic basis. The VERNALIZATION2 (VRN2) gene mediates vernalization and encodes a nuclear-localized zinc finger protein with similarity to Polycomb group (PcG) proteins of plants and animals. In wild-type Arabidopsis, vernalization results in the stable reduction of the levels of the floral repressor FLC. In vrn2 mutants, FLC expression is downregulated normally in response to vernalization, but instead of remaining low, FLC mRNA levels increase when plants are returned to normal temperatures. VRN2 function therefore stably maintains FLC repression after a cold treatment, serving as a mechanism for the cellular memory of vernalization.

No abstract

Summary Ten human ovarian carcinoma cell lines have been studied as a potential in vitro screen for the development of novel anticancer platinum complexes. Lines have been established and developed both from solid and ascitic tumours, from pretreated and untreated patients, and are available at a range of in vitro passage numbers. The biological properties of the lines were consistent with them being human, epithelial and of ovarian carcinoma origin. Using a tritiated thymidine or leucine uptake method, and a 96 hour continuous drug exposure, the lines have been calibrated against four platinum-containing chemotherapeutic agents: cisplatin, iproplatin, carboplatin and tetraplatin. Striking differences in cytotoxicity were observed across the lines for each agent. Some lines were consistently resistant, others generally sensitive, whereas some showed clear evidence of differential sensitivity to a particular agent. Statistical analysis (Spearman rank correlation) involving the six possible pairings of drugs showed that cisplatin, iproplatin and carboplatin elicit a very similar pattern of response in these lines whereas tetraplatin elicits a completely different response pattern. Similar cytotoxicity values were obtained using a soft agar cloning assay. Results using a tetrazolium dye reduction assay, however, gave somewhat higher and more variable values, particularly with tetraplatin. The thymidine uptake assay will be adopted in further studies on a selected panel of six lines. This panel encompasses the spectra of sensitivities identified for each of the four agents against the original ten lines and may provide a useful screening facility for the development of novel platinum drugs, in that it detects both cell line-determined and structure-determined differences in cytotoxicity.Traditionally, the development of new drugs for the treatment of malignant diseases has relied predominantly on transplantable murine tumour models, such as those used by the National Cancer Institute (NCI) (Frei, 1982;Venditti, 1983). Such models include the P388 leukaemia, L1210 leukaemia, Lewis lung carcinoma, B16 melanoma, Colon 38 and CD8F1 mammary carcinoma. Our earlier work, which predicted the clinical antitumour activities of the platinum analogues JM8 (carboplatin) and JM9 (iproplatin), exploited predominantly the platinum-sensitive ADJ/PC6 murine plasmacytoma (Harrap et al., 1980;Harrap, 1985). Other workers have generated cisplatin-resistant variants of the L1210 and P388 tumours in attempts to identify novel platinum drugs which might exhibit wider spectra of antitumour activities (Burchenal et al., 1979(Burchenal et al., , 1980. Tetraplatin exhibits no cross-resistance in such models and is currently under preclinical development at NCI (Anderson et al., 1986). A recent reappraisal of screening models at the NCI has resulted in the replacement of the in vivo murine panel in favour of a range of in vitro human tumour cell lines representative of the major histological types (Boyd, 1986).Clinical trials using platinum-con...

Flowering in many plant species is accelerated by a long period of cold temperature, known as a vernalization period. This research investigates how this cold temperature signal is perceived by plant cells and the mechanism by which it influences the transition to flowering. Mutagenesis of the late-flowering, vernalization-responsive, Arabidopsis mutant, fca, has yielded five independent mutations (termed vrn mutations) conferring an altered vernalization response. Allelism tests showed that these mutations fall into at least three complementation groups defining three loci named VRN 1, 2 and 3. The vrn1 and vrn2 mutations did not affect the acclimation response as judged by expression of cold-induced transcripts and freezing tolerance assays. vrn1-1 affected the short-day vernalization response of Landsberg erecta and reduced the vernalization response of other late-flowering Arabidopsis mutants. The acceleration of flowering by GA3 was not affected by vrn1-1. The VRN 1 locus was mapped to chromosome 3.

Tension pneumothorax and hemothorax are life-threatening emergencies that require immediate treatment. Field stabilization of trauma patients often requires rapid surgical drainage of these injuries but inevitably delays departure for hospital. Conventional treatment involves the insertion of a chest drain but we describe a modified technique of simple thoracostomy that is faster and simpler to perform and avoids the risks associated with insertion of the chest drain. Following use of a simple thoracostomy as an alternative to chest drain insertion in 45 patients at the roadside, this technique appears to have important advantages over conventional techniques and warrants further clinical evaluation.