THE EXPRESSION OF SUBUNITS OF THE MITOCHONDRIAL COMPLEX I-HOMOLOGOUS NAD(P)H-PLASTOQUINONE-OXIDOREDUCTASE DURING PLASTID DEVELOPMENT

NAD(P)H-Plastoquinone-Oxidoreductase during Plastid Development Martina Fischer, Edgar Funk and Klaus Steinmüller Institut für Entwicklungsund Molekularbiologie der Pflanzen. Heinrich-Heine-Universität Düsseldorf, Universitätsstrasse 1, D-40225 Düsseldorf, Germany Z. Naturforsch. 52c, 481-486 (1997); received May 12/May 28, 1997 Chloroplast Development, Etioplast, NAD(P)H-Plastoquinone-Oxidoreductase Plastids contain a NAD(P)H-plastoquinone-oxidoreductase which is homologous to the eubacterial and mitochondrial NADH-ubiquinone-oxidoreductase (complex I), but the meta­ bolic function of the enzyme is still not yet understood. The enzyme consists of at least eleven subunits (NDH -A-K), which are all encoded in the plastid chromosome. In this study we have investigated the tissue-specific and light-dependent expression of the subunits N DH -H and NDH-K in maize, rice and mustard by western blot analysis. No NDH-proteins were found in root tissue, indicating that the presence of the enzyme is confined to leaf plastids. Analysis of the expression during the light-dependent development from etioplasts to chloro­ plasts showed that high amounts of NDH-H and -K are present in etioplasts. The same result was found for subunits of the ATPase. In contrast, components of the photosynthetic electron transport chain (PSII-B, cytochrome f and PSI-D) accumulated only after illumination. In an second investigation, the expression of NDH-proteins along the natural chloroplast develop­ mental gradient from proplastids to chloroplasts in light-grown maize leaves was analysed. N D H -H and NDH-K as well as the ATPase were present at the youngest stages of chloro­ plast development, while the massive accumulation of subunits of the photosystems and the cytochrome Z>6//-complex took place in older leaf sections. We conclude from these studies that a functional NAD(P)H-plastoquinone-oxidoreductase is present in etioplasts and devel­ oping plastids. We suggest that the enzyme serves the generation of a proton gradient across the prothylakoid membrane that is necessary for protein integration into the membrane at developmental stages where a functional photosynthetic electron transport chain is not yet operating.