Abstract
The extent to which Cl− is replaceable as the major anionic constituent of the vacuole of Chara corallina was investigated. It was found that external Cl− is not essential in order for nongrowing cells to increase internal osmotic pressure. After growth of cells in low (9 micromolar) Cl−, the vacuolar Cl− concentration is one-half that of cells grown at normal external Cl− concentration (850 micromolar). In contrast, both internal osmotic pressure and total concentration of the major cations, K+ and Na+, in the same cells were found to be only slightly sensitive to the external Cl− concentration. Thus, it is proposed that, at limiting external Cl− concentration, the cell is able to 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 both 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.
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Selected References
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