BLUE-LIGHT INDUCED CHLOROPLAST MOVEMENTS

Chloroplast movements are one of the mechanisms enabling plant acclimation to changing light intensity. They are widespread in the plant kingdom, in different taxonomic groups. In weak light chloroplasts perform the accumulation response, positioning themselves under the cell walls perpendicular to the direction of incident light. This allows to optimize photosynthesis by increasing the area of light absorption by chloroplasts. In strong light chloroplasts move towards the cell walls parallel to the light direction. This avoidance response protects chloroplasts against damage by excess light. In terrestrial angiosperms chloroplast relocation are controlled by blue light photoreceptors phototropins. The movement mechanism is based on the actin cytoskeleton. However, the signal transduction pathway from phototropins to the effector proteins is still not fully understood. Specific roles of several proteins and secondary messengers in chloroplast accumulation and avoidance point to the existence of separate signaling pathways for both responses. The study of cross-talk with other signal transduction pathways contributes to better understanding of phototropin signaling in chloroplast movements. This is especially important in the context of the physiological role of chloroplast relocations as a response to changing environmental conditions.