Regulation of Ribosomal RNA Accumulation by Auxin in Artichoke Tissue

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Abstract
Artichoke (Helianthus tuberosus L.) tuber tissue cultured in the presence of the auxin 2,4-D accumulates rRNA at a rate of 0.135 M/h per explant whereas there is little accumulation in nontreated tissue. The addition of auxin enhanced the transcription of the 2.5 .times. 106 precursor 3.5-fold and increased the rate of processing 1.8-fold. The major effect of auxin was a vast increase in the rate of processing of the 1.39 .times. 106 precursor to the 1.3 .times. 106 mature rRNA. The incorporation of label into the 0.7 .times. 106 mature rRNA of treated tissue was in 10-fold excess over the control after a 30 min 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 h of continuous labeling, decreasing from an initial value of 40-fold excess. A complication in the processing of rRNA is the apparent increase in the stability of the 0.7 .times. 106 mature RNA with auxin treatment.