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Ammonium uptake and cellular alkalisation in roots of Arabidopsis thaliana : The involvement of cytoplasmic calcium1
Author(s) -
Plieth Christoph,
Sattelmacher Burkhard,
Knight Marc R.
Publication year - 2000
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.2000.1100414.x
Subject(s) - aequorin , calcium , biophysics , cytoplasm , biochemistry , egta , ammonium , chemistry , biology , intracellular , organic chemistry
Using roots from Arabidopsis thaliana expressing the recombinant calcium indicator aequorin, we show that NH 3 uptake and alkalisation of plant cells act as a stimulus which induces transient elevations of the cytoplasmic free calcium concentration ([Ca 2+ ] c ). The magnitudes of these [Ca 2+ ] c elevations are dependent on the concentration of the membrane permeable form, NH 3 , and hence, particularly dependent on the pH in the external medium. EGTA and La 3+ are able to significantly suppress the [Ca 2+ ] c transients showing that Ca 2+ influx through the plasma membrane is likely to be involved. Verapamil and nifedipine had no inhibitory effects, which suggests that Ca 2+ release from internal stores might not contribute significantly to the NH 3 ‐triggered [Ca 2+ ] c response. Pre‐incubation in l ‐methionine‐ dl ‐sulphoximine – an inhibitor of the glutamine synthetase – did not alter the NH 3 ‐induced [Ca 2+ ] c responses at all. These results are consistent with previous studies where NH 3 ‐induced changes of cytoplasmic and vacuolar pH were investigated in maize roots. Furthermore, the similarity between the kinetics of NH 3 ‐driven cellular pH changes demonstrated in previous studies and the [Ca 2+ ] c transients shown here suggests a direct relationship between [Ca 2+ ] c and cellular alkalisation (cytoplasmic pH and/or vacuolar pH). However, the mechanism behind this possible causal relation remains to be elucidated.