Influence of the Photosystem I-light Harvesting Complex I Antenna Domains on Fluorescence Decay

The time-resolved fluorescence decay of plant PSI-LHCI has been analyzed and compared with its component parts, the PSI core and the peripheral antenna LHCI, in an attempt to (i) define the physical domains associated with the multicomponent decay-associated spectra (DAS) and determine the origin of the kinetically slow steps responsible for them, (ii) formulate a clear working hypothesis for the positive decay-associated spectral amplitudes of the two slowest decay components, and (iii) determine the impact of the peripheral antenna complexes (LHCI) on the effective trapping rate for the photosystem. The results for PSI-LHCI indicate that the three exponential component DAS description, previously reported in the literature, is not numerically unique. The fit minimum is rather broad, which necessitated the introduction of other fit criteria in addition to the purely numerical one. The analysis demonstrates that (i) the physical domains associated with the multicomponent decay are associated with the antenna and particularly with the low-energy spectral forms, (ii) the positive DAS amplitudes of the two slowest decay components are suggested to be due to energy transfer kinetic heterogeneity to different F735 low-energy forms, and (iii) the peripheral antenna slows down the effective photosystem photochemical rate by about 3 times, and this is approximately half due to antenna degeneracy and half due to the low-energy forms.