Rethinking the influence of chloroplast movements on non-photochemical quenching and photoprotection.

: Under blue light, plant chloroplasts relocate to different areas of the cell. The photoreceptor phototropin 2 (phot2) mediates the chloroplast movement mechanism under excess blue light alongside the chloroplast unusual positioning 1 (chup1) protein. Recently, it has been proposed that leaf transmittance changes associated with chloroplast relocation affect measurements of non-photochemical quenching (NPQ), resulting in kinetic differences due to these movements (termed 'qM'). We evaluated these claims using Arabidopsis (Arabidopsis thaliana) knock-out mutants lacking either phot2 or chup1 and analysed the kinetics of both the onset and recovery of NPQ 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 (qPd), which measures the redox state of QA within photosystem II without any of the complications of traditional Fv/Fm measurements. Whilst 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 NPQ onset or recovery. Therefore, we were unable to replicate the 'qM' component and its corresponding influence on the kinetics of NPQ 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 NPQ. Therefore, the influence of chloroplast movements on photoprotection should be thoroughly reevaluated.