Chromatin, RNA Polymerase, Potato Tuber Tissue, Aging Phenomenon The synthesis of RNA by chromatin-bound RNA polymerase (E.C. 2.7.7.6.) from white potato tubers proceeds at a low rate, which is enhanced after slicing the tissue, however. Concomitantly DNA template availability as measured with saturating amounts of Escherichia coli polymerase is diminished drastically. Nearest neighbor frequency analysis proved that the RNA synthesized on chromatin of intact tubers is different from that synthesized on chromatin of sliced tissue.
The RNA polymerase of white potato tubers is dependent on all four ribonucleoside triphos phates and a divalent metal ion such as Mg2+ or Mn2+ and totally inhibited by the presence of pyrophosphate. Actinomycin D blocks the formation of the RNA product, which could be shown to be a heteropolymer by nearest neighbour frequency technique. The Km of the chromatin-bound enzyme with regard to ATP, GTP, CTP and UTP was 5.1 X10-5 M, 1.6X10-5 M, 0.9X10-5 M and 0.45 X 10-5M/1 respectively, α-amanitin inhibits the overall activity to about 50%, which indicates the presence of equal amounts of polymerase I and polymerase If.
Chromatin-bound, DNA-dependent RNA polymerase (EC 2.7.7.6) activity and chromatin template availability, as measured with saturating amounts of E. coli RNA polymerase, changes rhythmically during the formation, dormancy, and sprouting of potato tubers. Active growth processes coincide with the highest RNA polymerase activity as well as the greatest template accessibility, during tuberization and sprouting. Consequently, chromatin-associated RNA and protein content is highest in young developing tubers and in old tubers at the onset of sprouting. Ribosomal RNA content, in turn, is maximal in small tubers, remains constant during dormancy, and decreases when sprouting begins, probably due to the translocation of rRNA into the sprouts. The nucleolus changes its shape and size concomitantly with the process of tuberization.
The reaction of potato tuber tissue upon wounding and gibberellic acid (GA3) treatment is strictly dependent on the tuber age. Young, rapidly growing tubers decline both chromatin-bound, DNA-dependent RNA polymerase (EC 2.7.7.6) activity and template availability as a consequence of wounding and are not responsive toward GA3. At the onset of dormancy, ripened tubers do not at all respond to wounding or hormones, but later on develop the ability to increase their transcriptional rate and template accessibility, both after injury and treatment with 10(-7) mol l(-1) GA3. The size of the nucleolus and the rRNA content of the ribosomal population follows the same pattern.
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