The role of calcium in turgor regulation in Chara longifolia.

The salt-tolerant alga Chara longifolia (Robinson) is capable of regulating its turgor in response to hypotonic pressure of the medium. This regulatory process takes only 40 min in small cells (length ⩽ 10 mm), but requires 3 d in large cells (length ⩾ 30 mm). Turgor regulation in small cells is comprised of two phase is inhibited by reducing the contration of Ca²⁺ in the external medium from 4.6 to 0.01 mol m^-3; the first phase is less affected by the reduction of Ca²⁺. In the first 5 min of stress, the membrane depolarizes in a voltage-dependent transiently and cytoplasmic streaming is inhibited. When the external Ca²⁺ concentration is lowered, conductance does not increase and streaming continues unaffected. In the medium for turgor regulation. To test the hypothesis that there is increased Ca²⁺ entry from the medium during turgor regulation, we measured the influx of ⁴⁵Ca²⁺ into the cell. We found an increased influx of Ca²⁺, from 18 to 36 nol m^-2 s^-1 during the first 30 to 90 s following osmotic stress. This increase was evident only in cells below about 7 mm in length, and was more marked in smaller cells. [ABSTRACT FROM AUTHOR]