| Active oxygen species in seedlings of Bermudagrass (Cynodon dactylon) and Common centipede grass (Eremochloa ophiuroides.L) treated by PEG6000, and the effects of exogenous ABA on the antioxidant system were studied. Some indexes as activitives of the several antioxidant enzymes and contents of deoxidized ascorbic acid and reduced glutathione in seedling were measured to understand the drought-resistant mechanism and the effect of AEA on the antioxidant system during water stress.The results were showed as followed.1. Drought resulted in H2O2 accumulation, the relative water content and chlorophyll content reduction, MDA content increase, proteins degradation and DNA special fragment.2. Bermudagrass and Common centipede grass were not unanimous in response to PEG stress. Bermudagrass was more susceptive than Common centipede grass to the stress. Compared with Common centipede grass ,the response of antioxidant in Bermudagrass seedlings to H2O2 was earlier and the antioxidant content was elevated more highly, however, at the late phase of the stress(3d,4d of PEG stress), antioxidant content and enzyme activities dropped more quickly, the activities of GST, GPX and GR in the seedlings of Bermudagrass treated for 1d of 20% PEG, APX in seedlings treated for Id and 2d of 20% PEG, and the activity of GR and CAT in the seedlings of Bermudagrass treated by 40% PEG were higher than those of contemporaneous counterpart of Common centipede grass. The GSH level and As A level in the seedlings of Bermudagrass treated for 1d, 2d, 3d of PEG and in CK was higher than that of the others. Otherwise the ratio of electrolyte leakage and H2O2 content in the seedlings of Bermudagrass were higher than that of Common centipede grass, but chlorophyll content in the seedlings of Bermudagrass was dropped more quickly in comparison with Common centipede grass.3. ABA level in the seedlings of Common centipede grass pretreated by ABA was increased. Common centipede grass with ABA treatment for 24h could significantly enhanced ABA level. Under severe osmoses conditions (40% PEG treatment for 2d) and drought (stopped to water for 20d) Common centipede grass seedlings could both keep ABA content high. However, application of drought treatment in the presence of water decreased the ABA level close to the control group value.4. Compared to CK, ABA pretreatment could make the level of H2O2 increase in two grasses, but make H2O2 content, MDA content, RWC and Chi content reduce, and make some antioxidant enzyme activities , such as GPX and GR, increased in two grasses during water stress and make the level of AsA and GSH increase.5.POD isoenzyme was showed as followed: POD isoenzyme bands in the seedlings of Centipede grass and Bermudagrass mostly appeared in two zones, the POD isoenzyme bands in Centipede grass seedlings existed in about Rf 0.12 and 0.5, whose colour in Rf 0.12 was more thick and band width was wider in comparison with Rf 0.5, the POD isoenzyme bands in Bermudagrass grass seedlings were mostly in Rf 0.5 and 0.8, but their color was light and band width was narrow in Rf 0.1. The POD band colour in the seedlings of Common centipede grass became thicker in Rf 0.12 and Rf 0.45 and POD activity trended to increase with 20% PEG treatment, However the POD activities in theCommon centipede grass seedlings pretreated for 24h of ABA were decreased under 20% PEG stress, especially the seedlings treated for 4d of PEG treatment. OD Peak 0.56 in CK seedlings was disappeared slowly with PEG treatment time, and a new band, OD peak 0.342, was emergenced in the seedlings treated for 4d of PEG stress, which might be induced by ABA pretreatment for 24h. Some new bands about Rf 0.22 also were induced.6.From the soluble protein bands of Bermudagrass seedlings treated by 40% PEG by SDS-PAGE, some protein bands (Rf 0.046, 0.29, 0.38, 0.804, 0.871, molecular weight 198.4, 93.3, 70.6, 19, 15.5Kb respectively) were disappeared with water stress time, meanwhile new proteins (Rf was 0.104, 0.138, 0.354, 0.629, 0.97,...
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