Plastoquinonerelated

Plastoquinone-related refers to compounds, processes, and proteins associated with plastoquinone, a lipid-soluble benzoquinone that functions as a key electron carrier in the photosynthetic thylakoid membrane. The term also includes the reduced form, plastoquinol, and the redox cycling between PQ and PQH2 that drives energy conversion in photosynthesis.

In plants, algae, and cyanobacteria, plastoquinone is predominantly plastoquinone-9, a molecule with a polyisoprenoid tail that anchors it in the thylakoid membrane. The head group participates in redox chemistry, cycling between oxidized and reduced states as electrons are transferred along the photosynthetic electron transport chain.

Functionally, plastoquinone plays a central role in photosynthesis. Electrons liberated at photosystem II are transferred to the plastoquinone pool, reducing PQ to plastoquinol. Plastoquinol then donates electrons to the cytochrome b6f complex, contributing to the proton gradient used to synthesize ATP. The PQ/PQH2 pool thus couples light-driven electron transfer to proton translocation. Beyond electron transport, plastoquinone is implicated in protecting membrane lipids from oxidative damage and may participate in chloroplast signaling pathways that regulate photosynthetic efficiency and stress responses.

Biosynthesis and variation occur in plastids, where the head group and tail are assembled and appended to form functional plastoquinone. Tail length and composition vary among organisms, giving rise to species such as PQ-9 in higher plants and various forms in algae and cyanobacteria.

Inhibitors targeting plastoquinone cycling are studied in plant physiology and pharmacology. Herbicides and research compounds can disrupt electron flow at the plastoquinone reduction or transfer steps, impairing photosynthetic energy production.