Mitochondrial Biogenesis during Germination in Maize Embryos

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.

Single-seed oxygen consumption measurements and population-based threshold models link respiration and germination rates under diverse conditions

“…Such broad parallel behaviour across all of these conditions suggests the possibilities that all of these factors act on germination through their effects on respiration or that sensitive feedback relationships operate to adjust metabolic rates to developmental progress. Following imbibition and during germination, ATP production in the mitochondria is the primary source of metabolic energy in seeds (Hourmant and Pradet, 1981;Al-Ani et al, 1985) generated through oxidative phosphorylation (Frey and Mannella, 2000;Logan et al, 2001). Progress toward germination relies on respiration, as shown here by the effects of the respiratory inhibitors KCN and SHAM.…”

Changes in the Mitochondrial Proteome during the Anoxia to Air Transition in Rice Focus around Cytochrome-containing Respiratory Complexes

“…DISCUSSION The existence of mitochondrial structures that require specific biogenesis triggers to initiate a pathway to maturation and proliferation has been documented in a variety of eukaryotes (38 -40). Reduced mitochondrial structures have been observed in both dried seeds and in meristematic zones in a variety of plants (41)(42)(43). Anaerobiosis is another scenario where such protomitochondria have been proposed to exist in both plants and yeast (2,6,12,19,23).…”

Remodeled Respiration in ndufs4 with Low Phosphorylation Efficiency Suppresses Arabidopsis Germination and Growth and Alters Control of Metabolism at Night

“…In a dry seed, mitochondria are barely functional, but during the very early stages of germination, mitochondria are transformed into a mature active form (Howell et al, 2006). During the first few hours, they are mainly powered by external alternative dehydrogenases (Logan et al, 2001) to allow the import of energy-producing components such as the TCA cycle enzymes or the respiratory chain complexes (Howell et al, 2006). It could be predicted that a complex I mutant should not be affected at this stage of germination.…”