Excess Light Stress: Probing Excitation Dissipation Mechanisms through Global Analysis of Time- and Wavelength-Resolved Chlorophyll a Fluorescence

This chapter outlines current views of the ecophysiology, biophysical theory and time-resolved chlorophyll fluorescence methods pertaining to the study of the acclimation of photosynthetic organisms to excess light stress. The chapter’s theme and content are structured around the integrated framework of a ‘four point’ plan describing acclimation of plants to environmental limitations to photosynthetic productivity. This plan includes: 1) ‘down-regulation’ of delivery of excess light to reaction centers from the antenna, 2) ‘down-sizing’ of the antenna to reaction center ratio to reduce excess light absorption, 3) ‘increased productivity’ as feed forward stimulation of the photosynthetic capacity to utilize absorbed light and finally, 4) reorganization and or permanent or seasonal liquidation of reaction center and antenna protein-pigment components. The chapter outlines the current views of each phase of the plan with respect to biophysical theory and experimental results. Both time-domain and frequency-domain global statistical analysis methods for fluorescence lifetime distributions are presented. Recent advances are described including three exemplary applications, namely, (1) light-harvesting and energy transfer between light-harvesting complex (LHC) lib and the Photosystem (PS) II core, (2) energy-dissipation in PS II as mediated by the PsbS protein, intrathylakoid acidification and the xanthophyll cycle and (3) changes in the chlorophyll a fluorescence lifetime distributions, xanthophyll cycle and PS II quantum efficiency associated with deacclimation from winter photosynthetic depression in an evergreen Eucalyptus species. Finally, plans for future achievements and increased understanding of excess light acclimation and its measurement and analysis with chlorophyll a fluorescence are described.