Intron-mediated gusA expression in tritordeum and wheat resulting from particle bombardment

The promoterless maize ubiquitin first exon and intron fragment can drive g usA expression in immature tritordeum inflorescences and immature wheat scu tella. In fluorescence assays, this fragment induces gusA expression in tri tordeum inflorescences to 50 times higher than background. The activity of the complete promoter, exon and intron cassette was up to 20 000-fold highe r than background but the maize ubiquitin promoter in isolation had very lo w activity. A construct with the maize alcohol dehydrogenase first exon and intron had low activity, visible in histochemical assays. Both intron sequ ences have promoter-like features and in the ubiquitin intron there is a se quence homologous to the opaque-2-binding box. We suggest that the combinat ion of these elements may explain the promoter activity detected in these i ntrons.