Development of the O2(-)-detoxification system during adaptation to air of submerged rice seedlings
1992
Ushimaru, T. | Shibasaka, M. | Tsuji, H.
Changes in activities of enzymes and levels of antioxidant substrates involved in the O2(-1)-detoxification system in seedlings of rice (Oryza sativa L. cv. Yamabiko) in response to variations in the oxygen environment were studied. Activities of superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase and catalase, expressed either on the basis of fresh weight of shoots or relative to levels of soluble protein were much lower in seedlings germinated under water for 6 days than in those germinated in air for the same period of time. When submerged seedlings were exposed to air, the activities of these six enzymes increased to or exceeded the levels in aerobically grown controls during 24 h of adaptation to air. Ascorbate and glutathione, which act as antioxidant substrates in the O2(-1)-detoxification system, were present in submerged seedlings at nearly the same levels as those found in aerobically grown controls. On exposure of submerged seedlings to air, the level of ascorbate increased slightly, but the level of glutathione showed a rapid increase, reaching 7 times that in aerobically grown controls within 12 h of adaptation to air. Levels of all six antioxidative enzymes and of two substrates involved in the detoxification of the superoxide radical increased with increases in oxygen tension in the environment. Moreover, the development of this system consisted of two steps, namely, a rapid increase in the level of glutathione and a subsequent slow increase in the activities of antioxidative enzymes.
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