Regulation of ribosomal RNA accumulation by auxin in artichoke tissue.

Artichoke (Helianthus tuberosus L.) tuber tissue cultured in the presence of the auxin 2,4-dichlorophenoxyacetic acid accumulates ribosomal RNA at a rate of 0.135 micrograms per hour per explant whereas there is little accumulation in nontreated tissue. The addition of auxin enhanced the transcription of the 2.5 x 10(6) precursor 3.5-fold and increased the rate of processing 1.8-fold. The major effect of auxin, however, was a vast increase in the rate of processing of the 1.39 x 10(6) precursor to the 1.3 x 10(6) mature ribosomal RNA. The incorporation of label into the 0.7 x 10(6) mature ribosomal RNA of treated tissue was in 10-fold excess over the control after a 30-minute pulse and remained so throughout the remainder of the labeling period. This level, however, was not reached for the complementary 1.3 mature RNA until 3 hours of continuous labeling, decreasing from a initial value of 40-fold excess. A complication in the processing of ribosomal RNA is the apparent increase in the stability of the 0.7 x 10(6) mature RNA with auxin treatment.