STUDIES ON ENERGY STATUS AND MITOCHONDRIAL RESPIRATION DURING GROWTH AND SENESCENCE OF MUNG BEAN COTYLEDONS

Several characteristics of mitochondrial respiration and energy status have been studied during growth and senescence of mung bean (Phaseolu s radiatus L.) cotyledons. The results showed that mitochondrial oxyge n consumption, respiratory control, ADP:O ratios, and energy charge ch anged in the cotyledons during germination and growth of the seedlings . The respiration rate of intact cotyledons approximately reflected th e trend of the oxidative activities of the isolated mitochondria. An i ncrease was observed in both whole cotyledon respiration and mitochond rial oxygen uptake at the onset of senescence of mung bean cotyledons (day 3 after germination), which thereafter declined gradually. The ca pacity and activity of the alternative pathway increased markedly in m itochondria isolated from senescent cotyledons. After the onset of sen escence, the mung bean cotyledon mitochondria exhibited a decrease bot h in the respiratory control ratios and ADP:O ratios, and the cotyledo ns exhibited a gradual decline in energy charge. All these results sho wed an irreversible deterioration of energy conservation in mung bean cotyledons. The role(s) of the alternative pathway in senescent mung b ean cotyledons is discussed.