Mitochondria purified from cotyledons of soybean seedlings five to ten days old have the capacity to rapidly oxidize glutamate (measured as glutamate dependent oxygen consumption). This capacity was greatest at ten days after planting but was very low prior to emergence of cotyledons from the vermiculite and during senescence. Solubilized glutamate dehydrogenase activity, on the other hand, was substantial at two days after planting, peaked at seven days, then declined and rose again during senescence. It is suggested that mitochondrial glutamate oxidation plays a role in reserve mobilization and amino acid metabolism during seedling growth. Leaf mitochondria and those from senescing cotyledons could not sustain rapid rates of glutamate oxidation despite ready oxidation of other substrates and high solubilized glutamate dehydrogenase activity, suggesting an alternative role for the enzyme in these tissues. Possible controlling factors are discussed.
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