Effect of ammonium on nitrate utilization by roots of dwarf bean

Se estudio el efecto de NH4+ exogeno en la absorcion de NO3- y en la actividad reductasa in vivo de NO3- (ARN) en raices de Phaseolus vulgaris cv. Witte Krombek, antes, durante y despues de la induccion aparente del ARN de la raiz y de la absorcion de NO3-. no afecto ni el patron Cuando se suministro NH4+ al comienzo de la nutricion con NO3-, el patron de tiempo de absorcion de NO3- fue el mismo que el de plantas que no recibieron NH4+. ARN de la raiz resultaron inhibidos por el NH4+ hasta un max de 45 y 60 por ciento, resp. de la concn. de NH4Cl. inmediatamente y se presento un poco de restauracion durante la segunda hora. Durante la tercera hora, la TAN se volvio constante. de NH4+ de 2 mM y mayores causaron una estimulacion rapida y transitoria de la absorcion de NO3-seguida otra vez por una disminucion en la primera, una recuperacion en la segunda, y un estado fijo en la tercera hora. inhibicion max. de la TAN fija fue del 50 por ciento. con NO3-, el ARN de la raiz respondio menos y mas lentamente al NH4+ que la TAN. glutamato sintasa, resp., mitigaron la inhibicion de la TAN de plantas inducidas con NO3-. depende de la asimilacion de NH4+. los niveles mas bajos y mas altos de NH4+ evaluados (0.04 y 25.00 mM). (RA-CIAT) spa

The effect of exogenous NH4(+) on NO3(-) uptake and in vivo NO3(-) reductase activity (NRA) in roots of Phaseolus vulgaris cv. Witte Krombek was studied before, during, and after the apparent induction of root NRA and NO3(-) uptake. Pretreatment with NH4Cl (0.15-50.00 mm) affected neither the time pattern nor the steady state rate of NO3(-) uptake. When NH4(+) was given at the start of NO3(-) nutrition, the time pattern of NO3(-) uptake was the same as in plants receiving no NH4(+). After 6 h, however, the NO3(-) uptake rate (NUR) and root NRA were inhibited by NH4(+) to a max. of 45 and 60 percent, resp. The response of the NUR of NO3(-)- induced plants depended on the NH4Cl concn. Below 1 mM NH4(+), the NUR declined immediately and some restoration occurred in the 2nd hour. In the 3rd hour, the NUR became constant. In contrast, NH4(+) at 2 mM and above caused a rapid and transient stimulation of NO3(- ) uptake, followed again by a decrease in the 1st, a recovery in the 2nd, and a steady state in the 3rd hour. Maximal inhibition of steady state NUR was 50 percent. With NO3(-)-induced plants, root NRA responded less and more slowly to NH4(+) than did NUR. Met. sulfoximine and azaserine, inhibitors of glutamine synthetase and glutamate synthase, resp., relieved the NH4(+) inhibition of the NUR of NO3(-)-induced plants. It was concluded that repression of the NUR by NH4(+) depends on NH4(+) assimilation. The repression by NH4(+) was least at the lowest and highest NH4(+) levels tested (0.04 and 25.00 mM). (AS) eng