Hotorespiration, or “photo- respiration”, is a process in plant metabolism by which RuBP (a sugar) has oxygen added to it by the enzyme (rubisco), instead of carbon dioxide during normalphotosyn thesis. This process reduces efficiency of photosynthesis in C3 plants.
Photorespiration can occur when carbon dioxide levels are low, for example, when the stomata are closed to prevent water loss during drought. In most plants, photorespiration increases as temperature increases. Photorespiration produces no ATP and leads to a net loss of carbon and nitrogen (as ammonia), slowing plant growth.
Potential photosynthetic output may be reduced by photorespiration by up to 25% in C3 plants hotorespiration is said to be an evolutionary relic. Photorespiration lowers the efficiency of photosynthesis by removing carbon molecules from the Calvin Cycle.
The early atmosphere in which primitive plants originated contained very little oxygen, so it is hypothesized that the early evolution of RuBisCO was not influenced by its lack of discrimination between O2 and carbon dioxide. Photorespiration cycle Although the functions of photorespiration remain controversial it is widely accepted that this pathway influences a wide range of processes from bioenergetics, photosystem II function, and carbon metabolism to nitrogen assimilation and respiration. The photorespiratory pathway is a major source of H2O2 in photosynthetic cells.
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Through H2O2 production and pyridine nucleotide interactions, photorespiration makes a key contribution to cellular redox homeostasis. In so doing, it influences multiple signaling pathways, in particular, those that govern plant hormonal responses controlling growth, environmental and defense responses, and programmed cell death.