Pyrenoid
The pyrenoid is a spatially limited structure in plastids of various groups of algae and hornworts , which is often easily recognizable with a light microscope, and consists mainly of paracrystalline RuBisCO , the key enzyme in photosynthesis . Since RuBisCO instead of carbon dioxide also highly undesirably oxygen in the ribulose-1,5-bisphosphate installs ( photorespiration ), the organisms have developed various mechanisms to Kohlenstoffdioxidanreicherung to increase the efficiency of photosynthesis. Algae accumulate carbon dioxide locally in the pyrenoid, while vascular plants have developed the C 4 or CAM mechanism. The pyrenoid is thus a functional analogue of the carboxysomes in cyanobacteria .
The pyrenoid also serves to deposit reserve materials . For example, in green algae, the starch grains form around the pyrenoid.