Plant Physiol, October 2001, Vol. 127, pp. 497-504
External Ca2+ Is Essential for Chloroplast Movement
Induced by Mechanical Stimulation But Not by Light
Stimulation1,[w]
Yoshikatsu
Sato,
Masamitsu
Wada, and
Akeo
Kadota*
Department of Biological Sciences, Graduate School of Science,
Tokyo Metropolitan University, Minami-Osawa 1-1, Hachioji, Tokyo
192-0397, Japan (Y.S., M.W., A.K.); and National Institute for Basic
Biology, Myodaiji, Okazaki 444-8585, Japan (M.W.)
In the fern Adiantum capillus-veneris, chloroplast
movement is induced by mechanical stimulation as well as by light
stimulation. Directional movement of both types depends on an
actin-based motile system. To investigate the physiological
relationship between mechanical and light signaling in the regulation
of chloroplast movement, we examined the mechano-response of
chloroplasts whose motility had been already restricted after
photo-relocation. Chloroplast mechano-avoidance movement was induced
under all of the photo-relocation conditions tested, indicating that
mechano-specific signals generated by mechanical stimulation dominate
over the light signals and reactivate the motility of chloroplasts.
When the effects of external Ca2+ on the induction of
mechano- and light responses were examined, strikingly different
requirements of external Ca2+ were found for each. In
medium without Ca2+, the mechano-response was suppressed
but no effects were observed on photo-response. Mechano-relocation
movement of chloroplasts was inhibited by 100 µM
lanthanum (La3+), a plasma membrane calcium channel
blocker, and by 10 µM gadolinium (Gd3+), a
stretch-activated channel blocker. However, the same concentrations of
these drugs did not affect the photo-relocation movement at all. These
results suggest that the influx of external Ca2+ is crucial
for the early signaling step of chloroplast mechano-relocation but not
for that of photo-relocation. This is the first report showing the
separation of signaling pathways in mechano- and photo-relocation of chloroplasts.
1
This work was supported by the National
Institute for Basic Biology Cooperative Research Program (grant no.
1-120), and in part by the Japan Society for the Promotion of
Science (Grant-in-Aid for Scientific Research [C] no. 11640651 to
A.K. and Grant-in-Aid for Scientific Research [B] no. 09440270 to
M.W.), by the Program for Promotion of Basic Research Activities for
Innovative Biosciences (to M.W.), by the Research Fellowships of the
Japan Society for the Promotion of Science for Young Scientists (grant
no. 12740202 to Y.S.), and by the Japan Science Society (Sasagawa
Scientific Research Grant to Y.S.).
[w]
Indicates Web-only data.
*
Corresponding author; e-mail kadota-akeo{at}c.metro-u.ac.jp; fax
81-426-77-2559.
© 2001 American Society of Plant Physiologists
