Cell-type-specific expression of a wheat-germ agglutinin gene in embryos and young seedlings of Triticum aestivum.

We have investigated the levels of cell-specific expression of wheat-germ agglutinin (WGA) during the development of embryos and in 3-d-old seedlings. Southern blot analysis of genomic DNA derived from hexaploid and diploid wheat (Triticum) species indicates that the isolated cDNA (complementary DNA) clone is specific for isolectin B (WGA-B). Specific accumulation of transcript for WGA-B was determined by RNA blot analysis and in-situ hybridization. The WGA-B mRNA increased tenfold during embryogenesis between 10 and 40 d post-anthesis and then declined again as the seed reached maturity. The root tips of 3-d-old seedlings contained approximately threefold more WGA-B mRNA than mature seeds. In-situ hybridization experiments showed that during embryogenesis, WGA-B mRNA was present only in the epidermal layers of the radicle and the coleorhiza, while in 3-d-old seedlings it was found in the root-cap cells. To analyze de-novo transcription of WGA-B mRNA a new variation of in-situ hybridization was developed. RNAs from developing embryos and seedlings were labeled with [(3)H]uridine and then hybridized in-situ with unlabeled antisense and sense transcripts. These experiments demonstrated that accumulation of WGA-B mRNA in embryos and 3-d-old seedlings resulted, at least partially, from de-novo transcription. All cells containing WGA-B mRNA also contained WGA, as shown by immunocytochemistry.