A Correlation between a Ribonucleic Acid Fraction Selectively Labeled in the Presence of Gibberellic Acid and Amylase Synthesis in Barley Aleurone Layers

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The effects of gibberellic acid on the incorporation of radio-active uridine and adenosine into RNA of barley aleurone layers were investigated using a double labeling method combined with acrylamide gel electrophoresis. After 16 hours of incubation, gibberellic acid stimulated the incorporation of label into all species of RNA, but the effects were very small (0-10%) for ribosomal and transfer RNA and comparatively large (up to 300%) for RNA sedimenting between 5S and 14S. This result was obtained for both isolated aleurone layers and for layers still attached to the endosperm. A similar but less marked pattern occurred in layers incubated for 8 hours, but the effect was not observed after 4 hours. The gibberellic acid-enhanced RNA labeling was not due to micro-organisms. The following evidence was obtained for an association between the gibberellic acid-enhanced RNA synthesis and α-amylase synthesis: (a) synthesis of α-amylase took place in parallel with incorporation of label into gibberellic acid-RNA; (b) actinomycin D inhibited amylase synthesis and gibberellic acid-RNA by similar percentages; (c) 5-fluorouracil halved incorporation of label into ribosomal RNA but had no effect on amylase synthesis and gibberellic acid-RNA; and (d) abscisic acid had little effect on synthesis of RNA in the absence of gibberellic acid, but when it was included with gibberellic acid the synthesis of both enzyme and gibberellic acid-RNA was eliminated. We conclude that large changes in the synthesis of the major RNA species are not necessary for α-amylase synthesis to occur but that α-amylase synthesis does not occur without the production of gibberrellic acid-RNA. Gibberellic acid-RNA is probably less than 1% of the total tissue RNA, is polydisperse on acrylamide gels, and could be messenger species for α-amylase and other hydrolytic enzymes whose synthesis is under gibberellic acid control.

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