RATE OF PHOSPHORUS UPTAKE BY PHAEODACTYLUM TRICORNUTUM

¹ Woods Hole Oceanographic Institution, Woods Hole, Massachusetts

Portions of a phosphorus-deficient culture of Phaeodactylum tricornutum Bohlin were dispensed into fresh media containing phosphate concentrations from 8 to 80 µM. The instantaneous initial phosphate uptake rates were 12 to 24 x 10^-17 mole/cell·min. The concentrations of phosphorus in the cells extended from a high of 66 x 10^-15 mole/cell after 12 hours' exposure to phosphate-rich (32 and 80 µM) media to a low of 2 x 10^-15 mole/cell when PO₄ depletion of the medium limited further growth. In another experiment Phaeodactylum was prepared with varying intracellular P concentrations in media with very low PO₄ concentrations. Radioactive phosphate was then added, the time course of P³² distribution was followed, and the rate of phosphate uptake was calculated. The initial rates ranged from 10^-17 to 3 x 10^-17 mole/cell·min. These were about one order of magnitude less than the uptake rates during the first two hours of the first experiment, even though the PO₄ concentrations were two to four orders of magnitude lower. Radioisotope analysis showed that Phaeodactylum decreased the phosphate in the medium to as little as 7.2 x 10^-10 M, a concentration much below the limit of sensitivity of the chemical analytical method.