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Plant Physiol, May 2000, Vol. 123, pp. 161-176
Use of Recombinant Aequorin to Study Calcium Homeostasis and
Monitor Calcium Transients in Response to Heat and Cold Shock in
Cyanobacteria1
Ignacio
Torrecilla,
Francisco
Leganés,
Ildefonso
Bonilla, and
Francisca
Fernández-Piñas*
Departamento de Biología, Facultad de Ciencias, Universidad
Autónoma de Madrid, Madrid, 28049, Spain
We investigated the possibility of Ca2+ signaling in
cyanobacteria (blue-green algae) by measuring intracellular free
Ca2+ levels ([Ca2+]i) in a
recombinant strain of the nitrogen fixing cyanobacterium Anabaena strain sp. PCC7120, which constitutively
expresses the Ca2+-binding photoprotein apoaequorin. The
homeostasis of intracellular Ca2+ in response to increasing
external Ca2+ has been studied in this strain. The resting
level of free Ca2+ in Anabaena was found to
be between 100 and 200 nM. Additions of increasing
concentrations of external Ca2+ gave a transient burst of
[Ca2+]i followed by a very quick decline,
reaching a plateau within seconds that brought the level of
[Ca2+]i back to the resting value. These
results indicate that Anabaena strain sp. PCC7120 is
able to regulate its internal Ca2+ levels. We also
monitored Ca2+ transients in our recombinant strain in
response to heat and cold shock. The cell's response to both stresses
was dependent on the way they were induced. The use of inhibitors
suggests that heat shock mobilizes cytosolic Ca2+ from both
intracellular and extracellular sources, while the Ca2+
source for cold shock signaling is mostly extracellular.
1
This work was supported by Direccion General de
Ense anza Superior (grant nos. PB96-0487 and
PB98-0114-CO2-01). I.T. holds a fellowship from Comunidad Autonoma
de Madrid.
*
Corresponding author; e-mail Francisca.Pina{at}uam.es; fax
34-91-3978344.
© 2000 American Society of Plant Physiologists
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