Photorespiration has a dual origin and manifold links to central metabolism.

Photorespiration is a Janus-headed metabolic process: it makes oxygenic photosynthesis possible by scavenging its major toxic by-product, 2-phosphoglycolate, but also leads to high losses of freshly assimilated CO(2) from most land plants. Photorespiration has been often classified as a wasteful process but is now increasingly appreciated as a key ancillary component of photosynthesis and therefore the global carbon cycle. As such, the photorespiratory cycle is one of the major highways for the flow of carbon in the terrestrial biosphere. Recent research revealed that this important pathway originated as a partner of oxygenic photosynthesis billions of years ago and is multiply linked to other pathways of central metabolism of contemporary land plants.