The speed of intracellular signal transfer for chloroplast movement.

The photoreceptors for chloroplast photorelocation movement have been known, but the signal(s) raised by photoreceptors remains unknown. To know the properties of the signal(s) for chloroplast accumulation movement, we examined the speed of signal transferred from light-irradiated area to chloroplasts in gametophytes of Adiantum capillus-veneris. When dark-adapted gametophyte cells were irradiated with a microbeam of various light intensities of red or blue light for 1 min or continuously, the chloroplasts started to move towards the irradiated area. The speed of signal transfer was calculated from the relationship between the timing of start moving and the distance of chloroplasts from the microbeam and was found to be constant at any light conditions. In prothallial cells, the speed was about 1.0 μm min(-1) and in protonemal cells about 0.7 μm min(-1) towards base and about 2.3 μm min(-1) towards the apex. We confirmed the speed of signal transfer in Arabidopsis thaliana mesophyll cells under continuous irradiation of blue light, as was about 0.8 μm min(-1). Possible candidates of the signal are discussed depending on the speed of signal transfer.