Hydrogen Peroxide And Nitric Oxide Are Required For Abscisic Acid-Regulated Maize Primary Root Growth At Low Water Potentials

In this study, the role of hydrogen peroxide(H₂O₂) and nitric oxide(NO) and the relationship between them in the maintenance of maize(Zea mays L.) primary root growth by ABA at a low water potentials (-1.6MPa) induced by polyethylene glycol(PEG6000) were investigated.The results of this experiment indicated that at low water potentials, maize primary root maintenance growth by zccumulation ABA and at normal water potentials, low concentration of exogenous H₂O₂ (0.5 mM, 1 mM) accelerated primary root growth and high concentration of exogenous H₂O₂ (5 mM)largely inhibited primary root growth of maize. The result of TEM indicated that there is some H₂O₂ accumulated in the primary root of maize at low water potentials, if we use the scavengers of H₂O₂ such as dimethythiourea(DMTU), potassium iodide(KI) and Na-Pyruvate(Na-pyr) pretreated the seedlings of maize and then explored them into low water potentials, we found that the primary root almost stopped growth, suggesting that a little amount of H₂O₂ accumulated in primary root of maize is required for maintain primary root growth at low water potentials, if all the H₂O₂ is removed at low water potentials, the elongation of the primary root will be greatly inhibited. As a result of heavily water stress, though ABA can activate the antioxidant system to maintain primary root growth at first, however, as the time goes by, the primary root of maize will accumulate a huge mass of H₂O₂ and inhibit the growth of primary root.We also found that, at normal water potentials, low concentration of SNP (0.05 mM, 0.1 mM) which is a NO donor could accelerate primary root growth and high concentration (0.2 mM) will inhibit primary root elongation. The result of LSCM indicated that NO involved in ABA maintained primary root growth, fluridone experiment showed that ABA maybe induces NO accumulation in primary root under low water potentials. Pretreated with scavengers such as 2- (4-carboxy-phenyl) - 4,4,5,5 - tetramethylimi - dazoline - 1 - oxyl - 3 - oxide (c-PTIO) and inhibitors of NO such as N^G-nitro-L-Arg-methyl ester (_L-NAME) and sodium azide(NaN₃), and then explored seedlings to low water potentials will largely inhibited primary root growth. These results suggesting that NO involved in ABA maintain maize primary root growth at low water potentials, if remove NO will greatly inhibited primary root growth.Above experiments improved both H₂O₂ and NO are involved in ABA maintain maize primary root growth, what we interested is the relationship between H₂O₂ and NO. The seedlings were pretreated with scavengers and inhibitors and then cultured in low water potentials, using TEM to observe the H₂O₂ accumulation in primary root and found! that there is almost no different with the seedlings without pretreated with the scavengers and inhibitors of NO at low water potentials. Pretreated with scavengers of H₂O₂ and then explored the seedlings to low water potentials, the fluorescence of NO in primary root is obviously lower than without pretreated with scavengers of H₂O₂, suggesting that H₂O₂ may function upstream of NO.In conclusion, our data suggest that both H₂O₂ and NO are involved in process of ABA maintain primary root growth and H₂O₂ may function upstream of NO.