Studies on the control mechanism of RNA polymerase I activity in higher plants

Studies on the control mechanism of RNA polymerase I activity in higher plants

In order to study the relationship between ribosomal function and rRNA synthesis, three-day old soybean seedlings were immersed in distilled water and bubbled with N2 gas for various durations. The brief N2-gas treatment caused a decrement of the polyribosomal level in the meristematic region and a reassociation of monomeric ribosomes to polyribosomes by aeration as previously reported. The treatment with N2 gas also significantly decreased the RNA polymerase I activity as expressed in the isolated nuclei. Using a three-hour treatment, the RNA polymerase I activity expressed in the isolated nuclei dropped to 35% of the initial activity. However after solubilization of the enzyme from the isolated nuclei and then fractionation on DEAB- cellulose column, the RNA polymerase I activity was similar to that from the control. After two-hour treatment of N2 gas and then aeration for two hours, the RNA polymerase activity in meristematic region return to its original level. These results indicated that there is a close relationship between the polyribosomal level (protein synthesis) and the rRNA synthesis. When ppGpp (one of the stringent factors in E. coli) was added to the in vitro synthetic reaction mixtures, even at a half concentraction of the GTP nucleotide substrate, used in the assay, there was no inhibition of RNA synthesis. SDS-gel analysis of the nuclear proteins by electrophoresis showed no distinct differences between the N2-gas treated tissues and the control tissues. The regulation of rRNA synthesis in the meristematic region of soybean hypocotyl needs further study.