We have defined four stages in the development of cowpea seeds: I(9–11 days after flowering), II (13–15), HI (17–19) and IV (22–24). Poly A+RNA fractions were prepared from cotyledons of developing (stages I–IV) and germinating (0, 12, 24 and 48 h after imbibition) seeds. Poly A+RNAs from stages I–III exhibited high translation activities with a maximum at stage II, and the activity was markedly reduced at stage IV. In cotyledons of germinating seeds, the translation activity was low until 12 h after the onset of imbibition but rose thereafter. Analysis of in vitro translation products with SDS-polyacrylamide gel electrophoresis and fluorography showed that the abundant mRNA population underwent a distinct change between stages II and III of seed development. Since the mRNA population at stage III was very similar to that of stage IV (mature seeds), it appears that, as far as mRNA species are concerned, the prerequisites for germination are fully available in the developing seeds by stage III. This assumption was supported by the fact that immature seeds at stage III exhibited high germination rates and normal axial growth and producedα-amylase at levels similar to those produced by mature seeds. Several polypeptides which have been regarded as translation products of stored mRNA (poly A+RNA from dry seeds) were detected at earlier stages of
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