TRANSCRIPTIONAL ACTIVITIES IN DRY SEED NUCLEI INDICATE THE TIMING OF THE TRANSITION FROM EMBRYOGENY TO GERMINATION

To investigate processes regulating the reinitiation of growth and differentiation during seed germination, we have studied the transcriptional activities of sets of genes that are expressed at specific stages of embryogeny and postgermination in the higher plant Brassica napus L. We show that transcripts from a subset of the genes are elongated in nuclei isolated from dry seeds, indicating that these genes are competent to be transcribed in desiccated and quiescent mature embryos. Analysis of the specific transcripts produced in dry seed nuclei indicates that the changes in gene expression patterns associated with germination are not initiated during late embryogeny. The results suggest that the transition from an embryonic to a postgerminative program of development occurs after seeds are rehydrated.