The concentrations of adenine nucleotides were determined in germinating lettuce (Lactuca sativa) seeds after transitions from air to hypoxic or anoxic atmospheres. The ratio ATP/ADP and the energy charge were rapidly lowered after the transitions and remained stable at low values for hours. The energy charge in anoxia stabilized at a value close to 0.3. After 24 h in anoxia the energy charge rose rapidly to high values (0.9) when N2 was replaced by air. The metabolic properties of lettuce seeds had then been conversed for hours at low energy charge. In hypoxia the O2 uptake was decreased and the energy charge was stabilized at values intermediate between that in air and that in anoxia. When the O2 partial pressures (pO2) were 5 and 2kPa, the values of O2 uptake were one-third and one-sixth of that in air, and the energy charges were 0.7 and 0.5. These results show that the energy charge is regulated over a wide range of values. The ratio ATP/ADP and the energy charge are indicators of the limitation of metabolic activity by hypoxia.

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