Chlororespiration is the phenomenon by which oxygen is consumed by a putative respiratory electron transfer chain (ETC) within the thylakoid membrane of the chloroplasts and ATP is produced. It is a process that involves the interaction with the photosynthetic ETC in which the NAD(P)H dehydrogenase enzyme transfers electrons to oxygen molecules with the assistance of the photosynthetic Plastoquinone (PQ), which acts as a non-photochemical redox carrier. Initially described in the unicellular alga Chlamydomonas reindhartdii, chlororespiration was highly disputed for years until the discovery of a NAD(P)H-dehydrogenase (Ndh) complex (plastidic encoded) and plastid terminal oxidase (PTOX) (nuclear encoded) in higher-plant chloroplasts. The PTOX, which is homologous to the plant mitochondrial alternative oxidase, has the role of preventing the over-reduction of the PQ pool while the Ndh complexes provide a gateway for the electrons to form the ETC and consume oxygen. As a result of this process there is a cyclic electron flow around the Photosystem I (PSI) that has been reported to be activated under stress conditions acting as a photoprotection mechanism and could be involved in protecting against any other stress that implies the increase of ROS formation.
Communicated by Huete-Ortega M 2020-06-30
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