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Restriction enzyme digestion of the ribosomal RNA genes of the nucleolar organisers of wheat has revealed fragment length polymorphisms for the nucleolar organiser on chromosome 1B and the nucleolar organiser on 6B. Variation between genotypes for these regions has also been demonstrated. This variation has been exploited to determine the recombination frequency between the physically defined nucleolar organiser on 1B (designatedNor1) and other markers; two loci,Glu-B1 andGli-B1 which code for endosperm storage proteins andRf3, a locus restoring fertility to male sterility conditioned byT. timopheevi cytoplasm.Gli-B1 andRf3 were located on the short-arm satellite but recombine with the nucleolar organiser giving a gene order ofNor1 - Rf3 - Gli-B1. Glu-B1 is located on the long arm of 1B but shows relatively little recombination withNor1, which is, in physical distance, distal on the short arm. This illustrates the discrepancy between map distance and physical distance on wheat chromosomes due to the distal localisation of chiasmata. The recombination betweenNor1 andRf3 indicates that, contrary to previous suggestions, fertility restoration is not a property of the nucleolar organiser but of a separate locus.

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The incidence and clinical implications of unusual patterns of expression of leucocyte differentiation antigens in acute leukaemia were assessed on 568 newly diagnosed paediatric and adult cases undergoing immunophenotyping with a panel of monoclonal antibodies at a single centre. Among patients with the precursor B (common) form of acute lymphoblastic leukaemia (ALL), the major variant seen was the group of 15 cases with expression of myeloid surface antigens. 4.5% of ALL cases tested with antibody to CD-11b were positive, 5.1% were CD-13+, and 10.8% CD-33+. All 15 patients achieved a complete remission with chemotherapy, with six of eight children and four of seven adults remaining disease free. A smaller proportion (1.5%) of precursor B ALL patients showed expression of the T lineage marker, CD-7. The only significant variant seen in the precursor T-ALL group was expression of HLA-DR antigen, which was found in five of 35 cases; although all responded to treatment, only one remains a disease-free survivor. Among patients with acute myeloid leukaemia (AML), expression of the lymphoid markers terminal transferase (TdT) and CD-7 were commonly seen (22.2% and 28.4% respectively of cases tested). Other lymphoid markers detected on AML cases were CD2 (11.1%), CD-10 (1%) and CD-19 (4.4%). These results confirm that examples of lineage infidelity are regularly seen in large series of patients with acute leukaemia. Prospective studies using uniform treatment protocols are required to establish whether these patients have significantly different disease outcomes.

SUMMARYThe induction of male sterility in wheat by application of Ethrel at different concentrations and times was investigated in glasshouse‐grown Triticum aestivum cv. Sirius. The results obtained agree with our previous findings, that to induce full sterility, Ethrel must be applied before meiosis is initiated in the oldest florets of the ear. However, to ensure full emergence of sterilized ears, the application has to be made as close to this stage as possible using a concentration of between 1000 and 2000 ppm. Ethrel application thus shows promise as a method for detecting heterotic combinations by producing sufficient F1 seed for small‐scale field trials.

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Blast cells from untreated cases of acute leukemia were examined for expression of terminal transferase enzyme (TdT) by immunofluorescence and for myeloid lineage commitment as demonstrated by the presence of myeloperoxidase enzyme at the ultrastructural level. In three cases, an overlapping expression of the "lymphoid-specific" marker TdT was found on peroxidase-positive myeloblasts. These results indicate either the clonal expansion of a rare TdT-positive myeloid precursor or inappropriate expression of TdT by malignant myeloblasts, and further illustrate that TdT expression must be interpreted with caution when distinguishing between lymphoid and myeloid leukemias.

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