Aiming to evaluate the alterations that occur during the dormancy period of irrigated rice seeds, three experiments were carried out at different storage conditions. Seeds from Rio Grande cultivar, highly post-harvest dormant seeds, after preparation, were placed in multilayered paper bags and stored for 12 months, in a cold and dry (10oC and 50% of relative humidity) and in three conventional
storage. Every three months, water content, germination, alterations in the electrophoretical profile of the isoenzymes Polyphenoloxidase (PPO), Peroxidase (PO), Alpha-amylase (á-AM), Beta-amylase (â-amylase) in polyacrilamide gel and reducing groups by spectrophotometer were evaluated. Storage conditions and duration have influenced the dormancy breakage, and, in the conventional storage environment, rice seeds have broken dormancy faster than the ones stored in cold and dry chamber. Changes in á-AM and PPO activities are related to alterations in the germination percentage, that is, while the α-AM activity increases, PPO activity decreases as dormancy is broken, suggesting these enzymes activities as a promising indicator of dormancy intensity. However, PO and β-AM activities are not related to dormancy in rice seeds.