The synthesis of rRNA and ribosomes in pear fruit cells is stimulated by a gamma radiation dose of 250 Krad; the effect persists for several days. A 1000-Krad dose results in complete cessation of ribosomal synthesis with no subsequent recovery. Neither dose has a marked effect on the relative amounts of monosomes and polysomes as determined by sedimentation analyses. For the cells in question the increment in radiation dose that inhibits ribosomal synthesis also results in a transition from reparable to irreparable mitochondrial damage. Implications for the dynamics of intracellular repair are discussed.

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