Enhancement of antioxidative enzyme activities in chilled rice seedlings

Responses of activities of seven antioxidative enzymes after exposure of rice seedlings to low temperature were investigated. The stress caused rapid transient increases in activities of ascorbate peroxidase (EC 1.11.1.11) and guaiacol peroxidase (EC 1.11.1.7) and then slow gradual increases in those of superoxide dismutase (SOD; EC 1.15.1.1), monodehydroascorbate reductase (MDAR; EC 1.6.5.4) and glutathione reductase (EC 1.6.4.2), indicating differential regulations of these enzymes. Activities of catalase (EC 1.11.1.6) and dehydroascorbate reductase (EC 1.8.5.1) were not significantly affected. Protein levels of antioxidative enzymes examined, except for cytosolic MDAR, did not fluctuate significantly by this stress, while the protein level of cytochrome c (respiratory marker) was decreased.