The effect of ionizing radiation on ribosomal RNA synthesis in grand rapids lettuce seeds

Germination of Grand Rapids lettuce seeds was effectively delayed by exposure to 100 kiloroentgens (kr) gamma-irradiation. Both gibberellic acid and kinetin were able to slightly overcome this delay in germination imposed by ionizing radiation. Incubation in 5-fluorouracil significantly depressed germination in irradiated seeds while it did not affect unirradiated seeds.

A dose of 100 kr ionizing radiation was effective in decreasing incorporation of [³H]-uridine into high molecular weight RNA but did not decrease incorporation into transfer RNA. 5-Fluorouracil reduced incorporation of labeled precursor into both RNA components while gibberellic acid stimulated the synthesis of ribosomal and transfer RNA.

The results indicated that ribosomal RNA synthesis was not necessary for germination to occur as 5-fluorouracil did not prevent germination in unirradiated seeds. However, 5-florouracil did delay germination after exposure to ionizing radiation indicating that ribosomal RNA synthesis may be involved in radiation damage and subsequent repair processes. From these data it appeared that ionizing radiation delayed germination of Grand Rapids lettuce seeds through an inhibition of ribosomal RNA synthesis.