Fotorespiraatio

Fotorespiraatio is a metabolic process that occurs in plants, algae, and cyanobacteria, primarily under conditions of high light intensity and low carbon dioxide concentration. It is essentially a light-dependent oxygen consumption and carbon dioxide release that occurs alongside photosynthesis. The process involves the enzyme RuBisCO, the same enzyme responsible for carbon fixation in the Calvin cycle. However, in photorespiration, RuBisCO acts on oxygen instead of carbon dioxide, leading to the production of a toxic byproduct called phosphoglycolate. This byproduct must then be processed and detoxified through a complex series of reactions involving chloroplasts, peroxisomes, and mitochondria, consuming ATP and reducing equivalents in the process. While seemingly wasteful as it reduces the efficiency of carbon fixation and can lead to a loss of fixed carbon, photorespiration is thought to play a protective role. It may help dissipate excess light energy under stressful conditions, preventing photodamage to the photosynthetic apparatus, and can also contribute to nitrogen assimilation. Despite its negative impact on photosynthetic yield, photorespiration is an unavoidable consequence of RuBisCO's dual activity and is thus an integral part of plant metabolism.