Respiration and Mitochondrial Biogenesis in Germinating Embryos of Maize

Abstract

Function of the cyanide-sensitive mitochondrial electron transport system was required for germination of the Zea mays embryo. Respiration of the standard electron transport system (rather than the alternate oxidase) began immediately upon initiation of imbibition. This respiration depended upon cytochrome c oxidase and ATPase that were conserved in an active form in the quiescent embryo rather than upon newly synthesized or assembled enzyme complexes. Immunoprecipitation of radiolabeled subunits of these enzymes showed that the initiation of mitochondrial biogenetic activities, including de novo synthesis of nuclear- and mitochondrial-encoded enzyme subunit peptides, was strongly induced after 6 hours of embryo germination. Undetectable or very low levels of transcripts for subunits 1 and 2 of the F₁-ATPase and subunit 2 of cytochrome c oxidase were present in the quiescent embryo; these transcripts accumulated rapidly between 6 and 12 hours of germination and their translation products were rapidly synthesized between 6 and 24 hours. An exception was the gene for subunit 9 of the ATPase; transcripts of this mitochondrial gene were abundant in the dry embryo and rapidly accumulated further upon initiation of imbibition; they were translated actively during the first 6 hours. We isolated and sequenced a near full-length cDNA for subunit 2 (beta) of the F₁-ATPase, and we compared the deduced protein sequence with related sequences of other organisms.