Free Radical Injury in Rice Leaf under Zn Deficiency

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Under Zn deficiency, the Cu/Zn-SOD protein content and activity are reduced in rice meristem and the Zn-deficient rice plant is prone to photo-oxidative stress. In the present study, the generation and effect of free radical in rice leaf were examined under Zn-deficient conditions. The SOD activity was depressed and the content of thiobarbituric acid-reactive substances, an index of lipid peroxidation, increased in the rice leaves grown under Zn-deficient conditions. The amplitude of the ESR signal increased in the Zn-deficient leaves. When the oxidative stress level increased by paraquat treatment, the bleaching of the pigment associated with the destruction of chlorophyll in leaves was observed in Zn-deficient leaves. The increase in the amplitude of the ESR signal and the bleaching of pigment by paraquat treatment occurred before any Zn deficiency symptoms appeared in the plants cultured without Zn. Among the Zn nutrition problems of rice plants, one predominant factor which causes Zn deficiency symptoms may be the failure of O_2^-scavenging due to the shortage of Cu/Zn- SOD. Therefore, when the oxidative stress level is likely to be high, the Zn level has to be sufficient in rice plants.
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