Effects of ammonium uptake on the changes of plasma membrane potential of rice roots

Changes of the plasma membrane potential on root tips of two rice(Oryza sativa L)cultivars,i.e.,Wuyujing 3(Japonica) and Yangdao 6(Indica) were monitored using microelectrodes under different concentrations of NH4+(0.025,0.05,0.1,0.5,1.0 and 1.5 mmol/L).The results were as follows: NH4+ uptake by the roots made plasma membrane(potential) depolarized;however,depolarization to the certain degree,it appeared the partial repolarization and hyperpolarization in some parts of rice roots during the absorption of NH4+.The magnitude of depolarization increased with the increasing of NH4+ concentrations until a stable state.The course of NH4+ uptake process conformed to Michaelis-Menten (kinetics).The two rice cultivars had different depolarization modes in which the average values depolarized were 16.5 mV(Wuyujing3) and 22.6mV(Yangdao 6).Under low concentration of NH4+(1mmol/L),with its higher average level of depolarization(17.5mV),Yangdao 6 was more sensitive to NH4+ being higher compared to Wuyujing 3(10.7 mV),and there existed a significant difference in the size of depolarization between these two cultivars(p0.05).This suggested that Yangdao 6 had the stronger capability to take up NH4+ than Wuyujing 3.The results obtained in this experiment were consistent with those of kinetics of NH4+ influx.