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

In the present paper marked changes in photosynthetic trapping time over the absorption/fluorescence band of isolated PSI-LHCI are studied by means of time resolved fluorescence decay measurments: For emission at 680-690 nm the effective trapping time was about 17-18 ps and represnets the effective trapping time from 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 the reaction centre. These data, together with the steady state emission spectrum permit calculation of the overall trapping time for PSI-LHCI, estimated to be approximatelu 40 ps. The data indicate that photosystem I is about 55% diffusion limited.