PHOSPHATE UPTAKE KINETICS IN EUGLENA GRACILIS (Z) (EUGLENOPHYCEAE) GROWN IN LIGHT/DARK CYCLES. II. PHASED PO4‐LIMITED CULTURES1

Abstract

SUMMARYThe characteristics of phosphate uptake and photosynthetic capacity were studied in P‐limited populations of Euglena gracilis Klebs (Z), using both P‐limited batch cultures in stationary phase and cyclostat cultures grown on 14:10 LD.P uptake obeyed Michaelis‐Menten kinetics between 0 and 150 μM PO4 under both growth conditions. The value of Vmax was 35% lower in the dark than in the light in the stationary phase cells. The value of K8 was not affected by light conditions, and uptake was completely inhibited in the presence of 1 mm KCN.P uptake (at 2.0 μM PO4) and photosynthetic capacity showed diel periodicity with peak rates occurring just before the beginning of the dark period for P uptake, and 8 h into the light period for photosynthetic capacity. Vmax for P uptake increased by a factor of 1.5 over the light period, whereas K8 remained constant at 1.4 μM PO4. These patterns were displayed by both nondividing stationary phase cells and populations in which less than a third of the cells divided each day, indicating that the rhythmicity is not coupled to cell division.