Chloroplast movement

Abstract

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.

Estimation of chlorophyll in Quercus leaves using a portable chlorophyll meter: effects of species and leaf age

“…67 (2010) 108 F. Silla et al Thompson et al, 1996). Second, chloroplasts can modify their orientation in response to incident irradiance (Haupt and Scheuerlein, 1990), and seasonal changes in irradiance could affect chlorophyll meter readings, as reported for the natural night-day-night cycle (Hoel and Solhaug, 1998). Accordingly, leaf structural changes that affect absorption, transmission and scattering of light across the leaf could provide different CCI readings even though the chlorophyll content per unit area has not changed.…”

Detection of a Calcium-Activated Protein Kinase in Mougeotia by Using Synthetic Peptide Substrates

“…and Mesotaenium caldariorum, and a higher plant, Pisum sativum, were tested. Mesotaenium is an unicellular alga that also exhibits a lightdependent chloroplast rotation response (9,12). Spirogyra was selected since it is another member of the order Zygnematales and is closely related to Mougeotia but does not exhibit the chloroplast rotation response.…”

“…Based on the observations discussed above, it has been suggested that light activation of phytochrome leads to a localized increase in intracellular calcium that activates the actomyosin cytoskeleton that drives chloroplast movement (9). Although this proposal is attractive, detailed biochemical analyses of the targets of calcium regulation and their modulation of the actomyosin cytoskeleton are lacking.…”

“…Among the well-studied biological model systems of calcium regulation of organellar motility is light-dependent chloroplast movement in Mougeotia. Mougeotia has a single, ribbon-shaped chloroplast that is rotated about the cell axis in response to changes in light direction and intensity (9). Upon administering a low-intensity, directional light stimulus, the chloroplast is reoriented so that it faces the stimulus.…”

“…Upon administering a low-intensity, directional light stimulus, the chloroplast is reoriented so that it faces the stimulus. Based on the action spectrum of the response, it has been proposed that phytochrome is the primary photoreceptor under conditions of low light fluence (9).…”