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Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology
RESEARCH ARTICLE

Relationships Between Chloride Transport and Electrical Potential Differences in Carrot Root Cells

WJ Cram

Australian Journal of Plant Physiology 2(3) 301 - 310
Published: 1975

Abstract

The Cl- influx across the tonoplast increases at about 3 days after excision, and is inhibited by carbonyl cyanide m-chlorophenylhydrazone in well-washed tissue, while the influx of Cl- across the plasmalemma and the cellular electrical potential difference both remain constant under these conditions. The transport of Cl- within the cell therefore appears not to be electrogenic.

When SO42- is substituted for Cl-, keeping the external K+ concentration constant, the cell potential difference (p.d.) increases from - 54 mV in 10 mol m-3 KCl to -65 mV in 5 mol m-³ KSO42- if the p.d. were solely a diffusion potential, then substituting SO42- for Cl- would be expected to reduce it. This prediction is based on the Goldman equation with a term for SO42- introduced, and various estimates of the parameters involved. It is therefore suggested that a small part of the p.d. in carrot may be due to the activity of a Cl- pump inwards across the plasmalemma, which is linked either to a larger cation influx or to a larger anion (e.g. OH-) efflux.

During accumulation of KCl, the cell p.d. increases slightly, from - 54 mV in the non-loaded cell in 10 mol m-3 KCl to -59 mV in the KCl-loaded cell in 10 mol m-3 KCl. This small change is not inconsistent with the response of the p.d. to changes in external salt concentration.

From these results, the electrochemical potential of Cl- in the vacuole is calculated to be greater than in an external solution of 1 mol m-3 KCl by 17 kJ mol-1 in non-loaded tissue and by 23 kJ mol-1 in KCl-loaded tissue. This increase in the gradient opposing Cl- entry is probably not sufficient to account for the fall in the active influx of Cl- during accumulation of KCl.

https://doi.org/10.1071/PP9750301

© CSIRO 1975

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