MAPK Cascade Regulates The Antioxidizing Defence Response Of Maize Seedlings To Abiotic Stress

The growth and development of plants are inevitably affected by various stresses. Drought stress, salt stress and cold stress are the main factors in limiting crops'distribution and production, and there is interaction among the stresses to plants. MAPK (mitogen-activated protein kinase) cascade is one of the important signal modules which mediates plants'response to environment.We treated maize seedlings with mannitol, NaCl, low temprature and the cross stresses and also abscisic acid (ABA) and H₂O₂. PD98059,which is considered as an inhibitor of MAPKK activity, was used to estimate the effect of MAPK cascade to the enzymatic reactive oxygen species defense system. The results show that MAPK cascades are involved in signaling in response to all of the stresses described above. The defence system of enzymatic reactive oxygen species was obviously regulated by MAPK cascades during the stress treatments as well as the recovery. The main results are as follows:1.The total activities of SOD, POD and CAT in maize seedlings were induced obviously under mannitol, NaCl and low temprature treatment. Such induction was weakened by PD98059 to varying extent. During the recovery from the treatments described above, the maize seedlings still occupied higher enzyme activities in contrast with those treated with PD98059 though the enzyme activities gradually reduced. And after the treatment of PD98059, the MDA content raised.2. The total activities of SOD, POD and CAT in maize seedlings were induced obviously by ABA and H₂O₂ treatment. Such induction was weakened by PD98059 to varying extent. During the recovery from ABA and H₂O₂ treatment, the maize seedlings still occupied higher enzyme activities in contrast with those treated with PD98059 though the enzyme activities gradually reduced. And after the treatment of PD98059, the MDA content raised.3. The difference of the activities of SOD, POD and CAT in maize seedlings treated with PD98059 and without PD98059 was more significant during low temprature treatment and recovery than the treatment of ABA or H₂O₂, especially SOD. And the difference of the content of MDA also raised.4. The total activities of SOD, POD and CAT in maize seedlings were induced obviously under the cross treatments of drought and salt, drought and cold, and salt and cold. Such induction was weakened by PD98059 to varying extent. During the recovery from the cross treatments decribed above, the maize seedlings still occupied higher enzyme activities in contrast with those treated with PD98059 though the enzyme activities gradually reduced. And by the treatment of PD98059, the MDA content raised.5. Compared with those to single stress treatments at the same intensity, the total activities of SOD, POD and CAT raised and the MDA content decreased after cross treatments both in maize seedlings with or without the treatment of PD98059. And the effect of MAPK cascade on the activity of SOD was more significant than to the other two enzymes during the cross treatment of mannitol and NaCl compared with that during the single treatment of mannitol or NaCl.