Effect of light on the nucleotide composition of rRNA of wheat seedlings.

Both qualitative and quantitative differences in the minor nucleotide constituents of rRNA from normally grown and from etiolated wheat plants (Triticum aestivum L.) were established. Using different degradation methods and separation techniques the 18S+26S RNA of 8-day-old wheat seedlings grown in the light was found to contain 5-methylcytidine, 3-methylcytidine, 5-methyluridine, 3-methyluridine, 5-carboxymethyluridine, 1-methyladenine, N-methyladenine, 5-hydroxymethylcytidine, O(2')-methyluridine, O(2')-methylcytidine, pseudouridine, O(2')-methylpseudouridine, N(2),N(2)-dimethylguanine, 1-methylguanine, ribothymidine and some unknown minor constituents. On the other hand, there were only a few minor nucleotides in the rRNA of etiolated wheat seedlings. Cycloheximide, a cytoplasmic protein synthesis inhibitor, simulated etiolation in that it reduced the number of minor nucleotides in rRNA, whereas chloramphenicol, a chloroplast protein synthesis inhibitor, had no significant effect on the minor nucleotide content of rRNA. This finding suggests that illumination may cause de novo synthesis of cytoplasmic modifying enzymes leading to the formation of highly modified rRNAs.