CHANGES IN MESSENGER-RNA POPULATIONS DURING LOBLOLLY-PINE (PINUS-TAEDA) SEED STRATIFICATION, GERMINATION AND POSTGERMINATIVE GROWTH

Changes in the patterns of gene expression were examined during loblol ly pine (Pinus taeda L.) seed stratification, germination, and post-ge rminative growth. In both the megagametophyte and the embryo, DNA cont ents remained relatively constant at all stages examined. RNA contents , however, increased in both tissues following seed germination, parti cularly in the embryo where a 7-fold increase in the RNA content was o bserved 5 days after germination. Poly(A)(+) RNA, extracted from megag ametophytes and embryos was translated in vitro in a rabbit reticulocy te lysate cell-free system. Analysis of [S-35]-methionine-labelled tra nslation products by two-dimensional electrophoresis/fluorography indi cated that there were changes in the populations of mRNAs during all d evelopmental stages examined. In both the megagametophyte and the embr yo several distinct mRNA populations, including one constitutively pre sent at all stages examined, were identified. One mRNA population, pre sent in the mature seed, decreased during seed stratification. Another population, not present in the mature seed, rose during the period of stratification that coincided with an increase in seed germinability. A third population, which appeared during seed germination, increased steadily during post-germinative growth. Besides these similarities, specific differences between megagametophyte and embryo were noted. Fo r trample, one mRNA population, which was present in the megagametophy te of the mature seed and remained constant during the stratification period, disappeared immediately following seed germination. In the emb ryo, one set of messages was germination specific. In total, these res ults show that mRNA populations change in a temporal fashion that is c onsistent with the patterns of de novo protein synthesis known to occu r in loblolly pine during the same developmental periods.