SummaryEmbryo 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 sequencespecific 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.

Summary Wild oat plants of types fA, fB and fC were grown at a constant 15 or 20°C during the period of seed maturation. Seed of the three types differed little in dormancy when grown at 15°C, but at 20°C a larger proportion of seeds of type fA were dormant compared with fB or fC. Overall, dormancy of seed produced at 15 and 20°C was 97 and 63% respectively. Plants of another collection of type fB were grown from seed at 15 or 20°C with or without water stress applied only from the time of panicle emergence. Water stress and high temperature reduced viable seed production. Seed dormancy was tested immediately after collection by planting the seed in soil, and by Petri dish tests. Further Petri dish tests were made after 6 months storage. Seedling emergence in the first autumn from seeds of plants matured without water stress at 15°C was 10% compared with 30% for seeds grown at 20°C. Seeds grown with water stress at 15°C gave 47%, and at 20°C 78% emergence. The majority of emergence from seeds formed at 15°C without water stress occurred in the second spring after burial. Petri dish tests support these findings and suggest that seeds produced in hot dry summers are less dormant than those produced in cool moist ones.

Nine microsatellites were used to screen 131 samples of Barren Brome (Anisantha sterilis: synonym Bromus sterilis) collected from within the fields of three English farms [from Oxfordshire (Oxon), Leicestershire (Leics) and Wiltshire (Wilts)] and eight seeds taken from samples of each of 10 farms across England, UK. Most individuals (approximately 97%) were homozygous. Polymorphism occurred at all nine loci in all three farms sampled at the field scale, and at most loci for nine of the other 10 farm samples. Between three and 11 alleles were found per locus. Gene diversity (D = 1 - summation operator p(i)2) ranged from 0.088 to 0.760. Polymorphism occurred among individuals within and among fields, and farms. Some alleles were found in only one farm. On the basis of the alleles at all nine loci in the 211 sampled plants, a total of 92 (44%) different genotypes was identified. Clustering analysis using the unweighted pair group method with arithmetic averages (UPGMA) for the combined Oxon, Wilts and Leics samples did not cluster them into their respective farms. Similarly, a phenogram of samples from all 10 farms showed considerable mixing of individuals with respect to farm origins. Identification of genotypes on field plans showed evidence of both spatial localization and mixing. Previous reports have suggested that A. sterilis is strictly inbreeding with little intrapopulation variation at the genetic level. Our data reveal that A. sterilis exists as numerous separate and genetically different lines, which are maintained by inbreeding but which very occasionally outcross. Possible explanations for this pattern of high genetic diversity are discussed.

demonstrates the possibility of developing robust generic models for simple predictions of emergence timing across populations.

SummaryThe Avena fatua (wild oat) homologue of VIVIPAROUS 1 (AfVP1) has been implicated in controlling the maintenance of embryo dormancy in mature imbibed seeds, but the detailed mechanisms by which this transcription factor family activates embryo maturation pathways and simultaneously represses germination are not known. A two-hybrid screen in yeast identi®ed three proteins that interacted speci®cally with AfVP1 (AfVP1 interacting proteins; AfVIPs). AfVIPs 2 and 3 interacted with the C-terminus of AfVP1, which contains the B2 + B3 domains, previously shown to bind DNA, whereas AfVIP1 interacted with the isolated B3 domain. Using puri®ed proteins in in vitro experiments, all three AfVIPs were shown also to interact with the Arabidopsis homologue ABSCISIC ACID INSENSITIVE 3 (ABI3). The three AfVIPs were expressed in both dormant and non-dormant embryos, but the abundance of AfVIP1 and 3 transcripts was greater in germinated than dormant seeds, whereas transcripts of AfVIP2 (and AfVP1) were more highly expressed in dormant embryos. The AfVIP3 protein has homology to a human cell-crisis gene with a predicted role in the cell cycle; AfVIP2 contains a ring-type zinc ®nger motif. These homologies, together with analysis of expression studies, suggest that these proteins may play speci®c roles in AfVP1-mediated regulation of the dormancy to germination transition in A. fatua seeds.