No abstract

Mitochondrial biogenesis and metabolism were investigated during maize (Zea mays) seed germination. Mitochondria from dry and imbibed seed exhibited NADH-dependent O 2 uptake that was completely inhibited by KCN and antimycin A. Mitochondria in the dry seed had a lower rate of succinate-dependent O 2 uptake relative to that measured in imbibed and germinated seed. The activities of the tricarboxylic acid (TCA) cycle enzymes, pyruvate dehydrogenase complex, 2-oxoglutarate dehydrogenase complex, NAD-malic enzyme, and citrate synthase, are similarly low in mitochondria from dry seed and this correlates with a lower relative abundance of the mitochondrial matrix-located citrate synthase and pyruvate dehydrogenase complex E1␣-subunit polypeptides. Electron microscopy revealed that mitochondria in the dry seed have a poorly developed internal membrane structure with few cristae; following 24 h of germination the mitochondria developed a more normal structure with more developed cristae. The mitochondria from maize embryos could be fractionated into two subpopulations by Suc density gradient centrifugation: one subpopulation of buoyant density equivalent to 22% to 28% (w/w) Suc; the other equivalent to 37% to 42% (w/w) Suc. These two subpopulations had different activities of specific mitochondrial enzymes and contained different amounts of specific mitochondrial proteins as revealed by western-blot analysis. Both subpopulations from the dry embryo were comprised of poorly developed mitochondria. However, during imbibition mitochondria in the heavy fraction (37%-42% [w/w] Suc) progressively acquired characteristics of fully functional mitochondria found in the germinated seedling in terms of structure, enzymic activity, and protein complement. In contrast, mitochondria in the light fraction (22% to 28% [w/w] Suc) show no significant structural change during imbibition and the amounts of specific mitochondrial proteins decreased significantly during germination.

No abstract

The 3'-termini of the mRNAs for subunit II of the cytochrome oxidase (COX II) and for the alpha-subunit of the mitochondrial ATPase (ATPA) have been determined in Oenothera mitochondria by two independent methods. Analysis of both transcripts by S1 protection experiments and of cloned cDNAs show an identical terminal 50 nucleotide sequence, to which homology is found 3' to some gene sequences in the maize mitochondrial genome. These regions can be folded into potential secondary structures similar to bacterial terminators.

No abstract