Silicic-acid uptake in diatoms studied with [(68)Ge]germanic acid as tracer

Uptake of silicic acid in the diatoms Navicula pelliculosa and Nitzschia alba was studied, using the natural isotope, (28)Si, or a radioisotope, (31)Si. The rate of uptake of silicic acid was also determined by using [(68)Ge]germanic acid as a tracer of silicic acid. At a given silicicacid concentration in the growth medium, the fractions of [(68)Ge]germanic acid taken up followed closely the fraction of silicic acid taken up in the same time period. When the initial concentration of silicic acid was varied at a constant (trace) concentration of [(68)Ge]-germanic acid, the uptake of (68)Ge followed the fraction of silicic acid removed, and not the absolute amount removed from the medium, at all silicic-acid concentrations. The usefulness of this approach in studying silicic-acid uptake is discussed.