Control of ribosome biosynthesis in plant cell cultures under heat-shock conditions: ribosomal RNA

The immediate block of ribosome biosynthesis in heat-shocked tomato cell cultures is primarily caused by the complete inhibition of pre-rRNP processing. Depending on the heat-shock conditions synthesis of pre-rRNP goes on, though at a reduced level. Synthesis and/or preservation of pre-rRNP during heat shock as well as its efficient processing in the recovery period are thoroughly improved by preconditioning of cells to the hyperthermic treatment. Such preinduced cultures are characterized by their content of preformed heat-shock proteins, whose dominant representative (hsp 70) becomes highly enriched in the characteristic granular rRNP material observed in nucleoli of heat-shocked cells. This is shown by immune fluorescence staining and microautoradiography.