Abstract

WHEAT EMBRYO germination is characterised by an increase in fresh weight during the first 40 min of imbibition, followed by a lag period of 5 h and finally, a phase of cell elongation during which fresh weight increases at a sustained rate1. An essential step in seed germination is de novo synthesis of proteins, but for the first 40 min it is mediated by preformed mRNA transcribed during embryogenesis2 Previous reports have shown that although there is a 2.5–3-fold increase in the relative rate of protein synthesis during the lag period (40 min–5.5 h)3, there is no appreciable change in the rate of RNA synthesis4–7 With the recently developed sensitive assays for ribonucleoside triphosphates8,9, the rate of RNA synthesis and its mode of regulation in early germination of wheat embryos was reexamined10 In contrast to previous findings4–7, our results clearly show a two- to threefold increase in the rate of RNA synthesis during the lag period of wheat embryo germination This increase in RNA synthesis could conceivably account for the threefold increase in the rate of protein synthesis4 and raises the possibility that protein synthesis may depend on RNA synthesis after the first 40 min of germination We describe here experiments undertaken in wheat (Triticum aestivum L.) embryos to study the effect of inhibition of RNA synthesis on the rate of protein synthesis. Our data suggest that protein synthesis depends on RNA synthesis, and that the substrate level of mRNA is not a rate-limiting determinant for protein synthesis during the early hours of germination.

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