Dissection of photosynthetic short and long-term acclimation to fluctuating light reveals specific functions within the chloroplast thioredoxin network

Abstract

Thioredoxins (TRX) play an important role in controlling photosynthetic acclimation to fluctuating light (FL), while the underlying mechanisms remain unclear. Here we used Arabidopsis mutants lacking NADPH-dependent TRX-reductase C (NTRC) or parts of the light-dependent TRX systems to investigate specific functions of this network in FL. In the wildtype, photosynthetic acclimation required three days to develop and stabilized after five days of growth in FL. In the ntrc mutant, these acclimation responses were strongly attenuated, leading to decreased PSII acceptor availability, increased non-photochemical quenching (NPQ) and impaired PSII quantum efficiency. Moreover, PSI performance decreased, while acceptor-side limitation of PSI increased. This was due to a specifically strong decline in the reduction states of 2-Cys-peroxiredoxins and fructose-1,6-bisphosphatase, resulting in decreased CO₂-fixation rates and delayed relaxation of NPQ in the low-light phases of FL. Since this was not reflected by changes in de-epoxidation of violaxanthin, state transition or chlorophyll a level, ntrc mutants showed an apparent lack of photoprotective responses that may explain their increased vulnerability under prolonged growth in FL. Results show that NADPH-dependent NTRC is balancing chloroplast redox-systems and Calvin-Benson-cycle activity during prolonged light variability, to optimize PSI, PSII and water-use efficiency, while having no direct effect on photoprotective mechanisms.

Arabidopsis thaliana, plant physiology, photosynthesis, thioredoxin, acclimation, light response, fluctuating light, Calvin-Benson Cycle

Accepted manuscripts

Accepted manuscripts are PDF versions of the author’s final manuscript, as accepted for publication by the journal but prior to copyediting or typesetting. They can be cited using the author(s), article title, journal title, year of online publication, and DOI. They will be replaced by the final typeset articles, which may therefore contain changes. The DOI will remain the same throughout.