Effects Of Pretreatment On Antioxidant Enzymes And Endogenous Hormone Of Rice Under Water Stress

Rice(Oryza sativa L.)is an important crop in China, which need a lot of water for its growth.Drought is one of natural disasters in China, and it can affect rice yield. It is the key issue thathow to improve the tolerance to water stress. In this paper, antioxidant enzymes (superoxidedismutase (SOD), peroxidase (POD), catalase (CAT)) activities, MDA content, proline contentand endogenous hormone content of rice seedlings were determined when rice seeds werepretreated with H2O,10%PEG,100mMNaCl,1mMSA and0.1mMABA respectively before15%PEG stress. We analyzed the relationship between the different pretreatments and thedrought resistance of rice. The results were showed as follows:1. The membrane lipid preoxidation of rice seedlings with pretreatment maintained a lowerlevel than CK, and lower MDA content. After6days of pretreatment, it also had a lower level ofMDA content with ABA pretreatment of rice seedlings. Thus exogenous ABA can significantlydecrease membrane lipid peroxidation.2. Effects of different pretreatments on antioxidant enzyme activity indicated thatpretreatment enhanced the drought resistance of rice. There were different changes ofantioxidant emzymes. POD activity were enhanced, however SOD and CAT activity wereenhanced first and then depressed. SOD and POD activity in leaves of rice with H2O, ABApretreatment were higher than any other groups, and CAT activity with SA pretreatment wassignificantly higher than others.3. In this experiment, the proline content with different pretreatments was less than control,and the reason may be due to the higher antioxidant enzyme activity with pretreatment whichreduced the damage of water stress. Thus there is no need to synthesis a large number of prolinefor osmotic adjustment.4. Under water stress, ABA and SA in rice leaves were increased, while IAA and GA3weredecreased. ABA can regulate stomatal closure and the increasing of its content can reduce waterloss. IAA and GA3can promote the growth of plants, and the decline of theirs content willalleviate the pressure by the plant growth. ABA content with NaCl pretreatment was higher thanother groups.5. In this study, the ratio of IAA/ABA, GA3/ABA and (IAA+GA3)/ABA showed adownward trend under water stress.Above all, different pretreatments can effectively improve the antioxidant enzyme activity, reduce the production of MDA, IAA and GA3, and promote the synthesis of ABA and SA,which will enhance the ability of plants against water stress.