Chloroplast Movements in Response to Environmental Signals

Plants use light not only as an energy source for photosynthesis but also as an environmental signal for developmental regulation. In most plants, the photosynthetic organelle, the chloroplast, does not rest in the same position of the cell but instead relocates in response to external stimuli in order to maximize photosynthetic activity. Genetic and reverse genetic studies using Arabidopsis thaliana have allowed rapid progress in our knowledge of this field. Extensive advances in the last five years have identified and characterized new components controlling chloroplast movement, including blue-light receptors, phototropins and an actin-binding protein associated with chloroplast movements called “CHUP1” (chloroplast unusual positioning 1). This chapter gives integrated current information about the mechanisms of chloroplastmovement. In the first part of this review, we summarize most recentwork on light-induced chloroplast movement and in the following section we describe the new type of chloroplast movement induced by mechanical stimulation. In the last section, we discuss the ecological significance of chloroplast movement.