It is proposed that desiccation tolerance in the embryo of seeds depends upon the capacity to repair damage to genomic DNA when the desiccated embryo is rehydrated. From a study of imbibed and hydrated embryos of rye (Secale cereale) and wild oat (Avena fatua) evidence is provided that it is neither the extent of water uptake by the cells, the ensuing stability of the DNA to desiccation, nor the onset of S-phase DNA synthesis in the first cell cycle of germination that determines whether the desiccated embryo will survive. It is shown that when α- and β-polymerases of DNA repair are inhibited by aphidicolin and dideoxythymidine-5'-triphosphate, respectively, a γ-irradiation-induced DNA fragmentation cannot be fully repaired. It is shown that in hydrated embryos, at a stage when desiccation tolerance is lost, embryo cells still repair irradiation-induced damage, but this repaired DNA is unstable to desiccation and cannot be rerepaired when water is again made available. The failure to re-repair on rehydration appears to be critical to embryo survival and successful germination.
