The roles and regulation of phosphoenolpyruvate carboxykinase in C_4 and CAM plants

摘要

The photosynthetic CO_2-concentrating mechanisms found in plants with C_4 photosynthesis, Crassulacean Acid Metabolism and some aquatic organisms are characterised by a variety of decarboxylases, including the malic enzymes and PCK (Leegood et al., 1996; Reiskind and Bowes, 1991; Reinfelder et al., 2000). PCK catalyses the ATP-dependent decarboxylation of oxaloacetate (OAA) to phosphoenolpyruvate (PEP). C_4 plants are classified into three subtypes, depending upon the principal decarboxylase presentin the bundle sheath. In PCKtypes, such as Panicum maximum, PCK acts in tandem with NAD-malic enzyme to decarboxylate C_4 acids (Burnell and Hatch, 1988), while in some NADP-malic enzyme types, such as maize, PCK appears to act as an auxiliary decarboxylase involved in the decarboxylation of aspartate (Walker et al., 1997; Wingler et al., 1999).