Evidence for Cotransport of Nitrate and Protons in Maize Roots: II. Measurement of NO3− and H+ Fluxes with Ion-Selective Microelectrodes

摘要: We report here on an investigation of net nitrate and proton fluxes in root cells maize (Zea mays L.) seedlings grown without (noninduced) with (induced) 0.1 millimolar nitrate. A microelectrode system described previously (IA Newman, LV Kochian, MA Grusak, WJ Lucas [1987] Plant Physiol 84: 1177-1184) was utilized to quantify ionic from the measurement electrochemical potential gradients for NO3− H+ within unstirred layer at surface. The nitrate-inducibility, pH dependence, concentration dependence uptake correlated quite closely electrical response roots under same experimental conditions (as PR McClure, RM Spanswick, JE Shaff [1990] 93: 281-289). Additionally, it found that inhibitors plasmalemma H+-ATPase (vandate, diethylstilbestrol), which were shown abolish (in 281-289), dramatically inhibited absorption. These results strongly indicate is due operation a transport cells. Furthermore, inhibitor studies linked H+-ATPase, presumably as NO3−/H+ symport. This further supported by (inhibition alkaline values) change flux moderate efflux absence NO3−, zero after exposing exogenous Although these can be explained other interpretations, simplest model fits both responses data symport NO3−:H+ stoichiometry >1, whose stimulation influx protons through cotransport system.