NITRATE TRANSPORT IN ZEA-MAYS CELL-SUSPENSION CULTURES - THE EFFECT OF SOLUTION COMPOSITION AND CELL AGE

Nitrate transport characteristics of an amino acidgrown Zea mays P3377 cell culture line were studied. Age (days after subculturing) of the cells was shown to have a significant effect on NO3- transport; older stationary phase cultures did not absorb nitrate from the medium as ra pidly as younger growing cultures. Solution composition had a pronounc ed impact on induction of accelerated nitrate transport and transport rates. Maximum uptake rates required fresh culture media rather than s imple solutions. Differences in ionic strength among uptake solutions of equal NO3- concentration were shown to affect the apparent uptake r ates by changing the activity coefficient of NO3-. The uptake kinetics were established by following uptake for 24 h in a wide range of nitr ate concentrations. Uptake patterns of cells in solutions ranging from 0.02 to 2 mM were as typically reported for plants. The kinetic const ants for the Zea mays cell suspension cultures concurred with reports of other solution-cultured cells. When cells were placed in solutions containing NO3- greater than 2 mM, uptake patterns suggested a signifi cant passive uptake component. Passive diffusion of NO3- was estimated by Nernst analysis and indicated to be an important component of nitr ate uptake in maize cell suspension cultures grown in the absence of n itrate then transferred into nitrate-containing media.