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The potato R locus is required for the production of red pelargonidin-based anthocyanin pigments in potato (Solanum tuberosum L.). Red color also requires tissue-speciWc regulatory genes, such as D (for expression in tuber skin) and F (expression in Xowers). A related locus, P, is required for production of blue/purple anthocyanins; P is epistatic to R. We have previously reported that the dihydroXavonol 4-reductase gene (dfr) co-segregates with R. To test directly whether R corresponds to dfr, we placed the allele of dfr associated with red color under the control of the CaMV 35S promoter and introduced it into the potato cultivar Prince Hairy (genotype dddd rrrr P-), which has white tubers and pale blue Xowers. Transgenic Prince Hairy tubers remained white, but Xower color changed to purple. Three independent transgenic lines, as well as a vectortransformed line, were then crossed with the red-skinned variety Chieftain (genotype D-R-pppp), to establish populations that segregated for D, R, P, and the dfr transgene or empty vector. Markers were used to genotype progeny at D and R. Progeny carrying the empty vector in the genetic background D-rrrr produced white or purple tubers, while progeny with the same genotype and the dfr transgene produced red or purple tubers. HPLC and LC-MS/MS analyses of anthocyanins present in Chieftain and in a red-skinned progeny clone with the dfr transgene in a D-rrrr background revealed no qualitative diVerences. Thus, dfr can fully complement R, both in terms of tuber color and anthocyanin composition.

Idiopathic thrombocytopenic purpura (ITP) may be associated with other autoimmune diseases and the development of lymphoproliferative malignancies. In Sjogren's disease, Graves' disease, and essential mixed cryoglobulinemia, which are also associated with the development of B-cell neoplasia, clonal B-cell expansions have been detected. Eleven patients with ITP were investigated for the presence of a clonal excess (CE) using kappa-lambda flow cytometry and DNA analysis for rearrangement of immunoglobulin heavy and light chain genes in blood and/or spleen lymphocytes. In 10 of 11 patients, clonal B-cell populations were found by one or both tests. In three of these patients, oligoclonal B-cell populations were suggested by the combined findings. In all four patients with a small paraproteinemia, the isotype was confirmed by either flow cytometry or DNA rearrangement analysis. Our data suggest that the oligoclonal expansions are not restricted to CD5+ B cells, as in the majority of patients this subset was below the detection level of flow cytometry or DNA rearrangement analysis. None of the patients developed clinical manifestations of malignant lymphoma during a follow-up period of 10 to 44 months after sampling. We conclude that clonal excess populations of B cells are not a unique feature of malignant lymphoma, but may occur in autoimmune diseases, suggesting a benign (oligo)clonal B-cell proliferation.