Rethinking the Influence of Chloroplast Movements on Non-photochemical Quenching and Photoprotection

• Published in: Plant physiology (Bethesda) Vol. 183; no. 3; pp. 1213 - 1223
• Main Authors: Wilson, Sam, Ruban, Alexander V
• Format: Journal Article
• Language: English
• Published: United States 01-07-2020
• Subjects: Chloroplasts - metabolism; Chloroplasts - radiation effects; Kinetics; Light; Movement; Photochemical Processes - radiation effects; Photosystem II Protein Complex - metabolism; Plant Leaves - metabolism; Plant Leaves - radiation effects; Up-Regulation - radiation effects
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.20.00549

Under blue light, plant chloroplasts relocate to different areas of the cell. The photoreceptor phototropin2 (phot2) mediates the chloroplast movement mechanism under excess blue light alongside the chloroplast unusual positioning1 (chup1) protein. Recently, it has been proposed that leaf transmittance changes associated with chloroplast relocation affect measurements of nonphotochemical quenching (
), resulting in kinetic differences due to these movements (termed "qM"). We evaluated these claims using Arabidopsis (
) knock-out mutants lacking either phot2 or chup1 and analyzed the kinetics of both the onset and recovery of
under equivalent intensities of both red and blue light. We also evaluated the photoprotective ability of chloroplast movements both during the early onset of photoinhibition and under sustained excess light. We monitored photoinhibition using the chlorophyll fluorescence parameter of photochemical quenching in the dark, which measures the redox state of Q
within PSII without any of the complications of traditional
/
measurements. While there were noticeable differences between the responses under red and blue light, the chloroplast movement mechanism had no effect on the rate or amplitude of
onset or recovery. Therefore, we were unable to replicate the "qM" component and its corresponding influence on the kinetics of
in Arabidopsis grown under "shade" conditions. Furthermore, chloroplast relocation had no effect on the high-light tolerance of these plants. These data cast doubt upon the existence of a chloroplast movement-dependent component of
Therefore, the influence of chloroplast movements on photoprotection should be thoroughly reevaluated.