Spectroscopic characterization of isolated PSI-200 complexes from plants devoid of the PSI-G, PSI-K, PSI-L and PSI-N subunits

Abstract

We present a spectroscopic analysis of isolated PSI-200 particles from Arabidopsis thaliana and its mutants lacking the PSI-G, PSI-K, PSI-L and PSI-N subunits. Low-temperature absorption and linear dichroism spectra indicate that the PSI-200 particles from wild-type plants and plants lacking PSI-N are identical, suggesting the absence of pigments in PSI-N, whereas the particles lacking PSI-G showed decreased absorption of a carotenoid and those lacking PSI-K showed smaller contributions from the LHCI antenna, most likely Lhca2 and Lhca3. The largest changes were observed in particles without PSI-L, in which several chlorophyll absorption bands were affected. Time-resolved fluorescence measurements at room temperature, detected with a synchroscan streak camera, revealed excitation equilibration lifetimes of about 4 and 20 ps and excitation trapping lifetimes of about 45 and 115 ps in all particles. The largest differences among the mutants were observed in a long-living component caused by unconnected molecules, which was less pronounced in the PSI-L less particles.