The effects of cation-induced and pH-induced membrane stacking on chlorophyll fluorescence decay kinetics

We have compared the effects of thylakoid membrane appression by electrostatic screening and by charge neutralization on the room-temperature chlorophyll fluorescence decay kinetics of broken spinach chloroplasts. Monovalent and divalent metal cations induce both a structural differentiation of thylakoid membranes and a lateral segregation of pigment-protein complexes. These phenomena have distinct effects on the F0- and Fmax-level chlorophyll fluorescence decay kinetics at different levels of added cation. We further find specific cation effects, particularly on a 1-2 ns decay component at the Fmax fluorescence level, that are proposed to be related to the effectiveness of electrostatic screening as determined by the hydrated metal ionic radius. Distinct pH-induced effects on chlorophyll fluorescence decay kinetics are associated with the alternative mechanism of electrostatic neutralization to induce membrane stacking. These observations are used to construct a model of chlorophyll fluorescence emission that accounts for the variable kinetics and multiexponential character of the fluorescence decay upon membrane appression.