Abstract
Abstract Metabolism of foliar-applied [14C]urea and accumulation of 14C by developing fruits was investigated in trimmed tomato (Lycopersicon esculentum) plants. Carrier-free, high-specific-activity [14C]urea, applied to the single source leaf, resulted in production of 14C-labeled neutral compounds (presumably sugars) that were exported from this leaf and recovered from the single developing fruit after 6 and 24 hr. [14C]urea also was recovered from the fruit, but it possessed only one-half as much 14C activity as neutral compounds. Using an in vivo assay, leaf pieces also exhibited linear rates of urea-dependent NH3 production (2.17 ± μpmol°g−1 fresh weight per hour) that was inhibited (96%) by acetohydroxamate, a compound specific for the enzyme urease. Thus, urea is metabolized to NH3 and CO2 in tomato leaves via the enzyme urease, and the released CO2 is assimilated in a fashion similar to that of external CO2. Foliar application of [14C]urea may be useful for studying source-sink relations in tomato plants.
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