Photochemical trapping heterogeneity as a function of wavelength, in plant photosystem I (PSI-LHCI)

In the present paper the marked changes in photochemical trapping time over the absorption/fluorescence band of isolated PSI-LHCI are studied by means of time resolved fluorescence decay measurements. For emission at 680-690 nm the effective trapping time is close to 17-18 ps, and represents the effective trapping time from the bulk antenna. At wavelengths above 700 nm the effective trapping time increases in a monotonic way, over the entire emission band, to attain values in the range of 70-80 ps near 760 nm. This is argued to be caused by “uphill” energy transfer from the low energy states to the core antenna and reaction centre. These data, together with the steady state emission spectrum, permit calculation of the overall trapping time for maize PSI-LHCI, which is estimated to be approximately 40 ps. The wavelength dependence of the trapping time indicates, that in PSI-LHCI there exists at least one red form which emits at lower energies than the 735 nm state. These data indicate that Photosystem I is about 55% diffusion limited.