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Short‐term regulation of cytosolic Ca 2+ , cytosolic pH and vacuolar pH under NaCl stress in the charophyte alga Nitellopsis obtusa
Author(s) -
OKAZAKI Y.,
KIKUYAMA M.,
HIRAMOTO Y.,
IWASAKI N.
Publication year - 1996
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.1365-3040.1996.tb00390.x
Subject(s) - aequorin , photoprotein , cytosol , chemistry , biophysics , nuclear chemistry , calcium , sorbitol , biochemistry , intracellular , biology , enzyme , organic chemistry
Isolated characean internodal cells of Nitellopsis obtusa can be stored in artificial pond water for many days, but they cannot survive in 100mol m −3 NaCl solution unless more than several mol m −3 Ca 2+ is added. Short‐term effects of NaCl stress on the cytosolic concentration of Ca 2+ ([Ca 2+ ] c ), cytosolic pH (pH c ) and vacuolar pH (pH v ) were studied in relation to the external concentration of Ca 2+ ([Ca 2+ ] e ). Changes in [Ca 2+ ] c were measured with light emission from a Ca 2+ ‐sensitive photoprotein, semisynthetic fch ‐aequorin which had been injected into the cytosol. Both pH c and pH v were measured with double‐barrelled pH‐sensitive microelectrodes. When internodal cells were treated with 100 mol m −3 NaCl (0–1 mol m −3 NaCl (0.1 mol m −3 [Ca 2+ ] e ), [Ca 2+ ] c increased and then recovered to the original level within 60 min. The time course of the transient change in [Ca 2+ ] c was not influenced by the level of [Ca 2+ ] c (0.1 and 10 mol m −3 ). In some cases, the transient increase in [Ca 2+ ] c was induced only by increasing external osmotic pressure with sorbitol. In response to treatment with 100 mol m −3 NaCl (0.1 mol m −3 [Ca 2+ ] c ), pH c decreased by 0.1–0.2 units after 10min but recovered after 30–60 min, while pH v increased by 0.4–0.5 units after 2–50 min and tended to recover after 60 min. The initial changes in both pH c and pH v were suppressed when [Ca 2+ ] e was raised from 0.1 to 10mol m −3 . These results show that the charophyte alga Nitellopsis can regulate [Ca 2+ ] c , pH c and pH v under NaCl stress in the short term and that the protective effect of Ca 2+ on salinity stress is apparently unrelated to perturbation of Ca 2+ and pH homeostasis.