Cytokinins in tRNA Obtained from Spinacia oleracea L. Leaves and Isolated Chloroplasts

Cytokinin-active ribonucleosides have been isolated from tRNA of whole spinach (Spinacia oleracea L.) leaves and isolated spinach chloroplasts. The tRNA from spinach leaf blades contained: 6-(4-hydroxy-3-methyl-2-butenylamino)-9-beta-d-ribofuranosylpurine (cis and trans isomers), 6-(3-methyl-2-butenylamino)-9-beta-d-ribofuranosylpurine, and 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-beta-d -ribofuranosylpurine (cis and trans isomers). A method for isolation of large amounts of intact chloroplasts was developed and subsequently used for the isolation of chloroplast tRNA. The chloroplast tRNA contained 6-(3-methyl-2-butenylamino)-9-beta-d-ribofuranosylpurine and 6-(4-hydroxy-3-methyl-2-butenylamino)-2-methylthio-9-beta-d -ribofuranosylpurine (the cis isomer only). The structures of these compounds were assigned on the basis of their chromatographic properties and mass spectra of trimethylsilyl derivatives which were identical with those of the corresponding synthetic compounds. The results of this study indicate that ribosylzeatin was present in spinach leaf tRNA, but absent from the purified chloroplast tRNA preparation.