Pyruvate carboxylase temperature

Recall that the oxygenase activity of ruhisco increases more rapidly with temperature than does its carboxylase activity. How then do plants, such as sugar cane, that grow in hot climates prevent very high rates of wastefiil photorespiration Their solution to this problem is to achieve a high local concentration of CO2 at the site of the Calvin cycle in their photosynthetic cells. The essence of this process, which was elucidated by M. D. Hatch and C. R. Slack, is that four-carbon (Cf compounds such as oxaloacetate and malate carry CO2 from mesophyll cells, which are in contact with air, to bundle-sheath cells, which are the major sites ofphotosynthesis (Figure 20.17). Decarboxylation of the four-carbon compound in a bundle-sheath cell maintains a high concentration of CO2 at the site of the Calvin cycle. The three-carbon compound pyruvate returns to the mesophyll cell for another round of carboxylation. 

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