CHLOROPHYLL FLUORESCENCE ANALYSES OF PHOTOSYSTEM-II REACTION CENTER HETEROGENEITY

This paper summarizes recent fluorescence investigations which probe the heterogeneity displayed by photosystem II (PS II) reaction centers. Those studies which reveal PS II functional and structural heterogeneity using chlorophyll fluorescence transients and steady state intensities are highlighted. Chlorophyll fluorescence measurements are especially well suited for revealing the existence of heterogeneity within PS II reaction centers in terms of both their antenna composition and their efficiency of electron flow to the plastoquinone pool. The spectroscopic characteristics of chlorophyll fluorescence - in particular, the intensity and induction kinetics of the steady state room-temperature emission - reflect the fundamental properties of the chlorophyll molecules and their environment. Although numerous other effective tools for the elucidation of PS II heterogeneity are available, this discussion is limited to considerations of the de-excitation of electronically excited chlorophyll molecules via fluorescence emission as an indicator of PS II organization and function.