Comparison of CAM with Other Carboxylation Pathways in Plants

5 Comparison of CAM with Other Carboxylation Pathways in Plants 

The nonautotrophic CO2 fixation pathway (Fig. 3.14, see also section Terminology) functions largely in the synthesis of malate for ionic balance and osmotic adjustment (see e.g., Bernstein, 1963 Raschke, 1975a Smith and Raven, 1976 Osmond, 1976 b). 

Further the malate may be decarboxylated to pyruvate with the subsequent generation of NADPH (Ting and Dugger, 1966 Peak et al., 1973). This pathway, therefore, results in an effective transhydrogenation of the H from NADH to NADPH at the expense of one ATP equivalent. In the direct pathway from P-enolpyruvate kinase. 

In comparison with CAM, the pathway to malate appears to be quite similar with perhaps the exception of the insoluble carbohydrate generator (Sutton, 1974a). 

In CAM, the switch from malate production to malate consumption is largely governed by the light-dark cycle, whereas in the nonautotrophic pathway the flow through to pyruvate would be governed by the extent to which malate is used for ionic and osmotic adjustment, and NADPH is required for biosynthetic or other reactions. 

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