Editing Photorespiration (section)

====C<sub>2</sub>====
[[File:C2 Photosynthesis.svg|thumb|right|In C<sub>2</sub> plants, the mitochondria of mesophyll cells have no glycine decarboxylase (GDC).]]
'''C<sub>2</sub> photosynthesis''' (also called '''glycine shuttle''' and '''photorespiratory CO<sub>2</sub> pump''') is a CCM that works by making use of &ndash; as opposed to avoiding &ndash; photorespiration. It performs ''carbon refixation'' by delaying the breakdown of photorespired glycine, so that the molecule is shuttled from the [[mesophyll]] into the [[bundle sheath]]. Once there, the glycine is decarboxylated in [[mitochondria]] as usual, releasing CO<sub>2</sub> and concentrating it to triple the usual concentration.<ref name=Cee2>{{cite journal |last1=Lundgren |first1=Marjorie R. |title=C 2 photosynthesis: a promising route towards crop improvement? |journal=New Phytologist |date=December 2020 |volume=228 |issue=6 |pages=1734–1740 |doi=10.1111/nph.16494 |pmid=32080851 |doi-access=free}}</ref>

Although C<sub>2</sub> photosynthesis is traditionally understood as an intermediate step between C<sub>3</sub> and C<sub>4</sub>, a wide variety of plant lineages do end up in the C<sub>2</sub> stage without further evolving, showing that it is an evolutionary steady state of its own. C<sub>2</sub> may be easier to engineer into crops, as the phenotype requires fewer anatomical changes to produce.<ref name=Cee2/>