Embryo dormancy is a reversible developmental state during which germination is repressed. In this study, inbred lines of Avena fatua were used to analyse the influence of genotype and environment on the dormant phenotype, and on expression of the homologue of the maize transcription factor VIVIPAROUS 1 (afVP 1). The cDNA for afVP 1 was cloned from mature embryos. Analysis of the predicted protein sequence revealed a high degree of similarity to other VP 1/ABI 3-related transcription factors, in particular in four regions previously shown to be highly conserved, including the BR2 region that has been shown to interact with several classes of sequence-specific DNA binding proteins. The potential of imbibed mature embryos for dormancy was analysed and shown to be determined primarily by genotype and secondarily by previous environmental experience of the mature seed acting on embryo genotype. Under all conditions studied, expression of afVP 1 and the A. fatua homologue of Em (shown in maize to be regulated by VP 1 during embryo maturation) were positively correlated with the dormant phenotype, whereas expression of A. fatua AMY-related RNAs was negatively correlated with dormancy (in barley AMY 6-4 has been shown to be repressed by VP 1). Expression of afVP 1 RNA was also shown in the dry seed to be positively correlated with the length of time required for seeds of the inbred lines to after-ripen. These results suggest new functions for the VP 1 transcription factor family in the control of dormancy-related processes in embryo cells of mature seeds, and the up-regulation of afVP 1 and afEm RNAs in the dormant state suggests that they are regulated by a switching mechanism in the mature seed that shows some aspects of reversibility.