CHIMERIC NATURE OF PRECOCIOUSLY-GERMINATING BRASSICA-NAPUS EMBRYOS - MESSENGER-RNA ACCUMULATION PATTERNS

During precocious germination, Brassica napus L. embryos exhibit featu res of embryo maturation and features of post-germinative growth at th e same time, which raises important questions about the nature of thes e developmental programmes and the transition between them. To investi gate the possibility that the two programmes are segregated spatially rather than temporally in these embryos, embryos of different ages (ex cised at 38, 47, and 60 d post-anthesis) were placed in culture to ind uce precocious germination, and total RNA was isolated from the cotyle dons and axes or hypocotyls. cDNA sequences (two marking embryo matura tion and four marking the onset of postgerminative growth) were used a s probes on dot blots to compare mRNA population dynamics in these org ans. We find that individual organs accumulate mRNAs characteristic of only one developmental programme at any given time and conclude that the programmes are both distinct and potentially mutually exclusive. E mbryos are able to 'switch' from accumulating embryo maturation mRNAs to accumulating post-germinative mRNAs in culture, but the transition occurs at different times in different organs.