Dependence on Light of the Reversible Uptake of Inorganic Phosphate by Hydrodictyon

Abstract

IN the colony-forming green alga, Hydrodictyon reticulatum, uptake and metabolism of phosphate have been followed up by ordinary analytical methods (fractionation by the conventional trichloracetic acid technique, determination of phosphates with a modified procedure of Fiske and Subbarow1). The predominant feature in the changes of the phosphate fractions during a long-term culture with intermittent illumination (12 hr. light: 12 hr. darkness) is a marked increase in the large cells of the alga of the inorganic phosphate-level during the time of illumination. A comparable light-dependent accumulation of ions has been reported for other objects (reviewed by Brauner2), most recently for chloride by van Lookeren-Campagne3. In the case of Hydrodictyon, however, the accumulation of inorganic phosphorus in the light is reversible4, since the low level of intra-cellular phosphate is completely restored during the dark time. This is shown in Fig. 1. The changes of the inorganic phosphorus have been found in the cells and, at the same time, in the surrounding nutrient solution. The differences in the phosphorus-level are not directly induced by pH. changes in the medium.