Chloroplast movement

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Abstract
Chloroplasts redistribute and/or reorientate in the cell as a response to the light direction, resulting in patterns typical for light of low or high fluence rate, respectively. Usually, the main photoreceptor pigment is a blue‐UV‐absorbing pigment (‘cryptochrome’), but in a few exceptional cases, the reversible red/far‐red system phytochrome is involved. Detection of light direction is based on light refraction and/or on dichroic orientation of photoreceptor molecules. Membrane effects, intracellular calcium redistribution and calcium‐calmodulin interaction are discussed as likely steps in signal transduction. In the response mechanism the actin‐myosin system is involved. However, several details of perception, transduction and response are still unsolved and open for discussion. Particularly interesting are the cases of multiple photoreceptor systems, i.e. those where separate transduction chains are started which coact or interact with each other. This raises the question as to the evolution of multiple photoreceptor systems under the assumption that light‐oriented chloroplast movements serve to optimize photosynthesis.