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Introduction 1st paragraph:"All photosynthetic eukaryotes use ribulose-bisphosphate carboxylase/oxygenase (Rubisco) for the net fixation of atmospheric CO2. As a result, they can also oxygenate ribulose bisphosphate (RuBP), creating two-carbon molecules that must be metabolised back to RuBP in the process termed photorespiration. In terrestrial plants and their closest green algal relatives, photorespiration encompasses the classic, textbook metabolism involving the conversion of glycolate to glycine in the peroxisome, and the decarboxylation of glycine by the glycine decarboxylase/serine hydroxyl-methyltransferase complex in the mitochondria (Taiz & Zeiger 2006). Because photorespiration consumes RuBP, competes for Rubisco catalytic sites and releases previously fixed CO2 and NH3, it is inhibitory for carbon gain, with the degree of inhibition rising with reductions in atmospheric CO2 and increasing temperature (Sharkey 1988). Above 25 °C, photorespiratory inhibitions of carbon assimilation can reduce the rate of photosynthesis by over 20% (primary source)." |