Mitochondria from leaf mesophyll cells of C4 plants are deficient in the H protein of glycine decarboxylase complex

SummaryMesophyll mitochondria from green leaves of the C4 plants Zea mays (NADP-ME-type), Panicum miliaceum (NAD-ME-type) and Panicum maximum (PEP-CK-type) oxidized NADH, malate and succinate at relatively high rates with respiratory control, but glycine was not oxidized. Among the mitochondrial proteins involved in glycine oxidation, the L, P and T proteins of glycine decarboxylase complex (GDC) and serine hydroxymethyltransferase (SHMT) were present, while the H protein of GDC was undetectable. In contrast, mesophyll mitochondria from etiolated leaves of Z. mays oxidized glycine at a slow rate and with no respiratory control, and contained the H protein as well as the other GDC proteins and SHMT. The T and P proteins and SHMT were present in the mitochondria from etiolated leaves at significantly higher levels than in those from green leaves of Z. mays. The content of the L protein was almost identical in all three C4 plants examined and close to the value obtained for mesophyll mitochondria from the C3 plant Pisum sativum, whereas the other GDC proteins and SHMT were less abundant than the L protein. We discuss possible reasons for the H protein's absence in mesophyll mitochondria of C4 plants, as well as the role(s) the other GDC components could play in its absence.