Increased Potassium Absorption Confers Resistance to Group IA Cations in Rubidium-Selected Suspension Cells of Brassica napus.

Cell lines of suspension cultures of Brassica napus cv. Jet Neuf were identified for their ability to tolerate 100 millimolar Rb(+), a level which was double the normally lethal concentration. Ten spontaneous isolates were obtained from approximately 5 x 10(7) cells, one of which was reestablished as a cell suspension. This cell line, JL5, was also resistant to the other group IA cations- Li(+), Na(+), K(+), and Cs(+)-and this trait was stable for at least 30 cell generations in the absence of Rb(+) selection pressure. The growth characteristics were similar to those of sensitive cells under nonselective conditions. The selected JL5 cells were shown by analysis to have effected more net accumulation of K(+) and Rb(+) and less of Na(+) than did the unselected cells. JL5 and unselected cells after 14 days of culture in basal medium contained 597.2 and 258.2 micromoles of K per gram dry weight, respectively. Michaelis-Menten kinetic analysis of K(+) influx showed that JL5 possessed an elevated phase 1 V(max), but there was no alteration in its K(m). This is the first time that a plant mutation has been shown to have both increased influx and net absorption of a major essential cation.