Physiological Control of Chloride Transport in Chara corallina: II. THE ROLE OF CHLORIDE AS A VACUOLAR OSMOTICUM

Sanders, D.

Plant Physiology 68(2): 401-406


ISSN/ISBN: 0032-0889
PMID: 16661924
DOI: 10.1104/pp.68.2.401
Accession: 006118129

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The extent to which Cl- is replaceable as the major anionic constituent of the vacuole of C. corallina was investigated. External Cl- is not essential in order for nongrowing cells to increase internal osmotic pressure. After growth of cells in low (9 .mu.M) Cl-, the vacuolar Cl- concentration is one-half that of cells grown at normal external Cl- concentration (850 .mu.M). Both internal osmotic pressure and total concentration of the major cations, K+ and Na+, in the same cells were only slightly sensitive to the external Cl- concentration. At limiting external Cl- concentration, the cell may transport or synthesize another anion for vacuolar use rather than utilize a neutral solute. Although the total vacuolar (K+ + Na+) concentration is relatively insensitive to low Cl- conditions, a large increase in K+ was recorded. This increase in K+ was offset by a correspondingly large fall in Na+. This is unrelated to any mechanistic dependence of Na+ on Cl- for entry into the cell but may indicate a control system acting on vacuolar sequestration of Na+ and Cl-. Cells grown in low Cl- display an ability to take up Cl-, at enhanced rates, from the medium. The enhancement of Cl- influx is maintained for several hours after external Cl- is raised to a high level and indicates the existence of a control on Cl- influx acting in addition to that of cytoplasmic Cl- concentration, which has a shorter decay time. The results are discussed in relation to similar work on higher plants.