External Ca(2+) is essential for chloroplast movement induced by mechanical stimulation but not by light stimulation.
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 Ca(2+) on the induction of mechano- and light responses were examined, strikingly different requirements of external Ca(2+) were found for each. In medium without Ca(2+), the mechano-response was suppressed but no effects were observed on photo-response. Mechano-relocation movement of chloroplasts was inhibited by 100 microM lanthanum (La(3+)), a plasma membrane calcium channel blocker, and by 10 microM gadolinium (Gd(3+)), 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 Ca(2+) 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.
Sato
Y
Y
Department of Biological Sciences, Graduate School of Science, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachioji, Tokyo 192-0397, Japan.
Wada
M
M
Kadota
A
A
D000199:Actins / Q000378:metabolism*; D001696:Biomechanical Phenomena; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002736:Chloroplasts / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D003599:Cytoskeleton / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D005682:Gadolinium / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D008027:Light; D008954:Models, Biological; D009068:Movement / Q000187:drug effects / Q000528:radiation effects; D009218:Myosins / Q000378:metabolism; D010812:Physical Stimulation; D029625:Pteridaceae / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D015398:Signal Transduction
D000199:Actins; D002121:Calcium Channel Blockers; D007811:Lanthanum; D005682:Gadolinium; D009218:Myosins; D002118:Calcium