Abstract
Chloroplasts show intracellular photomovements regulated by phototropin 1 and 2. We have shown in Arabidopsis that during avoidance movement, chloroplasts migrate using a unique mechanism involving short chloroplast actin filaments (cp-actin) localized to the leading edge of chloroplast (Kadota et al. 2006). Here, we further analyzed the roles of cp-actin during chloroplast accumulation response. Accumulation response was induced by microbeam irradiation with low fluence-rate blue light and cp-actin organization was examined. After irradiation, chloroplasts transiently increased their speed and migrated towards the beam area. Cp-actins were observed to be localized to the leading edge of the moving chloroplast as in the case of avoidance movement. Close correlation between the difference in fluorescence intensity between front and rear halves of chloroplast and the movement speed was evident. These results indicate that both avoidance and accumulation responses have the same movement mechanism involving cp-actin localization on the chloroplast.
