Leucyl Transfer RNA Synthetase Changes during Soybean Cotyledon Senescence

Previous work has shown the complement of leucyl transfer RNA (tRNA(Leu)) isoaccepting species present in soybean cotyledons to change during cotyledon senescence. Of the six tRNA(Leu) species resolved by Freon-column chromatography, the capacity of species 1-4 to accept leucine is decreased between 5 and 21 days of age. Parallel changes in tRNA(Leu) synthetase activity are reported here during the same time period. There is a reduction in the capacity of the synthetase from 21-day-old cotyledons to aminoacylate tRNA(Leu) 1-4, while the capacity to charge tRNA(Leu) 5-6 remains high. When tRNA(Leu) derived from 5-day-old cotyledons is maximally charged with the 21-day synthetase, the subsequent addition of synthetase from 5-day-old cotyledons promotes additional charging, primarily of species 1-4. These results suggest the presence of tRNA(Leu) "subspecies" within the individual peaks resolved on a Freon column, differing in synthetase specificity.