RESUMEN
The effect of light on nucleotide modifications in the tRNA of cucumber (Cucumis sativus L. var. Guntur) cotyledons was studied by chromatographic, electrophoretic and immunological methods. The tRNA from light-grown tissue showed the absence of 2-methylguanosine and a decrease in the relative proportions of ribothymidine and cytokinin-active ribonucleosides when compared to those produced from dark-grown tissue. On the other hand, a significant amount of one species of 2'-O-methyldinucleotide was observed in the tRNA of light-grown tissue which was not detected in the dark-grown tissue. Also, tRNA from light-grown tissue had higher levels of another species of 2'-Omethyldinucleotide. The results showed no difference in the amounts of other modified nucleosides in tRNA between tissues grown under the two conditions. 2'-O-Methyl-lmethyladenosine, a nucleotide modified both in the base and the ribose, apparently specific to plant tRNAs, has been found to be present in the RNA of both light- and dark-grown tissues. These results on the variation in modified nucleotides suggest that light has some role in nucleotide modification and, consequently, in cellular functions.