Mitochondria from leaf mesophyll cells of C-4 plants are deficient in the H protein of glycine decarboxylase complex

Mesophyll mitochondria from green leaves of the C-4 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, white 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 mitachondria 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 C-4 plants examined and close to the value obtained for mesophyll mitochondria from the C-3 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 C-4 plants, as well as the role(s) the other GDC components could play in its absence. (C) 2007 Elsevier GrnbH. All rights reserved.