Abstract
To survive under highly variable environmental conditions, higher plants have acquired a large variety of acclimation responses. Different strategies are used to cope with changes in light intensity with the common goal of modulating the functional antenna size of Photosystem II (PSII). Here we use a combination of biochemical and biophysical methods to study these changes in response to acclimation to high light (HL). After 2 h of exposure, a decrease in the amount of the large PSII supercomplexes is observed indicating that plants are already acclimating to HL at this stage. It is also shown that in HL the relative amount of antenna proteins decreases but this decrease is far less than the observed decrease of the functional antenna size, suggesting that part of the antenna present in the membranes in HL does not transfer energy efficiently to the reaction center. Finally, we observed LHCII monomers in all conditions. As the solubilization conditions used do not lead to monomerization of purified LHCII trimers, we should conclude that a population of LHCII monomers exists in the membrane. The relative amount of LHCII monomers strongly increases in plants acclimated to HL, while no changes in the trimer to monomer ratio are observed upon short exposure to stress.
Highlights
IntroductionOn an evolutionary time scale, this is enough time to evolve highly sophisticated acclimation responses to allow survival as a sessile organism under variable environmental conditions
Land plants appeared on Earth around 568–815 million years ago (Clarke et al, 2011)
The parameter related with linear electron flow (LEF), Photosystem II (PSII), was higher when the plants were grown under higher light intensities
Summary
On an evolutionary time scale, this is enough time to evolve highly sophisticated acclimation responses to allow survival as a sessile organism under variable environmental conditions. The acclimation responses to different light conditions are essential adaptations. They provide balance between the harvesting of enough energy for metabolic and anabolic processes and the protection against excess excitation energy (EEE). EEE represents a risk associated with the lightharvesting systems as it increases the probability of reactive oxygen species (ROS) generation, which can be highly destructive for the photosynthetic apparatus and the cell (reviewed in Asada, 2006). As light interception occurs in the chloroplast, it is there that the first steps and coordination of the light intensity acclimation take place. Functionality and amount are dynamically adjusted in response to changes in light conditions (Ballottari et al, 2007; Betterle et al, 2009; Johnson et al, 2011; Belgio et al, 2014; Kono and Terashima, 2014; Dietz, 2015; Suorsa et al, 2015)
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