Abstract
Reactive oxygen species (ROS), such as singlet oxygen (1O2), superoxide anion-radical ( \({\text{O}}_{2}^{{\bullet - }}\) ) and hydrogen peroxide (H2O2), are currently considered as obligatory participants in the regulation of the structural and functional organization of the photosynthetic apparatus by involvement into cellular signal network including retrograde signaling. As shown, plastoquinone is also incorporated in retrograde signaling in plant cells under stress conditions. The cooperative action of the plastoquinone pool and ROS in signaling pathways has been proposed, but the mechanism of such action has long remained unknown. This review provides a brief overview of the mechanisms of ROS formation in the leaves of higher plants, with an emphasis on their formation in chloroplasts, including the plastoquinone pool-dependent pathways. Further, the review summarizes the results demonstrating the role of the plastoquinone pool and H2O2 in the acclimatory regulation of the expression of nuclear-encoded genes of the external pigment-protein antenna complex of photosystem II, leading to a change in the photosystem II antenna size that adjusts the photosynthetic function of plants. The molecular mechanism of this H2O2/plastoquinone pool-dependent retrograde signaling pathway is considered. Another aspect of the review is dedicated to oxidized derivatives of plastoquinone A (PQ A), hydroxyplastoquinones or PQ C, the molecules with one or more hydroxyl groups in the isoprenoid side chain resulting from the interaction of PQ A with 1O2. PQ C has been proposed to alter photosynthesis when accumulated in thylakoid membranes under stress conditions. We suggested that the accumulation of PQ C in thylakoids primarily affects the activity of photosystem II. The changed functioning of photosystem II can initiate 1O2/plastoquinone pool-dependent retrograde signaling, giving insight into a new possible 1O-based signaling pathway in plant cells.
