Response of Spirogyra chloroplast to local illumination

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Abstract
1. The chloroplast of Spirogyra grows diffusively over its entire length even when irradiated only locally. Illumination of a disconnected chloroplast fragment also enhances the growth of other disconnected, non-illuminated fragments in the same cell. —2. When irradiated locally, the chloroplast becomes deformed to bring a greater part of it into the lighted area. Deformation caused by local illumination occurs only in the vicinity of the light-dark boundary. The chloroplast ribbon in this region shifts toward the lighted area not in parallel with the cell axis but obliquely to it. —3. Only light from the blue region induces the deformation. —4. The ability of the chloroplast to be centrifuged decreases in the illuminated region and increases in the shadowed region close to the light-dark boundary. —5. In a cell in which only the longitudinal half is illuminated, the chloroplast helix deforms to allow a greater part of the green ribbon to come into the illuminated half without changing its helical pitch.