Physiological Control of Chloride Transport in Chara corallina: I. EFFECTS OF LOW TEMPERATURE, CELL TURGOR PRESSURE, AND ANIONS.
The rate of Cl(-) transport at the plasma membrane of the freshwater alga Chara corallina is investigated with respect to possible in vivo controls acting in addition to the two 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 also investigated. It was found that neither the influx of Cl(-) nor that of K(+) or HCO(2) (-) 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 20-4 C) Cl(-) transport displays a slow, time-dependent rise. Return of cells from 4 C to 20 C results in a large stimulation of Cl(-) influx in comparison with cells maintained at 20 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 therefore 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.
Sanders
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Botany School, Cambridge CB2 2EA, England.