Chloride accumulation in plant cells as a homeostatic system: Energy supply as a dependent variable

Abstract

During the accumulation of KCl by excised tissue of the carrot storage root, Cl−, influx falls by 90% or more. The possibility that this reduction is caused by depletion of respiratory substrate and consequent limitation of Cl− influx by energy supply is disproved. If energy were limiting, then after accumulating KCl (i) the rate of O2 uptake would be less; (ii) the ATP content might be less; (iii) external glucose and/or sucrose would stimulate O2 uptake and Cl− influx; and (iv) respiratory uncouplers would stimulate O2 uptake less. In each case the opposite was found. The ratio of O2 uptake in KCl-loaded tissue to that in nonloaded tissue was 1.25±0.21 (7); the ATP concentration was the same after KCl loading; glucose did not stimulate O2 uptake (except indirectly in the same way as a nonmetabilized glucose analogue) nor did glucose or sucrose stimulate Cl− influx; and the maximal O2 uptake in the presence of the uncoupler ClCCP was the same after KCl loading.