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Redox regulation of the plant cell cycle has long been postulated but not been clearly demonstrated. Using an in vivo reduction-oxidation (redox) reporter (roGFP2), we show that a transient oxidation of the cytosol and then the nuclei occurs in the synchronised dividing cells of the embryonic root meristem of germinating Arabidopsis seeds at G1 followed by reduction at G2 and mitosis. The redox cycling at G1/G2 was perturbed in mutants with low redox buffering capacity as a result of impaired synthesis and accumulation of ascorbate. The nuclei in the dividing cells of these mutants showed a significant increase in the degree of oxidation, together with an impaired capacity to increase in size during the early stages of the cell cycle. Seed phenotypes and dormancy release were similar in all genotypes but the dry seed transcriptome was strongly influenced by low redox buffering capacity in the mother plant, having much higher levels of defence and cell cycle transcripts. Moreover, the embryos of the imbibed seeds were much larger when redox buffering capacity was low compared to the wild type. In contrast, there were fewer cells in the proliferation zones of the embryonic roots.