The developmental biochemistry of cotton seed embryogenesis and germination. IV. Levels of cytoplasmic and chloroplastic transfer ribonucleic acid species.

We have measured the amount of tRNA in cotton cotyledons that can be charged with each of the 20 amino acids at four developmental stages in cotyledon embryogenesis and germination. We have examined the number and relative levels of isoaccepting tRNA species for 15 amino acids at the same developmental stages by RPC-2 (Freon) chromatography and by the chromatography of RNAse T1 digests of aminoacyl-tRNA. We have made the same measurements with tRNA from cotton root tissue and from partially purified cotton chloroplasts. The results suggest that there are no differences in the levels of cytoplasmic tRNA species between cotyledons of various developmental stages nor between cotyledons and roots. There is, however, a large increase in the amount of chloroplastic tRNA per cell that occurs during early germination, and this increase is not induced by a light stimulus. Chloroplast tRNA exists in young embryogenic cotyledons and roots, and the amounts of the individual chloroplastic isoaccepting tRNA species do not change relative to each other as they increase in the cotyledon cells during germination. It is concluded from these data that developmental changes in cotton seedlings are not accompanied by changes in the capacity for translating individual code words.