Fluorescence properties of chlorophyll d-dominating prokaryotic alga, acaryochloris marina: studies using time-resolved fluorescence spectroscopy on intact cells

Antenna components and the primary electron donor of the photosystem (PS) II in the Chlorophyll (Chl) d-dominating prokaryote, Acaryochloris marina, were studied using time-resolved fluorescence spectroscopy in the ps time range. By selective excitation of Chl a or Chl d, differences in fluorescence properties were clearly resolved. At physiological temperature, energy transfer was confirmed by a red shift of emission maximum among PS II antenna components, and the equilibrium of energy distribution among Chl a and Chl d was established within 30 ps. A fluorescence component that can be assigned to delayed fluorescence (DF) was observed at 10 ns after the excitation; however, it was not necessarily resolved by the decay kinetics. At -196 degrees C, a red shift of emission maximum was reproduced but the equilibrium of energy distribution was not detected. DF was resolved in the wavelength region corresponding to Chl a by spectra and by decay kinetics. The lifetime of the DF was estimated to be approx. 15 ns, and the peaks were located at 681 and 695 nm, significantly shorter wavelengths than those of Chl d. These findings strongly suggest that an origin of DF is Chl a, and Chl a is most probably the primary electron donor in the PS II reaction center (RC). These results indicate that the constitution of PS II RC in this alga is essentially identical to that of other oxygenic photosynthetic organisms.