6533b827fe1ef96bd1287086

RESEARCH PRODUCT

Combined dynamics of the 500–600 nm leaf absorption and chlorophyll fluorescence changes in vivo: Evidence for the multifunctional energy quenching role of xanthophylls

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Carotenoids (Cars) regulate the energy flow towards the reaction centres in a versatile way whereby the switch between energy harvesting and dissipation is strongly modulated by the operation of the xanthophyll cycles. However, the cascade of molecular mechanisms during the change from light harvesting to energy dissipation remains spectrally poorly understood. By characterizing the in vivo absorbance changes (Delta A) of leaves from four species in the 500-600 nm range through a Gaussian decomposition, while measuring passively simultaneous Chla fluorescence (F) changes, we present a direct observation of the quick antenna adjustments during a 3-min dark-to-high-light induction. Underlying spectral behaviours of the 500-600 nm Delta A feature can be characterized by a minimum set of three Gaussians distinguishing very quick dynamics during the first minute. Our results show the parallel trend of two Gaussian components and the prompt Chla F quenching. Further, we observe similar quick kinetics between the relative behaviour of these components and the in vivo formations of antheraxanthin (Ant) and zeaxanthin (Zea), in parallel with the dynamic quenching of singlet excited chlorophyll alpha ((1)Chl alpha*) states. After these simultaneous quick kinetical behaviours of Delta A and F during the first minute, the 500-600 nm feature continues to increase, indicating a further enhanced absorption driven by the centrally located Gaussian until 3 min after sudden light exposure. Observing these precise underlying kinetic trends of the spectral behaviour in the 500-600 nm region shows the large potential of in vivo leaf spectroscopy to bring new insights on the quick redistribution and relaxation of excitation energy, indicating a key role for both Ant and Zea The presented study was supported by the first author's postdoctoral scholarship VEGALUZ (Grant no. APOSTD/2018/162) funded by the Generalitat Valenciana and co-funded by the European Social Fund. The work also frames within the Algorithm retrieval and product development study for the future Fluorescence Explorer/Sentinel-3 (FLEX-S3) tandem mission funded by the European Space Agency (ESA contract no. 4000122680/17/NL/MP) and the FLEX-L3L4 project (advanced products for the FLEX mission) funded by the Spanish Ministry of Science and Innovation (no. RTI2018-098651-B-C51). Further we acknowledge funding from the Basque Government (UPV/EHU IT-1018-16) and in addition we thank Luis Alonso and Zbyn.ek Malenovsky for support and advice in the lab. Open access funding was provided by the University of Helsinki