Characteristic fluorescence components in photosynthetic pigment system of a marine dinoflagellate, Protogonyaulax tamarensis, and excitation energy flow among them. Studies by means of steady-state and time-resolved fluorescence spectroscopy

Abstract

Excitation energy flow in intact cells of the marine dinoflagellate Protogonyaulax tamarensis was studied by steady-state and time-resolved fluorescence spectroscopy in the picosecond time range. At 15°C, one dominant emission band was found at 684 nm (F684) with a minor band at 673 nm (F673), irrespective of the excitation conditions of Chl a, Chl c and peridinin. The 684 nm emission was DCMU-sensitive. At −196°C, four major emission bands originating from Chl a were resolved at F670, F683, F689 and F698, as well as a minor component at F724. The F670 and F683 correspond, respectively, to the F673 and F684 at 15°C. F689 was the strongest and assigned to a comparable component at F695, a characteristic band of CP-47. F698 and F724 were assigned to Photosystem (PS) I Chl a. When peridinin was excited, the F670 increased selectively, indicating that it is the energy acceptor of peridinin. Time-resolved fluorescence spectra at −196°C revealed all the components above as well as a new component at F709. Upon the excitation of peridinin, the rise and decay kinetics of the component bands clearly showed the energy flow in the order of F670, F683 and F689, and also indicate that the energy is distributed to PS I antenna complexes via F683 (spill-over) but not through F689. Chl c does not mediate the energy flow from peridinin to Chl a. The transfer time from peridinin to the acceptor Chl a (F670) was estimated to be shorter than 20 ps at −196°C. Based on these results, a model for the energy flow in P. tamarensis was proposed.