Potassium and Photosynthesis in the Marine Diatom Phaeodactylum tricornutum as Related to Washes with Sodium Chloride

Abstract

Three washes of Phaeodactylum tricornutum with potassium free sodium chloride solution reduced the potassium content of the cells to approximately 7% of the control value at pH 7.0. There was a concomitant reduction of the light induced evolution of oxygen to a value of approximately 20% of the control value. This reduction was less at pH 8.0. Addition of potassium to the washed cells gave rise, after 15 min, to a partial regain of the photosynthetic activity and of cellular potassium.Activities of the two photosystems as assayed here were not dependent on the maintainance of a high potassium content in the cells. The level of ribulose‐1,5‐diphosphate carboxylase activity was the same whether the cells had been washed with potassium free or potassium containing saline.Ruptured cells rapidly lost their ability to catalyse the photoreduction of dichlorophenolindophenol by water.