Mitochondrial Activity and ATP Synthesis

The ATP content of isolated wheat embryos has been found to increase substantially during the first hour of imbibition, followed by only a small increase 

Experi- ment Time after imbibition starts (h) Adenine nucleotide content (nmol/125 mg embryos) Energy charge 

Seeds were placed in water at 20° C for 4h before ATP content was measured. Ching, 1973 [33] 

Metabolism of the germinating seeds themselves may not depend upon or be controlled by ATP content alone. Levels of ADP and AMP may also play a role. Protein synthesis is an early event during seed imbibition, and while it is a process which requires ATP, it can also be inhibited by high levels of ADP and AMP. Both of these latter adenine nucleotides decrease in wheat embryos after the first hour of imbibition (Table 5.2), at a time when protein synthesis is increasing markedly [76]. Similarly in both pea and lettuce seeds there is a depletion of AMP coincidental with ATP synthesis, with ADP levels remaining constant [22, 103]. 

The amount of metabolically-available energy which is momentarily stored in the adenylate system of a living cell is linearly related to the mole fraction of ATP plus half of the mole fraction of ADP. Expressed in terms of concentration of the nucleotides, this available energy is called the energy charge [26], which can be calculated from the following formula  

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