Keeping imbibed seeds at low temperatures for a certain period, so called seed vernalization (SV) treatment, promotes seed germination and subsequent flowering in various plants. Vernalization-promoting flowering requires GSH. However, the expression patterns analyzed by GeneChip arrays showed that increased GSH biosynthesis partially mimics SV treatment in Arabidopsis thaliana. SV treatment (keeping imbibed seeds at 4C for 24 h) induced a specific pattern of gene expression and promoted subsequent flowering in wild-type plants. A similar pattern was observed at 22C in transgenic plants (35S-GSH1 plants) overexpressing the -glutamylcysteine synthetase gene GSH1, coding an enzyme limiting GSH biosynthesis, under the control of the cauliflower mosaic virus 35S promoter. This pattern was strengthened at 4C but flowering was less responsive to SV treatment. There was a difference in the transcript behaviour of the flowering repressor FLC between wild-type and 35S-GSH1 plants. Unlike other genes responsive to SV treatment, SV-dependent decrease in FLC in wild-type plants was reversed in 35S-GSH1 plants. SV treatment increased GSSG level in wild-type seeds, whereas GSSG level was high in 35S-GSH1 plants, even at a non-vernalizing temperature. Taking into consideration that low temperatures stimulate GSH biosynthesis and bring about oxidative stress, GSSG is considered to trigger low temperature response, but enhanced GSH synthesis was not enough for mimicking SV treatment. To complete it, it essentially required the cellular redox retransition from the oxidized to the reduced state that is observed after the seed vernalization treatment.