Global fluorescence lifetime distribution analyses of PSII energy dissipation mechanisms at low physiological temperatures

Abstract

This study documents the spectral and kinetic resolution of the main energy dissipation processes that influence the PSII photochemical yield in vivo at low physiological temperatures. The primary experimental approach involves global statistical analysis of both fluorescence lifetime distribution data and steady state fluorescence data from pulse-amplitude-modulation instruments and 77K excitation-emission spectral maps. The materials of interest include marine prasinophyte algae, eucalyptus seedlings and a selection of Arabidopsis mutants exhibiting varying xanthophyll and PsbS protein concentrations. Global statistical analysis of the time-resolved data was augmented with independent data including the steady-state intensity, pH-estimates, PsbS protein levels and xanthophyll concentrations. At low temperatures, Mantoniella squamata cells exhibited dark-sustained nigericin-sensitive and antheraxanthin-dependent energy dissipation components independent of PSII photoinhibitory damage. Arabidopsis leaves also exhibited low temperature induced and sustained energy dissipation components that correlated with the PsbS titre and xanthophyll levels. Further, the PsbS deficient mutants facilitated definitive resolution of fluorescence lifetime distribution changes associated with PSII photochemistry, xanthophyll dependent photoprotection and photoinhibition. Sun and frost exposed snow gum seedlings exhibited complex fluorescence spectral-kinetic characteristics including components that correlated with deepoxidized xanthophylls and other components obviously associated with protein synthesis and or structural reorganization of the PSII core inner antenna. It is concluded that fluorescence lifetime distribution analysis provides quantifiable information regarding separate populations of PSII as they are influenced by reaction center photochemistry and both photoprotective and photoinhibitory energy dissipation mechanisms.