The role of tRNA in development

Experiments that suggest a developmental regulatory role for tRNA in translation (such cytokinins in tRNA, suppressor mutations, tRNA methyases, excessive number of isoaccepting species, and others) are briefly presented. Reports that link changes in the tRNA population of cells with developmental changes are collated. Our attempts to find changes in tRNA acceptor concentrations and in isoacceptor levels in the cotyledons of cotton seeds during their embryogenesis and germination are presented in detail. In this study we have found no pattern of change in the relative concentration of acceptors for each of the amino acids among the cytoplasmic tRNAs of the cotyledons during development. In fact the relative acceptor concentrations of the cotyledons are indistinguishable from those of cotton roots. We have observed a 7-fold increase per cell in the levels of chloroplastic tRNA that takes place during the first 5 days of germination. This increase does not require a light stimulation, and, further, chloroplastic tRNA is present in roots. The assumptions and genetic implications of a system of developmental regulation based in part on tRNA levels and code word frequency in mRNA are discussed.LEON S. DURE III AND WILLIAM C. MERRICK, Department of Biochemistry, University of Georgia, Athens, Georgia