Salt Tolerance in Suspension Cultures of Sugar Beet

Cell suspension cultures of sugar beet were grown at various salinities (0-200 millimolar NaCl). Their tolerance to Na(+) was comparable to that of the intact plant. Tonoplast vesicles were prepared by sucrose density gradient centrifugation of microsomal membranes and shown to be highly purified. The vesicles were subjected to a pH jump in the presence of acridine orange and the rate of recovery of fluorescence after addition of Na(+) was used as a measure of Na(+)-dependent H(+) efflux. In the presence of K(+) and valinomycin, the Na(+)/H(+) antiport showed saturation kinetics. Increasing Na(+) in the growth medium did not change the apparent K(m) for Na(+), but increased V(max) to about twice the control value, suggesting a specific induction of antiport synthesis by salt.