Studies of the uptake of nitrate in barley. I. Kinetics of 13NO3(-1) influx

13NO3(-1) was used to investigate patterns of NO3(-1) influx into roots of barley plants (Hordeum vulgare L. cv Klondike) previously grown with ('induced') or without ('uninduced') a source of external NO3(-1) ([NO3(-1)]o). In both induced and uninduced plants, 13NO3(-1) influx was biphasic in the range from 0.005 to 50 moles per cubic meter [NO3(-1)]o. In the low concentration range (less 1 mole per cubic meter for induced plants and less 0.3 mole per cubic meter for uninduced plants), influx was saturable and Vmax and Km values for influx either increased or decreased according to NO3(-1) pretreatment. By contrast, 13NO3(-1) influx in the high concentration range revealed a strictly linear concentration dependence. These fluxes appeared to be mediated by a constitutive, rather than an inducible, transport system