Effects Of Water Stress And ABA Treatment On Subcellular Antioxidant System In Leaves Of Maize Seedlings

The effects of water stress induced by PEG 6000 (-0.7MPa) and ABA treatment on the activities of several major antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR)] and their isoenzymes, and the contents of antioxidant metabolites [ascorbate acid (ASC) and reduced gluthione (GSH)] in different subcellular compartments such as chloroplasts, mitochondria, peroxisomes, cytosol and apoplast in leaves of maize (Zea mays L., cv. Nongda No.108) seedlings were investigated in this study.The results showed that under water stress and ABA treatment, the activities of SOD, CAT, APX and GR in chloroplastic fractions were increased significantly from 4h to 12h, and declined to the control level at 24h; and the contents of ASC and GSH were also increased significantly from 4h to 12h, and declined to the control level at 24h. But in apoplast, under water stress and ABA treatment, the activities of SOD, CAT, APX and GR were increased significantly at 4h, and increased slowly at 8h to 12h, even that under ABA treatment the activity of GR was declined from 12h; the contents of ASC and GSH were increased significantly from 4h to 8h and declined after then. Under water stress and ABA treatment, the activities of SOD, CAT, APX and GR and the contents of ASC and GSH in mitochondria, peroxisomes and cytosol had similar changes compared with those in cytosolic fractions. These results indicated that water stress and ABA treatment could cooperate the components of antioxidant defense systems in different subcellular compartments.The results also showed that in chloroplast, there were four kinds of SOD isoenzymes, three were Cu/Zn-SOD and one was Fe-SOD, three kinds GR isoenzymes and two kinds APX isoenzymes; under water stress and ABA treatment, the activities of all antioxidant enzymes' isoenzymes increased from 4h to 12h and declined at 24h. In mitochondria, there were four kinds of SOD isoenzymes, one was Cu/Zn-SOD, one was Fe-SOD and the other two were Mn-SOD, four kinds of GR isoenzymes but only one kind of APX isoenzyme; under water stress and ABA treatment, the activities of all antioxidant enzymes' isoenzymes increased from 4h to 12h and declined at 24h, but also higher than the control except of APX isoenzyme. In peroxisome there were three kinds of SOD isoenzymes, one was Cu/Zn-SOD and the other two were Mn-SOD, two kinds of GR isoenzymes, one kind of APX isoenzyme and two kinds of CAT isoenzymes; under water stress and ABA treatment, the activities of SOD isoenzymes increased from 4h to 12h and declined at 24h but also higher than control except of Cu/Zn-SOD, the activities of GR, APX and CAT isoenzymes also increased from 4h to 12h and declined at 24h. Cytosol had five kinds of SODisoenzymes, four were Cu/Zn-SOD and one was Fe-SOD, two kinds of GR isoenzymes and four kinds of APX isoenzymes; under water stress and ABA treatment, the activities of all kinds of SOD isoenzymes increased from 4h to 12h, but also higher than control though declined at 24h, and GR isoenzymes had the highest activities an 12h, and the activities of two APX isoenzymes: cytAPXâ…£ and cytAPXâ…¢ increased from 4h to 12h, but the activities of the other two APX isoenzymes did not significant change. In apoplast, there were six kinds of SOD isoenzymes, four were Cu/Zn-SOD, one was Fe-SOD and one was Mn-SOD, and there were one kind of CAT isoenzyme, three kinds of GR isoenzymes and two kinds of APX isoenzymes; the activities of Mn-SOD and Fe-SOD declined at the beginning and the increased from 8h under ABA treatment but declined all long under water stress, and under water stress and ABA treatment, the activities of Cu/Zn-SOD increased from 4h to 12h, the CAT isoenzymes had the highest activities at 12h, and apoGRâ…£ disappeared under water stress and ABA treatment but the activities of the other four GR isoenzymes were higher than control, and the activities of APX isoenzymes increased gradually. These results suggested that different kinds of antioxidant isoenzymes in different subcellular comp...