Physiological Control of Chloride Transport in Chara corallina

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Abstract
The rate of Cl- transport at the plasma membrane of the freshwater alga C. corallina is investigated with respect to possible in vivo controls acting in addition to the 2 well established ones of cytoplasmic Cl- and cytoplasmic pH. In contrast with results from many other plant tissues, halides appear to be the only anions capable of inhibiting Cl- transport, either from the outside or inside surfaces of the plasma membrane. Cell turgor pressure was investigated. Neither the influx of Cl- nor that of K+ or HCO3- is sensitive to turgor. Internal osmotic pressure is also insensitive to turgor, a situation contrasting with that in closely related brackish water charophytes. After temperature downshift (from 20 to 4.degree. C), Cl- transport displays a slow, time-dependent rise. Return of cells from 4.degree. to 20.degree. C results in a large stimulation of Cl- influx in comparison with cells maintained at 20.degree. C throughout. This stimulation persists for several hours and is also apparent (to a reduced extent) in cells which have had cytoplasmic composition controlled by intracellular perfusion. The stimulation arises, in part, from a change in plasma membrane properties. The results are discussed with respect to recent work on membrane fluidity as a function of temperature.