Chloroplasts can move in any direction to avoid strong light
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- Tsuboi, H. & Wada, M. J Plant Res (2011) 124: 201. doi:10.1007/s10265-010-0364-z
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Chloroplasts migrate in response to different light intensities. Under weak light, chloroplasts gather at an illuminated area to maximize light absorption and photosynthesis rates (the accumulation response). In contrast, chloroplasts escape from strong light to avoid photodamage (the avoidance response). Photoreceptors involved in these phenomena have been identified in Arabidopsis thaliana and Adiantum capillus-veneris. Chloroplast behavior has been studied in detail during the accumulation response, but not for the avoidance response. Hence, we analyzed the chloroplast avoidance response in detail using dark-adapted Adiantumcapillus-veneris gametophyte cells and partial cell irradiation with a microbeam of blue light. Chloroplasts escaped from an irradiated spot. Both duration of this response and the distance of the migrated chloroplasts were proportional to the total fluence irradiated. The speed of movement during the avoidance response was dependent on the fluence rate, but the speed of the accumulation response towards the microbeam from cell periphery was constant irrespective of fluence rate. When a chloroplast was only partially irradiated with a strong microbeam, it moved away towards the non-irradiated region within a few minutes. During this avoidance response two additional microbeam irradiations were applied to different locus of the same chloroplast. Under these conditions the chloroplast changed the moving direction after a lag time of a few minutes without rolling. Taken together, these findings indicate that chloroplasts can move in any direction and never have an intrinsic polarity. Similar phenomenon was observed in chloroplasts of Arabidopsisthaliana palisade cells.
KeywordsAdiantum capillus-veneris Arabidopsis thaliana Avoidance Blue light Chloroplast movement Microbeam
This time-lapse movie shows chloroplast avoidance movement induced by three sequential blue microbeam irradiations from which the data of Figs. 5, 6 and 7 were taken. Note the linear movement of the chloroplast escaping from the beam. Images were acquired in 15-sec intervals