RESPIRATORY METABOLISM AND GENE-EXPRESSION DURING SEED-GERMINATION

Oxygen uptake and carbon dioxide release rapidly increase in seeds during imbibition. The oxygen uptake is associated with oxidative phosphorylation through cytochrome oxidase. During the early stage of germination substrate level phosphorylation may also contribute to ATP production. All indications suggest that this route of ATP production is insignificant during aerobic germination. However, during oxygen stress, substrate level phosphorylation does significantly contribute to ATP production in some species. Carbohydrate oxidation plays a significant role in the germination process. Up to two thirds of the carbon from carbohydrate breakdown enters the tricarboxylic acid cycle through the phosphoenolpyruvate carboxylase reaction. This anapleurotic input into the Krebs cycle most probably reflects the high demand on intermediates from the cycle for biosynthesis. The extent to which other substrates are utilized for respiration is uncertain. Information regarding the levels of key metabolites and enzymes, as well as their cellular distribution is limited. The involvement of gene expression in the regulation of respiratory metabolism is poorly characterised. Several genes which have been cloned are only expressed during germination. With the exception of the early methionine labeled polypeptide, little is known about the function of these genes.