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The role of calcium in turgor regulation in Chara longifolia
Author(s) -
BISSON M. A.,
KIEGLE E.,
BLACK D.,
KIYOSAWA K.,
GERBER N.
Publication year - 1995
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1995.tb00346.x
Subject(s) - turgor pressure , chara , biophysics , calcium , osmotic pressure , chemistry , conductance , cytoplasmic streaming , osmoregulation , tonicity , osmotic shock , botany , biochemistry , biology , cytoplasm , salinity , ecology , mathematics , organic chemistry , combinatorics , gene
The salt‐tolerant alga Chara longifolia (Robinson) is capable of regulating its turgor in response to hypotonic stress resulting from a decrease in the osmotic pressure of the medium. This regulatory process takes only 40 min in small cells (length ≤ 10 mm), but requires 3d in large cells (length ≥30mm). Turgor regulation in small cells is comprised of two phases, a fast phase reducing the increased turgor by about 25% in the First 5 min, and a second phase reducing the turgor to near the original value within 40 min. The second phase is inhibited by reducing the concentration of Ca 2+ in the external medium from 4.6 to 0.01 mol m −3 ; the first phase is less affected by the reduction of Ca 2+ . In the first 5 min of stress, the membrane depolarizes in a voltage‐dependent fashion, electrical conductance of the membrane increases transiently and cytoplasmic streaming is inhibited. When the external Ca 2+ concentration is lowered, conductance does not increase and streaming continues unaffected. In a low ionic strength medium, Ca 2+ is not required in the medium for turgor regulation. To test the hypothesis that there is increased Ca 2+ entry from the medium during turgor regulation, we measured the influx of 45 Ca 2+ into the cell. We found an increased influx of Ca 2+ , from 18 to 36 nmol 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.