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

During precocious germination, Brassica napus L. embryos exhibit features of embryo maturation and features of post-germinative growth at the same time, which raises important questions about the nature of these developmental programmes and the transition between them. To investigate the possibility that the two programmes are segregated spatially rather than temporally in these embryos, embryos of different ages (excised at 38, 47, and 60 d post-anthesis) were placed in culture to induce precocious germination, and total RNA was isolated from the cotyledons and axes or hypocotyls. cDNA sequences (two marking embryo maturation and four marking the onset of postgerminative growth) were used as probes on dot blots to compare mRNA population dynamics in these organs. 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. Embryos 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.