Far-Red Absorbing LHCII Incorporating Chlorophyll <i>d</i> Preserves Photoprotective Carotenoid Triplet–Triplet Energy Transfer Pathways

Chlorophyll <i>d</i> (Chl <i>d</i>) can be successfully introduced in reconstituted LHCII with minimal interference with the energy equilibration processes within the complex, thereby facilitating the development of plant light-harvesting complexes (LHCs) with enhanced capabilities for light absorption in the far-red spectrum. In this study, we address whether Chl <i>d</i> introduction affects LHCII's ability to protect itself from photo-oxidation, a crucial point for successfully exploiting modified complexes to extend light harvesting in plants. Here we focus on incorporating Chl <i>d</i> into Lhcb1 (the monomeric unit of LHCII), specifically studying the Chl triplet quenching by carotenoids using time-resolved electron paramagnetic resonance (TR-EPR) and optically detected magnetic resonance (ODMR). We also characterize the A2 mutant of LHCII, in which the Chl 612 is removed, to assist in determining the triplet quenching sites on the Lhcb1 complex reconstituted with Chl <i>d</i>. We found that far-red absorbing LHCII incorporating Chl <i>d</i> maintains the efficiency of the photoprotective process.