| Summary: | 碩士 === 國立中興大學 === 農藝學系所 === 97 === In order to explore the physiological mechanism of paraquat resistance of rice mutant, a sodium azide-mutated rice of cv. Tainung 67 (TNG 67) in Taiwan, whose resistance to this herbicide has been identified, and the role of antioxidative system was assessed. The susceptible (S) and resistant (R) mutants of rice were distinguished clearly by the maximal efficiency of photosystem II photochemistry (Fv/Fm) caused by 100 μM paraquat. While a 40% increment of malondialdehyde, an indicator for peroxidation damage to plant, in R-mutant was observed, that in S-mutant increased significantly by 130% at 9 hours after treatment (HAT) of 100 μM paraquat. Analysis of several antioxidants and pertinent enzymes revealed that superoxide dismutase (SOD) activity was decreased by paraquat 3 HAT in S-mutant and maintained at low activity afterward, which might cause more superoxide anion radicals accumulation. Besides, ascorbate peroxidase (APX) activity obviously increased after paraquat treatment in R-mutant, whereas none of increment in S-mutant; and a significantly low level of ascorbate existed throughout the experiment in S-biotype. Although the higher ratio of reduced glutathione to toal glutathione in R-mutant as compared with S-mutant was found till 9 HAT, coupled with a pronounced and fast increase of glutathione reductase (GR) activity in R-mutant, as well as the large decline of that in S-mutant, suggests that an active reduced glutathione/oxidized glutathione (GSH/GSSG) cycle is critical to paraquat resistance of rice mutant. This phenomenon has also been reported in tall fleabane (Chiang et al. 2008). The decisive contribution of a functional GSH/GSSG cycle to paraquat resistance through an enhancement of GR activity in this rice mutant was further confirmed by an experiment of exogenous application of ascorbate.
|
|---|
