Phosphate Incorporation by Euglena gracilis During pH‐dependent Photo‐inhibition1

Abstract

ABSTRACTInhibition of cell division in Euglena gracilis by visible light is pH‐dependent, being most severe in the pH range 3.5–5.0. Transfer of phototrophic cells from pH 6.8 to pH 4.2 can lead to cell death at modest light intensities (500 ft‐cd) and inhibition of division at lower intensities (300 ft‐cd). Inhibition is preceded by a large influx of phosphate, most of which remains in the cold PCA pool. It is suggested that light may act to reduce control over phosphate entry at these intermediate pH levels, and excess phosphate leads to inhibition of cell division or death.