The crucial roles of mitochondria in supporting C 4 photosynthesis

C photosynthesis involves a series of biochemical and anatomical traits that significantly improve plant productivity under conditions that reduce the efficiency of C photosynthesis. We explore how evolution of the three classical biochemical types of C photosynthesis (NADP-ME, NAD-ME and PCK types) has affected the functions and properties of mitochondria. Mitochondria in C NAD-ME and PCK types play a direct role in decarboxylation of metabolites for C photosynthesis. Mitochondria in C PCK type also provide ATP for C metabolism, although this role for ATP provision is not seen in NAD-ME type. Such involvement has increased mitochondrial abundance/size and associated enzymatic capacity, led to changes in mitochondrial location and ultrastructure, and altered the role of mitochondria in cellular carbon metabolism in the NAD-ME and PCK types. By contrast, these changes in mitochondrial properties are absent in the C NADP-ME type and C leaves, where mitochondria play no direct role in photosynthesis. From an eco-physiological perspective, rates of leaf respiration in darkness vary considerably among C species but does not differ systematically among the three C types. This review outlines further mitochondrial research in key areas central to the engineering of the C pathway into C plants and to the understanding of variation in rates of C dark respiration.