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- Title
Flexible Coupling of Phosphate Uptake in Dunaliella acidophila at Extremely Low pH Values.
- Authors
HIRSCH, R.; de GUIA, M.; FALKNER, G.; GIMMLER, H.
- Abstract
The acidophilic alga exhibits optimal growth at pH 1. We have investigated the regulation of phosphate uptake by this alga using tracer techniques and by performing intracellular phosphate measurements under different growth conditions including phosphate limitation. In batch culture with 2·2 mol m phosphate in the medium the uptake of phosphate at micromolar phosphate concentrations followed a linear time dependence in the range of minutes and rates were in the range of 1 μmol phosphate mg chl h, only. However, under discontinuous phosphate-limited growth conditions, tracer influx revealed a biphasic pattern at micromolar phosphate concentrations: An initial burst phase resulted in a 10-fold internal phosphate accumulation and levelled off after about 10 s. A double reciprocal plot of the initial influx rates obtained for phosphate-limited and unlimited algae exhibited Michaelis-Menten kinetics. Phosphate limitation caused a significant activation of the maximum velocity of uptake, yielding up to 1 mmol mg chl h as compared to values in the order of 50 μmol phosphate mg chl h for the second phase (this magnitude is also representative for non-limited batch cultures). Concomitantly the Michaelis constant was altered from 4 mmol m to 0·7 mmol m. The rapid uptake of phosphate was inhibited by arsenate and FCCP and was not stimulated by Na. The pH dependence of tracer accumulation and measurements of the intracellular phosphate pool under different growth conditions indicate that at low pH and low external phosphate concentrations the high proton gradient present under these conditions is utilized for a HPO uptake or a H/HPO cotransport. However, when the external phosphate concentration was increased to levels sufficiently high for transport to be driven by the positive membrane potential (10 mol m phosphate), the pH dependence of phosphate uptake was more complex, but could be explained by the uptake of HPO or a H/HPO-cotransport at low pH and a different type HPO-transport (with unknown type of ion coupling) at high pH-values. It is suggested that this flexible coupling of phosphate transport is of essential importance for the acid resistance of .
- Publication
Journal of Experimental Botany, 1993, Vol 44, Issue 8, p1321
- ISSN
0022-0957
- Publication type
Article