Mitochondrial biogenesis during germination in maize embryos.
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 E1alpha-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.
Logan
D C
DC
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, United Kingdom. dcl1@st-andrews.ac.uk
Millar
A H
AH
Sweetlove
L J
LJ
Hill
S A
SA
Leaver
C J
CJ
D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant; D018525:Germination / Q000502:physiology*; D008928:Mitochondria / Q000201:enzymology / Q000235:genetics / Q000648:ultrastructure*; D010088:Oxidoreductases / Q000378:metabolism; D010101:Oxygen Consumption; D010940:Plant Proteins / Q000235:genetics; D014867:Water / Q000378:metabolism; D003313:Zea mays / Q000196:embryology* / Q000201:enzymology / Q000235:genetics / Q000648:ultrastructure
D010940:Plant Proteins; D014867:Water; D010088:Oxidoreductases